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Publication numberUS3707681 A
Publication typeGrant
Publication dateDec 26, 1972
Filing dateMar 24, 1970
Priority dateMar 24, 1970
Publication numberUS 3707681 A, US 3707681A, US-A-3707681, US3707681 A, US3707681A
InventorsGrant Ronald D
Original AssigneeJfd Electronics Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Miniature tv antenna
US 3707681 A
Abstract
An antenna for TV reception predominantly in the low band and high band VHF ranges having dipoles of significantly reduced physical length as compared with conventional dipoles for reception of signals respectively in the low and high band VHF ranges. Inductive elements are employed to form a portion of the dipole length to permit significant reduction in the physical length of the dipole. The dipoles are electrically isolated from one another by suitable trap circuits to isolate high band VHF operation from low band VHF operation. Lossy components are deliberately added to the dipole section of the antenna to provide significantly improved noise matching and power transfer between antenna and amplifier. The inductive elements further provide good impedance matching between antenna and amplifier to optimize power transfer. The antenna is provided with end loads of the capacitive-type for improving both current magnitude and current distribution across the dipole in both low band and high band VHF operation. Separate amplifier channels are provided for low band and high band VHF signals to improve gain and reduce intermodulation and cross modulation effects, among other. A passive UHF section may be integrated into the array.
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United States Patent Grant [54] MINIATURE TV ANTENNA [72] Inventor: Ronald D. Grant, Urbana, Ill.

[73] Assignee: JFD Electronics Corporation,

Brooklyn, N.Y.

[22] Filed: March 24, 1970 [21] Appl. No.: 22,281

[52] US. Cl. ..325/368, 325/373, 343/722 [51] Int. Cl. ..H04b 1/06 [58] Field of Search ..325/373, 366, 376, 368;

[56] References Cited UNITED STATES PATENTS 2,888,678 5/1959 Weiss ..343/8l4 3,110,030 11/1963 Cole ..343/795 X 3,276,028 9/1966 Mayes "343/7925 3,339,205 8/1967 Smitka ..343/70l 3,496,566 2/1970 Walter ..343/701 3,508,269 4/1970 Snyder ..343/701 3,521,169 7/1970 Turner ..343/70l X OTHER PUBLICATIONS Mayes, P. E., Electronics World, March 1968, pp. 49-52. 0

:1?- .9715 97'- VIIIIIIIA i m Primary ExaminerRichard Murray Assistant Examiner-Kenneth W. Weinstein Attorney-Ostrolenk, Faber, Gerb & Soffen [57] ABSTRACT An antenna for TV reception predominantly in the low band and high band VHF ranges having dipoles of significantly reduced physical length as compared with conventional dipoles for reception .of signals respectively in the low and high band VHF ranges. inductive elements are employed to form a portion of the dipole length to permit significant reduction in the physical length of the dipole. The dipoles are electrically isolated from one another by suitable trap circuits to isolate high band VHF operation from low band VHF operation. Lossy components are deliberately added to the dipole section of the antenna to provide significantly improved noise matching and power transfer between antenna and amplifier. The inductive elements further provide good impedance matching between antenna and amplifier to optimize power transfer. The antenna is provided with end loads of the capacitive-type for improving both current magnitude and current distribution across the dipole in both low band and high band VHF operation. Separate amplifier channels are provided for low band and high band VHF signals to improve gain and reduce intermodulation and cross modulation effects, among other. A passive UHF section may be integrated into the array.

46 Claims, 10 Drawing Figures azz PATENTED DEC 2 6 I972 SHEET 1 [IF 6 wwl PATENTEDnsces :972 3.707.681

sum 2 or e PATENTED nzc 26 m2 SHEET 3 BF 6 PATENTED DEC 2 6 I972 SHEEI [1F 6 m I IH N MINIATURE TV ANTENNA The present invention relates to antennas, and more particularly to a novel antenna design for use in TV reception in which extremely high gain and directivity of the upper and lower VHF TV bands is obtained in which signals lying outside of these passbands are eliminated, and further in which the above advantages are derived through the use of an active antenna section of significantly reduced physical dimensions.

In general, the dipole length of an antenna designed for television reception (or transmission) is about onehalf of the wavelength at the lower part of the passband. This means that for the lower VHF-band, antenna length I if about 100. Thus, in order to develop an antenna of substantially diminished length, these dimensions would have to be reduced by a significant amount. Reduction of the length of an antenna, however, causes a corresponding reduction in impedance bandwidth which constitutes one of the primary limiting factors in television antenna design. The maximum possible 3 db. bandwidth of an antenna structure which can be enclosed in its sphere with radius r has been found to have a median frequency of the order of 69 MHz and a total bandwidth in the lower VHF band of approximately 5 MHz for an antenna having a length of the order of 30 inches. It is quite obvious that this bandwidth is insufficient for reception in the lower VHF- band which is the most critical band, since dipole length is inversely proportional to frequency and thereby dipole length increases with decreasing frequency.

. The antenna of the present invention is characterized by utilization of spiral wound conductors for providing requisite dipole electrical length while reducing the physical length of the antenna array by a significant amount. First and second dipole elements are employed, which elements are selectively electrically connected or isolated from the antenna feed points, depending upon the particular frequency desired to be received. Electrical isolation and/or connection is obtained through the use of passive circuits whose impedance varies with frequency. In order to increase the current values at the ends of the dipole and to permit higher voltage levels, end loads, which are primarily capacitive, are provided at the dipole ends, with the selective end loads connected in circuit with the dipoles at any given time being varied in accordance with the particular VHF frequency range desired to be received. I

Also, since the amplification means employed in conjunction with the antenna has an impedance which is primarily inductive in the low band VHF operation, the inductive elements further provide good impedance matching between antenna and amplifier. Significantly improved noise matching between the amplifier and l the antenna is obtained through the use of lossy components within the dipole structure. An amplifier circuit having separated VHF low band and high band channels has been found to yield excellent signal isolation as between channels to provide signals within the desired VHF low and high frequency bands of excellent gain while intermodulation and cross modulation is significantly eliminated.

It is, therefore, one primary object of the present invention to provide a novel antenna capable of both VHF low band and high band reception to the exclusion of all other frequency ranges, while at the same time providing an antenna of significantly reduced physical size.

Still another object of the present invention is to provide a novel antenna dipole section for use in reception of VHF high and low band frequency ranges to the exclusion of all other frequencies and which employs amplifier means for providing high gain amplification of the desired signals while blocking signals falling outside of the desired ranges and further preventing cross modulation or intermodulation between the signals of the low and high VHF bands.

Yet another object of the present invention is to provide a novel antenna dipole section for use in reception of VHF high and low band frequency ranges to the exclusion of all other frequencies and which employs amplifier means for providing high gain amplification of the desired'signals while blocking signals falling outside of the desired ranges and further preventing cross modulation or intermodulation between the signals of the low and high VHF bands, and further being comprised of lossy elements provided within the dipole arrangement to significantly reduce the contribution of amplifier noise due to antenna impedance.

Still another object of the present invention is to provide a novel dipole section for use in receiving signals in the VHF high and low band ranges to the exclusion of all other signals being comprised of first and second dipole components which are selectively electrically connected to the antenna feed points, dependent upon the frequency range in which the signal being received is included, and wherein the dipole sections, while providing excellent reception over both the VHF low and high frequency bands, are of significantly reduced physical size.

These as well as other objects of the present invention will become apparent when reading the accompanying description and drawings in which:

FIG. 1 is a top plan view showing a combined VHF- UHF antenna designed in accordance with the principles of the present invention. I

FIG. 2 is a schematic diagram of an amplifier which may be employed with the antenna array of FIG. 1.

FIG. 3 is a schematic diagram of the circuit employed to connect low frequency power to the amplifier circuit of FIG. 2, as well as the means for connecting the amplified signals of the amplifier of FIG. 2 to the TV receiver.

FIG. 4a is a top plan view showing an alternative embodiment for the VHF section of FIG. 1, and FIGS. 4a

and 4b show the effective operation of the array of FIG. 4 for the low and high band operation, respectively.

FIGS. 5 and 7 are schematic diagrams showing alternative amplifier circuits which may be employed with the embodiment of FIG. 4.

FIGS. 6 and 8 are plots of gain versus frequency for the antenna array of FIG. 4 employing the amplifiers of FIGS. 5 and 7, respectively.

Referring now to the drawings:

FIG. 1 shows a multiple passband antenna capable of receiving frequencies in the range from 54 to 88 MHz (low band VHF), 174-216 MHz (high band VHF), and 470 to 890 MHz (UHF) band and for blocking all other frequencies outside of the three above-mentioned passbands.

The dipole and parasitic components of the antenna 10, shown in FIG. 1, are each comprised of conductive coatings formed upon an insulating substrate 11, which components will be described in detail hereinbelow. The elements comprising the VHF low and high band section of the antenna, general-1y designated by the numeral 12, includes a dipole consisting of dipole arms 13a and 13b. The inner ends of arms 13a'and 13b are coupled through respective conductors 14a and 14b to terminals 15a and 15b which are respectively electrically connected to input terminals of an amplifier cirtive pads 41a, 41b, respectively, which have slender inwardly extending portions 42a, 42b, respectively, which form the L-shaped configuration. I

The upper ends of pads 41a and 41b are electrically connected to the outer ends of dipoles 13a and 13b by parallel-connected elements L C,, L,-C,, respectively, which parallel-connected elements have their opposite tenninals connected between terminals 39-43 cuit whose physical dimensions are represented-by represented by the dotted rectangle 16. The discrete v components are mounted upon the printed circuit board and the board is secured to the antenna insulating substrate 11 along the underside thereof in the position as shown by the dotted rectangle.

The inner ends of dipole arms 13a and 13b are further respectively connected to 'spiral wound elements 17a and 17b, which are coupled to the dipole arms at 18 and 19, respectively. The innermost points 20 and 21, respectively, of the spiral wound inductive elements are each electrically connected to a pair of capacitors C C,, C -C respectively. The opposite terminal of the capacitors C C are electricallyconnected to conductive leads 14a and 14b, respectively. The elements C 17a--C and C,l7b-C each comprisean M-derived filter which operates in a manner to be more fully described. The opposite terminals of capacitors C C are electrically connected at points 22 and 23, respectively, along a second pair of spiral wound inductive components 24a and 24b, respectively. The outermost terminals of spiral wound inductors 24a and 24b are electrically connected to a pair of resistors R ,R whose opposite ends are electrically connected to a ground pad 25 which is aligned substantially along the longitudinal axis of the antenna array, represented by phantom line 26. The inner ends 27 and 28 of spiral wound inductive elements 24a and 24b extend through theinsulating substrate 11' to the underside thereof where they are electrically connected to a pair of leads 29a, 29b, respectively, which both extend respectively outwardly from the longitudinal axis 26 to terminals 30 and 31 which extend through the insulating substrate 11 from the underside to the top side thereof wherethey are electrically connected to the inner ends of spiral wound inductive elements 32a and 32b, respectively, which are each'comprised of the spiral wound sections 33a-34a and 33b-34b. Each of the spiral-wound sections 33a34a and 33b-34b are electrically connected at their outer ends by means of resistors R,,R,, respectively. The inner ends of spiral wound sections 34a and 34b are electrically connected to terminals 35 and 36, respectively, which extend through the insulating substrate 11 to the underside thereof where they are electrically connected through leads 37 and 38, respectively, to terminals 39 and 40, respectively. The terminals 39 and 40 extend through insulating substrate 11 from the underside of the substrate to the top side thereof where they are electrically connected to a pair of substantially L-shaped conducand 4044, respectively.

A second pair of substantially L-shaped conductive pads a and 45b, respectively, have inwardly extending slender portions 46a, 46b, respectively,,forming the substantially L-shaped configuration. The conductive pads, 45a and 45b are electrically connected to pads 41a and 42b, respectively by parallel-connected elements C L, and C L,, respectively, whose opposite ends are electrically connected between terminals 46-48 and 47-49, respectively., I

The operation of the low band-high band VHF section 12 of antenna array 10 is as follows:

For low band reception, i.e., for reception of signal frequencies in the range from 54 to 88 megacycles, the parallel resonant circuits C -l7a (an inductance element), C -17b(also an inductance element) and C, present a low impedance (i.e., short circuit) to electrically couple elements 24a and 24b to leads 14a and 14b, respectively.

The inner ends of dipole arms 13a and 13b are further electrically connected through capacitor C, to spiral wound inductor 24a and through capacitor C, to spiral wound inductor 24b. These elements are in electrical series with respective elements 33a-R 32a and 33b'R 34b, respectively; This series circuit is further electrically connected through leads 37 and 38 to conductive pads 41a and 41b, respectively. In the low band VHF range, the elements C,l7a-C, and C,-17b-C, present a low impedance (i.e., short circuit) to electrically connect the conductive feed lines 14a, 14b to the aforementioned electrical series paths.

The inner end loads comprised of pads 41a and 41b are thus electrically connected to the inboard ends of dipole arms 13a and 13b, respectively, during operation (i.e., transmission or reception) in the low band VHF range. The inner end loads comprised of pads 41a and 41b, however, are disconnected from the outboard ends of dipole arms 13a and 13b as a result of the resonant circuits comprised of elements L -C L G, which present a high impedance throughout the low band VHF range. The resonant circuits C 1 C -L, connected between the inner end loads comprised of pads 41a and 41b to the outer end loads comprised of pads 45a and 45b present a low impedance (short circuit) throughout the low. band VHF range so as to effectively electrically connect the elements 45a and 45b to the inner end load elements comprised of pads 41a and 41b. I

Thus, a dipole comprised of dipole arms 24a-32a- 41a-45a, 24b-32b-42b-45b effectively operate as a single active dipole throughou t th low band VHF range with the effective length of the dipole being capable of being significantly reduced as a result of the use of the spiral wound inductive elements 24a-33a-34a and 24b-33b-34b and resistive loads R, and R respectively. For example, the distance between the outermost ends of outer end loads or pads 45a and 45b, in I one preferred embodiment, is 30 inches. A typical simple dipole arrangement in the low band VHF range would normally have a length of the order of 100 inches for a half-wave length dipole designed to operate in the lower part of the low band VHF range. The resistive elements R,, R, and R R are included within the active element configuration to improve the noise matching between the antenna and the amplifier circuit (to be more fully described), which resistive elements increase the antenna losses, but nevertheless have been found to enhance the operating charac-' teristics and efficiency of the antenna-amplifier combination.

For operation in the high band VHF range (174 to 216 MHz), the parallel resonant circuits L,C L,C,, present. a low impedance (effectively, a short circuit) throughout this range so as to electrically couple the inner end loads comprised of pads 41a and 41b to the outboard ends of dipole elements 13a and 13b. Likewise, the parallel tank circuits L,-C,,, L C, present a high impedance within the high band VHF range so as to electrically isolate the outer end loads comprised of pads 45a and 45b from the inner end loads comprised of the pads 41a and 41b, respectively. The M-derived filter circuit comprised of C C,, 17a and C C,, 17b, respectively, present a high impedance throughout the high band VHF range so as to electrically disconnect these elements as well as pads 41a and 41b from the inboard ends of dipole arms 13a and 13b, respectively.

The overall length of the effective dipole throughout the high band VHF range (measured between the extreme ends of inner end loads 41a and 41b) is, in one preferred embodiment, 22 inches as compared with a conventional half-wave dipole which, in the lower end of the upper VHF band, would have a length of the order of 33 inches.

In order to improve the gain and directivity of the antenna in the high band VHF range, director and reflector arrays are provided. The director array is comprised of a pair of conductive pads 50 and 51 symmetrically arranged with respect to the antenna longitudinal axis 26 and positioned in front of the active VHF region 12.

The reflector elements are comprised of a pair of conductive pads 52 and 53 having outer ends 52a-52b and 53a-53b of enlarged width and being arranged so as to be symmetrical about the antenna array longitudinal axis 26. The director and reflector arrays act to improve directivity of the antenna as well as improving the gain of the antenna throughout the high band VHF range. The director and reflector arrays have an almost negligible effect upon the operation of the VHF active region within the low band VHF range (i.e., 54-88 MHz).

FIG. 2 is a schematic diagram of the amplifier circuit whose physical location is represented by the dotted rectangle 16 of FIG. 1. FIG. 3 is a schematic diagram showing the electrical connections between the amplifier circuit and the power source and between the amplifier circuit and the UHF and VHF leads of a television receiver. The power for the amplifier circuit may be taken from a standard house current source through a conventional plug means 60 (see FIG. 3) which is connected to the primary winding 61 of a transformer TR,, whose secondary winding 62 is coupled across a series circuit comprised of resistors R and R Transformer TR, steps the voltage down to approximately 15 volts. The resistors R,,, and R form a voltage divider circuit with the portion of the output appearing across R being coupled to a coaxial line having outer conductor 63 and inner conductor 64 through the lower terminal of resistor R, and the upper terminal of resistor R and inductor L The coaxial cable comprised of center conductor 64 and outer conductor 63 preferably has a characteristic impedance of ohms. The center conductor 64, shown in FIG. 3, is electrically connected to terminal 67, shown in FIG. 2, so as to electrically connect the power source to the amplifier circuit. Since the output of the amplifier circuit is taken from terminal 67, a balun 68 comprised of the components B, and C m shown as dotted rectangle 68, is provided to transform the output impedance from 75 ohms unbalanced to 300 ohms balanced impedance to the UHF and VHF outputs, respectively, shown in FIG.

The center conductor 64 of the coaxial cable couples the low frequency power signal through output terminal 67, shown in FIG. 2, of the amplifier circuit through a second balun B, comprised of the components incorporated within the dotted rectangle 72. Balun B, acts to isolate the input terminals of the amplifier (i.e., both poles of the input terminals float above amplifier ground).

The low frequency a.c. signal is coupled through an inductor L and an inductor L,, to the anode of a diode D, which operates as a half-wave rectifier. A capacitor C,, is connected between the cathode of diode D, and a reference conductor 73 to act as a filter for the halfwave rectifier diode D,. Thus, a dc. bias source is provided for the transistors Q, and 0, whose collector electrodes are coupled to the cathode of diode D through inductors L, and L respectively.

The VHF band antenna section 12 has its electrical terminals 15a and 15b (see FIG. 1) electrically connected to the input terminals 74 and 75, respectively, of the amplifier circuit shown in FIG. 2.

The amplifier circuit shown in FIG. 2 may be considered to be first and second amplifier circuits for amplification of low band and high band VHF signals. The amplifier contained within dotted rectangle 76 is employed for amplification of signals within the low band VHF range (54-88 MHz), while the amplifier circuit contained within dotted rectangle 77 is employed for amplification of signals within the high band VHF range (l74-2l6 MHz). Considering the amplifier circuit within dotted rectangle 76, incoming signals are applied through input terminal 65 to a low passband filter circuit comprised of elements L C C L,, L and C,,, which filter is adapted to pass only those signals lying within the low band VHF range (54-88 MHz) to the base electrode of transistor 0 The incoming signals are amplified by transistor Q, and taken from the collector electrode where they are applied to a bandpass filter comprised of components L, C C C and L These elements operate as a bandpass filter to permit amplified signals lying within the low band VHF range to be coupled through inductor L and balun B, to the amplifier output circuit 67.

Inductor L acts to block high frequency signals from diode D,. Likewise, inductor L,, acts to present a high impedance to high frequency signals to isolate the high frequency signals from the anode of diode D The passband filter provided at the input of transistor 0, thereby prevents any signals which lie within the high band VHF range (174-216 MHz) from being applied to transistor 0,, as well as blocking all other unwanted frequencies. The bandpass filter provided between the output of transistor Q, and the amplifier output terminal 67 acts to prevent the application of any signals lying outside of the low band VHF range from being coupled to output terminal 67. This arrangement thereby prevents any unwanted harmonics which might possibly be generated by the transistor amplifier from appearing in the output circuit so as to interfere with signals lying in the high band VHF range which may be amplified by the circuit within the dotted rectangle 77. For example, let it be assumed that a signal frequency within the low band VHF range is applied to the base of transistor Q, and that a third harmonic of this signal is generated as a result of amplification. Such a third harmonic signal would lie within the high band VHF range (for example, the third harmonic of a 60 MHz signal would be 180 MHz which lies within the high band VHF range of 174-216 MHz). The bandpass filter arrangement thereby prevents any unwanted harmonics from appearing at the output of the low band VHF amplifier circuit so as to have a harmful effect upon high band VHF signals passed by amplifier channel 77. Similarly, second harmonic signals which could also affect operation in the high band range,are eliminated. For example, the second harmonic of a signal of the order of 88 MHz would be 176 MHz, which may have a harmful effect upon high band VHF signals occurring at the low end of the high band.

The amplifier circuit within dotted rectangle 77 is employed for amplification of signals within the high band VHF range (174-216 MHz) and is comprised of a bandpass filter coupled between input terminal 75 and the base electrode of transistor which filter is comprised of elements R C C L and C This filter circuit passes only signals lying within the high band VHF range while blocking all other signals. The signals passed by the filter circuit are applied to the base electrode of transistor Q which amplifies the signals and couples the amplified signals through its collector electrode and a high bandpass filter to output tenninal 67. The high bandpass filter is comprised of components C C C and L which form a filter circuit for passing only those amplified signals which lie in the high band VHF range.

inductor L prevents the high frequency amplified signals from being fed back to the cathode of diode D The high bandpass filter provided at the output of transistor Q functions to prevent any signals which may be passed by transistor Q, and which lie to either side of the high band VHF range from being coupled through the output 67 of the amplifier circuit into the VHF or UHF output terminals 71 or 70, respectively, so as to prevent any such extraneous signals from affecting the quality of the desired signals.

The low band VHF signals and high band VHF signals are superimposed upone one another at the lefthand terminal of inductor L and connected therethrough to balun B output terminal 67, and the center conductor 64 of a coaxial line to balun 13,. Balun B, acts to transform ohms unbalanced to 300 ohms balanced signals through leads 79 and 80 to capacitorsv C and C respectively. The output side of capacitor C is coupled through capacitor C to one terminal 70a of the UHF output terminal 70 and is coupled to one terminal 71a of the VHF output terminal 71 through a series connected inductor L The output side of capacitor C is coupled to one terminal 70b of the UHF output terminal 70 through a capacitor C and is coupled to one terminal 71b of the UHF output terminal 71 through a series connected inductor L The capacitors C and C which connect the output side of capacitors C and C respectively, to the UHF output terminals 70, present a high impedance to VHF signals and a corresponding low impedance to the higher frequency UHF signals so as to connect only the UHF signals to terminals 70. Inductor L connected across the UHF output terminals 70 acts to present a high impedance to the UHF signals applied thereto while presenting a low impedance to VHF signals.

The inductors L and L connecting the output ends of capacitors C and C respectively, to the VHF output terminals 71 present a low impedance to VHF signals while presenting a high impedance to UHF signals, thereby blocking UHF signals from connection to output terminals 71. Capacitor C which is connected across the VHF output terminals, acts to present a high impedance to VHF output signals while acting to present a short circuit to UHF signals, acting to further effectively isolate UHF signals from the VHF output terminals 71. C and C isolate the 60 ohms source from the 300 ohms output terminals.

As was previously mentioned, the lossy components, (i.e., R R and R R employed in the active section 12 of the VHF antenna act to provide a good noise impedance match between the antenna and the amplifier so as to match the internal impedance of the antenna (which may be considered to be a signal generator in series with an impedance) with the input impedance of the amplifier. Since one contributing component of the source impedance to the noise temperature T (measured in degrees Kelvin) of the amplifier is inductive in the low band VHF range, inductive elements which are effectively connected in circuit with the dipole during low band VHF operation act to provide an antenna impedance whose imaginary component is primarily inductive so as to power match the antenna impedance to minimize the contribution of the antenna impedance to the noise generated by the amplifier. The inductive elements may be eliminated from the dipole employed for high band VHF operation. The end loads (4la-4lb and 45a-45 of the VHF active dipole section are primarily capacitive in nature to permit higher voltage and higher current at the ends so as to improve the operation of the antenna in both the low band and high band VHF ranges.

The UHF active dipole region, generally designated by the numeral of FIG. 1, is comprised of three dipoles 86 through 88, each having an inboard section 86a, 86b through 88a-88b, respectively, and having a pair of outboard sections 86c-86d through 880-8841, respectively. As was previously described with respect to the VHF antenna section 12, the UHF inboard and outboard dipole sections are comprised of conductive coatings deposited upon the insulating substrate 11. Considering UHF dipole 86, for example, the outer ends of the inboard sections 86a and 86b are separated from the inner ends of outboard sections 860 and 86d, respectively, by small gaps 89a and 8%, respectively, which, in one preferred embodiment, are of the order of 1/16 inches wide to form a capacitive coupling between the dipole inboard and outboard sections. In operation, the capacitive coupling formed by the gaps 89a and 89b, for example, present a high impedance (open circuit) for operation in both the low and high VHF bands so as to electrically isolate the outboard sections 86c and 86d from their associated inboard sections 86a and 86b, respectively. Inboard sections 86 a, 86b through 880,881) are of electrical lengths which have an insignificant effect upon the operation of the antenna in the VHF low and high bands. In the UHF band, however, the capacitive couplings present a low impedance (effective short-circuit) so as to electrically couple the outboard sections 860 and 86d to their associated inboard sections 86a and 86b. The remaining UHF dipoles 87 and 88 are substantially similar in both design and operation.

Conductive sections 90a and 90b electrically connect the inner ends of inboard dipole sections 86a and 86b to the inner ends of inboard dipole sections 87a and 87b, respectively. Similarly, conductive sections 91a and 91b electrically connect the inner ends of dipole inboard sections 870 and 87b to the inner ends of dipole inboard sections 88a and 88b, respectively. The inboard ends of dipole inboard sections 88a and 88b are further electrically connected to terminals 92a and 92b, which terminals are respectively connected to the input terminals 93 and 94 of the amplifier circuit, shown in FIG. 2. Since the signal strength of UHF signals within a reception area is adequate, the UHF signals may be directly coupled through the output terminal 67 of the amplifier circuit, shown in FIG. 2, to the coaxial cable and isolating elements 68 to the UHF output terminal 70 without undergoing any amplification.

Element 95 forming a portion of the UHF antenna section, and connected to feed terminals 92a and 92b, is conventionally referred to as a hairpin inductor which forms part of a low pass-high pass trap, together with a pair of capacitive elements (not shown) preferably mounted upon the amplifier printed circuit board to electrically isolate VHF signals from UHF signals and vice versa.

The directivity and gain of the UHF active section may be enhanced through the provision of UHF director elements 96 and 97 which are positioned in front of the UHF active section 85 so as to enhance both directivity and gain of the array within the UHF operating range. Director 96 is an elongated conductive pad arranged so as to be symmetrical to the antenna longitudinal axis 26. Director 97 is comprised of pads 97a and 97b which are likewise symmetrically arranged relative to the array longitudinal axis 26.

FIG. 4 shows VHF antenna section 12 which may be substituted for the VHF section 12, shown in FIG. 1, while FIGS. 4a and 4b show the equivalent dipole arrangements for low band and high band VHF operation, respectively. Like elements as between FIGS. 1 and 4 have been designated by like numerals. The outer ends of dipole arms 13a and 13b are shown as tapering in width at 13c and 13, respectively. The spiral inductors L L have been designated by primes to indicate the fact that they are the electrical equivalents of the lumped parameter-type inductors L L shown in FIG. 1. The inner ends of spiral wound inductors L L are electrically connected to terminals 100 and 101, respectively, which extend through the insulating substrate 11 to the underside thereof where they are electrically connected to conductors 102,103, respectively. The opposite ends of conductors 102 and 103 are electrically connected to terminals 104 and 105, respectively, which extend through the insulating substrate 11 from the underside thereof to the top side thereof where they are electrically connected to small rectangular-shaped pads 106 and 107, respectively. These pads are, in turn, electrically connected to hollow, cylindrical end caps 108 and 109, respectively, which are shown as dotted rectangles, for purposes of simplicity. It should be understood, however, that the end caps are hollow, cylindrical-shaped conductive members each surrounding an end portion of the VHF active dipole section and being closed at their left and right-hand ends, respectively, by a disk-shaped conductive member 108a and 109a, respectively, so as to form effectively a hollow, electrically conductive can open at one end thereof.

The inner ends of spiral wound inductor sections 33b and 34b are shown as being electrically connected through leads 37 and 38 and terminals 39 and 40 to the rectangular conductive pads 106 and 107 which, as was previously described, are, in turn, electrically connnected to the end loads (i.e., cans) 108 and 109, respectively.

The inner ends of dipoles 13a and 13b are provided with terminals 15a and 15b for electrically connecting the dipoles to an amplifier circuit whose conductive coatings are shown as being positioned in the central region of the insulating substrate 11 and between the inner ends of the dipole arms 13a and 13b. The amplifier circuit employed herein may be generally of the same type as shown in FIG. 2 and described hereinabove.

Whereas the VHF antenna section, shown in FIG. 4, may be employed as a separate entity apart from the director and reflector components and the UHF section and its associated directors, it should be understood that the VHF section of FIG. 1 may also be so employed, depending only upon the needs of the user.

The operation of the alternative embodiment of FIG. 4 will now be described for both VHF low band and high band operation in connection with the equivalent diagrams of FIGS. 4a and 4b, respectively.

For low band VHF operation, the series resonant circuits comprised of components l7a-C, and 17b-C present a low impedance (effective short-circuit) to signals within the low band VHF range so as to electrically couple dipole arms 13a and 13b to spiral wound inductive elements 240 and 24b, respectively, as shown by the electrical leads 112 and 113. Thus, a series electrical circuit is connected from dipole arm 13a through conductor 112, a portion of spiral wound inductor 24a, conductor 29a, portions 33a and 344 of double spiral wound inductor 32a, conductor 37 and rectangular conductive pad 106 to end load 108. A similar circuit is established between dipole arm 13b and its end load 109. It should also be noted that the outermost ends of spiral wound inductors 24a and 24b are electrically connected to a ground reference center pad 25.

The inductive elements 24a-32a and 24b-32b act to increase the effective length of the dipole within the VHF low band range so as to permit a significant reduction in the overall tipto-tip length of the antenna. Impedance matching between the dipole and the amplifier is maintained throughout the low band VHF range to provide for optimum transfer of power therebetween.

Operation in the high band VHF range (174-216 MHz) is such that the series connected elements 17a-C and 17b-C, present a high impedance so as to effectively decouple the spiral wound inductors 24a 32a from the inner end of dipole 13a and 24b-32b from the inner end of dipole arm 13b. However, the spiral wound inductors L L and capacitors C C form a parallel tuned circuit which prevent a low impedance (effective short-circuit) during high band VHF operation so as to electrically connect the outer ends of dipole arms 13a and 13b to the end loads 108 and 109 effectively in the manner as shown in FIG. 4b. The same parallel tuned circuits (i.e., L '-C L -C act to present a high impedance during low band VHF operation so as to decouple the outer ends of dipole arms 13a and 13b from the end loads 108 and 109, as shown best by the equivalent dipole arrangement of FIG. 4a.

It can, therefore, be seen that the VHF low and high band antenna of FIGS. 4 through 4b is quite similar in design and operation to the VHF section 12 of FIG. 1, with the primary distinction being the utilization of lumped parameter inductors in FIG. 1 in place of the spiral wound inductors of FIG. 4 (i.e., the lumped parameter inductors L L of FIG. 1 are substituted by the spiral wound inductors L L of FIG. 4). In a like manner, although not specifically shown, it should be understood that the spiral wound inductors 24a-32a and 24b-32b may also be replaced by lumped parameter components.

FIG. is a schematic diagram showing another alternative embodiment for the amplifier and power supply circuit for amplification of the VHF low and high band signals. The amplifier arrangement 150 of FIG. 5 is comprised of a pair of input terminals 151 for electrical connection to the feed lines of the active sections of FIGS. 1 or 4. These input terminals are coupled through capacitors 152 and 153 to the base electrode of a transistor 154 and the lead 155, respectively. Signals applied to the base electrode are amplified and appear at the collector electrode of transistor 154. The signals are coupled through capacitor 156 and parallelconnected resistor 157 to an inductor 158 and a balun 159 whose output terminals 160 and 161 are electrically coupled to a 300 ohm twin lead cable 162 whose opposite end is electrically connected to a pair of input terminals 163 and 164, respectively, which couple amplified signals through series-connected capacitors 165 and 166, respectively, to a pair of output tenninals 167 and 168, respectively, which are coupled to the VHF input terminals of a TV receiver. Terminals 163 and 164 are further coupled to a pair of input terminals 169 and 170, respectively, through inductive elements 171 and 172, respectively. Terminals 169 and 170 may be connected to a d-c output source for providing a voltage of the order of 16 to 22 volts across terminals and 170. In order that the voltage may be maintained constant, a zener diode 173 is electrically connected across input terminals 169 and and a capacitor 174 is connected in electrical parallel with zener 173. The inductors 171 and 172 act to block high frequency signals from terminals 169 and 170. In a like manner, the low frequency signals (i.e., d-c) are blocked from the TV receiver connecting terminals 167 and 168 by capacitive elements 165 and 166, respectively.

The amplifier circuit 150 of FIG. 5 may be employed, for example, with the embodiment of FIG. 4 as a result of the fact that the antenna design itself provides fairly good rejection of the frequency bands which lie on either side of low band VHF and on either side of high band VHF. FIG. 6 is a curve showing the transmission factor of an antenna of the type shown in FIG. 4 employed with the single stage amplifier 150 of FIG. 5. It can be seen that the gain over a conventional half-wave dipole averages about 4 db. The slope of the transmission factor from channel 6 to the FM band (88 to 108 MHz) can be seen to be fairly steep. The high VHF-band gain averages about 6 db. Thus fairly good frequency isolation is provided in the absence of bandpass filter circuits.

FIG. 7 shows a two-stage amplifier circuit which may, for example, be employed with the antenna embodiment of FIG. 4. The embodiment of FIG. 7 is provided with a pair of input terminals 151 coupled through capacitive elements 152 and 153 to bus 155 and the base electrode of a transistor 154. Amplified signals appear at the collector of transistor 154 and are applied through parallel-connected components 181-182 and serially connected capacitor 183 to the base electrode of transistor 184. Signals applied to the base of transistor stage 184 appear amplified at the collector electrode and, in turn, are applied through inductive elements 185 and 186 to a coaxial cable 187 having a characteristic impedance of 75 ohms. The opposite end of the coaxial cable 187 is electrically connected through leads 188 and 189 to a d-c source connected across terminals 190 and 191, respectively. Inductive element 192 coupled between lead 188 and terminal 190 acts to isolate the high frequency signals from the d-c source. Capacitor 193 acts to smooth the d-c voltage applied across terminals 190 and 191. Balun 194, which is connected between lead 188 (through capacitor 195) and the output terminals 195 and 196 which are adapted to be connected to the inputterminals of a TV receiver acts to provide good impedance matching between the output of the amplifier and the TV receiver as well as isolating the TV receiver from the d-c bias. FIG. 8, which is a curve plotting gain versus frequency, indicates that extremely efiective operation of the antenna is obtained with the two-stage amplifier of FIG. 7, in spite of the fact that bandpass filter circuits are not employed. The transmission factor of an antenna of the type shown in FIG. 4 with the two-stage amplifier of FIG. 7 indicates that the average gain of the antenna is of the order of 8 db. The slope of the transmission factor from channel 6 to the FM-band is quite steep and, in fact, is steeper than the slope shown in FIG. 6, which is the curve for an antenna of the type shown in FIG. 4 operating in conjunction with a single stage amplifier. In any case, FM-band rejection is considerable with both antennas (i.e., with the antenna using either of the two amplifiers) so that any cross modulation or interrnodulation is substantially eliminated. The high VHF-band gain can be seen to be of the order of 6 db. and is slightly better for the low end of the high VHF range for the two-stage amplifier.

It can be seen from the foregoing description that the present invention provides a novel miniature antenna which provides excellent reception from the viewpoint of both directivity and gain for low band and high band VHF operation while excluding all outside frequency bands and which provides good impedance matching through both lower and upper VHF bands between antenna and amplifier and which provides a good noise match therebetween.

Although this invention has been described with respect to particular embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and, therefore, the scope of this invention is limited not by the specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

l. A first antenna section for receiving signals lying within first and second discrete frequency bands lying within spaced intervals in the frequency spectrum, said frequency bands being the VHF high and low band ranges, comprising:

a pair of feed terminals;

a first dipole having first and second dipole arms for receiving signals in said first frequency range;

the inner ends of said first and second dipole arms being respectively connected to said feed terminals;

second dipole means having first and second dipole arms for receiving signals in said second frequency range;

first and second frequency sensitive impedance means respectively coupled between said feed terminals and the inboard ends of said second dipole arms;

said first and second frequency sensitive impedance means each being adapted to present a short circuit to signals lying within said first frequency band to electrically connect said second dipole to said feed terminals during operation in said first frequency band and each being adapted-to present a high impedance to signals lying within said second frequency band to electrically isolate said second dipole from said feed terminals during operation in the second frequency band;

said antenna further comprising an insulating substrate;

said first and second dipoles being deposited upon said substrate in the form of thin conductive coatings; the length of said first dipole being less than 40 inches.

2. The antenna of claim 1 wherein the electrical length of said first dipole is selected so as to have an insignificant effect upon antenna operation in said second frequency operating band.

3. The antenna of claim 1 wherein said first and second frequency sensitive impedance means are each comprised of at least one inductive element and one capacitive element to form a resonant circuit.

4. The antenna of claim 1 wherein said first and second frequency sensitive impedance means are each further comprised of a second capacitive element connected in series with said resonant circuit.

5. The antenna of claim 1 further comprising at least one director element being positioned adjacent said second active section for enhancing the directivity and gain of the antenna.

6. The antenna of claim 1 wherein the dipole arms of one of said first and second dipoles are each comprised of a substantially straight conductive coating.

7. The antenna of claim 1 wherein the dipole arms of one of said first and second dipoles are further comprised of at least one inductive element.

8. The antenna of claim 7 wherein each inductive element is a flat spiral wound conductive coating, said inductive elements being coplanar.

9. The antenna of claim 1 further comprising: amplifier means having input terminals connected to said antenna feed terminals and having output terminals adapted for connection to a signal receiver.

10. The antenna of claim 9 further comprising at least first and second lossy components respectively connected at spaced intervals along the arms of one of said first and second dipoles for providing improved noise matching between said antenna and said amplifier means whereby the noise contribution of said amplifier means is minimized.

11. The antenna of claim 9 wherein saidamplifier means is comprised of first and second amplifier channels each being connected between said amplifier input and output terminals;

said first amplifier channel beingcomprised of first and second bandpass filters and a first amplifier stage having an input and an output;

said first bandpass filter being connected between said input terminals and the input of said first amplifier stage for passing only those signals lying within one of said first and second discrete frequency bands;

said second bandpass filter being connected between said output terminals and the output of said first amplifier stage for passing only those signals lying within said one of said first and second discrete frequency bands.

12. The antenna of claim 11 wherein said second amplifier channel is comprised of third and fourth bandpass filters and a second amplifier stage;

said third bandpass filter being connected between said input terminals and the input of said second amplifier stage for passing only those signals lying within the remaining one of said first and second discrete frequency bands;

said fourth bandpass filter being connected between said output terminals and the output of said second amplifier stage for passing only those signals lying within said remaining one of said first and second discrete frequency bands.

13. The antenna of claim 12 further comprising an ac. power source;

balun means coupling the output of said a.c. source to said amplifier means output terminals and said first and second amplifier stages, said balun means being adapted to isolate said amplifier input terminals from ground potential.

14. The antenna of claim 13 further comprising means for rectifying and filtering the output of said a.c. source to couple dc. power to said first and second amplifier stages.

15. The antenna of claim 1 further comprising at least one reflector element being positioned adjacent said first and second dipoles for enhancing the directivity and gain of the antenna.

16. The antenna of claim 1 further comprising at least one director element being positioned adjacent said first and second dipoles for enhancing the directivity and gain of the antenna.

17. The antenna of claim 1 further comprising a second antenna section positioned adjacent said first and second dipoles for receiving signals lying within a third discrete frequency band lying a spaced interval in the frequency spectrum from said first and second discrete frequency bands;

said second active section including at least; one

dipole, the dipoles of said antenna sections all being substantially coplanar.

18. The antenna of claim 17 wherein said dipole in said second antenna section is comprised of first and second dipole arms, each arm having an inboard and an outboard section;

the inner ends of each inboard section being electrically connected to said feed terminals;

the outer end of each inboard section being positioned in close proximity to the inner end of its associated outboard section to form a small gap therebetween to effectively form a capacitive coupling between said inboard and outboard sections;

said capacitive coupling presenting a high impedance to signals lying in said first and second discrete frequency bands to decouple the inboard sections from the associated outboard sections during operation in either said first or second discrete frequency bands and presenting a short circuit to signals lying in said third discrete frequency band to electrically connect associated inboard and outboard sections during operation in said third frequency band.

19. The antenna of claim 18 further comprising frequency sensitive impedance means connected between said second active section and said feed terminals to isolate signals received by each of said active sections from interacting with one another.

20. The antenna of claim 17 further comprising an insulating substrate; said dipoles of said active sections being deposited upon said substrate in the form of thin conductive coatings.

21. The antenna of claim 1 further comprising:

first and second electrically conductive end loads each being conductive coatings respectively positioned adjacent the outer ends of said first and second dipoles;

first and second conductor means for respectively electrically connecting said first and second end loads to the outer ends of said first dipole arms;

third and fourth frequency sensitive impedance means each being respectively connected between said first and second end loads and the outer ends of the first and second arms of said second dipole; 5 said third and fourth frequency sensitive impedance means each being adapted to present a short circuit to signals lying within said first frequency band to electrically connect said second dipole to said feed terminals during operation in said first frequency band and each being adapted to present a high impedance to signals lying within said second frequency band to electrically isolate said second dipole from said feed terminals during operation in the second frequency band.

22. The antenna of claim 21 wherein said end loads are thin fiat conductive members being substantially coplanar with one another.

23. The antenna of claim 21 wherein said end loads are each comprised of a hollow cylindrical shaped conductive shell being closed at one end thereof and being open at the opposite end;

said closed ends being directed away from said feed terminals;

said third and fourth frequency sensitive impedance means each'being respectively connected to one of said end loads at a point adjacent the open ends thereof.

24. An antenna of substantially reduced physical dimensions as compared to conventional half wavelength dipoles for receiving signals within a predetermined frequency band comprising;

an insulating substrate;

1st and 2nd conductive coatings on said substrate forming the first and second arms of a dipole;

a pair of feed terminals respectively connected to the inner ends of said first and second dipole arms;

each of said arms having electrically isolated inboard and outboard sections;

a lossy impedance element connected in series between the outer end of said inboard section and the inner end of said outboard section;

amplifier means having input and output means;

said input-means being connected to said feed terminals for amplifying signals received by said dipole;

said amplifier means comprising at least one transistor amplifier having a noise temperature impedance characteristic lying within predetermined limits;

the electrical length of said dipole being substantially less than a conventional one-half wavelength dipole designed for receiving signals in said frequency range;

said lossy elements being adapted to increase the impedance of said dipole and to minimize the noise contribution to the transistor by said antenna.

25. The antenna of claim 24 wherein said lossy ele- 60 ments are resistors.

26. The antenna of claim 24 wherein said inboard sections include an inductance element.

27. The antenna of claim 24 wherein said outboard sections include an inductance element.

28. The antenna of claim 24 wherein said inboard and outboard sections are each comprised of an inductance element; a

said lossy element being a resistor connected between said inboard and outboard sections;

said lossy elements being adapted to smooth the frequency response of said dipole over said frequency operating band.

29. An antenna for operating over the low band VHF frequency range having a physical size substantially less than the length of a typical half-wave dipole whose electrical length is of the order of 100 inches for receiving signals at the lower frequency limit of said VHF low band comprising:

a thin flexible sheet formed of an insulation material;

a first dipole having first and second dipole arms comprised of first and second thin metallic coatings secured to one surface of said sheet;

the inboard ends of said coatings forming terminals adapted to be coupled to a receiver facility;

the outer ends of said arms comprising large conductive coatings of substantially large surface area being secured to said sheet;

said arms further comprising substantially narrow elongated conductive members each electrically joining an associated one of said terminals to an associated one of said outer ends;

the length of said arms from the outer edges of said outer ends being less than one half the length of said typical dipole.

30. The antenna of claim 29 wherein said length of said narrow conductive members is greater than the distance between the inner edges of said outer ends.

31. The antenna of claim 29 wherein at least a portion of each of said narrow conductive members is formed to operate as an inductive element.

32. The antenna of claim 29 wherein at least a portion of each of said narrow conductive members is formed in a loop to operate as an inductive element.

33. The antenna of claim 29 wherein a resistive element is provided in each of said narrow conductive members;

each of said resistive elements is electrically connected between inner and outer portions of its associated narrow conductive member.

34. The antenna of claim 29 further comprising a transistor amplifier mounted upon said flexible sheet;

said transistor amplifier having a pair of input terminals; each of said first dipole terminals being coupled to said associated one of said amplifier terminals.

35. The antenna of claim 34 wherein a resistive element is provided in each of said narrow conductive members;

each of said resistive elements is electrically connected between inner and outer portions of its associated narrow conductive member.

36. The antenna of claim 34 wherein said resistive elements each have resistive values adapted to increase the resistance of said dipole to more closely match the input impedance of said transistor amplifier.

37. The antenna of claim 29 further comprising a second dipole for receiving signals in the VHF high band frequency range;

said second dipole comprising first and second dipole arms;

each of said arms being comprised of a second narrow elongated conductive member secured to said insulating heet' I means coup mg the inboard ends of said second dipole to associated ones of the inboard ends of said first dipole;

first and second conductive end portions of large surface area being secured to said insulation sheet and being electrically coupled to the outer ends of said second dipole narrow conductive members; the length of said second dipole being less than the length of said first dipole.

38. The antenna of claim 37 wherein said coupling means further comprises frequency sensitive impedance means for decoupling signals in said upper frequency band appearing at said first dipole inboard ends from said second dipole inboard ends and for coupling signals in said lower frequency band appearing at said first dipole inboard ends to said second dipole inboard ends.

39. The antenna of claim 38 further comprising a transistor amplifier mounted upon said flexible sheet;

said transistor amplifier having a pair of input terminals; each of said first dipole terminals being coupled to an associated one of said amplifier terminals.

40. The antenna of claim 39 wherein a resistive element is provided in each of said narrow conductive members;

each of said resistive elements is electrically'connected between inner and outer portions of its associated narrow conductive member.

41. The antenna of claim 40 wherein said resistiveelements each have resistive values adapted to increase the resistance of said dipole to more closely match the input impedance of said transistor amplifier.

42. The antenna of claim 34 further comprising first filter means coupled between the inboard ends of said second dipole and the input of said transistor amplifier for passing only those signals lying in said lower frequency range.

43. The antenna of claim 42 further comprising second filter means coupled to the output of said transistor amplifier means for substantially attenuating all receiving signals from said transistor amplifier which lie outside of said lower frequency range.

44. The antenna of claim 43 further comprising second transistor amplifier means mounted upon said flexible sheet;

third filter means coupled between the inboard ends of said second dipole and the input of said second transistor amplifier for passing only those signals lying in said upper frequency band.

45. The antenna of claim 44 further comprising the filter means coupled to the output of said second traNsistor amplifier for substantially attenuating all signals received from said second transistor amplifier which lie outside of said upper frequency band.

46. The antenna of claim 45 further comprising means coupling the outputs of said second and fourth filter means in common.

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US6326922 *Jun 29, 2000Dec 4, 2001Worldspace CorporationYagi antenna coupled with a low noise amplifier on the same printed circuit board
US6839038Jun 17, 2002Jan 4, 2005Lockheed Martin CorporationDual-band directional/omnidirectional antenna
US7042410 *Oct 29, 2003May 9, 2006Cushcraft CorporationMicrowave antenna feed with integral bandpass filter
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US7180449 *Nov 12, 2004Feb 20, 2007Accton Technology CorporationAntenna with filter
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Classifications
U.S. Classification455/275, 455/325, 343/722
International ClassificationH01Q5/02, H01Q5/00, H01Q19/00, H01Q19/30
Cooperative ClassificationH01Q5/00, H01Q19/30
European ClassificationH01Q5/00, H01Q19/30