US 3710337 A
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 in the above mentioned VHF ranges. Inductive elements are employed as an integral part of at least one of said dipoles for improving the bandwidth and raising the Q of the dipole. The dipoles are electrically isolated from one another by suitable frequency sensitive circuits to isolate high band operation from low band operation. Lossy components are also provided as an integral part of at least one of the dipole sections for significantly enhancing power transfer between the antenna and amplifier. The inductive elements further provide good impedance matching between antenna and amplifier to further optimize power transfer therebetween. The antenna is provided with capacitive end loads for improving both current magnitude and current distribution across the dipole in both low and high band VHF operation. Separate amplifier channels are provided for low band and high band signal amplification to improve gain and reduce intermodulation and cross-modulation effects. Input filter means in at least the low band amplifier channel is designed to counterbalance the reactive impedance of the antenna across the band width of interest. The antenna is contained within a lightweight weather-proof housing of simplified design which further facilitates handling and assembly. The antenna itself is lightweight, preferably being comprised of active and parasitic elements, deposited or otherwise formed upon a thin flexible insulating substrate. The two channel amplifiers are mounted directly upon the antenna and are contained within the lightweight antenna housing.
Claims available in
Description (OCR text may contain errors)
[.11 3,710,337 51 Jan. 9, 1973  MINIATURE TV ANTENNA Ronald D. Grant, Urbana, ll].
 Assignee: JFD Electronics Brooklyn, NY.
221 Filed: June28, 1971 21 Appl.No.: 157,106
Related US. Application Data  Continuation-impart of Ser. No. 22,281, March 24,
 Field of Search 343/701, 749, 751, 752, 802, 343/812, 814, 815, 817, 872; 325/373  References Cited UNITED STATES PATENTS 3,475,759 10/1969 Winecard ..343/701 Primary Examiner-Eli Lieberman Att0rneySamuel Ostrolenk et a1.
 ABSTRACT An antenna for TV reception predominantly in the low band and highband VHF-ranges having dipoles of significantly reduced physical length as compared with conventional dipoles for reception in the above mentionedVHF ranges. Inductive elements are employed as an integral part of at least one of said dipoles for improving the bandwidth and raising the Q of the. dipole. The dipoles are electrically isolated from one another by suitable frequency sensitive circuits to isolate high band operation from low band operation. Lossy components are also provided as an integral part of at least one of the dipole sections for significantly enhancing power transfer between the antenna and amplifier. The inductive elements further provide good impedance matching between antenna and amplifier to further optimize power transfer therebetween. The antenna is provided with capacitive end loads for improving both current magnitude and current distribution across the dipole in both low and high band VHF operation. Separate amplifier channels are provided for low band and high band signal amplification to improve gain and reduce intermodulation and cross-modulation effects. Input filter means in at least the low band amplifier channel is designed to counterbalance the reactive impedance of the antenna across the band width of interest. The antenna is contained within a lightweight weather-proof housing of simplified design which further facilitates handling and assembly. The antenna itself is lightweight, preferably being comprised of active and parasitic elements, deposited or otherwise formed upon a thin flexible insulating substrate. The two channel amplifiers are mounted directly .upon the antenna and are contained within the lightweight antenna housing.
18 Claims, 7 Drawing Figures PATENTEDJAN 9197s 3.710.337
sum 3 [IF 4 PAIENTEDJM 9197s 3. 7 l O 337 sum u 0F 4 INVENTOR. fan/410 .0. way/v7 ATTORNEYS MINIATURE 'rv ANTENNA The present invention isv a continuation-in-part of and an improvement of the copending application Ser. No. 22,281, filed Mar. 24, 1970 by the assignee of the present application.
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 bands is obtained and in which signals lying outside of these pass bands are eliminated, and further in which the above advantages are derived through the use of active antenna sections of significantly reduced physical dimensions.
As has been described in the above-mentioned copen'ding application,.nu rnerous problems have been encountered in attempts to develop a small size antenna capable of providing the gain and directivity characteristics not heretofore possible except through the use of conventional antennas of rather large size. Typical conventional antennas capable of providing good reception over the VHF low and high bands for both black and white and color reception usually run of the order of -12 feet in length and 3-5 feet'in width. The present invention is characterized by providing an antenna of extremely small size relative to conventional antennas having similar operating characteristics.
The present invention comprises first and second dipoles respectively provided for low and high band VHF operation. The dipoles comprise metallic means which are deposited or otherwise formed upon a thin, flexible, insulating substrate, thereby providing an extremely lightweight and yet high quality antenna insofar as operating characteristics are concerned. The first and second active dipoles are electrically isolated from one another by frequency sensitive means.
In order to increase the current values at the ends of the dipoles and to permit higher voltage levels, capacitive end loads are provided at the ends of each of the dipoles.
The amplifier circuit employed is provided with separate low band and high band VHF channels to provide excellent signal isolation while eliminating intermodulation and cross-modulation.
The physical length of each of the dipole sections is minimized. However, in order to remain within a particular noise temperature value, lumped parameter resistance elements are integrated into at least one of the dipole sections to provide for good power transfer between antenna and amplifier. The shortening of antenna length and compensating lumped parameter resistances added thereto are selected so as to provide operation of the antenna within a particular noise temperature profile, while at the same time limiting the contribution of thermal noise to the noise temperature profile so as to achieve a balance therebetween while at the same time optimizing the shortening of the antenna length.
Filter means are provided for passing the low band and high band signals to the appropriate amplifier channel, as well as for providing optimum power transfer.
The extremely lightweight small size antenna is comprised of metallic elements deposited or otherwise formed upon a thin, flexible, insulating substrate to provide an extremely lightweight antenna structure.
The amplifier means is mounted directly upon the insulating substrate. The insulating substrate carrying the antenna dipole members is sandwiched between lightweight resilient insulating members in order to protect the antenna assembly. A lightweight housing formed of a suitable insulating material such as, for example, plastic, completely contains and houses the antenna and amplifier structure while providing excellent protection against rain, sleet, dust, dirt and other harmful atmospheric influences. The lightweight rugged nature of the antenna assembly greatly simplifies assembly, handling and mounting thereof, while providing an attractive, small size antenna structure as compared with conventional antenna structures having similar operating characteristics.
It is therefor one primary object of the present invention to provide a novel antenna structure for low and high band VHF reception (or transmission) and which is of significantly reduced physical size and weight.
Another object of the present invention is to provide a novel antenna structure of significantly reduced size and weight comprising dipole sections deposited or otherwise formed upon an insulating substrate.
Another object of the present invention is to provide a novel antenna structure of significantly reduced physical size in which resistive components are employed for optimizing power transfer between antenna and amplifier means provided therefor.
Another object of the present invention is to provide a novel antenna structure of significantly reduced physical size in which resistive components are employed for optimizing power transfer between antenna and amplifier means provided therefor whereby the amplifier means is provided with impedance means for enhancing power transfer and minimizing VSWR.
Another object of the present invention is to provide a novel antenna structure comprising an extremely lightweight antenna assembly of dipole sections formed upon an extremely thin insulating substrate and sandwiched between resilient insulating means for protecting the antenna assembly and further comprising an attractive lightweight insulating housing which greatly simplifies antenna assembly, handling and installation.
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 an antenna designed in accordance with the principles of the present invention.
FIG. 2 is a schematic diagram of an amplifier designed for use with the antennaarray of FIG. 1.
FIG. 2a is a schematic diagram of an alternative amplifier designed for use 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 amplifier signals of the amplifier to a TV receiver.
FIG. 4 is a perspective view showing the antenna housing and mounting assembly.
FIG. 4a is a perspective view showing an alternative mounting arrangement for the antenna housing of FIG. 4
FIG. 5 is a sectional elevational view of the antenna assembly of FIG. 4.
FIG. 1 shows a multiple pass band antenna adapted for receiving (transmitting) frequencies in the range from 54-88 MHz (low band VHF), 174-216 MHz (high band VHF), and 47-890 MHz (UHF band) and for blocking all'other frequencies outside of the three above mentioned pass bands.
The active and parasitic components of the antenna of FIG. 1 are each comprised of conductive coatings deposited or otherwise formed upon an insulating substrate. The active elements comprising the VHF (low and high band) section of the antenna, generally designated by the numeral 12, includes an active dipole for VHF high band reception consisting of dipole arms 13aand 13b. The inboard ends of these dipole arms are coupled to terminals 14a and 14b, respectively, which in turn are connected to the input terminals of an amplifier circuit which will be more fully described in connection with FIG. 2 and whose physical dimensions are represented by dotted rectangle 16 which indicates the physical position of the amplifier structure relative to the antenna. The amplifier, in one preferred embodiment, is comprised of discrete components mounted upon a rigid printed circuit board whose outer dimensions are substantially as represented by dotted rectangle 16. The input terminals of the amplifier are appropriately electrically connected to the VHF and UHF antenna sections (the UHF antenna section will be discussed in more detail hereinbelow) and is further physically secured to the antenna housing in a manner to be described hereinbelow.
The inboard ends of dipole arms 13a and 13b are further respectively connected to the substantially L- shaped conductive strips 15a and 15b. The outermost ends of members 15a and 15b are electrically connected the innermost terminals 16a and 16b of a pair of spirally wound configurations 17a and 17b, respectively, through capacitors 18a and 18b, respectively. The capacitors 18a and 18b, together with the L-shaped sections 15a and 15b, each form a filter means which operate in a manner to be more fully described.
The outermost ends of the spiral shaped members 17a and 17b are electrically coupled in common to a centrally located conductive strip 19 which serves as ground reference. Lumped resistors 20a and 20b each have a first terminal thereof respectively connected to terminals 16a and 16b. The opposite terminals of resistors 20a and 20b are electrically connected to conductive strips 21a and 21b which are arranged so as to form the low band VHF antenna.
The outboard ends of the conductive strips 13a and 13b are electrically connected to conductive strips 22a and 22b which form capacitive end loads from the VHF high band antenna section to provide enhanced operating characteristics in a manner to be more fully described.
The outboard ends of undulating conductive strips 21a and 21b are similarly electrically connected to a pair of capacitive end load members 22a and 22b of substantially large surface areas. The undulating conductive strips 21a and 21b serve to increase the electrical length of the otherwise compressed-length low band VHF active dipole section as well as serving. as inductive components which are utilized to increase both the Q and the band width of the low band VHF dipole.
define a meandering or undulating pattern, which strips The operation of the low band VHF section of the antenna array 12 is as follows:
For low band reception, i.e., for reception of signals in the frequency range from 54-88 MHz, the series tuned circuits comprised of conductive strips 15a-15b and capacitors 18a and 18b present a low impedance to frequencies within this range to electrically couple the low band VHF antenna to terminals 14a and 14b.
It should be noted that the innermost ends of the spiral wound sections 17a and 17b are electrically coupled to the centrally located conductive strip 19. It should thus be noted therefore that the low band VHF dipole functions as a delta match with the electrical connection between the input terminals and 14b (which are coupled to the input of the amplifier means to be more fully described) and the antenna sections 21a and 21b are coupled to points removed from the innermost end (i.e., centrally located. conductive strip 19) so as to match the impedance of the low band VHF dipole to the amplifier input.
The low band VHF dipole provides operation over the entire VHF low band whereby the reduced physical (and hence electrical) length of the dipole is adequately compensated for by amplification of the received signal frequency by the amplifier means (to be more fully described) prior to application of the amplified signals to the receiver input.
As is well known, the radiation resistance of an antenna is directly proportional to its electrical length and thus any decrease in electrical length results in an accompanying decrease in radiation resistance. A further factor in antenna reception resides in the noise temperature of an antenna, which noise temperature is primarily a factor of atmospheric conditions as well as ambient noise which may be generated by electrical equipment in the general locale of the antenna. A reduction in the electrical length of the antenna reduces the noise temperature. However, in order to obtain optimum power transfer between the antenna and the amplifier, the antenna resistance most preferably should be equal to the real component of the amplifier input impedance. Thus, in order to reach an optimum condition, lumped parameter resistor elements 20a and 20b are provided in the arms of -the dipole to increase the antenna resistance to a suitable amount. The amount of resistance added must also be controlled, however, so as not to replace the otherwise reduced radiation resistance which affects noise temperature by thermal noise which may be generated by lumped parameter resistive elements of high Ohmic value. Preferably, the electrical length of the antenna is reduced to a point whereby the efficiency of the antenna is of the order of 5-20 percent of a conventional half-wave dipole. The amount of Ohmic resistance added to the dipole relative to the radiation resistance of the antenna is preferably in the ratio of 1:10. Through the application of this technique, it is thus possible to reduce antenna length to less than /4 wavelength of a full wave length dipole at the low end of the VHF low band while at the same time providing optimum power transfer between the antenna and the amplifier. The meandering path defined by the dipole sections 21a and 21b act to provide distributed inductance along the dipole arms to increase both the band width and the Q of the antenna. The conductive end sections 22a and 22b of substantially large surface area function as capacitive end loads which serve to improve band width and to increase the aperture of the VHF low band dipole. A conventional half-wave length dipole, employed for reception in the low band VHF range, is typically of the order of 100 inches in length and up to 120 inches in length at the low end of the VHF low band. The tip-to-tip length of the preferred embodimerit of the present invention is 30 inches which can be seen to constitute a significant reduction is physical size (as well as weight) as compared with a conventional half-wave length dipole.
The dipole consisting of arms 13a and 13b has no significant effect upon reception in the VHF low band. In VHF high band operation, the dipole consisting of arms 21a and 21b is decoupled from the output terminals 14a and 14b due to the series circuits comprised of strips 15a and 15b. and capacitors 18a and 18b, respectively, which present a high impedance between the output terminals 14a and 14b and the dipole arms 21a and 21b. Dipole arms 13a and 13b serve to cover the entire VHF high band rangeand, together with the amplifier means to be described more fully hereinbelow serve to provide a signal of high gain over the entire range. End sections 22a and 22b serve as capacitive end loads for the high band VHF dipole so as to improve band width and increase the aperture of the dipole. A conventional half-wave length dipole for the low end of the VHF high band is typically of the order of 30 inches. The high band dipole for one typical embodiment of the present invention is 18 inches, thus significantly reducing the physical size of the dipole employed for VHF high band reception.
In order to improve the gain and directivity of the antenna, director and reflector arrays are provided. The director array is comprised of a pair of conductive pads 23 and 24 symmetrically arranged with respect to the antenna longitudinal axis which is coincident with conductive strip 19. The director elements 23 and 24 are positioned in front of the active VHF region 12 as shown best in FIG. 1.
The reflector elements are comprised of a pair of conductive pads 25 and 26 which are likewise arranged to be symmetrical about conductive strip 19 and which are positioned immediately behind the VHF active section 12. Each of the pads have end portions of enlarged surface area, as shown by numerals 25a-25b and 260-26. The director and reflector arrays act to improve directivity of the antenna, as well as improving g the gain of the antenna throughout the high band VHF house current source through conventional plug means 30 which is connected to the primary winding 31 of a transformer TRl. The secondary winding 62 is coupled across a connector 33 for coupling a Ohm lead to the antenna. Inductor Ll isolates high frequency signals fromtransformer TRI. Aseries circuit comprised of resistor R7 and neon glow tube NE serves to indicate the fact that the circuit is powered when coupled into standard house current.
The opposite end of a 75 Ohm cable (not shown for purposes of simplicity) electrically couples the output of transformer secondary 32 (through connector 33) to connector 34 and serves as the power input to the amplifier circuit 40 of FIG. 2. Transformer TRl steps the voltage down to a relatively low level, usually of the order of 15 volts. The low voltage a.c. is coupled to a balun B1 whose output terminals are coupled to capacitors C23 and C24 and inductors L15 and L16, respectively. The opposite terminals of capacitors C23 and C24 are coupled to the input of the UHF antenna in a manner to be more full described. The opposite terminal of inductor L15 is coupled to a common bus 41 while the opposite terminal of inductor L16 is coupled in common to inductors L11, L14 and capacitors C18. The opposite terminal of inductor L11 is coupled to the anode of diode D1 whose cathode is coupled to the collector electrodes of transistors Q2 and Q1 through resistors R19 and R20, respectively. Capacitor C11, which is coupled between cathode diode D1 and common bus 41, serves to filter the rectified signal.
Transistors Q2 and Q1 form the low band and high band 'VHF amplifier channels. Output terminals 14a and 14b of the VHF antenna section 12 are coupled to the input terminals 42 and 43 of the amplifier circuit 40. Terminal 44 which forms part of the input circuit, is electrically coupled to conductive strip 19 of the antenna 10 shown in FIG. 1.
Input terminal 43 is coupled in common to one terminal of inductor L2 and one terminal of capacitor C1. The components L2, C20, C3, L4, C5 and L3 serve as the input filter circuit between input 43 and the base electrode of transistor 02. This filter circuit serves the dual functions of operating as a band pass filter and presenting a frequency sensitive impedance value which is the complex conjugate of the frequency-sensitive antenna impedance. The low band dipole of antenna 10 is primarily capacitive in the low end of the range. Conversely, at the low end of the range the impedance of the aforementioned filter circuit is inductive so as to maximize power transfer and significantly reduce VSWR. As frequency increases from the low end of the low band to the high end of the high band, the antenna impedance becomes less capacitive, is pure resistance as it crosses the zero axis and ultimately becomes inductive. The aforementioned filter circuit is initially inductive, becomes resonant at a particular increasing frequency and ultimately becomes more capacitive. Thus, the balance in reactive impedance as between the antenna and the input filter circuit is substantially maintained throughout the VHF low band range so as to optimize power transfer between the antenna and theamplifier and to minimize VSWR.
As was mentioned hereinabove, it is important that the antenna resistance and amplifier input impedance be noise matched. As a result of the significant reduction in electrical length of the antenna, radiation resistance of the antenna is likewise significantly reduced. Insertion of the lumped parameter resistor elements 20a and 20b serves to significantly increase the antenna resistance to a point where the antenna resistance is nearly equal to the real component of the amplifier input impedance so as to maximize power transfer therebetween.
Transistor Q2 amplifies the input signal applied to its base and couples this signal through its collector to the series circuit comprised of L13, C14, C16 and L14 to one terminal of inductor L16 which thereby couples the signal through balun Bl, connector 34 and a cable (not shown) to the connector 33 of the circuit 50 shown in FIG. 3. Reactive elements L13, C14, C16 and L14, together with capacitor C19 form a band pass filter circuit which serves to pass only those signals lying within the VHF low band frequency range, thereby preventing any harmonics from being passed to the input receiver.
As was described hereinabove, the VHF low band dipole comprised primarily of arms 21a and 21b is decoupled from the antenna output terminals 14a and 14b during VHF high band reception. The VHF high band antenna arms 13a and 13b are coupled to the input terminals 42 and 43 of the amplifier so as to couple any high band VHF signals through to the base electrode of transistor Q1. Elements C1, C2, L and C4 form a band pass filter which serves to pass only those signals whose frequencies lie within the VHF high band to the base electrode of transistor Q1, while blocking all other signals. The input filter coupled to transistor Q2 serves as the band pass filter to block any VHF high band signals from reaching transistor 02. The VHF high hand signals are amplified by transistor Q1 which couples the amplified signals appearing at its collector electrode through the series circuit comprised of capacitors C and C18 to one terminal of inductor L16. The components C15 and C18, together with the parallel connected components C17 and L12, form a band pass filter which serves to pass only those signals lying within the VHF high band while blocking all other signals, thereby preventing any harmonics from reaching the receiver.
Both the VHF and UHF signals are coupled through balun B1, connector 34, a 75 Ohm cable (not shown for purposes of simplicity) and connector 33 to an impedance matching circuit as shown in FIG. 3. Connector 33 is coupled across the input to balun B2 whose output is coupled in common to VHF output terminals 51 and UHF output terminals 52. Output terminals 51 are coupled to the output of balun B2 through inductors L9 and L10 which offer a high impedance to UHF signals. UHF output terminals 52 are coupled to the output of balun B2 through capacitors C25 and C26, respectively, which present a high impedance to VHF signals, thereby providing signal isolation for the output terminal sets 51 and 52.
The impedance matching circuit serves to match the output of the amplifier of FIG. 2 to a 300 Ohm input of the receiver (not shown for purposes of simplicity). A second set may be coupled to the coupling circuit 50 of FIG. 3 through a second connector 54 coupled in parallel with connector 33. Output terminals 55 which are coupled across connector 54 (through resistor R8) serve to provide for coupling of a second receiver having a 300 Ohm input. Connector 54 may be utilized in order to couple to a receiver having a 75 Ohm input.
It can thus be seen that the amplifier circuit of FIG. 2 provides complete isolation between VHF low band and high band signals, while the coupler circuit 50 of FIG. 3 provides isolation as between VHF and UHF signals. By providing filter circuits at both the input and output of the amplifiers any unwanted harmonics are prevented from reaching the receiver. For example, a third harmonic in the VHF low band would be erroneously interpreted as a valid signal lying within the high band. Such a signal is prevented from appearing in the output of the amplifier due to the filter circuit arrangement described hereinabove.
FIG. 2a shows an alternative amplifier circuit 40' which may be substituted for that shown in FIG. 2 and which basically differs from the circuit of FIG. 2 in that a UHF amplifier section 40a is provided for amplification of the UHF signals. As shown therein, the output of the VHF section of antenna 10 is coupled to input terminal 91 of a Balun B2 wherein the input signal is split between the VHF high band amplifier section comprising transistor Q1 and the VHF low band amplifier section comprising the transistor Q2. The signals after amplification are passed to the connector 34' which, in turn, is coupled to the connector 33 shown in FIG. 3 in the same manner as the amplifier circuit 40 of FIG. 2. The UHF output terminals 54 shown in FIG. 1 are coupled to the input terminals 44' of the UHF amplifier circuit and pass through capacitors C26 and C27 and Balun B4, as well as a filter section comprised of elements C25, inductor L8 and capacitor C24, so as to be applied to the input of a common base connected transistor Q3. The amplified output signal is passed through a filter circuit comprised of elements C19-C2l L9 and L10.
The input filter circuits to the high band and low band VHF amplifier sections, well as their associated output filter sections, operate in substantially the identical manner to that described hereinabove in conjunction with the amplifier circuit of FIG. 2. The input and output filter circuits of the UHF filter section 40a operates similarly so as to pass only UHF signals to the input emitter electrode of Q3 and to the coupler 34'.
Power is supplied to all three amplifier circuits by means of the full wave bridge rectifier comprised of diodes D1-D4 and the ripple eliminating circuit comprised of capacitors C26 and C27 and resistor R18. The DC. power is coupled through connector 33 and coaxial cable C (shown in broken form for purposes of simplicity) to connector 34'. The same connection is also utilized for coupling the UHF-VHF signals to the UHF output leads 91, VHF output leads 92 and an auxiliary set of UHF output leads 93. Balun B5 provides the necessary isolation between the output terminal sets 91-93 and the DC. supply. Inductors L14 and L15 act to present a high impedance to UHF signals so as to isolate these signals from the output terminal pair 92. Inductor L16 acts as a low impedance to VHF signals so as to isolate VHF signals from appearing at the output terminal pair 91. Lamp PLl serves to provide a visual indication of the fact that the A.C. powering circuit is energized.
Returning to a consideration of FIG. 1, it should be noted that the antenna array shown therein further comprises a UHF section 50 which includes three dipoles 51,52 and 53. A pair of output terminals 54 are electrically coupled to the dipoles through pairs of slender conductive strips 55, 56 and 57. Since the signal strength of the UHF signals within a reception area is typically quite adequate, the UHF signals are preferably directly coupled through the UHF antenna section output terminals 54 to the UHF input terminals 44 shown in FIG. 2. Capacitive elements C23 and C24 present a high impedance to signals lying in the VHF range while functioning effectively as a short circuit to signals in the UHF range (470-890 MHz).
The directivity and gain of the UHF section may be enhanced through the provision of director elements, one such director element 58 being provided at the forward end of the antenna array of FIG. 1 and in front of the shortest dipole 51. The signals in the UHF range are coupled through the UHF dipole section 50 to input terminals 44 of the amplifier circuit 40 and are isolated from the output of the amplifier circuit by means of inductors L15 and L16. The UHF signals are coupled in a like manner through coupler circuit 50 to the UHF output terminals 52.
Although the UHF dipole 'section is positioned in front of the VHF dipole section (receive signals approach the antenna in the manner shown by arrow A in FIG. 1) the extremely short length of the UHF dipoles has no significant effect upon reception in the VHF low and high band.
FIGS. 4 and 5 show the antenna of FIG. 1 installed within a housing assembly 60 comprised of upper and lower housing portions 61 and 62. Each of the housing portions are preferably formed of a light weight, durable molded plastic sheet such as, for example, acrylonitrite butadiene -styrene terpolymer. Upper housing member 61 is provided with a downwardly directed marginal lip 61a extending around the entire periphery thereof. The molded plastic member is provided with three molded depressions 61b-6ld, each being arranged in the rearward and forward corners of thehousing member. The bases of each of the depressions are provided with. openings 64 which are aligned with similar openings in lower housing portion 62. A molded raised pattern 65, substantially in the shape of a stylized arrowhead is provided on the surface of upper housing member 61 to improve the aesthetic appearance of the housing member as well as providing reinforcingstrength therefor.
The lower housing member 62 as shown best in FIG. 4a, has a shallow, disc-shaped configuration provided with an upwardly directed marginal portion 62a whose extreme marginal edge 62b is bent outwardly and downwardly so as to be received by the outer marginal edge 61a of upper housing member 61.
' A starburst pattern of narrow elongated depressions 66 is provided along the surface of the lower housing member 62. The forwardmost end rearward corners of the lower housing member are molded so as to provide flat surface areas 67a-67c, each of which are provided with openings 62' which are aligned with the openings 62 provided in upper housing member 61 so as to receive fastening means therethrough.
The antenna has a shape as is shown in FIG. 1 and is comprised of a thin mylar sheet having the electrical components of the antenna printed, deposited or otherwise formed thereon. The sheet is extremely flexible and light in weight. A pair of lightweight substantially resilient plastic sheets 69 and 70, preferably formed of polystyrene, are positioned above and below the insulating substrate 11 so as to sandwich the antenna structure therebetween. The amplifier circuit 40 shown in FIG. 2 is mounted in the position designated by the dotted rectangle 16 of FIG. 1. Suitable electrical connections between the UHFand VHF antenna output portion 71 which generally conforms to the contour of Q the downwardly depending amplifier printed circuit and which is further provided with an opening 71a for receiving the coaxial cable connector 34 of the amplifier (which is shown in schematic form in FIG. 2). A bracket member 76 is secured to the insulating substrate 77 upon which the components of amplifier 40 are mounted. The central portion of the bracket is provided with an opening (not shown) for receiving a fastening member 78 to rigidly secure the amplifier circuit to lower housing member 62. The coaxial coupling 34 is provided with a threaded portion 34a which receives a tapped fastening nut 79 to further secure the amplifier circuit to the lower housing member. The connector 34 mates with a suitable female connector of the connecting cable (not shown for purposesof simplicity) to couple the antenna and amplifier circuits to the coupling circuit 50 of FIG. 3 which is preferably mounted at a location remote from the antenna and which is typically mounted within the building upon which the antenna is installed. The coupling circuit, is preferably mounted within a housing which, in turn, is typically positioned in close proximity to the receiver unit.
The mating marginal edges of the housing covers 61 and 62 are sealed around their entire periphery by a suitable epoxy so as to prevent moisture, dirt or other external influences from entering into the housing, thereby providing a completely sealed enclosure for the antenna structure.
One mounting arrangement, shown best in FIG. 4, comprises substantially Z-shaped brackets a-75c, each of which is provided with openings at their upper and lower free ends. The upper ends of each of the brackets 75a75c are positioned against the flat corner surfaces of lower housing portion 62 in the manner shown so as to be joined to the antenna housing by fastening means 76a-76c. The lower free ends of each of the brackets 75a-75c may be secured to any suitable supporting surface by mounting screws 77a-77c, respectively. It has been found that the mounting assembly of FIG. 4 may be employed to mount the antenna assembly upon a wide range of grooves of either horizontal or sloping surfaces so long as the angle which the antenna forms with the horizontal plane is 40 or less.
In instances wherein it is desired to increase the type of the antenna structure relative to the mounting surface (i.e., roof and the like), the mounting assembly of FIG. 4a may be employed. As shown in this figure, a mast 81 is secured to the mounting surface by means of a base bracket 82 which may be screwed, bolted, or otherwise joined to the mounting surface. Guy wires 83 may be provided for holding the mast rigid. The upper end of mast 81 may becoupled by bracket means 84 and suitable fastening means 85 to a cylindrical shaped raised portion 86 provided along the underside of lower housing member 62. Three rigid insulating rods 87 have their lower ends secured to mast 81 and have their upper ends secured by suitable fastening means 88 to the corner portions of lower housing member 62 in the manner shown. Obviously, various other mounting hardware may be employed, depending only upon the needs of the particular installation.
As another obvious alternative, due to the highly directive characteristic of the antenna assembly, the mounting assembly employed may incorporate a rotating motor so as to align the antenna with signals received from transmitters which may be dispersed at predetermined angles relative to the receiver location.
Due to the significantly reduced size of the antenna, it is possible to mount the antenna within extremely confined interior spaces within a building structure such as, for example, attics, closets, storage spaces and the like.
The extremely lightweight and yet rugged nature of the antenna greatly enhances and facilitates handling and mounting of the antenna, while at the same time providing a sealed structure to protect the sensitive antenna components from damage or deterioration. The housing provides an attractive appearance for the antenna, as well as providing a minimum of wind resistance due to its substantially slender aerodynamic profile. The sensitive electrical components of the antenna are protected against any damage due to buffeting of the antenna caused by wind through the use of the resilient plastic sheets. The thin insulating substrate may preferably be joined to the thin plastic sheets by a suitable adhesive which is deposited at non-critical locations on the surface of the thin plastic insulating substrate. The plastic sheets are lightly sandwiched between the upper and lower housing covers and act to absorb any buffeting or impact imposed upon the antenna housing covers due to their resiliency.
It can be seen from the foregoing description that the present invention provides a novel antenna for UHF and primarily for VHF reception which is of significantly reduced size and weight and it is enclosed in an extremely lightweight and yet sturdy housing so as to greatly facilitate handling and assembly thereof. The antenna, although of greatly reduced physical size, is capable of providing high gain for all signals lying within the VHF and UHF range, while attenuating all signals outside of these pass bands. The antenna impedance is matched to the amplifier so as to provide optimum power transfer therebetween and extremely low VSWR.
Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.
What is claimed is:
1. An antenna for operation over a predetermined frequency range comprising:
a thin, insulating substrate;
a thin, flat, elongated conductive member mounted on said substrate; said member having an electrical length l, and a radiation resistance r,;
the electrical length l, of said member being substantially shorter than the electrical length I, of a halfwavelength dipole adapted to receive signals in the aforesaid predetermined frequency range and having a radiation resistance r the electrical length of said member, measured from tip-to-tip, being reduced relative to the aforesaid half-wavelength dipole until the efficiency (Eff) of said member relative to said half-wavelength dipole is between 5 20 percent;
a pair of antenna output terminals;
conductor means coupling said output terminals to said member at first and second connecting points lying a spaced interval apart along the length of said member;
said member having first and second gaps at spaced intervals along said member;
first and second lumped resistor means being respectively positioned in said first and second gaps and being electrically connected to said member to form continuous electrical paths between each free end of said member and the connecting point lying closest thereto;
amplifier means having an input coupled to said output terminals for amplifying signals lying within said predetermined frequency range;
the ohmic value of said resistor means being selected so that the sum of the radiation resistance (r, and r,) of said member and the resistance of said first and second lumped resistor means is substantially the same as the input resistance of said amplifier means.
2. The antenna of claim 1 wherein at least a portion of said member lying on opposite sides of said connecting points have an undulating pattern.
3. The antenna of claim 1 further comprising first and second capacitive end loads each being electrically coupled to opposite ends of said member;
each of said end loads being comprised of a thin flat conductive member mounted upon said sheet.
4. The antenna of claim 3 wherein said capacitive end loads are substantially rectangular in shape.
5. The antenna of claim 1 wherein first and second portions of said conductive member comprises first and second spiral shaped. loops, each being connected between one of said connecting points and an associated one of said resistor means.
6. The antenna of claim 1 wherein said predetermined frequency range is the VHF low band frequency range extending between 54 and 88 MHz;
the reactance component of the impedance of said antenna being a function of frequency;
filter means coupled between said antenna output terminals and the input of said amplifier means, the reactance component of the impedance of said filter means substantially reduces the reactance component of the antenna to reduce VSWR and optimize power transfer between the antenna and the amplifier.
7. The antenna of claim 6 wherein said filter means further comprises means for passing only those signals whose frequencies lie within said VHF low band.
8. The antenna of claim 1 further comprising a second thin flat substantially linear elongated conductive member positioned adjacent to said first mentioned elongated conductor;
said second member having a gap at its center forming first and second portions thereof;
conductor means electrically connected to the adjacent inner ends of said first and second portions;
. said second member being adapted to receive signals lying within a second predetermined frequency band whose low. frequency end is greater than the high frequency end of said first mentioned frequency band;
said conductor means including frequency sensitive impedance means having a high impedance at frequencies lying within said second frequency band to decouple signals in said second frequency band received by the first mentioned member from said antenna output terminals.
9. The antenna of claim 8 further comprising first and second capacitive end loads each being electrically coupled to opposite ends of said second member;
each of said end loads being comprised of a thin flat conductive member mounted upon said sheet.
10. The antenna of claim 8 further comprising second amplifier means;
second filter means coupled between the antenna output terminals and the input of said second amplifier means for passing only those signals whose frequencies lie within said second frequency band.
11. The antenna of claim 10 wherein said second predetermined frequency range is the VHF high band frequency range' extending between 174 and 216 MHz;
third and fourth filter means respectively coupled to the outputs of said first and second amplifiers for passing only those amplified signals which respectively lie within said UHF low and high bands.
12. The antenna of claim 8 further comprising a pair of thin flat linear elongated conductive members positioned in front of said first and second conductive members and adapted to be resonant in a third frequency range whose low frequency is substantially higher than the highest frequency end of said second predetermined frequency range;
an additional amplifier means;
said additional'amplifier means including an input filter and an output filter for passing only those signals lying within said third frequency range;
the inboard ends of said pair of members being spaced apart and having means forming output terminals for coupling to said additional amplifier input filter.
13. An antenna assembly comprising:
a thin insulating substrate;
dipole means being mounted on said substrate;
said dipole means comprising first and second dipole arms formed of thin flat elongated conductive members joined to said substrate;
amplifier means being mounted on said substrate;
the inboard ends of said arms being electrically coupled to the input of said amplifier means;
said amplifier means being a printed circuit of substantially low dprofile; first and secon substantially flat resilient insulating sheets being positioned on opposite sides of said substrate;
a housing comprising upper and lower shallow diskshaped cover members having similar shaped peripheries enclosing said substrate, said printed circuit and said first and second resilient sheets;
means for joining the marginal edges of said cover members substantially around their entire peripheries;
said lower cover member having an opening;
said amplifier means having an output connector extending through said opening;
fastening means securing said connector to said lower corner member supporting a plurality of mounting brackets for mounting said antenna upon a supporting face;
fastening means for joining said antenna to said mounting brackets;
a plurality of means provided at three points along the periphery of said housing for receiving said fastening means.
14. The assembly of claim 13 wherein said mounting brackets are substantially Z shaped, one free end of each of said brackets being joined to said housing.
15. The antenna assembly of claim 13 wherein said cover members are molded reinforced plastic members;
each of said members having a plurality of reinforcing ribs molded into their surfaces so as to form shallow depressions along the interior surfaces of said members and raised portions of low profile shaped configuration wherein the apex of said V- shaped configuration identifiesthe front end of said antenna assembly.
18. The antenna assembly of claim 13 wherein said substrate is formed of a thin flexible substantially inelastic sheet of plastic.