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Publication numberUS3599217 A
Publication typeGrant
Publication dateAug 10, 1971
Filing dateAug 19, 1968
Priority dateAug 19, 1968
Publication numberUS 3599217 A, US 3599217A, US-A-3599217, US3599217 A, US3599217A
InventorsGrant Ronald D
Original AssigneeJ F D Electronics Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Log periodic dipole antenna array
US 3599217 A
Images(4)
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Description  (OCR text may contain errors)

United States Patent J| Imentor Ronald D. Grant Urbana. Ill.

ill! Appl. No 753.590

22] Filed Aug. [9.1968

I45] Patented Aug. [0,197]

l 73] Assignee J. F, D. Electronics Corp.

Brooklyn, N.Y.

[54} L06 PERIODIC DIPOLE ANTENNA ARRAY 14 Claims, 13 Drawing Figs.

[52] L.S.CI l 343/7925,

343/8l5,343/882,343/8l8 l5l] lut.Cl. vHOlqll/IO {'50} Field ofSearch. 343/7925,

[ in] Reterenees Cited UNITED STATES PATENTS 2,69l,730 lO/l954 Lo..... 343/8l4 2,941,206 6/l960 Finneburgh 343/814 3,167,775 [H965 Cuertlcr 343/812 Primary Examiner---Eli Lieberman Attorney --Ostrolenk. Faber, Gerb & SolTen ABSTRACT: An antenna preferably designed in accordance with log-periodic principles having a superior radiation pattern and an excellent front-to-back ratio to provide exceptional performance in fringe areas. The antenna employs straight dipole arms and for VHF operation is comprised of a forward and rearward active region. The rearward active region is comprised of a plurality of dipoles having electrical lengths selected to operate in the M2 mode for low band VHF reception. The forward active region is comprised of dipoles selected to operate in the M2 mode for high band VHF reception. During low band VHF operation the forward active region has an insignificant efiect upon the rearward active region enabling signals in the low band VHF to be of high gain and having a good front-to-back ratio, as well as providing excellent directional characteristics.

PATENTED we] 0 m SHEET 2 [IF 4 LOG PERIODIC DIPOLE ANTENNA ARRAY During high band VHF reception the forward active region operates in the M2 mode while the rearward active region operates in the 3M2 mode yielding a current distribution pattern which causes the current distribution of dipoles in the active regions to be so phased as to eliminate inverted current half-cycles from the rearward active region dipoles so as to provide a unilobe directional pattern of substantially narrow beamwidth not heretofore achievable with conventional straight dipole antennas.

The element assemblies for each of the dipoles are provided with pivoting means for enabling the dipole arms to be aligned along the length of the antenna mast for packaging and shipment purposes to provide a compact package. Upon installation, the dipole arms may be rotated and locked into alignment perpendicular to the antenna mast. Transposition of the feeder harness is obtained even though straight parallel conductors are employed over the entire length of the antenna array by providing a pivoting assembly which is capable of positioning any of the pairs of the dipole arms on either side of the mast desired.

A technique for providing extremely broad band frequency response over a frequency bandwidth having a ratio of almost 2:1 is obtained through the use of a single dipole having a pair of closely spaced substantially long parasitic elements positioned adjacent thereto. The dipole is selected to have an electrical length of one-fourth wavelength close to the lower end of the operating frequency band, and the parasitic elements are designed to have electrical lengths relatively close to the electrical length of the dipole, preferably in the range from 70 percent to 90 percent of the electrical length of the dipole. The parasitic elements may be positioned either immediately above and below or in front of and behind the dipole, either of the two alternative techniques providing substantially equivalent operating characteristics. Whereas the frequency response has been found to be quite good for an operating frequency range of greater than 2:1, the range of 2;l has been found to provide a VSWR of substantially less than 3:1.

The present invention relates to antennas and more particularly to either transmitting or receiving antennas, preferably of the log-periodic design wherein the antenna array is comprised of forward and rearward active regions having electrical lengths to cause current distribution of received signals between the forward and rearward active regions to be phased so as to totally eliminate split-lobe patterns and further comprising novel active element mounting assemblies for positioning the dipole arms at any desired location along the antenna mast and further providing for transposition of the feeder harness even though spaced parallel conductors are employed for the feeder harness, and further wherein the element assemblies permit alignment of the dipole arms with the antenna mast to greatly reduce the size of shipping packages and hence to greatly simplify handling and transportation prior to the installation of antenna arrays.

One of the most dynamic developments in the outdoor receiving (and transmitting) antenna field is the log-periodic antenna which is capable of providing operation over a wide range of frequencies with a superior radiation pattern and excellent front-toback ratio so as to provide a highly directional antenna having exceptional performance in fringe areas.

From a mechanical design viewpoint, the most practical logperiodic antenna which can be constructed is the straight dipole array wherein each of the dipoles forming the logperiodic array are arranged substantially at right-angles to the supporting boom.

Such arrays, which are utilized to receive (or transmit) both the upper and lower VHF bands are normally designed so that their dipoles are of an electrical length in the low band VHF which will cause them to resonate in the fundamental or )t/2 mode for channels 2 through 6. The same elements of the array are caused, due to the log-periodic principle, to resonate in the 3M2 mode in order to receive channels 7 through 13. It

is a well-known fact that logperiodic antenna arrays employing straight dipoles whose design strictly adheres to every logperiodic design parameter will nevertheles yield a split-radiation pattern in the upper VHF band which is basically comprised of two major lobes so as to significantly reduce the directivity characteristics and thus the overall perfonnance of the antenna array.

A unique antenna design has been developed and is set forth herein, which incorporates all advantageous characteristics of the log-periodic antenna and which completely eliminates the split-lobe pattern developed by conventional log-periodic antennas having straight dipole arms.

One method which has been used in the past to correct the split-lobe radiation patterns is to V or bend the dipole arms forward toward the direction of reception (or transmission, as

the case may be) in order to produce a unilobed pattern in both the low band and high band VHF range. This approach is not completely effective and further yields a mechanically awkward, impractical antenna requiring more complex mechanical components which are difl'icult to handle from the viewpoint of production, shipping and installation. Also, it is extremely difficult with the use of so many mechanical parts to produce an antenna in which all dipole arms are bent at exactly the same angle so as to yield an excellent radiation pattern over all frequencies within the VHF upper band. Also, in installing such antennas, the handling of rather large arrays must be performed with extreme care in order not to upset the Veeing or bending of the dipole arms at the desired angle.

The present invention retains all of the advantageous characteristics of log-periodic design, while at the same time enabling the use of a straight dipole arrangement in order to take advantage of the simplicity of mechanical design while at the same time completely eliminating the split-lobe pattern normally encountered in log-periodic antennas employing straight dipoles.

The unique antenna array of the present invention is comprised of two active regions, namely a forward and rearward active region, with the dipoles of the rearward active region having electrical lengths selected to cause the dipoles in'this region to operate in the A/2 mode for low band VHF reception.

The forward active region which is spaced by a predetermined distance from the rearward active region (the spacing being a distinct departure from log-periodic concepts) is comprised of dipoles selected to operate in the M2 mode for high band VHF reception. During operation in the lower VHF band, the forward active region has an insignificant effect upon the rearward active region, enabling the antenna array to receive channels 2 through 6 and to produce signals of high gain having a good front-to-back ratio and excellent directional characteristics, as evidenced by a unilobe pattern of substantially narrow beamwidth.

During operation inthe high band VHF mode, the forward active region operates in the )t/2 mode, while the rearward active region operates in the 3M2 harmonic mode, yielding a current distribution pattern along the entire antenna array which causes the current distribution along each of the dipoles of the active regions to be so phased in relationship to one another with the current distribution along associated dipoles of the forward active region acting to eliminate the inverted current half-cycles developed 'in the rearward active region dipoles to thereby cause the split-lobe pattern normally obtained to be completely converted to a unilobe pattern of substantially narrow beamwidth.

The unique design of the antenna to be more fully described hereinbelow is also adaptable for use in antenna arrays designed for combined VHF-UHF reception. Such antennas are comprised of forward, middle and rearward active regions. One extremely advantageous design is comprised of a rearward active region having dipoles designed to operate in the fundamental or M2 mode for low band VHF reception (or transmission). At least one dipole, provided in the middle active region, is designed to operate in the M2 or fundamental mode for upper band VHF reception during which operation the rearward active region will operate in the harmonic or 3. M2 mode as was described hereinabove. The exact electrical length of the dipoles in the middle active region and the spacing from the rearward active region is selected so as to exactly phase the current distribution of dipoles from the middle and rearward active regions to produce an excellent unilobe pattern of substantially narrow beamwidth. The effect of the forwardmost active region is quite insignificant for both low band and high band VHF reception (or transmission).

The forward active region is comprised of one or more dipoles designed to operate in the fundamental or )t/ 2 mode in the UHF band. The middle active region has one or more dipoles selected to operate in the harmonic or 3M2 mode in the UHF range, causing the dipoles in the forward active region to operate as mode-encouraging elements for the dipoles of the middle active region to phase out the inverted half-cycle current portions of the current distributions along the middle active region dipoles so as to provide a unilobe pattern for UHF reception having a substantially narrow beamwidth. The uniqueness of the combined VHF-UHF receiving antenna array is that the middle active region functions in one case as a mode-encouraging region for the rearward active region during VHF operation and operates as the primary receiving active region during UHF operation, thereby performing two dissimilar functions in the antenna array.

Gain and radiation pattern characteristics can be further improved in either or both of the above antennas through the addition of parasitic elements which are selected to improve both directivity and gain. However, even in the absence of such parasitic elements, both of the above described antenna arrays provide advantageous characteristics of high gain (which is substantially constant across the frequency ranges of operation), extremely good front-to-back ratios, and a unilobe radiation pattern of substantially narrow beamwidth throughout all frequencies within the range of operation of the antenna array.

The single dipole employed for UHF reception is found to provide extremely broad band frequency response over a frequency ratio of better than 2:1 through the provision of closely spaced parasitic elements either in front of and behind the dipole, or above and below the dipole. In addition to providing extremely close spacing of the parasitic elements relative to the dipole, the parasitic elements have an electrical length which are quite close to the electrical length of the dipole itself, usually of the order of 70 percent to 90 percent of the electrical length of the dipole. This array, either operating as an independent array or in conjunction with the composite array of the present invention, provides extremely good frequency response and yields a VSWR of substantially less than 3:! for an operating frequency band of a ratio of almost 2:1.

A unique element assembly is provided for mounting dipole arms to the antenna boom. One of the major contributing factors in providing a good front-to-back reception (or transmission) radiation pattern is the provision of a transposed feeder harness so as to provide a 180 phase shift between adjacent dipoles arranged along the antennaboom. Prior techniques for providing the desired transposition have been either to physically cross the wires forming the transposed feeder harness over one another or to use bare wiresections arranged in a crisscross fashion for the transposition. Other techniques have been employed which require numerous connecting elements making the final design rather tedious and involved and requiring tedious and expensive assembly techniques.

The dipole arms of the antenna described herein provides transposition between adjacent dipole arms in the antenna array in spite of the fact that the transposed feeder harness itself is comprised of a pair of air dielectric (bare) conductors which are straight over substantially their entire length and which are arranged in spaced substantially parallel fashion. The element connecting assembly is comprised of a pair of insulators positioned on opposite sides of the antenna boom and fixedly coupled thereto by any suitable fastening means. A pair of brackets, formed of any suitable conductive material having a substantially high degree of resiliency are mounted each to one face of an associated bracket. Each bracket is provided with a preformed arcuate shaped portion for receiving and engaging a portion of an associated feeder harness wire.

Each dipole assembly is comprised of a pair of dipole arms having their inboard ends pivotally connected to an associated bracket and insulator to permit each of the dipole arms to be pivoted so as to be substantially in parallel alignment with the antenna boom so that the antenna, in its collapsed position, provides a significantly reduced overall assembly to greatly facilitate handling, packaging and transportation of the antenna array.

Upon installation, each of the dipole arms are pivoted away from their aligned position with the boom so as to be aligned substantially perpendicular to the boom. Alternate arms are disposed in opposite directions and are caused to bear down upon their associated bracket so as to assure firm mechanical and electrical contact with the transposed wire positioned beneath its associated bracket so as to provide excellent electrical contact between the feeder harness, as well as providing the desired transposition.

It is, therefore, one primary object of the present invention to provide a novel antenna array extremely advantageous for use in UHF and VHF reception (or transmission) and employing straight dipole arms in forward and rearward active regions having electrical lengths so as to completely eliminate split-lobe radiation patterns encountered in VHF and UHF reception.

Another object of the present invention is to provide a novel antenna array comprised of a single dipole and a pair of closely spaced parasitic elements whose electrical lengths are just slightly less than the electrical length of the dipole to provide operation over an operating frequency range of a ratio of nearly 2:1 having a VSWR of less than 3:1 over this range.

Still another object of the present invention is to provide a novel element assembly for use in antenna arrays in which dipole arms are pivotally coupled to the element assembly to enable alignment of the arms with the boom of the antenna array during handling, packaging and shipping to greatly reduce the overall dimensions of the antenna and further being pivotable to positions perpendicular to the boom of the antenna in either direction of perpendicularity so as to provide for transposition of the feeder harness in spite of the fact that the air dielectric feeder harness is comprised of a pair of straight wires arranged in spaced parallel fashion over their entire length.

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 simplified top view showing a conventional straight dipole antenna employing parasitic elements.

FIGS. 2a through 2c are schematic diagrams of an antenna array designed in accordance with the principles of the present invention and showing current distribution atterns for low band VHF, high band VHF and UHF reception, respectively, which distribution patterns are useful in describing the present invention.

FIG. 3a shows a polar pattern (i.e., a radiation pattern) for low band and high band VHF reception.

FIG. 3b is a polar pattern showing UHF reception.

FIG. 4a is a perspective view showing a dipole unit assembly for pivotally mounting the dipole arms in the array of FIGS. 2a through 20, for example.

FIG. 4b is an elevational view of the dipole unit assembly of FIG. 4a.

FIGS. 50 through 50 are side, top and end views showing the spring clip member of FIGS. 4a and 4b in greater detail.

FIG. 6a shows an isolated view of a portion of the UHF section of the composite antenna array shown in FIGS. 20 through 2c.

FIG. 6b shows a Smith Chart plot of the antenna impedance characteristics of the array of FIG. 6a plotted against increasing frequency.

Referring now to the drawings, FIG. 1 shows an antenna array 10 of conventional design employing a plurality of straight dipole arms 11 which are graduated in length from the rear to the front of the antenna. The front of the antenna is directed toward the source of signals being transmitted, as indicated by Arrow 12. Each of the active elements (i.e., dipoles) 11 is provided with a parasitic element 13 located in close proximity to its associated dipole and is substantially in front of its associated dipole so that all of the dipole elements 1 1 and parasitic elements 13 are substantially coplanar.

The parasitic elements 13 employed in the conventional straight dipole antenna of FIG. 1 block 30 percent of the aperture on low band Vl-IF reception, as is indicated by the trapezoidal-shaped shaded area which is defined at the front and rear ends by the forwardmost parasitic element and the rearwardmost dipole element, respectively, and which is defined along its diagonal sides by the extremities of the parasitic elements. In addition thereto, the suppresser parasitic elements are signal-sapping and add great expense and weight to the overall array.

FIGS. 2a through 2c all show a combined VHF-UHF antenna array which incorporates the principles of the present invention, it being understood that like elements are designated by like numerals.

The antenna array 20 shown therein is comprised of a plurality of active elements (i.e., dipoles) 21 through 25 and a plurality of parasitic elements 26 through 32, respectively, arranged substantially in coplanar fashion along the antenna boom (solid line) 33. i

The active elements 21 through 25 are electrically coupled by means of a transposed feeder harness 34 coupled to the inboard ends of each of the dipole arms making up the dipoles 21 through 25. Transposition provides a substantially 180 phase shift for adjacent dipoles.

The antenna array of FIGS. 2a through 20 is comprised of a forward active region which includes dipoles 24 and 25; a middle active region which includes dipole 24 (dipole 24 performs the dual function of being an integral part of both forward and middle active regions); and a rearward active region including dipoles 21 through 23. The dipoles 21 through 23 can be seen to be of gradually decreasing electrical length from the rear toward the front of the antenna which is pointed in the direction of reception shown by arrow 35 which indicates the direction of transmitted signals to bereceived by the antenna array. The electrical lengths of adjacent dipole arms may be related to one another by the factor 1- wherein 'r normally lies within the range from 0.650 to 1.00. The success of the antenna array described herein is not limited to strict adherence to such a log-periodic relationship. In addition thereto, the spacing normally employed in log-periodic arrays which normally decreases between adjacent dipoles in moving from the rear toward the front of the antenna wherein the spacing is normally related by a similar 7 factor which may or may not be equal to the 1 factor for the relationship between electrical lengths, the antenna of the present invention does not rely for its successful operation upon log-periodic spacing and, in fact, shows superior results when a log-periodic spacing is not employed. As one example, the ratio of the electrical lengths of dipoles 22 and 21 is more than l0 percent greater than the ratio of the electrical length of dipoles 23 and 22. The spacing between dipoles 22 and 23 is preferably greater than the spacing between dipoles 22 and 21 which would not be the case with an antenna array employing strict log-periodic dimensional relationships.

Considering the dipoles 23 through 25, it can clearly be seen that the spacing between dipoles 23 and 24 is greater than the spacing between any other two adjacent dipoles, while the spacing between dipoles 24 and 25 is substantially less than the spacing between any other two adjacent dipoles. This spacing is dictated, not by log-periodic principles but by the phasing relationship, to be more fully described, which functions to provide the unilobe radiation pattern for the antenna array over its entire frequency range of operation.

The parasitic elements act to further enhance and improve the gain and directivity characteristics of the antenna, but it should be understood that exceptional results are nevertheless obtained through the antenna array shown even with all of the parasitic elements 26 through 32 being eliminated from the array.

FIG. 2a shows the current distribution pattern obtained when operating at one frequency within the low band VHF range (i.e., television channels 2 through 6). The dipoles 21 through 23 are each of an electrical length causing them to resonate in the A/Z mode (at the particular frequency to which they are tuned). Considering dipole 21, for example, its electrical length is tuned to resonate in the M2 mode for one of the low band VHF TV channels so as to yield a current distribution pattern shown by the dotted line 210 which can clearly be seen to be a half-current cycle at the resonant frequency for dipole 21. In a like manner, the dipoles 22 and 23, when operating at their resonant frequencies, yield a half-current distribution pattern 220 and 23a, respectively. During low band VHF reception (ortransmission), the remaining dipoles 24 and 25 of the array 20 have no effect whatsoever upon reception (or transmission) yielding a low band radiation pattern 40, shown in FIG. 3a, which is a unilobe radiation pattern of relatively narrow beamwidth.

FIG. 2b shows the same antenna array 20 and its manner of operation in the VHF high band which encompasses television channels 7 through l3. During high band operation, the nature of the log-periodic principle is such as to cause the dipoles 21 through 23, whose electrical lengths are the same as the dipoles 21 through 23 of FIG. 2a to operate in the 3M2 mode.

Considering dipole 21, for example, when receiving (or transmitting) the particular frequency at which it resonates in the 3M2 mode, the current distribution pattern is comprised of three half-current cycles, as shown by the waveform 21b. Simultaneously therewith, dipole 24 has an electrical length causing it to resonate in the fundamental or M2 mode during VHF high band operation so that its current distribution pattern, when operating at the resonant frequency of dipole 21, for example, yields a half-cycle current waveform 24a. These two coexisting patterns, together with the phase relationship controlled by the length of the transposed feeder line between dipoles 21 and 24 act to substantially completely cancel the current half-cycle portion 21b so as to yield a unilobe radiation pattern 41 of the type shown in FIG. 3a which can clearly be seen to be of extremely narrow bandwidth, especially when compared with the radiation patterns obtained through the employment of straight dipole antenna arrays in the upper VHF band which are notoriously twin-lobed and of an extremely larger bandwidth when compared with the pattern 40 obtained through the use of the array of the present invention.

In a like manner, each of the remain ng dipoles 22 and 23 exhibit a current distribution pattern of three current half-cycles 22b and 23b, respectively, when the array is receiving (or transmitting) at the resonant frequencies of these particular dipoles. The dipole 24 yields a half-current pattern having a wavelength equal to the wavelength obtained by the current distribution patterns for the dipoles 22 and 23, depending upon which is resonating at any particular time. The current distribution along dipole 24, due to the phasing relationship determined by the length of the transposed feeder harness between the active dipoles 22 and 24 or 23 and 24, acts to substantially exactly cancel the half-cycle centrally located current portion 22b or 23b, depending upon the particular dipole (22 or 23) resonating at that given time.

In the case where a signal for a particular upper band VHF channel is being received (or transmitted) which has a frequency lying between the resonant frequencies of dipoles 21 through 23, these dipoles share" in the reception of such a signal and again the current distribution pattern along dipole 24 acts to cancel the centrally located half-cycle of current due to the phasing relationships between dipole 24 and the remaining dipoles 21 through 23 of the rearward active region so as to completely eliminate the split-lobed pattern normally obtained with straight dipole antenna arrays and to yield a unilobe radiation pattern of narrow bandwidth of the type shown by the pattern 41 of FIG. 3a.

The operation of the antenna array is quite similar for UHF reception. Considering FIG. 2c, for example, which depicts the same antenna array as FIGS. 2a and 2b, it should be noted that dipole 24, which constitutes the middle active region of the antenna array, is designed to resonate for all UHF channels in the 3M2 mode as shown by the current distribution pattern 24b which indicates the three-half cycles of current distributed along the dipole for one particular UHF TV channel being received (or transmitted). The dipole 25 is of an electrical length so as to cause it to resonate in the fundamental or M2 mode to yield a current distribution pattern which is comprised of a half-cycle of current, as shown by waveform 25a. The phasing between dipoles 24 and 25 which is controlled by the distance between the dipoles along transposed feeder harness 34, is such as to cause the centrally located half-cycle current waveform 24b to be exactly cancelled by the halfcycle of current 25a developed along dipole 25. This results in a radiation pattern, shown in FIG. 3b, which is a unilobe pattern 42 of substantially narrow beamwidth so as to completely eliminate a split or twin-lobed radiation pattern which is normally developed by straight dipole antenna arrays.

The colinear dual band director system comprised of directors 28 and 32 act to enhance directivity and gain for the array. Each of the directors 28 and 32 is separated into three colinear sections by means of insulator structures 45a-45b and 46a-46b, respectively. The two outboard directors 28a and 28b (and 32a and 32b) are effective during high band VHF operation, while the inboard section 280 (and 320) is effective during UHF operation to yield extremely sharp pictures for either color or biaclc and white reception.

For high band VHF reception, the directors 28 and 32 operate in the following manner:

The outboard sections 28a and 2812 (as well as sections 32a and 32b) yield a half-wavelength current distribution 28d and 28e (as well as 32d and 32e) during high band VHF operation (see the current distribution patterns of FIG. 2b) to enhance the gain of the antenna.

During UHF operation, the inboard section 280 (as well as 32c) yields a half-wavelength current distribution pattern 28]" (as well as 32f) (see the current distribution patterns of FIG. to enhance the gain of the antenna.

The shorter parasitic elements 29 through 31 yield similar half-wavelength current distribution patterns during UHF operation (see current pattern 31a of FIG. 20) to still further enhance the gain.

The composite antenna array of FIG. 2a further shows the use of two very closely spaced parasitic elements 26a and 26b positioned immediately in front and immediately behind dipole 25. Although FIG. 2a shows the parasitic elements 260! and 26b in dipole as lying substantially within a common horizontal plane, it should be noted that the parasitic elements may be positioned immediately above and below dipole 25 so as to lie substantially within a common vertically aligned plane.

As a further modification, the dipole 25 and parasitic elements 26a and 26b may all lie in a common plane which may be aligned diagonally relative to an imaginary horizontal plane, without affecting the operating characteristics of this array.

FIG. 6a shows this array isolated from the composite array of FIG. 2a. In one preferred embodiment in which it was desired to provide for UHF reception (or transmission) the electrical length of the dipole was selected to be one-fourth wavelength at an operating frequency of 560 megacycles. The parasitic elements are closely spaced to the dipole so as to lie a spaced distance from the dipole within the range from onefifth to one-sixtieth of a wavelength and preferably within the range from one-thirtiethto one fiftieth of a wavelength. The dipoles have an electrical length which lies within a range from percent to 90 percent of the electrical length of dipole 25. Thus, in one practical embodiment, the dipole which is selected to have an electrical length of one'fourth wavelength at an operating frequency of 560 megacycles is approximately 5% inches in length. The spacing between the dipole and each of the parasitic elements in the preferred range is of the order of less than three-fourths of an inch to less than one-half inch, while the electrical lengths of the parasitic elements lie in the range from approximately 3% inches to 4% inches.

The operation of the array of FIG. 6a is as follows:

Assuming a dipole is selected having the electrical length set forth above, a first parasitic element 26a is positioned in front of the dipole in the above-mentioned closely spaced fashion, and is provided with an electrical length which is substantially 80 percent of the electrical length of the dipole. At a frequency of 560 megacycles, the impedance of the antenna is real (i.e., pure resistance see FIG. 612). As the operating frequency increases beyond 560 megacycles, the impedance is both real and reactive (see curve 70). As the operating frequency approaches 590 megacycles, the reactive impedance component diminishes considerably until at 590 megacycles, the impedance is almost pure resistance. An increase in the operating frequency behind 590 megacycles shows that the reactive impedance component again increases significantly in magnitude. However, over an operating frequency from about 560 megacycles to about 620 megacycles, the VSWR is less than 3:1. By placing another parasitic element 26!) immediately behind dipole 25, which is approximately 90 percent of the electrical length of dipole 25 and which is spaced from the dipole in the above-mentioned preferred range, it is found that the impedance characteristics of the array of FIG. 6a is still further enhanced.

Turning to a consideration of the Smith Chart of FIG. 6b, the curve 70 represents a plot of impedance versus frequency for the array of FIG. (in. At 560 megacycles, the antenna impedance is real (i.e., pure resistance). As the operating frequency increases, the impedance becomes partially reactive with the magnitude of the reactive component increasing until the operating frequency of 590 megacycles is approached. Approaching an operating frequency of 590 megacycles, the reactive component diminishes considerably until the reactive component becomes almost insignificant at an operating frequency of 590 megacycles. AS the operating frequency increases beyond 590 megacycles, the reactive component again becomes appreciable in magnitude until, approximately midway between 590 megacycles and 620 megacycles, the reactive component diminishes considerably so that it is quite small in magnitude at an operating frequency of 630 megacycles, but is nevertheless slightly greater in magnitude than the reactive component existing at an operating frequency of 590 megacycles. The reactive component again increases in magnitude as the operat ng frequency increases beyond 630 megacycles and periodically approaches the real impedance axis 71'. of the Smith Chart plot, but at each time, the closest point of the reactive impedance value to the real axis becomes slightly further removed from the real axis 72 than the preceding approach to the real axis. It has been found that the antenna operation over an operating frequency band a from 470 to 800 megacycles yields a VSWR of less than 3:1,

and it is not until the operating frequency falls outside of this range that the VS'WR deteriorates.

Curve 71 of HO. 6!) is a plot of antenna impedance versus operating frequency for an array in which the forward parasitic element 26a has a length substantially equal to 70 percent of the electrical length of dipole 25, while the rearward parasitic element has a length substantially equal to percent of the electrical length of dipole 25. The general configuration of curves 71B and H can be seen to be quite similar, with the exception that the reactive impedance component undergoes much larger sweeps in the regions intermediate those points where it most closely approaches the real axis 72 of the Smith Chart. Even these electrical lengths, however, have been found to provide a VSWR of substantially less than 3:1 over the operating frequency range from 470 to 800 megacycles.

The frequency response characteristics of the array of FIG.

6a may further be enhanced by providing still additional dipole elements either in front of or behind (or, for that matter, above or below) those dipoles 26a and 26b already positioned immediately adjacent dipole 25. For example, additional parasitic elements 260 and 26d may be positioned in front of parasitic element 250, with the spacing between adjacent elements being within the range set forth above, and with the electrical length being of the order of 10 percent less than the electrical length of its immediate adjacent parasitic element. For example, parasitic element 260 should be of an electrical length substantially 90 percent that of parasitic element 26a, while parasitic element 26d should be of an electrical length substantially 90 percent that of parasitic element 26c. A similar impedance curve will be obtained for this array of an increased number of total elements wherein the improvement resides in the fact that the maximum reactive impedance component values do not move as far away from the real axis 72 of the Smith Chart, as is shown in curves 70 and 71.

FIGS. 40 and 4b are perspective and front elevational views, respectively, showing the element assembly for use in mounting active elements (i.e., dipoles) to the boom 51 of the antenna array. The assembly 50 shown in these figures is comprised of a pair of insulators 52 and 53 each being machined or otherwise formed so as to have a substantially C-shaped cavity or groove 52a and 53a, respectively, in order to embrace the boom 51. Each of the insulator members is further provided with a large diameter opening 52b and 53b, respectively, which narrows to a small diameter opening 526 and 536, respectively, for receiving a fastening member 54 which may, for example, be a rivet having its flattened heads 54a and 54b resting upon the shoulders which join the wide and narrow diameter openings 52b-52c and 53b-53c, respectively. The assembly 50 may be mounted anywhere along the length of the boom 51 by machining or otherwise forming two aligned openings (not shown) in the upper and lower surfaces 51a and 51b of the boom. The openings may be of a diameter just sufficient to accommodate the rivet member 54 or may, for example, be slightly elongated so as to permit slight adjustment of location of the element assembly 50 along the length of the boom 51.

Each of the insulator members 52 and 53 are further provided with wide diameter openings 52d and 53d, respectively, which are joined by smaller diameter openings 52c and 532, respectively, for receiving fastening members 55 and 56, respectively, which pivotally mount elongated ferrules 57 and 58, respectively, to the insulators 52 and 53. The fastening means 55 and 56, which may, for example, be rivets, have their flattened ends 55a and 55b, respectively, resting upon the shoulders which join the narrow and wide diameter portions 52e-52d and 53e--53d, respectively. The opposite ends of the rivets pass through suitable openings (not shown) in the ferrules 57 and 58 as well as passing through central openings provided in washers 59 and 60 to complete the pivotal mounting assemblies.

Since each of the ferrules are substantially identical in configuration and operation, only one of these ferrules will be described herein for purposes of simplicity. The ferrule 57 has a hollow interior and its right-hand end (relative to FIGS. 4a and 4b) is rounded at 57a and is of an inner diameter sufficient to receive the inboard end 61 of one dipole arm 21a. The lefthand end of dipole arm 21a is inserted into the hollow interior of ferrule 57 so that its extreme inboard edge 210' extends to the extreme left-hand edge of ferrule 57, as can best be seen in FIG. 40. With the elements 21a and 57 telescoped in the manner shown, the ferrule 57 is pressed or otherwise formed over the major portion thereof so as to provide a substantially rectangular cross-sectional configuration 57b which'acts' to provide an extremely good force fitting between the elements 21a and 57 as well as to enhance electrical contact between the transposed feeder harness and the dipole ann'in a manner to be more fully described.

The ferrule 57 and dipole arm 21a are further provided with suitable openings for receipt of the fasteningmember or rivet 55. The rivet 55 can clearly be seen to pass through a suitable opening (not shown) in a conductive bracket member 63 which has a substantially flat central portion 63a provided with a bent flange 63b near its lefthand end which fits into a cavity 52f formed in insulator member 52.

Each of the conductive brackets 63 and 64 is shown in greater detail in FIGS. 5a through 50 which depict the side, top and end views, respectively, of the bracket 63, it being understood that bracket 64 is substantially identical in both design and operation. As shown therein, the bracket 63 is provided with the previously mentioned flange 63b at one end thereof and with an opening 63c for receiving fastening member 55. The central or main body portion 63a is further provided with an arcuate-shaped portion 63c which bears upon and makes firm mechanical and electrical contact with one substantially straight bare conductor 66 (see FIGS. 4a and 4b).

A portion of the main body portion 63a is cut out to form an elongated slot 63d so as to effectively form a pair of resilient projections 63:: and 63f which are bent at a point 67 along their lengths and are joined at their extremities by an integrally formed rib portion 633, shown best in FIGS. 5b and 5c.

The distance across elongated slot 63d is slightly greater than the width of the rectangular cross-sectional portion of ferrule 57 and the bracket 63 operates in the following manner:

As shown best in FIGS. 40 and 4b, the arcuate formed portion 63c of bracket 63 makes substantially firm surface contact with the feeder harness conductor 66. During handling, packaging and shipment of the antenna array, each of the ferrules such as, for example, the ferrule 57, is pivoted in the direction shown by arrow 68 so as to be substantially parallel with boom 51 and so as to occupy the position shown by the dotted line configuration 57'. Thisarrangement measurably reduces the overall width of the antenna array to greatly facilitate packaging costs, the packaging operation itself and handling during transportation, as well as the overall transportational costs. a v

During final installation of the antenna each of the dipole arms 21a and 21b is rotated or pivoted from its position in alignment with boom 51 to the solid line positions shown best in FIGS. 4a and 4b wherein each of the dipole arms 21a and 21b is substantially perpendicular to the boom 51. In moving each of the dipole arms to the solid line positions of FIGS. 4a and 4b the ferrule portions are snapped" and locked into position by being embraced within the confines of the elongated slot 63d. In actuality, the ferrule 57, in moving to the position perpendicular to boom 51, causes one of the bracket arms, for example, arm 63f, to be forced or urged downw srdly toward the insulator 52 as the ferrule rides over this arm. As soon as the ferrule lies within the confines of elongated slot 63d, the natural resiliency of bracket 63 (which is preferably formed of a metal having sufficient resiliency) causes the bracket to spring upwardly again and thereby firmly lock the ferrule 57 of dipole arm 21a into a right-angle alignment with boom 51. In this position, rivet 55 which firmly secures the dipole arm and ferrule to insulator 52 causes the ferrule to press'the arcuate section 630 of bracket 63 into firm surface contact with the feeder harness wire 66 providing an electrical path from the bare wire 66 through the ferrule and dipole arm 57 and 21a, respectively, to provide good electrical contact therebetween. If desired, the transposed feeder harness wire 66, instead of being bare wire over its entire length, can certainly be covered with insulation except for the portions along its length where it is to make electrical contact with brackets The dipole arm 21b may be positioned in a like manner to provide a straight dipole alignment with each of the dipole arms being aligned perpendicular to boom 51. The bracket 64 can clearly be seen to make good electrical contact with the other transposed feeder harness wire 67, as shown best in FIG. 4b.

Transposition of the feeder harness, which is shown in schematic fashion in FIGS. 2a through 2:, can easily and readily be obtained simply by positioning the first dipole arms 21a and 21b of dipole 21 in the manner shown in FIG. 4a. The 180 transposition may be obtained simply by rotating ferrules 57 and 58 through 180 relative to their positions shown in FIG. 4a so that the dipole arm 21a of FIG. 4a projects to the left of boom 51 and so that the dipole arm 21b projects toward the right of boom 51. Obviously, the dipole anns for the next dipole should be numbered 22a and 22b. This arrangement yields the desired 180 transposition while providing a pair of (preferably bare) conductors 66 and 67, thereby completely eliminating the need for bending the feeder harness wires or otherwise providing a crossover arrangement, as is shown schematically in FIGS. 2a-2c, while at the same time providing the equivalent electrical characteristic of transposition. The arrangement of the present invention, in addition to greatly reducing shipping, handling and packaging costs, totally eliminates crossover wire harnesses which have high loss characteristics. When rotating or pivoting the dipoles 180 from their positions, shown in FIG. 4a, the left'hand end portions of the ferrules 57 and 58 are locked by the elongated slots such as, for example, the slots 63d shown in FIG. b in the same manner as the right-hand end of the ferrule portion of square shape is locked within this elongated slot. Thus the firm rigid positioning and appropriate perpendicular alignment of each dipole arm is obtained regardless of which perpendicular alignment each dipole arm assumes relative to boom 51.

It can clearly be seen from the foregoing description that the present invention provides a novel antenna array comprised of straight dipole arms which is capable of providing a highly directional radiation pattern of substantially narrow beamwidth over the entire VHF and UHF operating band wherein split-lobe or twin-lobe patterns are completely eliminated through the unique phasing of the dipole arms provided in rearward, middle and forward active regions along the antenna array.

A novel element assembly is provided for electrically :oupling dipole arms to the antenna boom wherein good electrical contact is made with the antenna feeder harness and the :nboard ends of the active elements while overall design of the array is greatlysimplified through the use of a pair of spaced narallel feeder harness conductors. Transposition of adjacent iipoles is accomplished through the use of pivotally mounted lipole arms which are rotatable to either side of the boom and ire locked into 90 alignment with the boom. When in the locked position, not only is good perpendicular alignment issured, but the electrical contact is greatly enhanced as a esult of the firm pressure engagement between the dipole arm 'errule, the bracket and the bare conductor which are all iressed in a first direction against their associated insulator nember.

Although I have described preferred embodiments of my novel invention, many variations and modifications will now ie obvious to those skilled in the art, and I prefer, therefore, to Ie limited not by the specific disclosure herein, but only by the .ppended claims.

Iclaim:

1. An antenna array for receiving signals in the lower and .pper VHF operating frequency bands and in the UHF operatag frequency band comprised of a plurality of straight dipoles rranged in spaced parallel fashion and being substantially ymmetrical about the longitudinal axis of the array;

said dipoles being of gradually increasing electrical length from a first end of the array toward the second end of the array;

at least one of said dipoles forming a rearward active region near the second end of said array;

at least the second one of said dipoles forming a forward active region in front of said rearward active region and toward said array first end;

at least a third one of said dipoles forming an intermediate active region positioned between said forward and rearward active regions;

a feeder harness electrically coupled to all of said dipoles;

a pair of terminals at one end of said harness for coupling signals received by said array to suitable utilization means;

the dipole of said rearward active region being of anelectrical length designed to resonate in the M2 mode during operation in the VHF low band range to develop a halfcycle current distribution across the dipole wherein A is the wavelength of the operating frequency of a signal being transmitted in the VHF low band;

the dipole of said rearward active region further being adapted to resonate in the 3M2 mode during operation in the VHF high band range to develop a three-half-cycle current distribution across the dipole wherein 3k is the wavelength of the operating frequency of a signal being transmitted in the VHF high band;

the dipole of said intermediate active region being of an electrical length designed to resonate in the M2 mode during operation in the VHF band range for the signal being transmitted in the VHF high band to develop a halfcycle current distribution across the dipole;

the dipoles of said intermediate and rearward active regions being coupled to said feeder harness at predetermined spaced intervals to cause the half-cycle current distribution of the forward active region dipole to cancel one half-cycle of the three-half-cycles forming the current distribution pattern along the rearward active region dipole when operating in the VHF high band to yield a unilobe radiation pattern of substantially narrow bandwidth;

the dipole of said intermediate active region further being adapted to resonate in the M2 mode during operation in the major portion of the UHF band for a signal being transmitted in the UHF band to develop a three-halfcycle current distribution across the dipole;

the dipole of said forward active region being of an electrical length designed to resonate in the M2 mode for a signal being transmitted in said portion in the UHF band to develop a half-cycle current distribution across the dipole;

the dipoles of said intennediate and forward active regions being coupled to said feeder harness at predetermined spaced intervals to cause the half-cycle current distribution of the forward active region dipole to cancel one half-cycle of the three-half-cycles forming the current distribution pattern along the intennediate active region dipole when operating in the UHF band to yield a unilobe radiation pattern of substantially narrow beamwidth,

2. An element assembly for antenna arrays employing a transposed feeder harness for coupling dipoles forming the array and being arranged at spaced int rvals along a boom wherein the feeder harness is comprised of a pair of substantially straight conductors arranged in spaced parallel fashion on opposite sides of said boom;

the improvement comprising a pair of insulating members each having a groove conforming to the periphery of the boom and each being positioned on opposite sides of said boom;

fastening means for securing said insulating members to said boom;

each insulating member being positioned between said boom and an associated one of said conductors;

a resilient conductive bracket fastened to each of said insulating members; each of said conductors being positioned between confronting surfaces of an associated bracket and insulating member to make firm electrical contact with its associated bracket;

each of said brackets having a pair of integrally formed resilient fingers each being bent so that their distal ends lie a spaced distance above their associated insulating member;

said fingers being spaced apart from one another by a predetermined distance to define an opening space therebetween;

a conductive ferrule pivotally mounted to each of said brackets; I

each ferrule having a hollow interior for receiving the inboard end of a dipole arm and being movable between a first position substantially colinear with said boom to either a second or a third position; said second and third positions aligning said ferrule perpendicular to said boom;

a portion of said ferrule being embraced between said fingers when moved to either said second or said third position causing its associated bracket to lock its associated ferrule into perpendicular alignment with said boom.

3. The element assembly of claim 2 wherein each of said brackets is provided with a bent portion intennediate its ends to conform to and embrace the periphery of its associated conductor.

4. The element assembly of claim 2 wherein each of said ferrules biases its associated bracket toward firm electrical engagement with an associated conductor when the ferrule is aligned perpendicular to said boom to further enhance electrical contact between each conductor and its associated bracket.

5. The element assembly of claim 2 wherein each dipole of the array is mechanically coupled to the boom and electrically coupled to the feeder harness by means of an element assembly of the type described in claim 2;

the ferrules of adjacent dipole first arms electrically coupled to one of said conductors being pivoted to perpendicularly align their associated dipole first arms on opposite sides ofsaid boom;

the remaining ferrules of adjacent dipole arms. electrically coupled to the remaining conductor being pivoted to perpendicularly align their associated dipole second arms on opposite sides of said boom;

the first and second dipole arms of each dipole being substantially colinear.

6. The assembly of claim 2 wherein the distal ends of said fingers are joined by an integrally formed rib.

7. A single dipole antenna array having a broad band operating frequency range of substantially 2:1; said dipole comprised of a pair of dipole arms each being provided with a terminal;

said terminals being adapted for coupling electromagnetic radiation received by said dipole to a utilization means;

a first parasitic element being positioned on one side of said dipole;

a second parasitic element being positioned on the opposite side of said dipole;

said elements and said dipole all lying substantially within a common imaginary plane;

said dipole having an electrical length equal to one-quarter wavelength (one-quarter A) of an operating frequency lying intermediate the upper and lower frequency limits of the operating frequency range and preferably closer to the lower frequency limit;

said elements each being spaced from said dipole by a distance lying in the range from one-fifth to one-sixtieth of the wavelength K; said elements each having an electrical length lying in the range from 70 percent to 90 length of said dipole. 8. The antenna array of claim. 7 wherein said first and second parasitic elements have lengths substantially equal, respectively, to percent and percent of the electrical length of said dipole.

9. The antenna array of claim 7 wherein said first and second parasitic elements have lengths substantially equal, respectively, to 70 percent and 80 percent of the electrical lenlgth of said dipole.

. The antenna array-of claim 7 wherein the midpoints of said dipoles and said first and second parasitic elements lie substantially along a common line.

11. The antenna array of claim 7 wherein said common imaginary plane is aligned substantially in a horizontal direction.

12. The antenna array of claim 7 wherein said common imaginary plane is aligned substantially in a vertical direction.

13. The antenna array of claim 7 wherein said common imaginary plane is aligned substantially in a diagonal direction.

14. An element assembly for antenna arrays employing a transposed feeder harness for coupling dipoles forming the array and being arranged at spaced intervals along a boom wherein the feeder harness is comprised of a pair of substantially straight conductors arranged in spaced parallel fashion on opposite sides of said boom;

the improvement comprising:

insulation means receiving said boom and having first and second mounting surfaces on opposite sides of said boom;

fastening means for securing said insulation means to said boom;

the mounting surfaces of said insulation means each being positioned between said boom and an associated one of said conductors;

a resilient conductive bracket fastened to an associated one of said mounting surfaces, each of said conductors being positioned between confronting surfaces of an associated bracket and mounting surface to make firm electrical contact with its associated bracket;

each of said brackets having a pair of integrally formed resilient fingers each being bent so that their distal ends lie a spaced distance above their associated insulating member;

said fingers being spaced apart from one another by a predetermined distance to define an opening space therebetween;

a conductive ferrule pivotally mounted to each of said brackets;

each ferrule having a hollow interior for receiving the inboard end of a dipole arm and being movable between a first position substantially colinear with said boom to either a second or a third position, said second and third positions aligning said ferrule perpendicular to said boom;

a portion of said ferrule being embraced between said fingers when moved to either said second or said third position causing its associated bracket to look its associated ferrule into perpendicular alignment with said boom.

percent of the electrical

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3931626 *Dec 7, 1973Jan 6, 1976Sylvan SimonsStaggered tuned TV receiving antenna with integrated UHF-VHF sections
US4010473 *Oct 14, 1975Mar 1, 1977Rca CorporationAntenna construction
US4398201 *Mar 16, 1981Aug 9, 1983Winegard CompanyAntenna director and method therefor
US5012256 *May 13, 1987Apr 30, 1991British Broadcasting CorporationArray antenna
US5666126 *Sep 18, 1995Sep 9, 1997California AmplifierMulti-staged antenna optimized for reception within multiple frequency bands
US5712643 *Dec 5, 1995Jan 27, 1998Cushcraft CorporationPlanar microstrip Yagi Antenna array
US6133889 *Jan 12, 1998Oct 17, 2000Radio Frequency Systems, Inc.Log periodic dipole antenna having an interior centerfeed microstrip feedline
US6747600 *May 8, 2002Jun 8, 2004Accton Technology CorporationDual-band monopole antenna
US6757908 *May 28, 1999Jun 29, 20043Com CorporationGraphical representation of impairment or other conditions in a data-over-cable system
US7429960Apr 27, 2006Sep 30, 2008Agc Automotive Americas R & D, Inc.Log-periodic antenna
US7626557Mar 31, 2007Dec 1, 2009Bradley L. EckwielenDigital UHF/VHF antenna
US7911406Mar 31, 2007Mar 22, 2011Bradley Lee EckwielenModular digital UHF/VHF antenna
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Classifications
U.S. Classification343/792.5, 343/815, 343/818, 343/882
International ClassificationH01Q11/10, H01Q11/00, H01Q1/12
Cooperative ClassificationH01Q11/10, H01Q1/1228
European ClassificationH01Q1/12B3, H01Q11/10