US3454950A - Multiple mode operational antennas employing reactive elements - Google Patents

Description

July 8, 1969 R. D. GRANT ET AL 3,454,950

MULTIPLE MODE OPERATIONAL ANTENNAS EMPLOYING REACTIVE ELEMENTS Filed Dec. 1, 1964 sheet of 5 ...FI-E: JA- '0R/0@ ART fr (3 -2/2 Magi) July 8, 1969 R. D. GRANT ET AL 3,454,950

MULTIPLE MODE OPERATIONAL- ANTENNAS EMPLOYING RECTIVE ELEMENTS Filed Dec. 1, 1964 sheet 2 of 5 g L l b 44.4 Mb 46.4 47.5 ab im 50,5 I I l July s, 1969 R. D. GRANT ETAL 3,454,950

MULTIPLE MODE OPERATIONAL- ANTENNAS EMPLOYING REACTIVE ELEMENTS Filed Dec. 1, 1964 sheet 5 of 5 52.5 f6.6 6 747 77:/ fa.; ya /ffc /a/ d, j v

l f y July 8, 1969 R. D. GRANT ET AL 3,454,950

MULTIPLE MODE OPERATIONAL ANTENNAS EMPLOYING REACTIVE ELEMENTS JIJ 4/ '547 274/ 7/a/ INVENTORS A70/Wm 0. @ew/V7 July 8, 1969 R. D. GRANT ET AL 3,454,950

MULTIPLE MODE OPERATIONAL ANTENNAS EMPLOYING REACTIVE ELEMENTS Filed Dec. 1, 1964 sheet 5 of 5 United States Patent O U.S. Cl. 343-751 9 Claims ABSTRACT OF THE DISCLOSURE An antenna array employing reactive elements positioned along the length of the arms of selected dipoles for altering the multimode frequency relationships and enabling a larger number of dipoles to contribute more effectively to the overall operation and gain in each operating frequency range thereby providing an antenna extremely advantageous for use in VHF and UHF applications. The outboard sections of selected dipoles in the UHF array act as directors contributing to a significant improvement in the gain characteristics of the antenna. Parasitic elements provided with reactive members separating their outboard sections from their inboard sections may be employed to further increase the gain characteristics of UHF and/or VHF antennas. The reactive elements are selected to have relatively high impedance in fundamental or lower harmonic frequency operating modes, with their impedance substantially decreasing when the elements operate in higher modes in order to attain the above objectives.

The instant invention relates to antennas and more particularly to antennas having wide band frequency response over a plurality of discrete frequency ranges Wherein reactive elements forming an integral part of the antenna dipoles within the dipole array and/or director array provides greater utilization of all of the elements within the antenna array.

An extremely large amount of research and development effort has been expended in the past ten years to develop an antenna array providing extremely broad frequency response. One specic antenna which has-been developed and which yields the above desirable characteristics is commonly referred to as the log-periodic antenna. Antennas of this general category are typically comprised of a plurality of 'dipoles arranged in either linear or V-contigurations wherein the length of and spacing between dipoles within the antenna array is chosen in such a manner as to provide a predetermined group of dipoles within the array which contribute to the reception (or transmission) of the electromagnetic wave.

Antennas of this general design are typically employed in the eld of television reception, but are designed with the intent of providing successful operation only over the discrete television frequency ranges of 54-88 mc. which constitutes the low VHF and 174-216 me. which constitutes the high VHF band.

The basic approach to the design of such antennas resides in the selection of dipole elements Which are resonant in the half wave length mode within the lower frequency range of 54-88 me. The lowest frequency at which the input impedance of an individual linear dipole becomes purely resistive occurs when the dipole is approximately one-half wavelength from tip to tip. Other relatively low resistive values of the input impedance are obtained when a Idipole is approximately an add multiple of half wavelengths. Even though variations in dipole construction may shift the resonant frequency so that it no longer corresponds exactly to one-half wave length ice from tip to tip of the dipole, it is nevertheless convenient to refer to the first resonance as the half-Wave length mode and similarly for the other resonances. Thus, it is common usage to say that the electrical length of a dipole at the lowest frequency resonance is one-half wave length even though the physical length may not be exactly equal to one-half wave length. A suflicient number of dipoles is selected in order to provide adequate reception within the one-half wave length mode frequency range.

An additional feature accruing from the selection of dipoles which resonate in the one-half wave length mode, the very same elements may provide satisfactory resonant operation within the three-halves wave length mode, thus a log-periodic array of V-elements (see U.S. Patents 3,150,376, 3,108,280 and 3,011,168) provides reasonably satisfactory results over two or lmore discrete frequency ranges with certain physical limitations. For example, some of the elements which are resonant in the M2 mode at the low band VHF channel frequencies (S4-88 mc.) will also be resonant in the 3 \/2 mode at the high band VHF channel frequencies (174-216 mc.).

A plot of the gain characteristics of such log-periodic antennas indicates that the gain over the high band VHF is substantially greater than the -gain obtained by the low band VHF operation.

In order to improve or peak the gain characteristics of such dual band operational antennas near the high frequency ends of 4the bands, it is quite typical to provide parasitic elements which are typically designated as directors, having dimensions which are chosen for providing such peaking. It has been typical to provide a director element of a first electrical length to provide for the peaking of the channel 6 frequency and further to provide another director element for peaking the gain of the channel 13 frequency. It can be seen from this overall design that only one of the director elements is utilized Within a discrete frequency range while the remaining director element serves no useful function in that frequency range. This is generally true of separate high and low band director elements such that any director elements employed to peak the gain characteristics Within one discrete frequency range of the television band widths serves no useful function whatsoever in the remaining television bandwidth.

While there are some dual band directors, they lack the proper ratio of resonant frequencies at rst and second operating modes.

The instant invention provides an element configuration employing reactive components which are integral with the director elements and of such a value as to provide elements which alter their resonant frequencies to perform dual functions which are extremely useful in both discrete frequency ranges within the television bandwidth, for example.

One primary object of the instant invention is to provide .a novel director element for use in dual band antenna structures which employ reactive elements forming an integral part of the director member thereby enabling a single director means to provide for the peaking of gain in both of the discrete frequency ranges.

The novel director element is comprised of a conductive rod arranged in either linear or V-contiguration along the antenna boom. In the preferred arrangement each half of the directorhas provided along its length one or more reactive elements inserted between otherwise insulated sections of each director arm. For VHF television applications, each director element is designed so as to have an electrical length which is on the order of 5% less than the electrical length needed for a dipole designed to be resonant in the one-half mode at the upper end of the lower frequency band, i.e.,l near 88 mc. At the upper end of the upper frequency band, i.e., at 216 mc.

the director element is so chosen as to be substantially 5% less in electrical length than a dipole designed to operate near 216 mc. in its three-halves wavelength resonant mode.

This arrangement thereby provides a single director configuration which provides substantially optimum results near the upper end frequency values of the lower and upper discrete frequency bands.

Comparing this operation against present day dual band antennas using director elements, the electrical length of such directors is usually chosen so as to be resonant near the high frequency end of the low VHF band, i.e., near 88 mc. For three-halves mode operation the same director configuration typically has a resonance at a frequency which is considerably above 216 mc., thereby failing to provide the optimum peaking desired. This has usually necessitated the provisions of rst and second director configurations for dual mode antennas with each of the directors being chosen to provide peaking of the gain characteristics -within one of the discrete frequency ranges. Through the use of the instant invention a single director configuration provided with reactive components will yield the optimum peaking of the gain characteristics over both the low and high band frequency ranges.

Still another application of the above concept lies in the utilization of the reactive elements so as to form an integral part of the driven dipoles within an antenna arrangement. Present day techniques for the design of log-periodic antennas providing wide band frequency response over the low and high television frequency bands, for example, is comprised of designing the dipoles so that their electrical lengths provide for resonant operation in the one-half mode with a sufiicient number of dipoles being provided for adequate reception of all channels in the low band (S4-88 mc.). These same elements will also resonate in the higher modes, i.e., threehalves, five-halves, seven-halves, et cetera, but within the VHF television band the primary concern is the onehalf and three-halves wave length operational modes. The dipole designed lto resonate in the one-half wave length mode for the frequency of 88 mc., for example, will resonate approximately at the frequency of 264 mc. in the three-halves wave-length mode, which frequency lies substantially beyond the upper end of the upper TV frequency band of 174-216 mc. Thus, the dipole which provides the major reception for the frequency of 88 mc. is effectively useless in the upper frequency band.

It is therefore another object of the instant invention to provide an antenna arrangement capable of providing multimode operation over at least two discrete frequency ranges in which all of the dipoles within the antenna array are more fully utilized.

As was previously mentioned, it can clearly be seen that certain dipole configurations which have electrical lengths which, in the one-halves mode, resonate at a frequency allocated to a TV channel within the 4lower frequency band will, in the three-halves wavelength mode have an electrical length which is significantly different from that needed for operation in the higher band. Through the employment of a reactive element which forms an integral part of the dipole arms, it is possible to provide a dipole configuration which has the proper electrical length to be resonant at a channel frequency in the low band and which, likewise has an electrical length for the three-halves mode which will be resonant ata channel frequency in the upper frequency band.

Each dipole element is comprised of dipole arms which may be arranged in either a linear or V-configuration. Each arm is further comprised of an inboard and one or more outboard sections with these sections being physically spaced from one another by suitable insulating means. Electrical connection between the inboard and outboard sections is provided through reactive elements having values which are so chosen as to establish electrical length for the dipole to substantially yield resonant operation at the one-half wave length mode.

In the higher operational mode, the reactive elements, due to the appreciable increase in the operating frequency, act in a different way to establish an electrical length for the dipole to substantially yield resonant operation at the higher modes. The overall antenna array through the incorporation of dipole configurations having such reactive components yields a structure in which all dipole configurations of the multiple dipole array can be utilized to an extremely high degree in several operating frequency bands. The application of the reactive elements for providing varying electrical lengths of the dipole configuration may also be very effectively employed in the UHF operational modes wherein dipole configurations are designed to provide resonant operation at the five halves, seven-halves, or other higher mode for the frequency ranges in the UHF band.

A most desirable objective is that of providing both VHF and UHF antenna sections in a simple structure which in turn, provides optimum reception (or transmission) characteristics over both UHF and VHF operating bands. One approach in such an all-band antenna design is that of providing a UHF section mounted in front of the VHF section, as discussed in the above-mentioned Patent No. 3,150,376. The dipole configurations of the dipoles comprising the UHF section are designed so as to have electrical lengths which will resonate at channel frequencies within the UHF band of 470-890 mc. If these dipoles operate in the one-half mode, they will have little effect upon the performance of the remaining elements designed to resonate at one-half mode, and three-halves modes in the low and high VHF bands, respectively. However, since the reception at UHF is more critical than at VHF frequencies, it is most desirable to provide more directivity and greater gain at UHF than can be achieved using the one-half mode. It is thus desirable that the dipoles resonate at five-halves, seven-halves, or some other higher mode. The longer dipoles of the UHF section would then have electrical lengths which are such as to make a significant effect upon the operating characteristics of all the all-band antenna within the VHF operating ranges. The dipoles of the UHF section, when the all-tband antenna array is operating in the VHF ranges, may act as reflective elements which tend to shield incoming channel frequencies so as to prevent them from reaching the dipoles of the VHF section in the all-band antenna array. Thus, while the UHF section may give satisfactory results when the all-band antenna array operates in the UHF region, this UHF section, nevertheless may damage the effectiveness of the VHF section, thereby preventing the design of an optimum all-band antenna.

Still another problem which resides in antenna arrays of the log-periodic design is that of successfully maintaining the antenna impedance constant over the operating frequency ranges. As an example, in a log periodic antenna array comprised of a plurality of dipole coniigurations larranged in either V or linear fashion, it has been found that a group of two or three immediate adjacent dipole contigurations normally contribute to the reception of any one channel frequency. In the case where this group of two or three immediately adjacent dipoles lies somewhere near the middle of the array, it has been found that the dipoles lying in front of the group of two or three dipoles -above mentioned, while they make no significant contribution to the reception of the previously mentioned predetermined channel frequency, nevertheless provide an extremely important function of maintaining the impedance constant by contributing to the impedance of the whole antenna by providing impedance matching between the active region (i.e., the previously mentioned three neighboring dipoles) and the feed point. This region of dead dipoles (i.e., dipoles which do not lie in the active region), are commonly referred to as the transmission region.

It is therefore an object of the instant invention to provide an al1-band antenna providing extremely constant reception characteristics over all of the VHF and UHF operating bands and which completely overcomes the shielding problem which the UHF section causes during VHF operation of the all-band antenna array, as well as providing elements within the UHF section of the antenna array which are designed so as to operate as the transmission region for the VHF section in order to provide the desired impedance match between the active region and the antenna feed point.

The all-band antenna array is comprised of UHF and VHF sections which may preferably, but no necessarily, be of the log-periodic design, with the UHF section being positioned within the array so that it lies in front of the VHF section. Each dipole in the VHF section is designed to have a specic electrical length with the dipoles cooperating to provide extremely good operation over both high and low bands of VHF operation. Thus, the dipoles are arranged so as to resonate in the onehalf mode when the antenna is operating in the lower VHF band and designed to resonate in the three-halves mode when the antenna array is operating in the upper VHF frequency band.

The UHF section of the antenna array may be preferably, but not necessarily, be of the log-periodic design and is comprised of a plurality of dipoles which are designed so as to effectively match the impedance when the al1-band array is operating in either the high or low VHF bands and further are designed so as to operate in the seven-halves or other higher order mode when the all-band antenna array is operating within the UHF band. These unique operational characteristics are made possible through the use of reactive elements which form an integral part of each arm of the dipoles, thereby providing dipole configurations of first and second arms with each arm being further comprised of an inboard section and an outboard section. The inboard section is electrically connected to the antenna feeder line. The outboard section is collinear with the inboard section and is electrically insulated therefrom. Electrical connection between the inboard and outboard sections is established by virtue of a reactive element. The impedance value of the reactive element may be so chosen as to effectively electrically decouple the outboard section from the inboard section when the all-band antenna array is operating in either of the two VHF frequency bands. The reactance values of the reactive elements which electrically couple the inboard and outboard sections of each dipole arm may be chosen so as to present 'an extremely high impedance during operation of the antenna array in the VHF bands. The electrical lengths of the inboard sections may then be chosen so as to cause them to operate as short dipole elements in the transmission region for the VHF section. The reactive elements provide la substantially open-circuit condition between infboard and outboard sections so that essentially only the inboard section acts to establish the electrical length of the dipoles in the UHF section of the antenna array as VHF frequencies.

Turning to the operation of the all-band antenna array in the UHF frequency range, the increase in operation frequencies is such as to cause the reactive elements to establish essentially a short-circuit between inboard and outboard sections so that both inboard and outboard section of the dipole arms act to establish the electrical length of the dipoles during UHF operation. The dipoles, during this operation, resonate in the seven-halves or other higher order mode and yield extremely good reception (transmission) characteristics over the entire UHF band.

Turning again to operation within the VHF bands, of the all-band antenna array, it has been noted that an additional feature of the all-band antenna, designed in the manner recited above, resides in the fact that the outboard `section of the arms in the UHF seption of the antenna being effectively electrically insulated from the inboard sections, and hence from the antenna feeder line, may operate as directors and act to provide a peaking of the gain characteristics for reception of the channel 6 and channel 13 frequencies.

It is therefore a primary object of the instant invention to provide a novel dual band antenna designed for operation over two discrete frequency ranges wherein reactive elements forming an integral part of the dipole arms are provided for the purpose of yielding an extremely high degree of utilization of the dipoles in both frequency ranges.

Still another object of the instant invention is to provide a novel dual band antenna array comprised of a plurality of dipoles, selected ones of which are provided with reactive elements forming an integral part of the dipole arms so as to yield maximum contribution from all of the elements within the array, thereby vastly improving the performance of the antenna.

Still another object of the instant invention is to provide a novel antenna array designed for dual band operation and having parasitic director elements, the arms of which are provided with reactive members as an integral part thereof to provide optimum peaking of the gain characteristics in both frequency bands of operation.

Still another object of the instant invention is to provide a novel antenna array having a constant gain characteristic over each of the UHF and VHF frequency bands in which the UHF section of the antenna array is provided with dipoles having reactive elements as integral parts thereof so as to completely avoid the shielding effect imposed by the UHF section upon the VHF section during VHF operation while at the same time substantially improving the impedance characteristic of the antenna throughout all of its operating ranges. These and other objects of the instant invention will become apparent when reading the accompanying description and drawings in which:

FIGURE la is a schematic diagram showing a typical dual band antenna of log-periodic design.

FIGURE lb is a schematic diagram showing a dual band antenna of log-periodic design employing the concepts of the instant invention.

FIGURE 2a is a schematic diagram showing a dual band antenna having parasitic director elements employing the concepts of the instant invention` FIGURE 2b shows a schematic diagram of a dual band antenna array of the type shown in FIGURE 2a, with the dipoles mounted in a V-configuration and further including a chart of element lengths and spacings.

FIGURE 3a is a schematic diagram showing an allband antenna array of log-periodic design.

FIGURES 3b-3d, respectively, are schematic diagrams of an all-band antenna array having a VHF section and a UHF section, both employing reactive elements as integral components of the dipole arms, which figures are provided to explain the operation of the all-band antenna with reactive elements in each of its operating frequency bands.

FIGURE 4a is a perspective drawing showing the elements of a typical dipole arm in greater detail.

FIGURE 4b is a perspective view showing a dipole arm designed for use in a UHF antenna section of the type shown in FIGURES Sla-3d.

FIGURE 4c shows a cross-sectional view of the dielectric disc member employed in the dipole arms of FIG- URES 4a and 4b.

FIGURE 4d shows an exploded side View of the dipole arm assembly of FIGURE 4a.

FIGURE 4e shows an exploded View of the dipole arm assembly of FIGURE 4b with some of the elements being removed to facilitate an understanding of the drawmgs.

Referring now to the drawings, FIGURE lo shows an antenna structure 10 which is comprised of a transposed feeder line 11 having electrically coupled thereto the arms 12a-19a and 12b-19b forming the dipoles 12-19, respectively. The arms of dipoles 12-19 are longest toward the left-hand end of the array and decrease in length gradually toward the right-hand end thereof. The take-olf point for the power, generally designated by the symbol 20, is electrically coupled to the transposed feeder harness 11 and may be a power source (transmitter) or sink (receiver) depending upon the manner in which the antenna is used. In the preferred construction the spacing between adjacent dipoles measured along the longitudinal axis of the antenna represented by the phantom line 21 decreases in a gradual manner from the left-hand to the right-hand end of the antenna array. The length of the antenna arms 12a-19a and 12b-19b and the spacing between adjacent dipoles may typically be determined in the manner set forth in U.S. Patent No. 3,108,280, entitled Log-Periodic Backward Wave Antenna Array, issued to Mayes et al. and assigned to the University of Illinois Foundation. Such log-periodic design yields an antenna array which provides constant gain characteristics over each of a wide range of discrete frequency bands. It is preferred that the antenna be symmetrical about the line 21 passing through the midpoints of the linear dipoles and the apexes of the V-elements, respectively, as shown.

When acting as a transmitting antenna, the antenna is fed at its narrow end from a conventional source of energy, depicted in FIGURE 1a, by Way of illustration only as alternator 20, by means of a balanced feeder line 11 consisting of conductors 11a and 11b. It will be seen that the crossed feeder lines 11a and 11b are twisted between connections to consecutive or adjacent elements of the antenna.

The length of an element (dipole or V-element) in the antenna shown in FIGURE la is designated herein as Ln, where n is used to designate any element of the antenna. Thus, for example, the longest element 12 in the antenna of FIGURE la is designated as L1, meaning element No. 1. Thus, in general, the subscript n indicates the order of the particular element. It should be noted that in the case of V-elements, the effective length of a V-element is taken to be the length which the arms of the V-element have from the feeder line connection to the free ends thereof.

The lengths of the elements in the antennas of the invention, and the spacing between these elements are preferably related by a substantially constant scale factor r which is defined by the following equations:

T L(n+1) :AStmLn Ln ASD where r is a constant having a value TS1, Ln is the length of a dipole element of the antenna, L(+1) is the corresponding length of the adjacent smaller element, ASn is the spacing between the element having the length Ln and the adjacent larger element, and AS(+1) is the spacing between the element having the length Ln and the adjacent smaller element.

In the foregoing, it will be observed that the same scale factor, f, may be used to determine both dipole length and spacing. This will, under normal conditions, represent optimum operational conditions. However, if efciency of a lesser degree can be tolerated, it is at times, possible to operate with a different scale factor for determining the dipole length from that which determines spacing. At such times, .a scale factor -rl may be used to determine the dipole length and a scale factor r2 may be used to control spacing the dipole sections.

As a more specific example, let it be assumed that the antenna array 10 of FIGURE 1a is designed for the purpose of providing constant gain characteristics in the high and low frequency bands of VHF television reception, namely, the frequency bands of 54-88 mc. and 174- 216 mc., respectively.

Considering lirst the low band extending from 54-88 mc., the dipoles 12/-19v have their arms designed so that the electrical lengths of the dipoles cause them to resonate in the M2 mode at the frequencies fm shown immediately adacent the -antenna arms 12a19a, respectively. Thus, for example, the dipole 15 comprised of arms 15a and 15b, respectively, has an electrical length which causes it to resonate in the M2 operating mode at a frequency of 62.0 mc. With the `design of the dipoles 12-19 to provide these electrical lengths the antenna array gives essentially constant gain characteristics over the entire low band from 54 to S8 mc.

When the antenna array 10 of FIGURE la is employed in upper band operation, however, it turns out that the electrical lengths of these dipoles 12-19 are such as to cause 3A/2 mode operation at the frequencies fm set forth immediately above the upper ends of the dipole arms 12a-19a, respectively. Thus, for example, the dipole 19 which in the M 2 mode resonates at a channel frequency of 86 mc. has -an electrical length such that in the 37\/2 mode it resonates at approximately 258 mc. Considering all other dipoles 12-1`8 of the antenna array 10, it can be seen that the ratio K of resonant frequencies for lower to upper band operation is approximately 1:3, i.e., K=flb+fhb. Thus, the only dipoles which clearly lie within the upper VHF television frequency band 174-216 mc. are the dipoles 15 and 16, thereby making the gain characteristic of the antenna, during high band operation, dependent exclusively upon three or four dipoles of the total array of eight dipoles so that no more than l/2 of the dipoles are effectively utilized for achieving directivity during the high band opeartion of the antenna array.

FIGURE lb shows an antenna array 10' employing the concept of the instant invention. The array 10 shows like elements of FIGURE la as bearing like designating numerals. Thus it can be seen that the transposed feeder line 11, source 20 and dipoles 12-1'5 are substantially identical in design and opeartion to the elements bearing like numerals shown in the array 10 of FIGURE la The array 10', however, differs from the array 10 in the design of the dipoles 1019, respectively. Since certain of these dipoles are substantially similar to one another, a description of dipole y16 will be given, it being understood that the other dipoles 17-19 are designed in a like manner.

The dipole 16 is comprised of an upper arm having an inboard section 16e and an outboard section 16d. These sections are electrically insulated from one another and an electrical coupling therebetween is established by the reactive element 16gI which capacitively couples inboard and outboard sections 16C and 16d, respectively. In a like manner, the lower arm of dipole 16 is comprised of an inboard and an outboard section 16e and 16j, respectively, inboard section 16e is electrically coupled to the transposed feeder line 11 and is electrically insulated form the outboard section 16f. The reactive element 16h capacitively couples inboard section 16e to outboard section 16f.

Analyzing the operational characteristics of dipole 16', the reactive elements 16g and 16h, which have substantially equal reactances have a reactance X which is equal to l/jwc where w is the radian frequency at which the antenna is operating; j is equal to the square root of minus 1 and C is the capacitance |value of reactive element 16g (or 16h). In operation of dipole 16 inthe M2 mode, i.e., in the band of 54-88 mc. the reactance X is large so that the outboard sections 16d and 163C are substantially decoupled from the inboard section 16a` and 16e, respectively. This causes a shift in the resonant frequency of the dipole 16 as compared to a dipole of the same physical length but of the type of dipole 16 in FIGURE la.V

During operation in the high band 174-216 mc. the quantity w is approximately three times greater than its value during low band operation, causing the reactance to be approximately 1/3 as large as its value during low band operation. This causes a more effective electrical connection between the inboard and outboard sections 16C-16d and 16e-16f, respectively. Hence, the shift in the resonant frequency in the higher mode is different from the shift in the lower mode.

Thus, during low band operation of the reactive elements dipole 16 may by an adjustment of the length of sections 16C and 16d, be made to resonate at a channel frequency of 67.3 mc. as also does dipole 16 of lFIGURE. la.

During high band operation, however, which is in the 31/2 mode, the electrical length is such as to cause dipole 16 to resonate at a channel frequency of 190 mc. rather than 207.9 as for dipole 16. Thus the ratio of low band to high band resonant frequencies hereinafter referred to as K, is equal to 0.355 in this case, rather than 0.333 as in the case of the conventional dipoles of FIGURE la. As was previously described, the ratio of low band to high band resonant frequencies for dipoles not employing reactive elements is more nearly K=0.333. The employment of the reactive element in the manner described above thereby permits a substantial departure from the conventional dipole in the ratio between lower land upper band resonant frequencies.

The dipoles 17-19 are designed in a like manner and likewise operate in a manner similar to dipole 16. It can be seen that the dipoles 17-19 in low band operation resonate at channel frequencies well within the low band which extends from 54-88 rnc. Also in the high band these dipoles 17-19 resonate at frequencies which lie substantially within the upper VHF band extending from 174-216 mc. Comparing the operating characteristics of the antenna arrays 10 and 10 of FIGURES la and lb, respectively, it can be seen that both antennas utilize all of their elements during low band operation. During high band VHF operation, antenna 10 utilizes primarily the dipoles 14, and 16. The antenna array 10, however, utilizes the dipoles 14, 15 and 16-19 such as to yield vastly superior gain characteristics over the entire upper frequency band as compared with array 10.

While the antenna array 10 of FIGURE lb shows its dipoles 12-15 and 1619' as having a Vd configuration, it should be understood that the design of dipole arms employing reactive elements as integral parts thereof may be employed with equal success in other antenna arrays wherein the arms of the dipoles are substantially collinear with respect to one another.

Comparing the ratios K for all dipoles 12-19 of antenna array 10 shown in FIGURE la, it can be seen that this ratio remains at substantially 0.33 throughout the entire array. Considering array 10' of FIGURE lb, the ratios of dipoles 12-15 are substantially equal to 0.33. However, it will be noted that the values of K for dipoles 16-19 show a signicant departure from the value 0.33 and increase to as much as 0.4. The inventors have found that through control of the value of the capacitor elements 16g-19g and 16h-19h and the positioning of the capacitive elements (i.e., their location between the ends of each arm of the dipole) it is possible to achieve a value of at least 0.418.

It has been found that in order to improve the gain characteristic of antenna array 10 through both low and high bands of VHF operation, it becomes advantageous to trim certain of the dipole arms within the array, thus constituting a slight departure from strict log-periodic design equations. However, it may generally be said that the antenna array is most heavily dependent upon the log-periodic design equations for its superior operational characteristics. It should be understood that the dipoles of the instant invention which employ reactive compoents as an integral of the dipole arms may be utilized with equal success in other log-periodic arrangements such as those antennas described in U.S. Patents Nos. 2,958,081, 2,985,879 and 3,011,168, as well as other patents and publications teaching log-periodic concepts. The

major consideration with regard to employment of the instant invention is the advantageous use to which the dipoles employing reactive elements having values selected so that ratios of resonant frequencies at various modes are altered from the values obtained with conventional dipoles. Operation of this type is dependent only upon design considerations effecting the value of the reactive element and its positioning between the ends of each dipole arm (i.e., the links of the inboard and outboard sections, respectively).

The basic approach to the design of a dipole utilizing a capacitive element is to rst select the reactance X and position along one dipole of the capactive element to provide the desired ratio K between resonant frequencies. This element can be scaled so as to yield the desired electrical length in one operating band in which the antenna array will function. The capacitive element in the dipole then yields the desired electrical length for the other frequency band. In instances where the antenna dipole is designed to resonate in the M2 and 3x/2 modes the outboard section of the dipole arm is never completely decoupled from its associated inboard section so that it does effectively add some length to the inboard section, thus establishing the necessity of positioning or locating the reactive element along the length of each arm of the dipole. The capacitive element, while varying in location with different dipole configurations, usually lies within a range from 0.2 to 0.7 of the distance from the center of the dipole to the extreme end of the dipole arm.

FIGURE 2a of the instant invention shows a dual band antenna array 30 comprised of a transposed feeder harness 31 and a plurality of dipoles 32-35 with each dipole, in turn, being comprised of dipole arms 32a-35a and 32h-35b, respectively. The chart accompanying FIG- URE 2b sets forth the dimensions of the dipoles h and l and the spacings between adjacent dipoles d. The dipole arms of each dipole are arranged in collinear fashion. For example, dipole arms 32a and 32b of dipole 32 are arranged so as to substantially lie along a straight line. Dipole arms 32a, 33b, 34a and 35b are electrically coupled to one side of feeder harness 31 while the arms 32b, 33a, 34h and 35a are electrically coupled to the opposite side of harness 31 with the sides of the harness 31 being transposed between adjacent dipoles in order to greatly improve the front-to-back ratio for the antenna. The source (transmitter) or sink (receiver) represented by the symbol designated by numeral 36 iS electrically coupled to the transposed feeder harness 31 in the manner shown. The dipoles are designed so as to yield log-periodic antenna characteristics in the same manner as previously described with the lengths of dipole arms decreasing gradually from left to right and with the spacing between adjacent dipoles preferably decreasing gradually from left to right.

In the case Where a log-periodic antenna of the type 30, shown in FIGURE 2a, has been designed for use in TV reception, for example, the dipoles are chosen so that their electrical lengths will give constant gain characteristics over the low and high VHF bands of 54-88 mc. and 174-216 mc., respectively. In order to peak, i.e., to increase the gain characteristics of the antenna array 30 near the high frequency end of the band, it has been typical to employ parasitic director elements. A parasitic director element is basically one that somewhat resembles a short-circuited dipole, but is not electrically coupled to the antenna transposed feeder line, hence the term parasitic element. Such an element directs the signal toward the antenna array by guiding it in such a manner as to improve or peak the performance at the desired channel frequency. Typically, for the low VHF television band the director element may have an electrical length such as to resonate approximately at a frequency of mc. The addition of one or more directors improves the gain characteristic primarily at the high end of the band, but also to a lesser degree at other frequencies in the band.

With a simple linear dipole director element operating at the M2 mode in low band, its resonant frequency at the 3M2 mode in high band operation is approximately 270 mc. which puts its resonant operation well beyond the upper end f the upper band which extends from 174-216 mc. Thus, conventionally a second director element must be provided along the antenna boom represented by the phantom line 37 in FIGURE 2a, in order to provide peaking or improvement of the gain characteristic at the upper end of the high VHF band.

The instant invention overcomes the need for two separate director elements through the employment of a dual band director element 38, shown in FIGURE 2a. The director element 38 is mechanically coupled to the boom 37, shown in dotted fashion, in any suitable manner so that it is electrically insulated from the transposed feeder harness 31. The director 38 is comprised of an upper arm and a lower arm with the upper arm, in turn, being comprised of an inboard section 38a and an outboard section 38b. The inboard section 38a is mechanically coupled to boom 37 and electrically coupled to one side of reactive element 38C. Outboard section 38b is electrically coupled to the opposite terminal of reactive element 38C. The lower arm is, in turn, comprised of inboard and outboard sections 38d and 38e, respectively, electrically coupled through a reactive element 38j. Inboard sections 38a and 38d are, in turn, either electrically connected at 38g, or formed of a single conductive member.

The capacitive value of the reactive elements 38C and 38jc which are substantially equal to one another are so chosen that its reactance value during low band operation effectively presents a high impedance between the inboard sections 38a and 38d from their associated outboard sections 38b and 38e, respectively. Thus the inboard sections 38a and 38d determine to a great degree the electrical length of director 38 which is chosen so as to resonate in the vicinity of the channel 6 frequency to provide peaking of the antenna gain characteristics.

During high band operation reactive elements 38C and 381 present a lower impedance value so as to provide a low impedance connection between outboard sections 38b and 38e and their respective inboard sections 38a and 38d, respectively. Thus, the overall length of the inboard sections 38u-38d and the outboard sections 38d- 38e tend to establish the electrical length for the director 38 at the high band frequencies. During high band operation, the director 38 functions in the 3M2 mode to resonate at a frequency near 216 mc. greatly improving or peaking the gain characteristics at the high end of the high band and also contributing a significant increase 1n gain at other frequencies in the high band.

Additional dual band directors (more than one which is shown) can be used and appropriately spaced along the boom to further increase gain. Although a logperiodic section offers advantages in uniformity of gain, the dual band directors described here can also be used with conventional driven elements such as single or two element arrays of folded dipoles.

FIGURE 2b shows an alternative embodiment 40 to that of FIGURE 2a and is comprised of a transposed feeder line 41 which is electrically coupled to the source (or sink) 42 in the manner shown. In the array 40 there are provided dipoles 43-50 coupled to the transposed feeder harness 41 in the same manner as previously described and being arranged with the upper and lower arms 43a-50a and 43b-50b, respectively, forming an angle 1p of substantially 40 with the vertical line 51. While t is being shown as being 40 in FIGURE 2b this is merely a preferred value. The preferred range, however, extends from 25-65. The dipoles 43-46 substantially resemble the dipoles 12-15 of the embodiments of FIGURES la and 1b, while the dipoles 47-50 substantially resemble the dipoles 16'-19' of array 10 shown in FIGURE lb. It can be seen that these dipoles employ 12 the reactive elements 47c-50c and 47d-50d for the same function as previously described.

The antenna array 40 is further comprised of dual band directors 52-57, respectively, having upper and lower inboard sections 52h-57a and 52b-52b, respectively, each of which are electrically connected together and mechanically coupled to the antenna boom 58 and all of which are electrically insulated from the transposed feeder harness 41. The upper outboard sections 52c-57c are electrically coupled to the upper inboard sections 52a-57a, respectively, by means of the reactive elements 52d-57d, respectively. In a like manner, the capacitive elements 52f-57f, respectively, electrically couple the lower outboard sections 52e-57e to their associated lower inboard sections 52b-57b, respectively.

The lengths of all of the dipole arms, as well as the spacing between adjacent arms and lengths of directors, as well as spacing therebetween of one embodiment of the invention is set forth in detail below. The utilization of a plurality of director elements, in addition to the dipoles 43-50, provides enhancement of the gain charac teristics throughout the entire lower and upper frequency bands within the VHF operation, being particularly effective near the high frequency end of both bands. In the same manner as was previously described, the M2 operational mode sees the outboard sections of the director elements as being somewhat decoupled from their associated inboard sections so that the inboard section lengths determine to a greater degree the electrical lengths of the diretcors. In the high band where the directors resonate in the SM2 operational mode each outboard section is coupled to a greater degree to its associated inboard section, causing both inboard and outboard sections to affect the electrical length of each director.

In the upper band the directors operate in the SM2 mode resonating at frequencies acting to enhance the gain characteristics across the entire upper band and being particularly effective at frequencies near the high end of the band. Thus, each director provides dual band operation to a degree which was heretofore realized only through the use of a greater number of separate director elements for each of the desired operational modes.

Whereas the description of the antenna arrays 30 and 40 of FIGURES 2a and 2b, respectively, are related to antennas for use in the VHF television upper and lower operating bands, it should be understood that the directors are not limited to use in the M2 and SM2 operational modes, but may employ reactive elements so as to provide operation in the SM2 and 7M2 operational modes, for example.

FIGURES 3a and 3b show still another television receiving application for the basic concept of the instant invention. In FIGURE 3a is shown an all-band antenna array 60, having a single boom represented by the phantom line 61, upon which is mounted a section 62 which contains dipoles primarily for VHF and a section 63, which contains dipoles primarily for UHF and FM.

Section 62 is comprised of dipoles 64 71, each in turn being comprised of upper and lower dipole arms 64a-71a and 64b-71b, respectively. The upper and lower arms are arranged so as to form a preferred angle t/J of substantially 40 with the vertical dotted line 72, with the preferred range for t/f being 25-65. The dipole arms are connected to a transposed feeder line 73 in the same manner as previously described, which in turn is connected to source (or sink) 81, in the manner shown.

In FIGURE 3a conventional dipoles are used and the dipole arms are so designed as to cause the dipoles to have electrical lengths which in the M2 operational mode causes the dipoles to operate approximately at the resonant frequencies shown adjacent each upper dipole arm in FIGURE 3a. In the 3M 2 operational mode the resonant frequencies of the dipoles are represented in FIGURE 3a immediately adjacent the upper end of dipole arms 64a- 71a, respectively.

Section 63 of all-band antenna array 60 is comprised of a plurality of dipoles 74-80, respectively, with each dipole being comprised of an upper element arm 74a-80a, respectively; lower element arm 74b-80b, respectively. The upper and lower arms are arranged so as to form an angle ,l/ substantially within the range of 25-75" relative to the vertical line 72.

In order to best understand the operation and decided advantages of all-band antenna array 60, it is best to consider the design of such an antenna in accordance with the present status of the art such as shown in FIG- URE 3a. With respect to the section 63 of such an allband antenna, the arms of the dipoles are designed so that their electrical lengths will provide resonant operation at predetermined frequencies within the UHF band extending from 470-890 mc. Such a UHF section is typically positioned in front of the section 62 in the same manner as shown in FIGURE 3a. In order to achieve the high values of directivity and gain needed in the UHF band it is desirable to use higher mode (SM2 or greater) operation of these elements at UHF. During VHF operation in either the lower band (S4-88 mc.) or upper band (174-216 me), the electrical lengths of certain of the dipoles in the UHF section operate in such a Way as to shield incoming waves, preventing them from reaching the dipoles of the VHF section and thereby so severely impairing the VHF operation as to render such an al1-band antenna as a totally impractical device. It thereby becomes necessary in the design of such an all-band antenna array to provide a UHF section which will not create any ill effect upon the VHF characteristics of the antenna array. This objective is easily and readily obtainable through application of the concept of the instant invention.

In FIGURE 3b the dipoles 74-80 of the UHF section 63 are each provided with reactive elements 74e-80e and 74f-80f, having values which are such as to provide a substantially high reactance X during operation of the all-band antenna array 60 in either the high or low VHF bands. The reactance of the elements 74e-80e and 74)- 80f is such as to effectively decouple all of the outboard sections 74c-80c and 74d-'80d from their associated inboard sections 74a-80a and 74b-80b, respectively. This occurs when the antenna is operating in either the M2 or the 3M2 operational mode, thus the inboard sections of dipoles 74-80 determine to a great degree the electrical lengths of these dipoles. The electrical lengths of these dipoles are such as to have no harmful effect whatsoever upon the operation of the VHF antenna section 62 and in fact may be designed to enhance the antenna performance in the FM band `88-108 mc.

During UHF operation of all-band antenna array 60 the antenna is functioning in the 7M2 and 9M 2 operational modes, for example, and the reactive elements 74e-80e and 74f80f, respectively, couple to a greater degree the associated inboard and outboard sections of the dipole arms, causing the inboard and outboard sections to cooperate and thereby establish the electrical length of each dipole 74-80, respectively. The substantially large distinction between VHF and UHF operational frequencies acts to provide almost ideal decoupling and coupling functions to be provided by the reactive elements.

Considering first the operation of all-band antenna array 60 for low band VHF and FM operation, attention is again directed to FIGURE 3b. In the M2 operational mode typical resonant frequencies for dipoles 64- 71 of VHF section 62 are shown adjacent the tips of the upper arms of these dipoles. The reactive elements 68e-7 1e and 68f-71f decouple the outboard sections associated therewith from their inboard sections to some degree so that the inboard sections 68a-71a and 68b-71b tend to establish the electrical lengths of dipoles 68-71. Thus, the VHF section 62 provides resonant dipoles ranging from 52.5 to 90.0 mc. with very small and relatively uniform frequency intervals between adjacent dipoles.

Since low band operation is in the M2 mode, the reactive elements 74e-80e and 74f-80f of UHF section 63 are also of extremely high reactance, causing all of the outboard sections to be effectively decoupled from their associated inboard sections. During low band VHF and FM operation only certain dipoles such as the dipoles 74, 77 and 80 make any contribution to the gain of the antenna array. These dipoles typically may have resonant frequencies of 93.0, 101.5 and mc., respectively, yielding good operation for the FM band which normally extends from 88-108 mc.

The M 2 operational mode causes the outboard sections of the UHF antenna section 63 to be so effectively decoupled from their associated inboard sections that these outboard sections thereby also being electrically insulated from the transposed feeder harness 73, may operate as director elements which have electrical lengths causing extremely effective peaking of the antenna gain characteristic during VHF and FM operation. Thus, the outboard sections of the dipoles in the UHF section 63 which ostensibly appear to be useless during VHF operation, operate in such a manner as to provide the advantageous characteristics of director elements.

The UHF antenna section `63 plays still another very important role in the operation of the all-band antenna array 60 within the VHF bands.

Considering the operation of a conventional log-periodic antenna which 'may be represented by the VHF section 62, shown in FIGURE 3a, let it be assumed that such an antenna is presently operating to receive a channel frequency of 66 mc. The dynamic characteristics of such an antenna have shown that the dipoles 66 and 68 which are on the immediately opposite sides of dipole 67 are considered to be the active dipoles together with dipole `67 which resonates at the channel frequency being received. These three dipoles 66-68 form the active region for the antenna array (section) 62. It has been shown, however, through extensive experimentation as well as along theoretical lines, that the dipoles -69-71 which are in front of the active region comprised of dipoles 66-68 play a very important role in the operation of the antenna. The dipoles 69-71, together with the feeder connecting these dipoles, form what is commonly referred to as the transmission region of the antenna and while they do not contribute to the reception pattern for the antenna, they do nevertheless contribute to the impedance of the whole antenna by providing the desired impedance matching between the active region comprised of dipoles 66-68 and the antenna feed point. This function is very suitably performed when the active region lies at the extreme left-hand end or the middle of the antenna array. However, when the received channel is represented by the dipole 71, for example, it can be seen that when no dipoles lie to the right of dipole 71 that no transmission region is provided in the antenna, thus severely affecting the impedance matching for the antenna array.

Thus, by selecting the lengths of the inboard sections of dipoles 74-80 in the UHF section 63, these elements operate as the transmission region for the antenna V'HF section 62 during low and high band VHF operation thereby keep ing the impedance of the antenna at a very suitable value throughout the entire VHF range.

The all-band antenna aray 60 of FIGURE 3b shows those dipoles which are utilized during VHF and FM operation as being in solid line fashion with the dipoles of the UHF section 63 which are not utilized during VHF and FM operation being in dotted line fashion. As was previously described, operation in the M2 mode for the conventional log-periodic antenna having dipoles in V-configuration which is the classification of the VHF section 62 of FIGURE 3a, all dipoles ofthe VHF section are utilized. In the case of operation of the SM2 mode only dipoles 66-68 are utilized as shown by the resonant frequencies in 15 the figure. For FM operation the dipoles 74-80 are utilized within the UHF section.

Considering FIGURE 3b which differs in the VHF section from that in FIGURE 3a in that the antenna employs the reactive elements 68e-71e and 68f71f, respectively, the elements utilized in the 7\/2 mode have substantially identical resonant frequencies to those utilized in the embodiment of FIGURE 3a. Resonant frequencies given in FIGURE 3b are those for the M2 operating mode.

Turning to FIGURE 3c, those dipoles shown in solid line fashion constitute the dipoles utilized when the allband antenna is operating in the VHF high band. From the resonant values biven it can be seen that five of the eight dipoles within the VHF section 62 are utilized during high band VHF operation (namely dipoles 66-70, respectively). While none of the dipoles in the UIHF section 63 of FIGURE 3c are utilized for VHF high band operation, it should nevehtheless be understood that the UHF section still performs the most important fuction as acting as the transmission region for VHF section 62 during high band VHF operation. In addition thereto, selected outboard sections of dipoles within the UHF section 63 function as director elements acting to significantly improve the gain characteristics of the all-band antenna during high band VHF operation.

FIGURE 3d shows, in solid line fashion, the dipole elements which become active and are utilized during UHF operation. Utilized elements are shown in solid line fashion, while those dipoles which do not contribute to the Operation of the antenna array 60 at UHF frequencies are shown in dotted fashion, in the same manner as previously mentioned. During UHF operation, the reactance values of reactive elements 74e-80e and 74f-80f become so small as to provide an effective coupling between inboard and outboard sections of the dipoles 74-80. Thus, the inboard and outboard sections act to establish the electrical length for the dipoles and in UHF operation these dipoles resonate in the 7A/2 and 9/2 modes and have electrical lengths which very capably cover the UHF band exteri'ding from 470 to 890 mc.

Thus, through the use of the reactive elements within the UHF section and within the VIHF section, if desired, the design of an all-band antenna array is made possible such that the 'UHF section does not act to shield incoming waves from reaching the VHF section and serves the further positive advantages of acting as the transmission region for the VHF section and having its outboard sections act as directors which improve or peak the antenna gain characteristics within VHF operation.

Reviewing the structure shown in FIGURE 3b, the antenna 60 operates on all the channels of VHF, UHF and FM. The VHF television frequencies are covered in the rear section of widely-spaced dipoles preferably set at an angle ,b of 40. The UHF television frequencies are covered in the front section 63 of closely spaced dipoles preferably set at an angle of 62.5 The FM band extends across the same front section 63 that is resonant on UHF.

The active region on the low band of VHF moves across all the widely spaced elements of the VHF section from the smaller front elements resonant on channel 6 (88 mc./s.) to the larger rear elements resonant on channel 2 (54 mc./s.). These elements resonate with a half-wave length current distribution (in the fundamental mode).

The active region on the high band of VHF appears substantially at the center of the widely spaced elements of the VHF section 62. These elements resonate effectively in the three-half wave lengths (or third harmonic) mode.

Thus, if a capacitor is inserted in each of the dipole elements and the value of the capacitance is adjusted as Well as its position along the dipole, the resonant frequency in the third harmonic mode can be shifted while maintaining the resonances inthe fundamental mode. If we now design an antenna that employes capacitor coupled dipole elements toward the front of the VHF section, the high band 16 active region is permitted to move to the front of this section at the upper end of the band.

The capacitors will not affect either the polar field intensity patterns or the gain on UHF. In the fundamental, or one-half Wave length mode, the longer inboard segments of the dipole elements are resonant on the FM frequencies.

Finally, the capacitors on the VHF elements increase the physical length of the dipoles compared to standard dipoles without capacitors. The larger dipoles have a greater physical length, and therefore a greater capture area and higher gain. This is especially true on the low band channels of VHF.

FIGURES 4a-4e show the design of a dipole arm employing a reactive element in greater detail. Referring specifically to FIGURE 4a, the dipole arm 100 shown therein is comprised of first and second metallic tubular rods 101 and 102. Both rods 101 and 102 are typically hollow and are preferably formed of aluminum, but any other suitable conductive material may be employed, depending only upon the needs of the user. Tubular rod 101 may be referred to hereinafter as the inboard section and tubular rod 102 as the outboard section of a dipole arm. Due to the symmetry of the overall design of dipole arm 100, it should be understood that either tubular rod may be used as the inboard section or the outboard section so long as the lengths of the sections are appropriately adjusted.

The tubular rod sections 101 and 102 are mechanically coupled to one another by the insulating rod 103. Insulating rod 103 is a solid, substantially cylindricallyshaped rod which is preferably formed of fiberglass, but may be formed of any other suitable insulating material. The outer diameter of the insulating rod 103 is of a value such as to require it being force-fitted within the tubular openings of conductive rods 101 and 102.

Positioned at the center of the fiberglass rod 103 is a dielectric disc member 104 formed from a suitable insulating material and having a substantially circular configuration (see FIGURES 4c and 4e, in addition to FIG- URE 4a).

The dielectric disc 104 is provided with a substantially circular rim portion 105 surrounding the entire periphery of the disc and constituting the thickest portion of the disc, as can best be seen in the cross-sectional view of FIGURE 4c. Both sides of the dielectric dise 104 are provided with recesses 106 and 107, respectively. A second recess is provided on opposite sidesthereof yand are the recesses 108 and 109, respectively, which are centrally located within the recesses 106 and 107 so as to form the substantially annular area bordered by shoulder 105e of rim 105 at its outer diameter and by shoulder 106e at its inner diameter. The opposite surface, which can best be seen in FIGURE 4c is bounded in a like manner by shoulder 10512 and shoulder 107a, respectively.

A substantially cylindrical projection 110 and 111 is provided on opposite sides of dielectric disc 104 which cylindrical projections generally form the opening 112 in dielectric disc 104 through which passes the fiberglass rod 103.

The arm 100 of FIGURE 4a is further provided with eyelets 113 and 114 which are rigidly crimped to the inboard and outboard sections 101 and 102, in a manner to be more fully described.

Before being mounted upon and crimped to its associated arm section each eyelet is generally comprised of a cylindrical portion 113a (114a) having an opening113b therethrough wherein the cylindrical portion is generally represented by the dotted line circle 113e such that its diameter is substantially greater than the diameterl of either the tubular sections 101 and 102, or the liber glass rod 103. One end of the cylindrical section 113a (114a) is flared out to form a disc-shaped end portion 113d having a diameter substantially equal to the diameter formed by the shoulder 106a of the dielectric disc 104. Eyelet 113, for example, is mounted to the dipole arm structure 100 by slipping the inboard section 101 through the opening 113b and seating the disc portion 113d in the recess 108. The cylindrical portion 113a of eyelet 113 is then crimped so as to form the configuration 113e which substantially resembles a keyhole configuration so as to be very rigidly and securely frictionally engaged with the inboard tubular section 101. The eyelet 114 for the outboard section 102 may be mounted in a similar manner. On one embodiment actually constructed, the thickness between recesses 108 and 109 as shown in FIGURE 4c, was approximately 0.05. This dimension, coupled with the total surface area of the disc portions 113d and 114d determine the reactive value of the reactive component. It should therefore be understood that the reactive, or capacitive Value of the reactive component may be altered by controlling the distance between the conductive disc portions 113d and 114d and also by controlling the diameter or total surface area of the discs 113d and 114d. Two different ways in which this can be carried out is by enlarging or decreasing the diameter of the discs to increase r decrease the capacitance value, or by providing openings around the surface of the disc as shown by the dotted circles 1131 so as to diminish the total surface area presented by the discs and thereby diminish the reactive value of the discs. Other modifications are obvious and will not be discussed to any length for purposes of simplicity.

The dipole arm 100, shown in FIGURES 4a: and 4d (which shows the dipole arm in exploded form), has been found to be useful in all of the antenna arrangements of FIGURES ltr-3d for the VHF sections shown therein. In the case of the UHF antenna section of FIG- URES 3er-3d, a modified dipole arm assembly has been designed and is shown best in FIGURES 4b and 4e. In the UHF embodiment, since operation is desired in the M2 mode, 3)\/2 mode, 7)\/12 mode and 9/2 mode, the capacitive value was required to be much smaller. This was achieved by providing the eyelets 113 and 114, shown in FIGURE 4b, wherein substantially all of the discshaped end portions have been removed. Thus the capacitance value of the reactive component is determined by the opposing end surfaces 113g and 114g of the eyelets 113 and 114, respectively. In order to still further control the capacitive value, insulating washers 115 and 116 are provided, which washer members have openings 115a and 116a, respectively, having a diameter which prevents the washers when positioned in the manner shown in FIG- URE 4e from receiving the projections 110 and 111 therethrough and thereby causing these cylindrical projections to rest up against the washers 115 and 116, respectively. The outer peripheries 115b and 116b of washers 115 and 116, respectively, are substantially greater in diameter than the diameters of eyelets 113 and 114 causing the eyelets to abut the washers 115 and 116, in the manner shown in FIGURE 4e. The washers 115 and 116 thereby act to establish the spacing between eyelet ends 113g and 114g with the spacing being represented by the character D, shown in FIGURE 4e. The eyelets 113 and 114 employed in the embodiment of FIGURES 4b and 4ey are crimped to their associated inboard and outboard dipole arm sections in the same manner as the eyelets 113 and 114 provided in FIGURES 4a and 4d, respectively. In the embodiment of FIGURES 4b and 4e the spacing D between eyelets 113 and 114 may thereby be controlled by virtue of controlling the thickness of washers 115 and 116, or by adding multiple washers to the structure where the cumulative thicknesses of all washers employed establish the spacing D. In the reverse direction, all washers may be removed, causing the eyelets to be spaced apart only by the thickness between the recess portions 108 and 109, which is approximately 0.05. In light of the embodiments of FIGURES 4d and 4e, it should be clearly obvious that in order to provide a reactive element with reactance lying somewhere between the values of the embodiments of FIGURES 4a and 4e, this may be done 18 by providing the disc-shaped end portion 113d (114d) of FIGURE 4a of the eyelet with a diameter greater than that of the cylindrical portion 113a (114a) of FIGURE 4a but less than the diameter of the disc-shaped portion shown in FIGURE 4a.

The substantially thick rim portion 105 of dielectric disc 104 acts as a rain shield so as to keep rain or other elements from falling down into the immediate region of the eyelets 113 and 114. In addition thereto, the rim portion 105 increases the length of any breakdown path between the eyelets 113 and 114 so as to provide a substantially reliable reactive value between the eyelet members.

While the structures of FIGURES 4a-4e show two practical manners for providing reactive element structures, it should be understood that these embodiments are merely exemplary and any other suitable reactive element structures may be employed in order to provide for the novel concept of the instant invention. In addition thereto, other structural alternatives may likewise be provided in assembling antennas which employ the concepts of the instant invention. For example, with the antenna shown in FIGURES 1-3 in place of the transposed feeder harness employed therein, it is possible to employ what is commonly referred to as a twin boom structure which, for example, is set forth in detail in U.S. Patent No. 3,150,376, entitled Multiband Log Periodic Antenna and filed by Mayes and Carrel. Taking the antenna 10 of FIG- URE la as an example, the boom represented by phantom line 21 is replaced by two booms arranged adjacent and parallel to one another with a first boom having electrically coupled thereto the upper dipole arms 12a, 14a, 16a and 18a and lower dipole arms 13b, 15b, 17b and 19b, respectively, while the second boom has electrically coupled thereto the remaining upper and lower dipole arms. Such a twin boom thereby provides the same cross-coupling arrangement as is provided by the transposed feeder harness.

In the case where such twin boom construction is employed in an antenna structure of the type shown in FIG- URE 2b, for example, which employs parasitic director elements, the twin booms are electrically coupled to the arms of dipoles 43-50 in the same manner as that described for the antenna array 10 of FIGURE 1w. At least one boom is long enough so as to be equal in length to the distance between the left-handmost and right-handmost elements of antenna array 40, shown in FIGURE 2b, with the director elements 52-57 being mechanically coupled to the booms. An additional insulator member is provided at 59 in array 30 of FIGURE 2a to insulate the directors and the boom supporting the directors from the antenna active elements, or dipoles 43-50, respectively.

As an alternative arrangement for the reactive elements shown in FIGURES 1-4 of the instant application, in instances where it may be desired to provide a dipole arm having inboard and outboard sections which are to be electrically coupled to one another in the M2 mode and are to be electrically decoupled in the BMZ or higher modes, it is thereby possible to substitute for the reactive elements of FIGURES l-4 an inductive element whose reactance increases with increases in frequency with such structure being applicable in still further controlling the ratio K between low band and high band frequency operation to still further enhance the gain characteristics of an antenna array and to approach utilization of the dipoles within an antenna array. Such a modification may likewise be used in the dual band director structures and the UHF antenna structures described herein wherein the inductive element is substituted for the capacitive element shown in the FIGURES l-4.

As another alternative, the reactive elements provided in the pair of arms of one dipole need not have identical reactive values. A departure from capacitances of equal magnitudes is permissible without causing an appreciable effect upon antenna performance and in certain instances such departures may enhance performance characteristics.

The antenna array 62, as a departure from the design technique described above, may employ a multiband design approach as described in U.S. Patent 3,150,376. This design departure requires only that selected dipoles forming a zone adhere to the equations set forth above. For example, the dipoles 64 through 67 constitute a first zone wherein the electrical lengths of the dipoles and the spacings between dipoles of the zone comprised of these dipoles generally adhere to the above recited design equations. The dipoles 68 through 71 then form a second zone, said second zone having its own length and spacing constants which may differ from the length and spacing constants of the first zone. In addition, more than two zone-s may be employed, if desired.

Whereas the instant invention finds substantially widespread use throughout a wide variety of dual band operating antennas, the invention provides extremely good results when employed in antenna arrays of the logperiodic design. Whereas the basic description of a logperiodic antenna has been set forth above, and further has been set forth in equation form, which equations may be employed for establishing length and spacing dimensions of the array, it should be understood that departures from the strict equation design of the antenna may be made without completely sacrificing the desired performance characteristics.

Consider, for example, the antenna of FIGURE lb. This antenna may be considered to be comprised of a plurality of cellsf Each individual cell is comprised of a pair of dipole arms and that section of the transposed feeder line between adjacent dipoles in the direction of increasing dipole length. For example, one such cell is comprised of the dipole arms 14a and 14b and the feeder harness section 11 and 11` Every other cell of the antenna is formed in a similar manner. One further example is the cell comprised of dipole 16 and the feeder segments 11a and 11a".

In considering the antenna 10, as an array comprised of cells defined above, the overriding consideration in the design of an antenna of the log-periodic type is such that the cell length generally decreases from one end of the antenna toward the other end. 'Ihe cell length is defined as follows:

An imaginary line may be drawn from the free end of a dipole element (for example, element 14a) to the midpoint (for example, midpoint 21' along phantom line 2l) betwen the cell harness section (11 and 11) connecting adjacent dipoles which, together with its associated dipole (dipole 14) constitute a celL This imaginary line is shown by the dotted line designated CL 14 which is interpreted as the cell lengt for the cell comprised of dipole 14. It is this dimension (i.e., cell 1ength) which generally decreases along one direction of the antenna array. Whether the decrease be exclusively attributed to the decrease of the dipole length or exclusively to the decrease of the spacing dimension is immaterial so long as the cell length does in fact decrease along one direction of the antenna array.

It can be seen from the foregoing that the instant invention provides a component for use in antennas eniployed in multiband transmission and reception applications which is `quite simple in design `and yet is an extremely powerful tool in operating to greatly improve the response characteristics of such multiband antennas. In addition to use as an integral part of active dipoles, the reactive elements may also be employed within parasitic director structures, causing such singular structures to provide dual band operation. Still further, the inventive concept permits the design of a feasible allband antenna larray comprised of VHF and UHF` sections. Regardless of the particular application, the inventive concept greatly improves the performance of any antenna structure in which it is employed.

While the foregoing description contains a theory of operation which is believed to be correct, the theory is presented for descriptive purposes only and should not be so construed as to restrict the application of the inventive results which have been proven experimentally.

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.

We claim:

1. Dual band antenna means for operation in the low and high band VHF frequency ranges comprising a plurality of dipoles arranged in log-periodic fashion and having electrical lengths causing all of said dipoles to operate in the M2 mode and substantially within the low band VHF range and to operate in the 3)\/2 mode in the high band VHF range where k represents the wavelength of the frequency at which each dipole is resonant;

the electrical lengths `of said dipoles gradually decreasing from the rear of the array towards the front; transposed feeder means coupled to all of said dipoles; each of said dipoles being comprised of first and second dipole arms arranged in a V-configuration; the dipole arms of selected ones of said dipoles near the front of said array, each being comprised of collinear inboard and outboard sections; said inboard sections being connected to said feeder means;

capacitance means electrically coupling lassociated inboard and outboard sections and physically coupling each outboard section to its associated inboard section;

each of said inboard sections being at least one-tenth (%0) the length of its dipole arm comprised of inboard and outboard sections;

said impedance means having a larger impedance value when said antenna is operating in the low band VHF range and having a smaller impedance value when said antenna is operating in the high band VHF range to alter the resonant frequencies of said selected dipoles in the high band VHF range to be less than three (3) times as great as their resonant frevvquencies in the low band VHF range thereby increasing the number of dipoles whose resonant frequencies lie substantially within and effectively contribute to the antenna operation in the high band VHF range.

2. The array of claim 1 further comprising director ymeans positioned in front of said dipole `array and being insulated from said feeder means and comprising at least one director member positioned in front of said dipole array; said director member comprising a central inboard section and first and second outboard sections; capacitance means connecting the first and second outboard sections of each director to the central section and for establishing an impedance between said first and second outboard sections from the central inboard section during operation within one of said discrete frequency ranges and for substantially decreasing the impedance between the first and second outboard sections to the central inboard section during operation in another of said discrete frequency ranges.

3. The multiband antenna means of claim 2 wherein said director sections are arranged in substantially collinear fashion.

4. The multiband antenna means of claim 2 wherein said director inboard section is arranged in a V-conguration.

5. All band log-periodic antenna means for VHF and UHF operation comprising feeder means; a. VHF section designed to operated in at least first and second discrete frequency bands within the VHF band and being comprised of a plurality of dipoles connected to said feeder means, each designed to resonate at first and second frequencies associated With said first and second frequency bands, respectively; each of the dipoles in said VHF section having a V-configuration; a UHF section positioned adjacent said VHF section and being comprised of a plurality of dipole means connected -to said feeder means, each of said dipole means being comprised of first and second dipole arms; said arms being fed by said feeder means and being arranged to form a V-configuration for each dipole; selected ones of said dipole means having each of said arms being comprised of an inboard and an outboard section; said inboard section being electrically coupled to said feeder means; insulating means for mechanically coupling said outboard section to said inboard section; impedance means electrically coupling said outboard section to said inboard section said impedance means having a reactive value selected to establish an impedance between the outboard and inboard sections when said antenna means is operating in one resonant mode and to substantially electrically decrease the impedace between said outboard and inboard sections when said antenna means is operating in another resonant mode;

selected ones of said outboard sections having electrical lengths providing parasitic director operation to improve the antenna gain characteristics during VHF operation.

6. All band log-periodic antenna means for low and high band VHF operation and UHF operation comprising feeder means; a VHF section designed to operate in at least lfirst and second discrete frequency bands within the VHF band and being comprised of a plurality of dipoles connected to said feeder means, each designed to resonate at first and second frequencies associated with said first and second discrete frequency bands, respectively; each of the dipoles in said VHF section having a V-configuration; a UHF section positioned adjacent said VHF section and being comprised of a plurality of dipole means connected to said feeder means, each of said dipole means being comprised of first and second dipole arms; said arms being fed by said feeder means and 'being arranged to form a V-configuration for each dipole; selected ones of said dipole means in said VHF section having each of said arms being comprised of an inboard and an outboard section; said inboard section being electrically coupled to said feeder means; insulating means for mechanically coupling said outboard section to said inboard section; said insulating means further including impedance means electrically coupling said outboard section to said inboard sectionsaid impedance means having a reactive value selected to establish an impedance between the outboard and inboard sections when said antenna means is operating in the low band V-HF range and to substantially electrically decrease the impedance between said outboard and inboard sections lwhen said antenna means is operating in th high band VHF range for increasing the number of dipoles which are effective in the VHF section; the electrical lengths of the dipole means in said UHF section are selected to resonate in first and second modes during VHF operation in the absence of said impedance means, where said operating modes are the modes wherein the effective electrical length of each dipole is M2 and 3 \/2 respectively, Where is the Wavelength of the operating frequency; said impedance means preventing the dipoles of said UHF section from resonating in the first and second modes.

7. All band log-periodic antenna means for low and high band VHF operation and UHF operation comprising feeder means; a VHF section designed to operate in at least first and second discrete frequency bands within the VHF band and being comprised of a plurality of dipoles connected to said feeder means, each designed to resonate at first and second frequencies associated with said first and second discrete frequency bands, respectively; each of the dipoles in said VHF section having a V-conguration; a UHF section positioned adjacent said VHF section and being comprised of a plurality of dipole means connected to said feeder means, each of said dipole means being comprised of first and second dipole arms; said arms being fed by said feeder means and being arranged to form a V-configuration for each dipole; selected ones of said dipole means in said VHF section having each of said arms being comprised of an inboard and an outboard section; said inboard section being electrically coupled to said feeder means; insulating means for mechanically coupling said outboard section to said inboard section; said insulating means further including impedance means electrically coupling said outboard section to said inboard section said impedance means having a reactive value selected to establish an impedance between the outboard and inboard sections when said antenna means is operating in the low band VHF range and to substantially electrically decrease the impedance between said outboard and inboard sections when said antenna means is operating in the high band VHF range for increasing the number of dipoles which are effective in the VHF section; the electrical lengths of the dipole means in said UHF section are selected to resonate in first and second modes during VHF operation in the absence of said impedance means and being resonant in a third mode during UHF operation, where said operating modes are the modes wherein the effective electrical length of each dipole is M2, 3/2 and 7}\/2, respectively, Where A is the wavelength of the operating frequency; said impedance means preventing the dipoles of said UHF section from resonating in the first and second modes.

8. All band log-periodic antenna means for low and high band VHF operation and UHF operation comprising feeder means; a VHF section designed to operated in at least first and second discrete frequency bands within the VHF band and being comprised of a plurality of dipoles connected to said feeder means, each designed to resonate at first and second frequencies associated with said 1first and second discrete frequency bands, respectively; each of the dipoles in said VHF section having a V-configuration; a UHF section positioned adjacent said VHF section and being comprised of a plurality of dipole means connected to said feeder means, each of said dipole means being comprised of first and second dipole arms; said arms being fed by said feeder means and being arranged to form a V-configuration for each dipole; selected ones of said dipole means in said VHF section having each of said arms being comprised of an inboard and an outboard section; said inboard section being electrically coupled to said feeder means; insulating means for mechanically coupling said outboard section to said inboard section; and insulating means further including impedance means electrically coupling said outboard section to said inboard section said impedance means having a reactive value selected to establish an impedance between the outboard and inboard sections when said antenna means is operating in the low band VHF range and to substantially electrically decrease the impedance between said outboard and inboard sections when said antenna means is operating in the high band VHF range for increasing the number of dipoles which are effective in the VHF section; the electrical lengths of the dipole means in said UHF section are selected to resonate in first and second modes during VHF operation in the absence of said impedance means and being resonant in a third mode during UHF operation, Where said operating modes are the modes wherein the effective electrical length of each dipole is M 2, 3M 2 and SM2, respectively, where )t is the wavelength of the operating frequency; said impedance means preventing the dipoles of said UHF section from resonating in the first and second modes.

9. All band log-periodic antenna means for low and high band VHF operation and UHF operation comprising feeder means; a VHF section designed to operate in at least first and second discrete frequency bands within the VHF band and being comprised of a plurality of dipoles connected to said feeder means, each designed to resonate at first and second frequencies associated 'with said first and second discrete frequency bands, respectively; each of the dipoles in said VHF section having a V-conguration; a UHF section positioned adjacent said VILH3 section and being comprised of a plurality of dipole means connected to said means, each of said dipole means being comprised of rst and second dipole arms; said arms being fed by said feeder means and being arranged to form a V-conguration for each dipole; selected ones of said dipole means in said VHF section having each of said arms being comprised of an inboard and an outboard section; said inboard section being electrically coupled to said feeder means; insulating means for mechanically coupling said outboard section to said inboard section: said insulating means further including impedance means electrically coupling said outboard section to said inboard section said impedance means having a reactive value selected to establish an impedance between the outboard and inboard sections when said antenna means is operating in the low band VHF range and to substantially electrically decrease the impedance between said outboard and inboard sections when said antenna means is operating in the high band VHF range for increasing the number of dipoles which are effective in the VHF section; the electrical lengths of the dipole means in said UHF section are selected to resonate in rst and second modes during VHF operation in the absence of said impedance means and being resonant in third and fourth modes during UHF operation, where said operating modes are the modes wherein the effective electrical length of each dipole is M2, 3)\/2, 7 \/2 and 9 \/2, respectively, where )t is the wavelength of the operating frequency; said impedance means preventing the dipoles of said UHF section from resonating in the first and second modes.

References Cited HERMAN KARL SAALBACH, Primaiy Examiner.

W. H. PUNTER, Assistant Examiner.

Us. C1. XR.

Images