US3564555A

US3564555A - Broad band transformer antenna and related feed system

Info

Publication number: US3564555A
Application number: US696762A
Authority: US
Inventors: Raymond A Rosenberry
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-01-10
Filing date: 1968-01-10
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16

Abstract

A BOARD BAND TRANSFORMER ANTENNA HAVING A SERIES OF OVERLAPPING TRIPLET ELEMENT CELLS IN A FISHBONE TYPE OF ARRANGEMENT OF SUCCESSIVELY SHORTER ELEMENT LENGTHS. EACH ELEMENT OF A TRIPLET IS SHORTER THAN AND SPACED FROM THE PRECEEDING ELEMENT BY SUCH CALCULATED INCREMENT AS WILL CAUSE THE STRADDLING ELEMENTS, AS WELL AS ALL OTHER ELEMENTS OF THE SERIES, TO BE PHASED THE SAME ELECTRICALLY IN RELATION TO THE RESONANT ELEMENT, AND CAUSE THE STRADDLING ELEMENTS TO HAVE COUNTER-BALANCING CURRENTS, VOLTAGES AND REACTIVE COMPONENTS WITH RESPECT TO THE CENTRAL RESONANT ELEMENT TO ELIMINATE SURGE IMPEDANCE AND CREATE A NULL REACTANCE SYSTEM WITH RESPECT TO A FREE SPACE WAVE. THE IMPEDANCE AT THE TEMINNATING FEED POINT OF ANY RESONANT ELEMENT IN AN ACTIVE TRIPLET IS UNIFORM AT EH APPLIED RESONANT FREQUENCY, EACH ELEMENT LENGTH AND IMPEDANCE IS COORDINATED TO ITS TRANSFORMER LINE LENGTH AND IMPEDANCE TO PRODUCE THE DESIRED MATCHED IMPEDANCE AT THE TRANSMISSION LINE FEED POINT, AND EXCELLENT BROAD BANDING IS ACHIEVED WITH RELATIVELY FEW ELEMENTS. AT ANY SELECTED FREQUENCY WITHIN THE ANTENNA RANGE, THE ELEMENTS OF THE NON-ACTIVE TRIPLETS PRESENT SUBSTANTIALLY INFINITE IMPEDANCE TO THEIR TRANSFORMER FEED POINTS. THE TRIPLET IS THE BASIC CELL UNIT, BUT ANY ODD NUMBER OF ELEMENT OR ELEMENT UNITS CAN BE PROPERLY SIZED AND SPACED TO CONSTITUTE SUCH A STRADDLE CELL.

Description

Feb 16, R, A, ROSENBERRY BROAD BAND TRANSFORMER ANTENNA AND RELATED FEED SYSTEM Filed Jan. 1o, 196s 3 sheets-sheet 1 D2, Dl D4 .D w s;

M M Az As Ns A\ i ATTCKNEYS Feb. 16, 1971 R. A. ROSENBERRY 3,564,555

BROAD BAND TRANSFORMER ANTENNA AND RELATED FEED SYSTEM Filed Jan'. 1 0, 1968 3 Sheets-Sheet 2 l l 7./j X 5f X 4/ X 4/ F\G. 5

5o!! Al Blf?" 5 FWG. 4 @f i A\ Boff l mx KLS:

AT TQ RNEY Feb- 16 1971 R. A. ROSENBEVRRY 3,564,555

BROAD BAND TRANSFORMER ANTENNA AND RELATED FEED SYSTEM Filed Jan. io, 1968 3 sheets-sheet s INVHTOR. l RAYMoNo A. Rosenaemvr BYWM;

ATTORNEYS Unted States Patent fce U.S. Cl. 343-811 Claims ABSTRACT OF THE DISCLOSURE A broad band transformer antenna having a series of overlapping triplet element cells in a shbone type of arrangement of successively shorter element lengths. Each element of a triplet is shorter than and spaced from the preceding element by such calculated increment as will cause the straddling elements, as well as all other elements of the series, to be phased the same electrically in relation to the resonant element, and cause the straddling elements to have counterbalancing currents, voltages and reactive components with respect to the central resonant element to eliminate surge impedance and create a null reactance system with respect to a free space wave. The impedance at the terminating feed point of any resonant element in an active triplet is uniform at the applied resonant frequency; each element length and impedance is coordinated to its transformer line length and impedance to produce the desired matched impedance at the transmission line feed point, and excellent broad banding is achieved with relatively few elements. At any selected frequency within the antenna range, the elements of the non-active triplets present substantially infinite impedance to their transformer feed points. The triplet is the basic cell unit, but any odd number of element or element units can be properly sized and spaced to constitute such a straddle cell.

This application relates generally to transmitting and receiving antennas for use on high and ultra-high frequencies, such as used in television, UHF, FM and amateur radio communications. This general range of operating frequencies is herein considered to be embraced within the designation of radio frequencies.

Much development work has taken place in the antenna art for the purpose of obtaining broad banding and improved gain characteristics in antenna systems. Perhaps a leading example of this type of development is the log periodic antenna system which is well known to the prior art. However, it has been observed that such log periodic antenna systems fall short of their intended objectives due to characteristics of surge impedance which are inherent in the arrangement and lwhich cause impedance mismatch at the feed terminals of the antenna.

It is a primary object of my invention to provide an antenna structure having broad band and high gain characteristics in which surge impedance and consequent impedance mismatch is substantially eliminated.

Another object of my invention is to provide a novel and improved feed arrangement for such an antenna system.

Other objects and advantages of my invention will become apparent during the course of the following description.

In the drawings, in which like reference numerals designate like parts throughout the same,

FIG, 1 is a diagrammatic plan view illustration of an antenna system embodying my invention.

FIG. 2 is a diagrammatic plan view illustration of a multiple array antenna system embodying the features of my invention.

Patented Feb. 16, 1971 FIG. 3 is a diagrammatic representation illustrating a cross-over feed arrangement for an antenna system.

FIG. 4 is a diagrammatic representation illustrating a modified form of feed arrangement for the antenna system.

FIG. 5 is a diagrammatic representation illustrating still another form of feed arrangement for the antenna system, utilizing coaxial cable transmission line.

FIG. 6 is a diagrammatic representation illustrating the utilization of the feed arrangement of FIG. 5 in another form of antenna arrangement.

In log periodic antenna systems a common scale factor is used for determining the lengths of the successive antenna elements and the spacing between the successive elements decreases correspondingly so that incoming space waves are not received on all elements of the antenna at a uniform phase angle at any condition of resonance. As a consequence, a condition of surge impedance results which, utilizing the feed arrangement of the log periodic antenna, causes the output impedance of the antenna to be considerably greater than the transmission line impedance so that undesirable impedance mismatch occurs.

In general, my form of antenna system departs from the teachings of the long periodic antenna system in utilizing a transformer type of antenna structure with predetermined transformation established by the transformer line to match element feed and transmission line feed impedance; with the transmission line feed points being located forward of the antenna. In addition, a uniform spacing is maintained between successive elements of the antenna and the change in electrical length of the successive antenna elements is also uniform and coordinated to the electrical length of the matched transformer line. In this manner, all elements of the antenna receive a particular wave at a uniformly increasing incremental phase angle and the impendance at the transmission line feed point is uniform for all elements. This geometrical relationship of the antenna elements produces an antenna system in which each of the resonant elements is straddled on opposite sides thereof by antenna elements whose inductive and capacitive reactive influence on the resonant element is counter-balanced as a consequence of the uniform incremental phase relationship so that currents and voltages tend to cancel or nullify each other in their influence upon the resonant antenna element and impedance mismatch is prevented. The broadbanding characteristics of my antenna system also permit the use of fewer antenna elements than in the log periodic antenna to cover an equivalent or greater range of frequencies.

The aforementioned characteristics of my antenna structure can better be understood by reference to FIG. l of the drawings lwhich diagrammatically illustrates a seven element broad-band antenna structure utilizing a half wave transformer line connected for parallel feed to the elements and with the transmission feed point terminals located forward of the antenna at the high frequency point.

The longest or most rearward element of the antenna is designated by the reference numeral 1 and the successively shorter elements are designated by the

reference numerals

2, 3, 4, 5, 6 and 7. For simplicity of explanation, these may be considered as half-Wave dipole elements connected, as indicated, to a half wave transformer line 30 having transmission line terminating feed points 31 forward of the antenna. The length of the transformer line, measured linearly, is designated by A with an appropriate sufx numeral to designate the length of transformer line from each of the antenna elements to the transmission feed point. The length of the elements is designated by D with a numerical suffix corresponding to the specic antenna element. The spacing between successive antenna elements is designated by S and a corresponding numerical sufiix. In the diagrammatic representation of FIG. 1, each of the elements is cut to a length D which is equal to the length A of the transformer line between that element and the transmission feed points 31 because the transformer line and the elements are all designed in this specific example to a half-wave characteristic which provides a 1:1 transformation ratio.

The

antenna elements

1, 2 and 3 define a triplet or antenna cell in which the element 2 is the resonant element which is straddled by the

elements

1 and 3 which, for purposes of explanation, may be considered as Ieector and director elements respectively. Similarly, another triplet cell is formed by the

antenna elements

2, 3 and 4, wherein element 3 is the resonant element; the element 4 is the resonant element in the triplet cell consisting of the

elements

3, 4 and 5; the

elements

4, 5 and 6 form another triplet cell with the element 51 being the resonant element; and the

elements

5, 6 and 7 form still another triplet cell with element 6 as the resonant element.

For purposes of explanation, it will be assumed that the antenna of IFIG. 1 is cut to cover a frequency range of 30-75 megacycles with resonant element cells for the desired band spread from 331/3 to 60 megacycles. For purposes of structuring the antenna, the most rearward resonant element, in this instance, half-wave element 2, is presumed to be the 180 element. The resonant element 2 will lead the element 1 and will be led by the next shorter half-wave element by a phase angle which is preferably in the range of l-20, but could under exceptional circumstances approach 90. The phase angle increment should be selected at a value such that the elements lwill be sufficiently close to each other to provide progressive transition or overlapping resonance between the successive resonant elements which cover the frequency band, but yet they should be far enough apart so that they do not lose their individual resonant identity; the preferred range of 10-20 for the phase angle increment achieves this objective for multiple cell antenna arrays. Inasmuch as the antenna consists of a series of triplet cells of successively higher resonant frequency in the forward direction, the phase angle of the triplet cells will increase uniformly at higher frequencies. Consideration must be given to this factor in designing the antenna, as undesirable and inefficient performance characteristics will result if the phase angle of the most forward triplet cell at resonance becomes unduly large in relation to the phase angle of the most rearward cell at resonance. In this context, when the phase angle of the most forward cell is in the ratio of 2:1 to the phase angle of the most rearward cell, it would be considered unduly large in proportion and inetiiciencies could be expected.

Keeping the foregoing in mind, the length of element 2 can be established on the basis of resonant frequency at 331/3 mc., the low end of the selected band spread, using formulas known to the prior art which would include factors for end effect and velocity factor. However, for purposes of illustration, these modifying factors will be ignored as their application is well known to the prior art in antenna design. The free-space element wave length in meters is computed by dividing 300` (a constant) by the desired resonant frequency, e.g. 300/331/3 to give a figure of 9.0 meters as the full wave length. Therefore the element 2 would nominally be cut to half the wave length which will produce the target frequency of 331/3 mc. This would result in a length for element 2 of 4.50 meters which, as previously indicated can be designated as D2. The high frequency end of the band has been postulated as i60 mc. so that the resonant element D6 would have a half-wave length of 300/60 =1/2 or 2.5 meters. In relation to D2 at 180, the element D6 has a phase angle of 331/3 /60 180 or 100. The phase difference of 80 would permit the use of three additional uniformly spaced intermediate elements D3, D4 and D5 4 and still provide only a 20 phase angle between the elements, which is within the preferred range. Therefore, an element D3 can be cut to a free-space half-wave length 160/ 180 X45 or 4.0 meters; the next shorter element D4 is cut to l80 4.5 or 3.5 meters; and the next shorter element D5 is cut to 120/180X4.5 or 3.0 meters.

In order to maintain the desired phase angle relationship for the iirst and last triplet cell, the length D1 of the element 1 can be established at 200/ 180 of the length of element 2 which would result in a figure of 5.00 meters; similarly the element D7 would be 80/ 180 0f the length of element D2 or 2.0 meters. The spacing S1 between the

parallel elements

1 and 2 would be established by the uniform phase angle relationship of 20 as 20/l80 4.5 or 0.5 meter, which for the 1:1 transformation provided by the half-way transformer line is equivalent to the difference between their lengths, using the formula which again would ordinarily be modied by velocity factors, which are not here considered. This would establish the spacing between all elements at .50 meter when a half wave transformer line is used. As the phase shift is uniform, the length of each of the remaining elements D3, D4, D5 and D7 could also be computed as being the length of the preceding element less the difference in length between the two preceding elements, e.g. the length of the element 3 is determined at 2(D2)-Dl; D4, the length of the element 4, is determined at 2(D3)-D2 and so forth, with the spacing between each of the elements being maintained uniform at the gure of .50 meter. The spacing S2 in terms of formula would equal A2 (D2-D3) XE and so forth for each of the spaces S1 through S6.

After the cuts of the elements have been established, and the transmission line feed point impedance and the element feed impedance have been determined, then the length of the transformer line 30 and its impedance and velocity factor in relation to the transmission line feed point for each element of the antenna at resonance is determined, taking into consideration any surge impedance factor, if necessary, in the manner known to the art, for the purpose of matching impedances at the selected wave length. This results in the spacing of the antenna elements and the length of transformer line, as previously described. The conventional impedance formula Zo=\/ZRZS is used to determine the theoretical impedance of the transformer, where ZR is the determined load or output impedance at each resonant element and ZS is the determined transmission line or input impedance at the feed point.

Having established the element lengths and their resonant frequencies to establish a broad band null reactance antenna system with transformation to achieve matched impedance, computations can be used to corroborate that the desired objective has been achieved. It is now possible to calculate the reactive component, represented by inductive reactance and capacitive reactance generally indicated by L and C respectively, using the known formula where f is the resonant frequency of the antenna element. By transposition,

and can be calculated for each of the antenna elements. By relating the reactive component values, as represented by \/LC, of the straddle elements of each triplet cell to the resonant element of each triplet cell, for example the

straddle elements

1 and 3 in relation to element 2 in the most rearward triplet cell of the antenna, the surge impedance ratios reflected t the resonant elements as a result of the reactive components and the rate of change of such ratios can be determined.

The results of such calculations are set forth in Table I below for both the antenna of FIG. 1 and for a log periodic antenna having an equal number of antenna elements. The first column of the table shows the element number and the small d between each of the element numbers designates a difference or incremental value 0f length in the second column and of reactive component ratio differences for each of the cells in the columns so designated. For each element, its length and equivalent frequency at resonance is indicated; and its square root I C reactive component factor is calculated and shown with two decimal points omitted, for convenience.

4, the reactive component ratio of 1.4287 is established between element 1 and resonant element 4 in the triplet cell C. In a similar manner, the reactive component ratios of the

elements

2, 3, 5, 6 and 7 can be calculated and are listed. It will be noted that there is a uniform difference of .1429 between each of the successive reactance component ratios.

The phase angle of each of the antenna elements is also calculated for each triplet cell and is indicated as having a value of 25.7 for each of the antenna elements in relation to the length of the resonant element 4 in cell C. Such computations are made for each of the triplet cells and are listed in Table I for the antenna of FIG. l.

In the lower half of Table I, comparable data is listed for a seven element log periodic antenna whose element 1 is of the same length as the element 1 of FIG. 1 and whose remaining antenna elements are of length in accordance with the log period system of applying a com- TABLE 1 1 CELL A (1-2-3) CELL B (213:4) CELL C (3-4-5) CELL D (4-5-6) CELL E (5-6-7) El Length Ilqii/a- 'f X53? h h h c- 1n nieen re- 1 ase Phase P ase f P ase Phase meut. ters quency, 1/ LCX angle, ilmlan e, ang il angle, LOUD angl Lcm) o. wave Ine/sec. 100 degrees 1/LC (2) degrees 1/ LC (3) degrees y/LC (4) degrees y/LC (5) degrees y/ LC (6) Applieant's FIG. l

Each of the overlapping triplet cells is indicated by an alphabetical designation, A, B, etc. and for each cell the phase angle of all antenna elements are shown as Well as the ratio of the reactive component square root LC of each element of the antenna to the resonant element of the particular cell. As previously indicated, the difference between these calculated ratios are also shown.

For purposes of illustration, the values of Table I will be explained in reference to cell C which consists of the straddle elements 3 and S with element 4 as the resonant center element. Following the element 4 across the columns of Table I, it will be seen that it has a length of 3.5 meters and is shorter and spaced from element 3 by .5 meter, and is longer and spaced from element 5 by .5 meter. The resonant frequency of element 4 is 42.86 mc., whereas the resonant frequency of the

straddle elements

3 and 5 are 37.5 me. and 50 mc., respectively. The reactive component of element 3, as cauculated is 0042464; that of element 4 is 0037155; and that of element 5 is .0031847, the difference between these respective reactive components being uniform at .005308, which is the uniform reactive component difference which exists between each of the antenna elements successively. Utilizing the \/I C thus obtained for each of the elements of the antenna, a reactive component ratio can be established between each of the antenna elements and the reactive component of the resonant element 4 of the triplet cell C. Using \/LC value of .53079 for element 1 in relation to the comparable value of .37155 for the resonant element mon scale factor to successive lengths. It will be noted that in the seven element log periodic antenna, the range is from a frequency of 30 mc. to 56.45 mc. in contrast to the overall range of 30-75 mc. in the antenna of FIG. 1. It will also be noted that the rate of change or differences in the reactive component ratios in the log periodic antenna are not uniform with respect to any one resonant element, but vary from one element to another so that all the resonant elements, at resonance, do not see the same impedance and there is no constant match of the load impedance to the line impedance. In contrast, in the antenna of FIG. 1, as shown in the upper half of Table I, the output impedance of each element at resonance is matched to the line impedance and the reactive component ratio rate of change is uniform for each element at resonance. The uniform difference between the ratios confirms the fact that the phase angle is the same for all the antenna elements in relation to each other when related to any one resonant element.

In FIG. 2 0f the drawings, I have illustrated diagrammatically an eleven element antenna whose elements 1-7 are the same as previously described with respect to FIG. l, but whose elements 8, 9, 10 and 11 represent a new series of triplet cells in the antenna, whose spacings S7, S8, S9 and S10 are uniform with each other but not uniform with the spacings S between the successive antennas elements 1-7. As was mentioned previously, when the phase angle of the forwaldmost triplet cell becomes unduly large in relation to the phase angle of the rearwardmost triplet cell of the antenna, inefficiencies and loss of gain result. As indicated on Table I for the antenna of FIG. 1, the phase angle of the cell E is 36 in relation to the phase angle of 20 for the cell A. This relationship approaches the unduly large ratio of 2: 1 whics was previously mentioned as a practical limit. In order to avoid this limitation on the number of elements and the range of the antenna7 the additional elements 8-11 of FIG. 2 utilize a uniform shorter spacing S and element lengths calculated in accordance with the formulas previously given, so as to initiate a new starting phase angle for this second series of triplet cells. The relationship of the elements 8-11 to each other and to the transformer line is comparable to that which has previously been described with respect to the elements 1-7 so that impedance mismatch is avoided.

For example, the element 8 could have a length of 1.80 meters and be spaced .20 meter from the element 7, and this .20 meter spacing S7 could be maintained uniform for S8 and S9, in which case the elements 9, 10 and 11 would be successively .20 meter shorter than each other and their 1:1 half wave length relationship to the transformer feed line would be maintained.

It is to be noted that the antennas of FIG. 1 and FIG. 2 can be utilized for horizontal polarization or vertical polarization or for either righthand or lefthand polarization using a bi-polar array. The great advantage of this triplet cell arrangement in a transformer antenna is its enhanced broad banding characteristic, which results from the fact there is constant and uniform impedance at the transformer line feed point for all the antenna elements at resonance, but that the antenna elements, other than the three active elements in a resonant triplet cell, present an infinite impedance to the transformer line which is not recognized by the feed points 31.

In FIG. 3 of the drawings, I have diagramatically illustrated the antenna of FIG. 1 utilizing a modified' crossover or transposed form of transformer feed. Similarly, in FIG. 4 of the drawings another form of feed arrangement is shown, known as an alternate feed system, which can be utilized with the antenna of FIG. 1. Whether the feed system used for the antenna is parallel, as illustrated in FIG. 1, or a cross-over as in FIG. 3 or an alternate system as in FIG. 4, the principle of operation of the transformer antenna and its broad banding characteristics remain as previously described, as long as the transmission feed point terminals 31 are located forwardly of the antenna elements and the described relationship between the elements and the transformer feed line is maintained.

It will be understood that the principles of the invention would apply with the same pertinence if the transformer line length were a different ratio to element length than the 1:1 relationship described above for a half-wave dipole and a half wave transformer line. For example, if a quarter-wave, instead of a half-wave transformer line were used for the antenna elements of FIG. l, the spacing S between the elements 1-7, using the formula etc., would be half of .50 meter or .25 meter, as A1 would be half of D1. The phase angle relationship would likewise be halved for the quarter wave transformer line.

In the 1:1 relationship of A to D, all the fed elements are matched to the actual transformer line impedance and the transmission line is matched to the actual transformer line'impedance so that all of these impedances are uniform. When the relationship of element length to transformer is changed from 1:1 to, for example, 2:1, the transformer line serves the function of transforming element feed impedances of one value to match transmission line feed impedance of another value in accordance with the Z impedance formula previously mentioned.

Thus, the principle of my transformerantenna is to utilize the transformer action to match impedances between the element feed connections and the transmission line feed points so as t0 maintain a uniform incremental phase angle relationship with respect to a free Space wave for all elements Within the frequency spectrum of the antenna.

When a 1:1 relationship exists, then the transmission feed points can physically lie on the transformer line at any point forward of the antenna, because of the uniform impedance characteristic of the transmission line, transformer line and antenna element feed points, although in an electrical sense the transmission feed points are still considered to lie at the appropriate distance A from the elements, as determined by the formula.

In FIG. 5 and FIG. 6 of the drawings I have diagrammatically illustrated an improved form of antenna transformer line feed system in combination with an unbalanced or coaxial transmission feed line to obtain a mirror image counterpoise, utilizing the 1:1 impedance matching characteristic, described above.

The antenna diagrammatically illustrated in FIG. 5 is a broad band antenna having eight elements, designated by the reference numerals 1219, and covers television channels 2-13, the FM band, and UHF on the third harmonic. The free-space element lengths and spacings are as indicated below:

An impedance matching feed line is used, having terminating feed points 20 and load-matched impedance, as previously fully described for a 1:1 relationship.

An unbalanced antenna feed is utilized in which all of the antenna elements are grounded to the boom 32 and to the shield of the coaxial cable 33, at their midpoints on one side of the element, as indicated by the reference numerals 21. On the opposite midpoint side of the antenna, each alternate antenna element is disassociated from ground and fed from a common transformer line, as indicated by the reference numeral 22, so that the grounded opposite side of each of these

alternate elements

13, 15, 17 and 19 produce a mirror image counterpoise or ground plane effect in the plane of the driven element. This feed arrangement not only improves antenna performance, but also permits grounding of the elements to the coaxial cable so that only a single boom has to be used.

The use of this novel antenna feed system is again illustrated in FIG. `6 of the drawings for a six-element antenna which embodies the features of my invention. In the antenna of FIG. 6, four of the elements, namely

element numbers

23, 24, 25 and 26 maintain the uniform spacing S which has been previously described. The element 27 is an added dipole having a greater spacing S26, and in combination with a director element 28 provides for television channels 7-13 and for UHF on a third harmonic frequency, whereas the elements 23-26 serve for television channels 2-6. The terminal feed points 29 are forward of the antenna elements 23-27 and a matching transformer feed line is used, as previously described. The same grounding arrangement to the shield of the coaxial cable is used for the antenna of FIG. 6 and was previously described with respect to the antenna of FIG. 5.

The free-space length and spacing characteristics of the antenna diagrammatically illustrated in FIG. 6, are aS follows:

The antenna of FIG. 6 thus consists of only six elements having broad band characteristics which cover television channels 2-13 as well as UHF on the third harmonic frequency, and also utilizes the unbalanced antenna feed system for producing a mirror image counterpoise in the plane of the driven elements for improved performance.

Although I have referred herein, by way of example to a three-element triplet cell, and have also referred to the condition that any odd number of elements can constitute a cell, it will be understood that in some circumstances two or more elements may be so intimately disposed as to be the equivalent of a single element unit for the purpose of selective broad banding or harmonic operation. In such an arrangement the intimate grouping is considered as one element in determining the odd number required for a cell.

Although not specifically shown, it will also be understood that inductive and/or capacitive couplings may be utilized with the transformer antenna in the manner and for the purposes known to the prior art.

It is to be understood that the forms of my invention, herewith shown and described, are to be taken as preferred examples of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, Without departing from the spirit of my invention, or the scope of the subjoined claims.

Having thus described my invention, I claim:

1. In a broad band transformer antenna for covering a given frequency band, the combination of a series of overlapping resonant cells, each of said cells consisting of a resonant antenna element and at least one parallel straddling antenna element disposed on each side of the resonant element, the rearmost resonant element of said series of cells being of a free-space length equivalent to the lowest frequency of said frequency band, the forwardmost resonant element of said series of cells being of a free-space length equivalent to the highest frequency of said frequency band, the straddling element rearward of any resonant element being longer than the resonant element by a linear difference d and the straddling element forward of any resonant element being shorter than the resonant element by said same difference d whereby all elements of a series diifer in length from each other by a uniform increment d corresponding to a uniform phase angle increment, the spacing S between successive elements being uniform and being substantially determined by the free-space formula wherein,

D2 is the length of the resonant element, D1 is the length of the rearward straddling element,

A1 is -the length of the transformer line from the feed point of the straddling element to the transmission line feed points which is required to match the input and output impedances, said transmission line feed points being disposed forwardly of the antenna elements,

each resonant element oell forwardly of the rearwardmost resonant cell utilizes a fonvard straddling element of its adjacent rearward cell as its resonant element, and a transformer line coupling the cells of the series to a transmission line at said feed points.

2. A combination as defined in claim 1, wherein the phase angle of the rearwardmost resonant cell in relation to its resonant element is not greater than 20.

3. A combination as defined in claim 1, wherein the phase angle of the forwardmost resonant cell in relation to its resonant element is not more than twice the phase angle of the rearwardmost resonant cell in relation to its resonant element.

4. A combination as defined in claim 1, wherein said antenna elements are fed by a transformer line whose length with respect to each resonant ele-ment is equivalent to a whole number multiple of a quarter wave length of the resonant frequency of the element.

5. A combination as defined in claim 1, wherein the ratio of the reactance component, \/LC, of any antenna element in said series of cells to the reactance component of a resonant element of a selected cell, varies by a uniform increment.

6. A combination as defined in claim 5, wherein the straddling elements of a resonant cell are phased the same electrically in relation to the resonant element of the cell.

7. A combination as defined in claim 6, wherein the impedance at the transformer line feed point of any antenna cell element at resonance is uniform, and the autenna elements of nonresonant cells present substantially infinite impedance to their transformer line feed points in relation to said uniform impedance value.

8. A combination as defined in claim 3, including a second series of overlapping resonant element cells, the rearwardmost cell of said second series being forward of the forwardmost cell of said first series and having a phase angle in relation to its resonant element of not more than 20.

9. A combination as defined in claim 4, wherein said transformer line is connected in parallel with each of said antenna elements at the low voltage point thereof.

10. A combination as defined in claim 4, wherein said transformer line is connected in cross-over relationship to said antenna elements.

References Cited UNITED STATES PATENTS 2,192,532 3/1940 Katzin 343-811 3,221,332 ll/l965 Kravis et al. 343-7925 3,321,764 5/1967 Winegard et al. 343-7925 3,396,399 8/1968 Winegard 343-811 3,427,659 2/ 1969 Finneburgh et al. 343-7925 ELI LIEBERMAN, Primary Examiner Us. C1. X.R. 343-7925, 814