US2878472A - High efficiency broadband antenna array - Google Patents

Description

w. G. STERNS HIGH EFFICIENCY BROADBAND ANTENNA ARRAY Filed Dec. 14. 1954 @mw HM --M March 17, 1959 United States Patent Oiice 2,878,472 Patented Mar. 17, 1959 HIGH EFFICIENCY BROADBAND ANTENNA ARRAY William G. Sterns, Phoenix, Ariz., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application December 14, 1954, Serial No. 475,052

Claims. (Cl. 343-853) which has radiating elements so placed along its electrical length, as in a waveguide with spaced slots in one surface, that for a broadside lobe the radiating elements are integral half transmission line wavelengths apart to provide a radiated wave whose phase front is apart to provide a radiated wave whose phase front is parallel to the conductor. For a phase front which is not parallel to the conductor, that is, a beam which is at some direction other than normal to the array of elements, either the frequency of the incident energy or.. the mechanical spacing yof the radiating elements may be changed, such that the elements are no longer separated by exact multiples of the transmission line wavelength of the transmitted energy. The principles involved in such scanning are discussed in U. S. Patents 2,403,729 and 2,409,944 to A. V. Loughren.

In prior art systems the admittance of the array is a critical function of frequency, and control of individual elements is Ioften made difcult by the interaction and interdependence of adjustment of energy coupling to each element. Also, the antenna efiiciency of prior art arrays is considerably below the 100% point.

Accordingly, it is an object of this invention to provide a broadband antenna array feed system which is more ecient than prior art systems. i

lt is another object to provide a highly efcient broadband antenna array feed system in which the input impedance is nearly perfectly matched.

control of the individual elements is achieved with eas and without the difculties in prior art systems.

Briefly, in accordance with this invention, R. F. power fed to the input of an array impinges upon an R. F. hybrid network where it splits equally into two separate outputs of the hybrid, which are connected through a pair of= adjustable irises to a rst pair of radiating elements. -The irises are adjusted to transmit a predetermined percentage of the power incident thereon and to reect the remainder back to the hybrid. The transmitted portion is coupled lines. The hybrid recombines the two components of f reflected energy into one output. The reected energy as combined is provided with a predetermined phase delay and then fed to a second hybrid network which, inthe same manner as the irst hybrid, splits -the incident energy into equal components to be fed to a second pair of radiating elements. The second pair of radiating elements ed to a radiating element D1. to the radiating elements which are matched to their feed functioning in the same manner as the first hybrid. This structure is repeated for as many pairs of radiating ele ments as are desired, each pair of irises coupling to the radiating elements a certain percentage of the energy incident on the irises. Further, for a uniformly illuminated array, all the radiating elements transmit equal parts of the total energy from the transmitter by virtue of the adjustable irises.

Y Alternatively, adjustable radiating elements of the character adapted to transmit to space a certain predetermined percentage of the energy incident on each radiating element and to reflect the remainder back into the hybrids and thence on ltoward subsequent sections of the array may be utilized, thus performing the same lossless reflective function as the irises in the previous embodiment.

The aforementioned phase delays would presumably be predetermined and ixed so as to electrically separate successive radiating elements by an integral number of half wave lengths of the center operating frequency. Then, when the frequency is shifted above or below this center frequency, the lobe will `shift from a broadside lobe to a left or `right direction. However, the same result may be achieved by using a constant operating frequency and selectively changing the phase delays between radiating elements.

The novel features which are believed to be characteristic of the invention, both as to itsorganization and method of operation, together with further objects and :advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing made a part of this specification. The scope of the invention is pointed out in the claims.

In the drawing Fig." l is a schematic diagram of one embodiment of the improved antenna array and feed system of the invention; l

. Fig. 2 is a frontal viewof one arrangement of the radiating elements of the array Vof Fig. l;

Fig. 3 is a frontal view of another arrangement of the radiating elements of the array of Fig. 1;; and

Fig. 4 is a partial schematic diagram of one section of a second embodiment of the array.4

Referring now to the drawing, and particularly to Fig. 1, an input transmission line 10 is connected to one terminal a1 of an R. F. hybrid network H1. Conductor 10 may be a waveguide or coaxial line. The hybrid may be of a type suitable for the operating frequency range to be used. Suitable for microwave frequencies, for example,

.is the rat race type of hybrid; this hybrid is described 50v lLaboratory Series, volume 14, chapter 8, page 357,'by

and discussed in Microwave Duplexers, MIT Radiation Smullin and Montgomery (McGraw-Hill Book Co., New York, N. Y., 1948) or the Rblet short slot coupler type -discussed in the Microwave Development Laboratories, 55.

brary of Congress Technical Information Division Inc., Quarterly Report, No. 5, 1950, available in the Li- MICRO-CARD U23l69, Investigation and Development I of Broad Band Single Slot Waveguide Hybrid Couplers by H. J. Rblet. Terminals b1 and c1 are the output terminals for energy incident at terminal a, and are connect- Interposed therebetween ineach line is an adjustable iris, reflective probe, or other adjustable lossless discontinuity, I1. Element D1 comprises a pair of energy apertures and preferably is matched to the line. Alternatively, D1 may be of a type which can be adapted to couple to space a predetermined percentage of the energy incident thereon and to reflect the remainder back along the waveguides toward hybrid H1,

Ain which case the lossless discontinuities are not used;

such a radiating element may be either a dipole pair or a slot pair in a waveguide. Terminal d1 of hybrid H1 isV the youtput -terminal for energy incident son' terminals Ysameestructure as phase delay F1.

conductors between the various-components.

b1 and c1 after reection from element D1. Terminal d1 is connected to a phase delay network F1, which may be a length of transmission line, any other type of fixed phase delay or a variable phase delay, the actuating means of which may be electrical, as with a solenoid, or may be mechanically coupled to a motor shaft. Actuator 14 is such a device andv is coupled to each of the phase delays if the embodiment to be utilized is one which makes use of variable phase delays.

Phase delay network F1 is also connected to the input terminal a2 of a hybrid H2, which, like hybrid H1, has terminals b2 and c2 connected to a radiating element D2. Again adjustable irises, I2, are interposed in the lines between the hybrid and the radiating element. Terminal d2 is coupled to a phase delay network F2, which is of the F2 is in turn coupled `to input terminal a2 of a third hybrid H3. Terminals b3 and c3 of hybrid H3 are coupled to radiating element D3 in the same manner; again, adjustable irises, I3, are interposed in the lines between the hybrid and the radiating element. l Output terminal d3 of hybrid H3 is coupled yto phase delay network F3.

In the same manner the structure of each section of the array is repetitive of the iirst, second and third sections, as described, for as many sections, l, 2, 3 n, as are to be included in the array. The energy reflected from the (n-1)th irises is fed through a phase delay network F 1 to the input terminal an .of hybrid Hn. Terminals bn and cn of hybrid Hn are coupled to a radiating element Dn. Output terminal dn of hybrid Hn is coupled tofan absorptive load 12. By matching the element Dn to the transmission'line, the amount of energy coupled to the absorptive load 12 can be made negligibly small, thus resulting in very high efficiency. Under these circumstances the load is necessary only for proper operation of the hybrid.

4The radiating elements preferably are physically spaced Ain twodirnensions and electrically spaced in one direction. In other words, and as indicated in Figs. 2 and 3, the elements are disposed in the same vertical plane and are parallel to each other. The phase delay networks F1, F2, F2 F 1 are all of the same structure and, if of the electrically controllable type, each is coupled to an actuating device 14. If the phase delay networks are to be actuated mechanically, the actuating device may represent a motor, and the'connections to the various phase delay networks would be mechanical. The array shown inthe drawing may be only one of a set of radiators going to make up a more complex array.

For purposes of explaining the operation ofthe invention it will be assumed that a microwave frequency is being transmitted and that waveguides are being used as The operation will first be described according to a frequencyshift embodiment in'which thephase delay networks F1 .F 1 provide'iixed phase delays. The input energy then would be at a lvarying frequency, centered,for example, about fo, at which frequency the radiating elements D1l D11 are each electrically separated by integral numbers ofhalf wavelengths. Energy incident upon terminal a1 of hybrid H1 `is equally split into two components whichV pass out of the hybrid at terminals b1 and c1, respectively, and impinge upon the irises'I1 and 111. The irises couple a certain predetermined percentage of the impingement energy to the radiating elements and reect the remainder back into the hybrid. The percentage lcoupled to the .radiating element D1 `and thence .to space is y of the total. transmitted energy in the case of a uniform array. The remainder is reflected back along the waveguides to terminals vb1 and c1. The energy incident upon the hybrid via terminals v'b1 andl c1 is recombined into a Phase delay network v single ycomponent which leaves at terminal d1. .This

energy then passes along the waveguide to phase delay network F1. The length of delay chosen for F1 is determined by the degree of frequency sensitivity desired to be given to the direction of the lobe. After being delayed by F1, the energy passes on to thel hybrid H2, where again it is split into two components and fed through irises I2 and I2 to the second radiating element D2 which likewise couples to the radiated lobe a certain percentage of the total energy. All the radiating elements D1---Dn are adapted to radiate an equal amount of energy, but successive ones will necessarily radiate increasingly greater percentages of the energy incident on the `respective irises.

Y the next xed Vphase delay'1`t2;Y In like manner, throughout the array the energy reflected from one pair of irises j i nn is a matched load. Thus it is seen that with the aid n i" of the hybrids, incident energy may vary in frequency causing a lobe .to scan without suffering the disadvantages, as discussed before, which are characteristic of prior art systems; It is seen also that with a controllable vfrequency of -incident energy, a controllable direction of lobe maybe achieved which need not vary periodically.

If it is desired to use a constant frequency input, scan ning vmay be achieved by changing the phase delay of each of the phase delay components F1-Fnl, and this may be achieved by .mechanically coupling actuator 14 to each of the .mechanical phase delay networks, or by electrically coupling actuator 14 to each of the electrical phase delay networks as previously indicated. Here again periodic ,lobe direction may be effected or a controllable lobe direction (not necessarily periodic) may be achieved by controlling actuator 14.

According to the above mentioned alternative embodiment indicated in Fig. 4, which utilizes adjustable radiating elements instead of irises or other lossless disconi tinuities in the feed lines to the radiating elements, each pair of radiating elements couples to space a different predetermined percentage of the energy incident thereon; and, in the case of a uniform array, each radiates an amount equal to that of each of the others in the array.

Certain R. F. hybrid networks have an inherent phase :shift between the output of terminal b and theoutput of Aterminal c which would result in an upward bias in the direction of pointing of the radiated lobe (assuming the lobe is being shifted back and forth in a horizontal plane). This may be corrected for, when such a hybrid is to be used, by the interposing of a fixed phase shifter of the order of 90 between terminal c and the respective integereach ofl said radiating elements having a pair of i apertures, each of said radiating elements having respec- 4tive iirst and second terminals associated respectively with said apertures; l through n radio frequency hybrids, each vof said hybrids having first, second, third, and kfourth terminals, iirst and second terminals of each radiating Aelement being connected to the first and second terminals of a respective hybrid; 1 through n fixed phase Shifters,

vrespective. `ones of saidixed. phase Shifters heinginter- In like manner, the energy reflected by irises I2 and I2 is recombined in hybrid H2 and sent on to posed betweensaid first terminal of respective ones of said hybrids and radiating elements; 1 through (n-l) phase delay networks, the respective third and fourth terminals of successive ones of said hybrids being coupled through respective ones of said phase delay networks; a resistive termination device, said device being coupled to the third terminal of the nth hybrid, and the fourth terminal of the rst hybrid being adapted to receive input signals, whereby the fourth terminal of said first hybrid constitutes the input to said array.

2. An antenna array system for frequency-shift scanning a predetermined space with a narrow radio frequency beam, said system comprising: 1 through n radiating elements spaced in one dimension` where n is any positive integer, each of said radiating elements having a pair of apertures, each of said radiating elements having respective first and second terminals associated with said apertures; 1 through n radio frequency hybrids, each of said hybrids having first, second, third, and fourth terminals, the first and second terminals of each radiating element being connected to the first and second terminals of a respective hybrid; 1 through n fixed phase Shifters, respective ones of said fixed phase Shifters being interposed between said first terminal of respective ones of said hybrids and radiating elements; l through (nl) phase delay networks, the respective third and fourth terminals of successive ones of said hybrids being coupled through respective ones of said phase delay networks, said hybrid networks being adapted to separate energy incident upon the fourth terminal into two separate halves obtained at the first and second terminals, and said hybrid networks being also adapted to combine energy incident upon the first and second terminals into one resultant obtained at the third terminal; a resistive termination device, said device` being coupled to the third terminal of the nth hybrid, and the fourth terminal of the first hybrid being adapted l,to receive input signals, whereby the fourth terminal of said first hybrid constitutes the input to said array.

3. An antenna array system as defined in claim 2 including: n-l first lossless discontinuities, each of said first lossless discontinuities being interposed between respective ones of said first terminals of said hybrids and said fixed phase shifter; and n-l second lossless discontinuities, each of said second lossless discontinuities being interposed between respective ones of said second terminals of said hybrids and said second terminals of said radiating elements.

4. An antenna array system for frequency-shift scanning a predetermined space, said system being of the character adapted to couple radio frequency energy to space through a plurality of energy apertures disposed along the electrical length of a conductor, said system comprising: l through n radiating elements, where n is any positive integer, electrically spaced in one dimension; 1 through n radio frequency hybrids, each of said hybrids being coupled to a respective radiating element; l through (n1) phase delay networks, said phase delay networks being coupled between successive radio frequency hybrids, each of said hybrid networks being adapted to receive energy and couple it to a radiating element and to couple reflected energy therefrom on toward the nth radiating element; a resistive termination device, said device being coupled to the nth hybrid network and being adapted to absorb energy reflected from the nth radiating element.

5. An antenna array system for frequency-shift scanning a predetermined space with a narrow radar beam, said system comprising: 1 through n radiating elements, where n is any positive integer, electrically spaced in one dimension, each of said radiating elements having a pair of apertures, each of said radiating elements having respective first and second terminals associated with said apertures; l through n radio frequency hybrids, each of said hybrids having first, second, third, and fourth terminals; 1 through n fixed phase shifters, said first terminal of each radiating element being connected to said first terminal of a respective hybrid, said second terminal of each radiating element being coupled through one of said fixed phase Shifters to the second terminal of a respective hybrid; 1 through (n-l) phase delay networks, the respective third and fourth terminals of successive hybrids being coupled through respective ones of said phase delay networks, each of said hybrid networks being adapted to separate energy incident upon its fourth terminal into two separate halves obtained at its first and second terminals and to combine energy incident upon the first and second terminals into one resultant obtained at the `third terminal; a resistive termination device, said device being coupled to the third terminal of the nth hybrid, and the fourth terminal of the first hybrid being adapted to receive` input signals whereby the fourth terminal of said rst hybrid constitutes the input to said array system.

6. An antenna array system for scanning a predetermined space with a narrow radar beam, said system comprising: l through n radiating elements electrically spaced in one dimension where n is any positive integer; 1 through n radio frequency hybrids, each of said hybrids being coupled to a respective radiating element; 1 through (n1) Variable phase delay networks, said phase delay networks being coupled between successive radio frequency hybrids and being adapted to have a controllable magnitude of delay responsive to an electrical signal, an electrical actuator device, said device being electrically coupled to each of said phase delay networks and being adapted to control in unison thereby the magnitude of phase delay associated with the phase delay networks, each of said hybrid networks being adapted to receive radio frequency energy and couple it to a respectiveradiating element and to couple reflected energy therefrom on toward the nth radiating element in a manner to provide unidirectional isolation between successive radiating elements; one through n fixed phase Shifters, each of said phase Shifters being coupled between respective ones of said hybrids and radiating elements; a resistive termina tion device, said device being coupled to the nth hybrid network and being adapted to absorb energy reflected from the nth radiating element. Y

7. An antenna array system for scanning a predetermined space with a narrow radar beam, said system being of the character adapted to couple radio frequency `energy to space through a plurality of energy apertures disposed along the electrical length of a transmission line, said system comprising: 1 through n radiating elements electrically spaced in one dimension where n is any positive integer; l through n radio frequency hybrids, each of said hybrids being coupled to a respective radiating element, each of said hybrid networks being adapted to receive energy and couple it to a radiating element and to couple reflected energy therefrom on towards the nth radiating element in a manner to unidirectionally isolate refiected energy from preceding radiating elements; l through n variable phase delay networks; a mechanical actuator device, said device being mechanically coupled to each of said variable phase delay networks and being adapted to control the magnitude of phase delay associated therewith; a resistive termination device, said resistive termination device being coupled to the nth hybrid network and being adapted to absorb energy refiected from the nth radiating element.

8. An antenna array system for scanning a predetermined space with a narrow radio frequency beam, said system comprising: l through n radiating elements, where n is any positive integer, electrically spaced in one dimension, each of said radiating elements having a pair of apertures, each of said radiating elements: having respective first and second terminals associated with said apertures; l through n radio frequency hybrids, each of said hybrids having first, second, third and fourth terminals, the first and second terminals of each radiating element being connected to the first and second terminals of a respective hybrid; 1 through n fixed phase Shifters, said phase shifters being interposed between respective ones of Vsaid vhybrids and said radiating elements; 1 through (nj- 1) variable phase delay networks, said variable phase delay networks being adapted to have a controllable magntude' of delay responsive to an electrical signal; an electrical actuator device, said device being electrically coupled to .each of said variable phase delay networks and being adapted to control in unison the magnitude of phase delay associated with the variable phase delay networks, each of said hybrid networks being adapted to separate radio frequency energy incident upon the fourth terminal thereof into'two separate halves of radio frequency energy obtainedl at its first andy second terminals, and said hybrid networks being also adapted to combine radio frequency energy incident upon said first and second terminals reflected from the respective one of said radiating elements into one resultant obtained at said third terminal; a resistive termination device, said device being coupled to the third terminal of the nth hybrid, and the fourth terminal of the first hybrid being adapted to receive radio frequency input signals whereby the fourth terminal of said first hybrid constitutes the input to said array.

9. 'An antenna array system for scanning a predetermined space with a narrow radio frequency beam, said system comprising: 1 through n radiating elements electrically spaced in one dimension where n is any positive integer, each of said radiating elements having a pair of apertures, each of said radiating elements having respective first and second terminals associated with said apertures; l through n radio frequency hybrids, each of said hybrids having first, second, third and fourth terminals, the first and second terminals of each radiating element being respectively connected to the first and second terminals of a respective hybrid; l through n fixed phase Shifters, said phase Shifters being interposed between the first terminal of respective ones of said hybrids and the first terminal of respective ones of said radiating elements; 1 through (rt-1) variable phase delay networks, respective ones of said variable phase delay networks being coupled between the third and the fourth terminals of respective adjacent ones of said hybrids, said variable phase delay networks being adapted to have a controllable magnitude of phase delay responsive to a mechanical action; a mechanical actuator device, said device being mechanically coupled to each of said variable phase delay networks and being adapted to thereby control the magntude of phase delay associated therewith, saidhybrid p networks beingV adapted to separate radio frequency energy incident upon the fourth terminal thereof; intov two separate halves of radio frequency energy 'obtained on the first and second terminals thereof, and said hybrid networks being also adapted to combine radio frequency energy incident upon the first and second terminals'ther'e of reflected from the respective one of said'radiating elements into one resultant obtained at the third terminal; and a resistive termination device, said device being cou pled to the third terminal of the nth hybrid, and the fourth terminal of the first hybrid being adapted to rei ceive radio frequency input signals whereby the fourth said apertures; 1 through n radio frequency hybrids, each i of said hybrids having first, second, third, and fourth terminals, first and second terminals of each radiating element being connected respectively to the first and second terminals of arespective hybrid; 1 through 2n adjustable lossless discontinuities, respective ones of said adjustable Y lossless discontinuities being interposed between said first and second terminals of respective ones of said hybrids and radiating elements;f1 through (r1-'1) phase delay' networks, the respective third and fourth terminals of successive ones of said hybrids being coupled throughrespective ones of said phase delay networks; a resistive termination device, said device being coupled to the third terminal of the nth hybrid, rand the fourth terminal of the first hybrid being adapted to receive inputfsignals, whereby the fourth terminal of said first hybrid constitutes the input to said array.

References `Cited in the file of this patent UNITED STATES vPATENTS Fox Nov. as, v1930 Alvarez July 29, 1952

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