US3522610A

US3522610A - Antenna array aperture multiplexing transmission feed and receive systems

Info

Publication number: US3522610A
Application number: US662764A
Authority: US
Inventors: Klaus G Schroeder
Original assignee: Collins Radio Co
Current assignee: Collins Radio Co
Priority date: 1967-08-23
Filing date: 1967-08-23
Publication date: 1970-08-04
Anticipated expiration: 1987-08-04

Description

ug 4, 1970 K. G. scHRoEDER 3,522,610

ANTENNA ARRAY APERTURE MULTIPLEXING TRANSMISSION FEED AND RECEIVE SYSTEMS Filed Aug. 23, 1967 2 Sheets-Sheet 1 R R E ya R S w m m N ww T N n/f A 55E 55m G w, wm IQ: mm zo.. s VN ,.i, W ww UH M L K Aug 4, 1970 K. G. SCHROEDER 3,522,610

ANTENNA ARRAY APERTURE MULTIPLEXING TRANSMISSION FEED AND RECEIVE SYSTEMS ATTORNEYS United States Patent O 3,522,610 ANTENNA ARRAY APERTURE MULTIPLEX- ING TRANSMISSION FEED AND RECEIVE SYSTEMS Klaus G. Schroeder, Dallas, Tex., assiguor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed Aug. 23, 1967, Ser. No. 662,764 Int. Cl. H01q 3/26, 2.7/00

U.S. Cl. 343-854 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates in general to antenna variable aperture multiplexing, and in particular, to antenna array aperture automatic, as a function of frequency, variable aperture multiplexing transmission feed and receive systems.

With many wide band antenna array systems the effective aperture generally does not most effectively suit the particular frequency being transmitted or received. To do so requires that the effective aperture be relatively narrow for the higher frequencies and be increased in width for the lower frequencies. Further, wide band antenna array systems using positive switching devices to vary the effective aperture give a step function operational result in effective beam width, and, particularly with respect to relatively high power signal transmission, the requirement is imposed for relatively complex, heavy duty, and expensive switching equipment in order to adequately perform the required function.

It is, therefore, a .principal object of this invention to provide an automatic variable aperture multiplexing antenna transmission feed and receive system with the automatic aperture variation a function of frequency.

A further object of such an automatic antenna variable aperture system is smooth operational transition from one frequency automatically activated mode of operation to another frequency determined mode of operation.

Features of this invention useful in accomplishing the above objects include, in various embodiments, automatic antenna variable aperture increase with signal frequency change from a high frequency mode of operation to a low frequency mode of operation. This aperture increase is to approximately twice the high frequency aperture with two added elements at each end of the antenna array. Hybrid circuits interconnect the added elements, and a low pass filter is included in the combined circuit path to a signal terminal, in the feed network, also connected to the antenna array elements of the high frequency aperture middle .portion of the array. The spacing span of such an antenna array is, generally, twice the span of the high frequency element portion of the array when the low frequency mode of operation is approximately one-half the high frequency mode of operation. Some embodiments also include high pass filtering in the combined circuit portion of the feed network connected to the antenna elements within the high frequency portion of the array.

Specific embodiments representing what are presently regarded as the best modes of carrying out the invention are illustrated in the accompanying drawings.

In the drawings:

f. ICC

FIG. 1 represents a schematic of an RF transmitting and/or receiving antenna array and the feed circuitry therefor with signal path means from a single feed circuit terminal to a middle array element high frequency aperture portion, and signal path circuitry between the single feed circuit terminal and outboard antenna array elements with low pass filter circuitry passing a low frequency mode range of operational frequencies through the signal path circuitry between the single feed circuit terminal and the outboard antenna elements;

FIG. 2, a schematic of an antenna array very similar in many respects to the antenna array and feed network embodiment of FIG. 1 with, however, high pass filter circuitry in the feed between the single feed network terminal and the middle array element high frequency aperture portion of the antenna array;

FIG. 3, a schematic of an embodiment similar in many respects to the embodiment of FIG. 2 with, however, additional filter circuitry including a high pass filter section between the single feed point and the middle array element high frequency aperture portion of the antenna array, and in addition to a low pass filter circuit, such as employed with the embodiment of FIG. 2, a further low pass filter circuit connected between the circuit path extending between the single feed network terminal and the outboard antenna array elements and the circuit path to the middle array element high frequency aperture portion at the junction of the high pass filter section with that portion of the antenna array system; and,

FIG. 4, a plot of the signal energy distribution through respectively the high pass filter circuitry and the low pass filter circuitry such as employed in the embodiment of FIG. 2 and such as passed by the high pass filter section and the low pass filter directly connected to the single feed circuit terminal in the embodiment of FIG. 3, with the pass bands of the respective low pass and high pass filter sections overlapping and being complementary so that they cross in a middle frequency range with each at substantially a -3 db level, and with each respective frequency increasing, or as the case may be, frequency decreasing signal energy being passed, while overlapping for a range, continually decreasing with respect to the frequency mode of operation the frequency shift is away from while the other increases until at the outer limits of frequency operation the frequency is entirely passed by one filter section or the other filter section, respectively, as the case may be.

Referring to the drawing:

The RF transmitting and/or receiving antenna array 10 of FIG. 1 includes four laterally spaced antenna groups 11 of

antenna elements

12a and 12b, each, in a middle array element high frequency aperture portion 13 of the antenna array 10 and two groups 14 of two

antenna elements

15a and 15b, each, comprising outboard antenna array elements laterally spaced outside the lateral spacing range of the middle array element high frequency aperture portion 13. The antenna structure 10 also includes a feed circuit network connected between a single feed network terminal 16 and the

antenna array elements

12a, 12b, 15a and 15b. The single feed circuit terminal 16 is connected to a hybrid circuit 17, of conventional nature, that has a port connection to a further hybrid circuit 18. In the middle array element high frequency aperture portion feed network section dual ports of the hybrid circuit 118 are in turn connected to additional duplicate hybrid circuits 19a and 19b from which dual output terminal ports in turn are connected to four

further hybrid circuits

20a, 20h, 20c and 20d, respectively, that have dual ports connected to

respective antenna elements

12a and 12b of the respective antenna groups 11. The other port of hybrid circuit 17 duplicating the port 18 is connected to and through a low pass filter circuit 21 that may be a filter circuit such as a transmission line or a lumped constant circuit configuration in accord with conventionally known filtering techniques, detail not shown, to hybrid circuit 22 equipped with dual ports connected respectively to

hybrid circuits

23a and 23b of the outboard antenna eletrnent groups 14 at the opposite outboard sides of the antenna array 10. With the antenna array configuration and the feed or combining network associated therewith the middle array element high frequency aperture portion 13 is used throughout the entire operational frequency range of the antenna array both in the high frequency area mode of operation and also in the low frequency mode of operation and for the intermediate transitory area of operation, while, the outboard

antenna array elements

15a and 15b come into effective usage only in the low frequency area mode of operation with signal energy being effectively passed through low pass filter 21.

'Referring now to the embodiment of FIG. 2 wherein the antenna array 10 is very similar to the antenna array 10 of FIG. l with the only really significant changes being that the hybrid circuit 17 is removed and a high pass filter 24 is employed, with the single feed network terminal 16 connected directly in common to both the low pass filter 21 and the high pass filter 24 and with the other side of the high pass filter 24 connected to the hybrid circuit 18. With this embodiment portions of the antenna array and the feed or combining circuitry are numbered the same as a matter of convenience and much of the explanation as applied to the embodiment of FIG. 1 is applicable in the same fashion with respect to the embodiment of FIG. 2. Please note at this point, however, that with the embodiment of FIG. 2 the middle array element high frequency aperture portion 13 is not used throughout the entire operational frequency range of the antenna array, and is used only through the high pass signal energy effective passing range of the high pass filter circuit 24. The two filters, the low pass filter 21 and the high pass filter 24, as connected and used in this circuit provide a simple high pass-low pass type complementary filter circuit structure useful in combining the signal from a basic eight port corporate feed connected to the high band center portion of the laterally extended bandwidth array, and with the signal from a four port corporate feed connected to the low band extension of the antenna system.

(Referring further to still another embodiment, that of FIG. 3, there are again many similarities between this antenna and the embodiments of both FIGS. 1 and 2. With this being the case, just as with the em-l bodiment of FIG. 2 components of FIG. 3 the same as with the embodiments of FIGS. l and 2 are numbered the same as a matter of convenience, and those numbers performing a similar function are in some instances given a primed number. With this embodiment, the single feed network terminal 16 is connected directly in common to both the low pass -lter 21 and the high pass filter section 24'. The filter section 24' may include two high pass filter circuits 25 and 26 interconnected by a length of signal transmission line 2.7 in order to optimumly minimize the stub length of leads from the respective high pass filter circuits 25 and 26. The connective leads involved include their connections, respectively, with the terminal 16 and the common junction of hybrid circuit 18 and an additional low pass filter 28. The low pass filter 28 is connected between the common junction of high pass filter circuit 26, of the high pass filter section 24', with hybrid circuit 18 and a port of hybrid circuit 29 another port of which is connected to hybrid circuit 22. Hybrid circuit 29 also has a terminal connection with and through low pass filter 21 to the common junction of the single feed network terminal 16 and the high pass filter 25 of high pass filter section 24'.

It is interesting to note at this point the plot of signal energy distribution of FIG. 4 with respect to high pass filter circuitry and low pass filter circuitry that are selected to be advantageously complementary when ernployed as the low pass filter circuit 21 and the high pass filter circuit 24 of the embodiment of FIG. 2 and as the low pass filter circuit 21 and the high pass filter circuit section 24 of the embodiment of FIG. 3. This is with the pass bands of the respective low pass and high pass filter sections overlapping and being complementary so that they cross in a middle frequency range with each at substantially a -3 db level. Further, as the operational frequency is shifted in the direction of one frequency mode, the overlapping frequency of the opposite mode of operation decreases in energy content until substantially the entire energy content is being passed solely by the filter for the mode of operation towards which the frequency shift had been occurring. Obviously desired design and operating criteria for some antenna array installations and usage may call for, in some instances, some departure from the complementary relation between the high pass and low pass filters described here without materially departing from the inventive concepts presented by applicants teachings herein. Please note further that low pass filter 2.8 in the embodiment of FIG. 3 in most instances is advantageously designed to pass substantially the same frequency range passed by the low pass filter circuit 21 in order to provide equal division of signal energy between the ports of the hybrid circuit 29 connected to hybrid circuit 22 and through the low pass filter 28 to the hybrid circuit 18, respectively.

The three embodiments of FIGS. 1, 2 and 3 are three array and feed combiner network systems having many features in common for extending the low frequency aperture of an antenna array and thereby narrowing the beamwidth at the low end of the operational frequency band. With the particular antenna element spacings employed for eight elements in the center sections, shown as a. middle array element high frequency aperture portion 13, the element spacing was such as to provide certain desired antenna array results in accord with antenna spacing criteria known to those skilled in the art. Further, in the embodiments shown the spacing of two additional elements laterally spaced to each side of the center section are shown as having twice the spacing for an aperture increase to twice the high frequency aperture with this structural approach. Obviously this can be varied one direction or the other as desired by variances in the spacings for particular criteria or in order that operational design requirements are anticipated. With the particular antenna element spacings employed in the embodiments of FIGS. 1, 2 and 3 and with, in the embodiments of FIGS. 2 and 3, the llow pass and high pass filter circuits being compatible as has been discussed, there is at least one point or area of operation where Substantially only half the power applied to each of the four outer elements is applied to each of the center elements, and that when all elements are excited the power density is substantially constant across the array since the element spacing in the center is half the spacing of the outer lower frequency mode of Operation elements. Obviously as has been suggested and described at least to some extent hereinbefore there may be variations in power feed division of signal power energy feed with respect to the different elements with variations in the spacing without materially departing from applicants teachings herein presented.

At least in a sense with the type of performance attained, structural arrangement and feed, some of the antenna structures may be considered as being akin to a log periodic broadside array in a direction perpendicular to the wave front. If a number of antenna element extensions are used each with the same element-to-element spacing and element-to-reector spacing in terms of wavelengths at the center frequency of each sub band, the analogy is particularly pertinent. With these antenna array configurations and feed systems, the dimensions of the structure in the direction of propagation are minimized.

However, in comparison to various other approaches that have lbeen employed, there is substantially no limit for the azimuth beamwidth because all elements are radiating in the same direction and, it is of interest to note that, with the addition of variable phase controlling circuitry of a conventional nature (not shown) with the various ernbodiments, the beam can be slewed. With these embodiments instead of slow wave active cell separation as in an endfire log periodic antenna, the separation of active.

regions is accomplished in the feed network by transmission line or lumped constant filtering techniques, as has been set forth hereinbefore. By way of reiteration to some extent substantially complete freedom of design is available with respect to choice of crossover frequencies in the interacting area of the active region with the embodiments of FIGS. 2 and 3 so that, for example, a limited number of narrow operating frequency bands (as in International Broadcasting) minimum azimuth beamwidth variation can be accomplished at some moderate increase in equipment cost. An additional interesting fact is that with these antenna array structures the real estate requirements are substantially the same as those imposed for a low frequency array antenna cell system alone.

With the FIG. 2 embodiment an eicient high pass-low pass type complementary filter feed network circuit is used to combine the signal from a basic eight point corporate feed connected to the high band center portion of the extended bandwidth array with the signal from a four port corporate feed connected to the low band extension. With this approach it should be noted that the crossover band must be fairly broad and the elements must be fairly close together, or grating lobes will occur at the low end of the extended operating band. Further, this in au increasing problem with an increasing number of elements in the high band array. The embodiment of FIG. 1 is one solution to this limitation with both array sections obviously being used at the low end of the operational frequency band. With this approach a loss in absolute gain of approximately 3 db is suffered at the high frequencies, but if cutoff frequency is chosen properly the gain should still be higher than the minimum absolute gain at the low end of the band.

With reference again at this point to the embodiment of FIG. 3, this is an embodiment utilizing full automatic crossover with both subarrays utilized at the low frequencies and with loss being kept quite minimal since the complementary filters are actually low loss devices. The complementary ring lter circuit configuration with the filter section 24 including filter circuits 25 and 26 and the low pass filter 21 along with the low pass filter 28 in the embodiment of FIG. 3 constitutes, generally speaking, an optimum receiving diplexer circuit with respect to the operational frequencies of the antenna array This is particularly so with the two high'pass filters 25 and 26 in the filter section 24' being so design selected as to work into each other instead of standard matched loads.

Whereas this invention is here illustrated and described with respect to specific embodiments thereof, it should ybe realized that various changes may be made without departing from the essential contributions to the art made by the teachings hereof.

I claim:

1. In a variable aperture transmission-receive antenna array system with automatic, as a function of frequency, aperture variation from a narrow high frequency mode of operation to a relatively wide low frequency mode of operation, a middle array element high frequency aperture portlon connected to a feed network terminal; outboard antenna array elements spaced outside the lateral spacing range of said middle array element high frequency aperture portion; hybrid circuit means interconnecting said outboard antenna array elements; low pass filter means connected in the feed circuit between said feed network terminal and said outboard antenna array elements; wherein an additional hybrid circuit is provided in the feed network between said low pass filter means and said feed network terminal; and with said additional hybrid circuit having a port connection to the middlehigh frequency aperture portion of the antenna array system.

2. In a variable aperture transmission-receive antenna array system with automatic, as a function of frequency, aperture variation from a narrow high frequency mode of operation to a relatively wide low frequency mode of operation, a middle array element high frequency aperture portion connected to a feed network terminal; outboard antenna array elements spaced outside the lateral spacing range of said middle array element high frequency aperture portion; hybrid circuit means interconnecting said outboard antenna array elements; low pass filter means connected in the feed circuit between said feed network terminal and said outboard antenna array elements; wherein circuit means provides a signal path for low frequency signal energy ybetween said feed network terminal and said middle array element high frequency aperture portion of the array system when the system is in the low frequency mode of operation.

3. The variable aperture antenna array system of claim 2, wherein high pass filter means is connected in the feed circuit between said feed network terminal and the middle array element high frequency aperture portion of the antenna array system; and a low pass filter connected in the feed circuit between said feed network terminal and the middle array element high frequency aperture portion of the antenna array system.

4. The variable aperture antenna array system of claim 3, wherein said low pass filter means is connected between said feed network terminal and a hybrid circuit having a port connected to said low pass filter connected in the feed circuit between said feed network terminal and the middle array element high frequency aperture portion of the antenna array system.

5. The variable aperture antenna array system of claim 3, wherein said high pass filter means includes two high pass filters interconnected by a length of signal transmission line.

References Cited UNITED STATES PATENTS 2,096,031 10/1937 Cork 343-853 3,255,450 6/1966 Butler 343-853 X FOREIGN PATENTS 1,031,031 6/ 1958 Germany.

1,074,676 2/ 1960 Germany.

ELI LIBERMAN, Primary Examiner T. I. VEZEAU, Assistant Examiner U.S. C1. X.R. 343-844