US 3766558 A
A broadside array antenna arrangement capable of scanning electronically in one or two planes, wherein the transmitted or received frequency remains fixed although beam steering is effected by progressive phase shifts introduced to the various array elements as provided by the expedient of frequency variations. A prime oscillator frequency fo is mixed with a variable steering oscillator frequency fs to produce sum and difference frequencies fo + fs and fo - fs. The latter is fed to a delay line having a plurality of taps spaced apart in accordance with the particular arrangement of array elements, the delay line providing in the frequency signal fo - fs progressive phase shifts from tap to tap. The individual tap outputs are separately mixed with the sum frequency signal fo + fs, wherein N separate outputs are simultaneously derived having the same frequency of 2fo but varying from one another progressively in phase. Variation of fs, which causes the phase relationship between the N outputs to change as they are fed to the radiators in one-to-one correspondence, thus provides a sweep of the beam in one plane. Raster type scanning is provided by introducing a multi-tapped secondary delay line at each tap of the primary delay line and mixing instead the tap outputs of each secondary delay line individually with fo + fs and applying the resultant 2fo outputs to individual ones of a corresponding element row of a two-dimensional array. The tapped spacings on each of the secondary delay lines relative to the tapped spacings of the primary delay line is such as to provide scanning of an order of magnitude more sensitive in one plane.
Description (OCR text may contain errors)
Elnite States Patent 1191 Kuechken Oct. 16, 1973 RASTER SCAN ANTENNA John A. Kuechken, Pittsford, NY.
International Telephone and Telegraph Corporation, Nutley, NJ.
Filed: Sept. 17, 1971 Appl. No.: 181,453
US. Cl. 343/100 SA, 343/854 Int. Cl. H01q 3/26 Field of Search 343/100 SA, 113 R,
References Cited UNITED STATES PATENTS ll/l97l McLeod, Jr. 343/100 SA 5/1963 Welty 343/100 SA l0/l97l Connolly 343/100 SA Primary ExaminerBenjamin A. Borchelt Assistant Examiner-Richard E. Berger At!0rneyC. Cornell Remsen, Jr. et al.
[5 7] ABSTRACT phase shifts introduced to the various array elements as provided by the expedient of frequency variations. A prime oscillator frequency f is mixed with a variable steering oscillator frequency f, to produce sum and difference frequencies f +f, and f, f The latter is fed to a delay line having a plurality of taps spaced apart in accordance with the particular arrangement of array elements, the delay line providing in the frequency signal f, -f, progressive phase shifts from tap to tap. The individual tap outputs are separately mixed with the sum frequency signal f +f,, wherein N separate outputs are simultaneously derived having the same frequency of 2f, but varying from one another progressively in phase. Variation of f,, which causes the phase relationship between the N outputs to change as they are fed to the radiators in one-to-one correspondence, thus provides a sweep of the beam in one plane. Raster type scanning is provided by introducing a multi-tapped secondary delay line at each tap of the primary delay line and mixing instead the tap outputs of each secondary delay line individually with f, +f, and applying the resultant 2f, outputs to individual ones of a corresponding element row of a twodimensional array. The tapped spacings on each of the secondary delay lines relative to the tapped spacings of the primary delay line is such as to provide scanning of an order of magnitude more sensitive in one plane.
3 Claims, 4 Drawing Figures a if, (a w zagr 0 s DELA Y L we 2?" RA STE/Q SCAN/WEI? 0 I6 l l 5 ram uvc PRIME OSCILLATOR 'osc/uAro/a To M/X'R RASTER SCAN ANTENNA BACKGROUND OF THE INVENTION This invention pertains to communications systems and more specifically to electronic raster type scan antenna arrangements particularly adapted to communications requirements calling for fixed rediated and received frequencies.
In, for example, high directivity microwave applications, the use of steerable array antennas has certain very substantial attractions compared to the more conventional two or three-axis gimbaled reflector. Potentially, the array will have a much smaller swept or inscribed volume and will be capable of steering the antenna beam in very short times compared with the mechanical motion of the reflector. In addition the mechanical mount or pedestal is heavy and expensive. Consequently, a great deal of effort has been expended in developing array antennas which may be steered in one or two planes by the expedient of applying linearly progressive phase shifts to the array elements to obtain electronic beam steering of planar arrays.
Whereas many of the problems have been solved in such arrays, several fairly severe and rather fundamental limitations remain:
I. It is extremely difficult for example to cause any planar array to scan more than i45 from braodside; and
2. On large arrays the gain proceeds approximately as the number of elements, with elements being required for instance to obtain 43 db of directivity. The first limitation implies that either four or five planar arrays are required to cover a complete hemisphere if no mechanical motion is to be used. The second implies that very large numbers of phase shifters are required if two-directional scan or steering is to be obtained. The latter problem is further compounded if a quantized phase shift is to be obtained because of the phase ripple on the aperture.
This phase ripple may be interpreted as constituting a second superimposed antenna excited only with errors, whose radiation pattern interferes with the real antenna pattern. If it is assumed that the RMS excitation of the error aperture is equal to one-half the quantum size error the following is obtained:
Approximate Error Phase Quantum Sidelobe Level 1r radians 0 db (two main beams) rr/Z 83 db 11/8 -l9.3 db
The error sidelobes may coherently add (voltagewise) to the normal sidelobe structure.
Accordingly, it may be seen that a fairly large number of quanta may be required if a reasonable sidelobe level is to be maintained at all scan angles. If an additive scheme is used for 17/4 quanta, then a four bit switching is required (22.5, 45, 90 and 180). (In a completely non-additive scheme bits would be required.) This number appears as a multiplier against the number of elements in two-dimensional scanning antennas using an interacting scan scheme whereby the phase to yield appropriate beam steering in both planes is independently determined for each radiator. A row and column scheme will simplify the logic at the cost of an extra row or columns worth of phase shifters.
In radar work a great deal of this complexity can be avoided by using a frequency scan scheme. Here the frequency is altered to provide the requisite phase shifts between taps on a delay line, thus each beam position is associated with a unique frequency. The device is a microwave analogue of an optical diffraction grating. Such arrays are most commonly built to scan in one plane and use mechanical motion in the orthogonal plane. However, a raster type scan motion could be obtained by using orthogonal delay lines where the frequency scanning in one plane is arranged to be an order of magnitude more sensitive in one of the planes with the successive grating lobes of the rapid scanning plane being used as the main lobe. The scan band would be discontinuous between successive raster lines, however; each usable frequency would be uniquely associated with a given point on one of the raster lines. This scheme is acceptable in radar work where the exact frequency is unimportant as long as the receiver local oscillator tracks the transmitter frequency. Unfortunately, this technique is not directly applicable for instance to satellite communications wherein the up link and down link frequencies are uniquely determined by outside requirements.
SUMMARY OF THE INVENTION It is therefore a principle object of this invention to provide a simplified electronic scan facility which avoids the above-mentioned drawbacks.
It is another principle object of this invention to provide electronic beam steering of planar array antennas in one or two planes by the expedient of applying (linearly) progressive phase shifts to the array elements.
It is yet another principle object of the invention to provide an electronic scanning technique for steerable array antennas whereby the radiated and received frequencies are fixed while the mechanism of frequency scanning is employed to provide requisite phase shifts.
It is still another object to provide an electronic antenna scanning technique predicated on phase shifts wherein a steering frequency is varied to provide uniform variations in requisite phase shifts between taps on one or more delay lines.
It is a further object of this invention to provide electronic beam steering of array antennas by way of the mechanism of frequency scanning wherein the long term stability of the steering frequency is unimportant.
It is yet a further object of this invention to provide an electronic scanning arrangement which is applicable to both communications antenna scanning systems and radar scanning systems.
According to the broader aspects of the invention there is provided an antenna scanning arrangement comprising first means providing signal frequencies of fl, j, and j}, 12, from a fixed prime frequency signal f, and variable steering frequency signal fi second means operating on said f, j, signal-frequency to provide N simultaneous f f, signals each having a unique phase which varies progressively from one another in predetermined increments; third means separately coupling each of said N simultaneous f, f, signals of said second means with said f +f}, signal frequency for providing N separate signals each having the same harmonic frequency of f and progressively varying in phase from one another in said predetermined increments; and N radiating elements in an array of predetermined arrangement coupled to said third means and radiating signal energy in response to said N separate signals coupled thereto in one-to-one correspondence.
A feature of the invention is that a two-dimensional electronic scanning array antenna arrangement is provided whereby the phase shifts yielding appropriate beam steering in both planes is independently determined for each radiator.
A further feature of the invention is that raster type scanning by way of requisite phase shifts is provided from steering frequency variations wherein orthogonal delay lines are employed to receive the steering frequency and to provide phase shifts such that the electrical length between adjacent taps on the one delay line are arranged with respect to the lengths between adjacent taps of the other, so as to provide scanning in the one plane to be in the order of a magnitude more sensitive.
BRIEF DESCRIPTION OF THE DRAWINGS The above mentioned and other objects and features of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:
FIG. 1A is a schematic representation of an array antenna scanning arrangement in the transmit mode according to the invention for scanning in one plane;
FIG. 1B is an operational plot of the scanning facility of the arrangement of FIG. 1A in terms of azimuth beam position and steering frequency;
FIG. 2A is a schematic representation of a raster type scanning array antenna arrangement according to the invention; and
FIG. 2B is a plot of the scanning facility of the arrangement of FIG. 2A in terms of beam position elevation and steering frequency.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1A and 18, there is illustrated therein respectively an electronic scanning array antenna arrangement according to the invention for scanning in the horizontal plane; and a diagram of the scanning facility of FIG. 1A in terms of azimuth angle of sweep and the steering frequency spectrum giving rise to the requisite phase shifts for beam steering. In FIG. 1A the transmit mode is depicted (primarily), although the inventive arrangement is intended to be reciprocal in capability, and to that end a switch connection is illustrated which pertains to the receive mode.
The frequency f of a prime oscillator l is combined in a mixer 3 of conventional design with the frequency f, of a steering oscillator 2, with the outputs respectively at and 11 being the sum and difference frequenciesf, +fl, and f -f,. While prime oscillator 1 remains fixed in frequency, steering oscillator 2 is intended to be capable of an output which is variable in frequency over a predetermined range, say f, f-. The difference frequencyf, f, is fed to a delay line 6 having taps A, B, C, etc. at predetermined points, the separations thereof being generally dependent upon the arrangement of and specifically the separation between the array elements. Delay line 6 provides phase shifts to f, -f, at the points A, B, C, etc. in accordance with the following relation:
Phase Shift (for example) A to B =[2n'(AB)]/ \d radians 1) where:
(AB) d the physical distance along the delay line in meters. A, in turm may be considered as being the following: M X )/(fo f,) X (V /C meters 2 and V /C the velocity of propagation in the delay line (numeric factor).
The various taps off of delay line 6 are in turn fed to individual mixers 4 wherein f -f, from each delay line tap or terminal is mixed independently with the f f, output from mixer 3. Mixers 4 are to be considered conventional in design and operation. As delay line 6, via the periodic taps A, B, C, etc., provides f, fl, with successive and, in the illustrated example here, linear phase shifts, that same phase relation between the respective outputs of mixers 4 will be maintained in view of the well known principle that phase remains undisturbed in a mixing process. By combining the f, f, output of mixer 3 with the phase staggered outputs at the taps A, B, C, etc. of delay line 6, the steering frequency fi, drops out leaving the N outputs of mixers 4 each having the same frequency, i.e. two times the frequencyf, of the prime oscillator l, but with the respective phase differences preserved. As the outputs are then coupled to radiators 5, the energy radiated by each is, therefore, of the same frequency but at some relative phase difference with adjacent and all other similarly radiated energies. Thus, asf, is varied, only the beam moves while the radiated frequency doesnt change. In the above and hereinafter as well, it is to be understood that conventional selective filtering accompanys each mixer defined in the arrangement in order to provide the desired mixer output(s).
The array of elements 5 may conventionally take the form ofa broadside driven array wherein all the radiators are in a line (a one-dimensional array), i.e. the antenna axis. The elements 5 may be either monopoles or dipoles appropriately arranged and fed to provide the preferred broadside operation. Delay line 6 may in actuality be any suitable means which provides simultaneous outputs off f, each with a unique phase successively varying from output to output in a predetermined manner depending on the arrangement of array elements, the delay lines here envisaged, however, being of conventional design. It is estimated that perhaps elements 5, and therefore mixers 4 as well, are needed to achieve a 1 beam width.
In operation, the arrangement of FIG. 1A could for instance commence a sweep with the beam at 0, i.e. normal with respect to the axis of the array. In this situation, the steering frequency f, is such as to provide an integral wavelength A in relation to the distances d, i.e. AB, BC, etc. An increase in steering oscillator frequency f, will for instance cause the beam to swing away from normal or broadside (0) to some angle O a 45 to the right of normal, as viewed in the direction of intended transmission. A continued increase in f, would cause the highly directional array beam to sweep finally to an angle 0l'--'45 with respect to normal (broadside). At this point it is advantageous to design into the system some facility wherein the scanning is interrupted, thus preventing a sweep of greater than 45. This is desirable because the beam at angles greater than 45 in general becomes sloppy, irregular and inadequate in directivity. Moreover, there is created from an increase in f, at the 45 beam sweep angle a new and second beam directed substantially 45 to the left of broadside as viewed in the general direction of intended transmission. Thus with the development of two beams, the advantages of electronic scanning with a highly directional beam are lost in the absence of some facility in the system for rejecting the now deteriorated initial swept beam and concentrating instead on the newly created beam.
One means of facilitating a substantially continual scan for further increases in f. while eliminating the dual-beam situation is to provide the steering oscillator 2 mechanism with the capacity of having its output to mixer 3 interrupted at the frequencies equivalent or corresponding to the 45 scan angle with minimal tolerance taken into consideration. In other words as the beam closely approaches the +45 sweep angle (i.e. 45 to the right of normal in broadside), f, is interrupted in reaching mixer 3 for a very small frequency band, wherein the steering oscillator output would be once more permitted to reach mixer 3 as a continued increase in f, meanwhile reached a frequency which would provide the new, highly directive beam at the 45 angle of sweep (i.e. 45 to the left of broadside). At this frequency of f,, the former beam would have dissipated beyond consideration. Now, as f, is yet continually increased the new beam would continue to sweep from the -45 angle through broadside and finally once again approach the +45 angle of sweep, at which time f, would once again be interrupted for a short frequency span. It is to be noted however, that the interrupted frequency bandwidth is intended to be equivalent to that required to provide a beam sweep of less than half the beam width.
It is also possible to arrange the array elements so as to allow the beam to disappear at the +45 sweep angle. In this manner the periodic discontinuities demonstrated in FIG. 1B of the variable steering frequency f, may be virtually eliminated. It is to be understood also that the discontinuities of f, in FIG. 1B (and also FIG. 2B) are not to scale, but rather have been emphasized to illustrate the existence of same.
In the inventive arrangement, steering oscillator 2, in having an arbitrary operative spectrum of f, f, f,,, may be arranged to begin at f and continuously vary upward in frequency to f and then immediately switch back to f, to begin a span of the band anew. Alternatively the operative design could instead be arranged so as to provide for f,,, in reaching f to reverse itself and decrease in frequency back to f It is entirely possible therefore in this latter consideration to shorten the operating range f f of steering oscillator 2. The variability of steering oscillator 2 may of course be provided by any conventional automatic or manual means.
It is particularly noteworthy that the long range stability of steering oscillator 2 is unimportant in as much as the frequency f, thereof cancels out in the inventive process, leaving only 2]), to be transmitted.
In general, uniform spacing of elements 5 is contemplated in the arrangement of FIG. 1A. However, unfilled aperture techniques for example can be accommodated equally well by simply making the delay line length between taps proportional to the respective radiator spacings.
For a broader understanding of electronic beam steering by the expedient of phase shifts or variations (primarily uniform) in broadside array antennas see Antennas and Transmission Lines" by John A. Kuecken, published in I969 by Howard W. Sams & Company, Inc.
In considering the arrangement of FIG. 1A in a receive mode, the connection 11 running from mixer 3 to the delay line 6 is to be substituted by a new line 12 leading to an additional mixer 13 by way of switch SW. The other input to mixer 13 is taken by way of lead 14 from the output of steering oscillator 2. The output of mixer 13 is in turn coupled to the receiver IF strip for providing the output in readily usable form. In this mode, the incoming signal of 2f, is received by the radiators 5. The received signal is treated in mixers 4 to provide from each an f f, output according to the relation:
where the f,, f, output of mixer 3 is supplied as before to mixer 4.
The resultant f fl, signal from delay line 6 is then combined with j", in mixer 13 to yield an f, output. This f output may then be treated by a conventional IF strip to provide the output in desired form. v
Thus it is seen that the inventive arrangement of FIG. 1A is capable of reciprocal operation.
Referring to FIGS. 2A and 2B, a two-dimensional or raster type scanning array antenna arrangement according to the invention is illustrated, together with a diagram showing the operation thereof in terms of elevation scan angle and the spectrum of steering frequency oscillator 2. Though the arrangement in FIG. 2A is depicted and to be described in terms of the transmit mode, it is to be understood here also that the inventive arrangement may be utilized in a receiver capacity, and therefore is reciprocal in nature. Duplicated portions of the arrangement of FIG. 1A have been given like reference designations in the arrangement according to FIG. 2A. The latter arrangement differs from the former particularly by inclusion of secondary delay lines 16, 16', 16", etc. at the taps A, B, C, etc. of delay line 6. These secondary delay lines are in turn themselves tapped at Aa, Ab, Ac Ba, Bb, etc. in predetermined fashion as illustrated at 17. The taps in turn are coupled to mixers 18, wherein once again the coupled energy from the delay lines is mixed conventionally with f j}. However, in this arrangement the radiators 19, 19', 19", etc. are arranged in a twodimensional array of rows and columns, thus requiring corresponding row and columns of mixers 18, 18, 18", etc. Thus each secondary delay line 16, 16', 16", etc. is associated for instance with its own element row or column, with the individual taps thereof being in oneto-one relationship with the associated mixers l8 and radiators 19.
Whereas, FIG. 1A provides for the N taps A, B, C, etc. from the one delay line 6 only, thus giving rise ultimately to the respective radiations of 2f,,, 2f, qr, 2f, 2 :11, 2f, 3 (I: 2j], N 111, the arrangement according to FIG. 2A provides, bp way of the N secondary delay lines 16, 16', 16", etc. operating from the taps of delay line 6, ultimately for the radiations of 2f, 41 A '11 2f p A 2 I11 etc. for the first row (or column), 2f, ill Ill 2f, 111 B 2 ill) etc. for the second row, and 2f ill N ll: 2f i1: N N i1; for the Nth row.
Similar to before, the lengths AB, BC, etc. and A A A A etc. between taps on the respective delay lines are proportional to the spacings of the elements in each row (or column) and now the spacing between the rows as well.
In operation, the plots of both FIGS. 1B and 2B indicate the true scanning operation provided by the inventive arrangement exemplified in FIG. 2A when considered together. As f, is varied between f and f the highly directional beam will scan azimuthally as described previously for instance from left to right in relation to the direction of intended transmission. As the +45 scan angle is finally reached, the steering frequency f, in reaching mixer 3 is once again rendered discontinuous over a small frequency span for the reasons noted hereinbefore. As a result, the elevational scan, as showing in FIG. 2B, is also rendered discontinuous. Thus, the pattern plotted shows the beam to continually increase in elevation as it sweeps from -45 to +45 in azimuth, with the next sweep, in terms of elevation commencing at some yet greater angle of elevation at which it would normally have arrived even if there had been no discontinuity in the frequency spectrum of f,. It is to be particularly noted, however, that the distance or length Z in FIG. 2B, which represents the amount of elevation scan corresponding to the discontinuity in f,,., is such as to be considerably less than one beam width in elevation. Therefore, as fi, continues to increase the elevation angle will continue to increase proportionally in a linear manner in the example illustrated here, with, however, the periodic discontinuities as mentioned.
The ultimate stated object of the example arrangement illustrated in FIG. 2A is to scan electronically in two planes, i.e. the vertical and the horizontal. Intended to be provided therewith according to a feature of the invention is the facility that the scan in one plane (in this example the horizontal plane) be of an order of magnitude more sensitive. To this end there is provided very rapid scan in the horizontal plane with respect to the vertical plane scan, which is directly attributable to the relationship between the lengths a and d between taps on the respective primary delay lines 6 and the secondary delay lines 16, 16', 16" etc. In this case the length AB for example is considerably greater than the A A Thus is realized a very rapid scan in the horizontal plane while simultaneously the beam is increasing continually in elevation but at a much slower rate. The result is that from a single run through the f f spectrum of the steering frequency oscillator 2, a very substantial area of space has been electronically raster scanned at great speed.
Both the primary delay line 6 and recording delay lines l6, 16, etc. of course respond to the relation of equations l and (2) above, but as stated the array of FIG. 2A will provide a beam of sweep rapidly from side to side while moving slowly in the vertical. It is to be noted that the phase shift of interest at each element is in general where 1; is any even integer. In other words, the beam condition repeats every 21r radians of phase shift. Between successive raster lines then, ill jumps by 211 radians in giving rise to the discontinuous frequency spectrum. Again, techniques may be employed, such as the use of directive radiating elements, whereby this discontinuity between raster lines could be virtually eliminated.
While in the arrangements of FIGS. 1A and 2A the outputs of mixer 3, i.e. the sum and difference frequenciesf,, +fl, and f, -f,, were respectively fed to mixers 4 (or 18) and delay line 6, it is entirely within the scope of this invention that the sum and difference frequency applications here be reversed. That is, the sum frequencyf, +1, may just as easily be arranged to be fed to the delay line 6 and in turn the f fl, frequency be fed to the row(s) of mixers 4 or 18. The operation would be the same with the output of mixers 4 or 18 again having the steering oscillator frequency j", drop out leaving the second harmonic of the primary oscillator frequency f,, to be radiated.
In the above there has been disclosed array antenna arrangements providing electronic scanning in one or two planes capable of both transmit and receive operation, wherein the beam steering is accomplished by the expedient of progressive phase shifts applied to the individual radiators as generated by frequency variations of a steering oscillator in being fed to a multitapped delay line. The embodiments disclosed are particularly adaptable for instance to satellite communications wherein the frequencies of operation are determined by outside requirements and must be considered fixed. Thus the inventive arrangements provide electronic beam steering by requisite phase shifts resulting from frequency variations in applications which cannot tolerate such frequency variations in communications operations. The variable steering frequency oscillator output is mixed with a fixed prime oscillator output to provide the sum and difference frequencies therefrom, with the difference frequency being applied to a delay line having periodic taps proportional to the radiator spacing of the array. The tap-offs from the delay line are in turn mixed individually with the derived sum frequency such that the steering frequency drops out leaving N outputs to be fed to the radiators, arranged essentially in a one-dimensional array, which outputs all have the same frequency of two times the prime oscillator frequency but which progressively vary from one another in phase as derived from the delay line. A variation in the steering oscillator frequency causes the phase relation between the N outputs to change thus providing a corresponding change in aximuth angle of the highly directional beam. For two-plane or raster type scanning, secondary multi-tapped delay lines are applied to the tapped outputs of the primary delay line, with the individual taps of each secondary delay line in turn being individually mixed with the derived sum frequency to eliminate the variable steering frequency and the outputs thereof in turn being fed to an associated row of radiators in a two-dimensional array.
While the principles of this invention have been described in the above with regard to specific apparatus, it is to be understood that this description is made by way of example only and is not to be considered as a limitation on the scope of the invention, and the objects and features thereof, as set forth in the appended claims.
1. An antenna scanning arrangement comprising:
a. first means for generating from a fixed prime frequency signal f and a variable steering frequency signal j; first and second frequencies of f, +f, and
b. second means operating on one of said first and second signal frequencies to provide N simultaneous signal portions thereof of the same frequency and each having a unique phase which varies progressively from one another in predetermined increments;
0. third means separately coupling each of said N simultaneous signal portions with the untreated other one of said first and second signal frequencies for providing N separate output signals each having the same harmonic frequency of f and progressively varying in phase from one another in said predetermined increments; and
d. N radiating elements in an array of predetermined arrangement coupled to said third means for radiating signal energy responsive to said N separate output signals applied thereto in one-to-one correspondence, wherein said second means is comprised of a primary phase shifting device having a plurality of terminals for providing simultaneous outputs varying in phase from one another progressively in said predetermined manner, and a plurality of secondary phase shifting devices each having a plurality of terminals for providing simultaneous outputs varying in phase from one another progressively in a predetermined manner, said secondary phase shifting devices each being separately coupled between a terminal of said primary phase shifting device and said third means, and wherein said radiating elements are arranged in a twodimensional array and said primary and secondary phase shift devices are comprised of delay lines having taps arranged periodically thereon.
2. The arrangement according to claim 1 wherein said first means includes a prime oscillator for producing said fixed prime frequency signal energy f,,, a steering oscillator providing said variable steering frequency signal energy f, and a first mixer coupling said f and f, signal energies for providing said f, +1, and f, -f, signal energies.
3. The arrangement according to claim 2 wherein when operation of the arrangement is in a receive mode, said first means further includes a second mixer coupled between said second means and the output of said steering oscillator wherein said steering frequency signal energy f, and the difference frequency f, f, from said second means are coupled to provide the frequency output f