Patent GB-805910-A (GB)
Title: Improvements in or relating to directional radio apparatus
IPC: G01S1/02
Filed: 1956-11-09
Abstract: 805,910. Aerials; radar. SOC. FRANCAISE RADIO-ELECTRIQUE. Nov. 9, 1956 [Nov. 18, 1955], No. 34307/56. Class 40 (7). A directional radio apparatus comprises an array of aerial elements in a vertical or nearvertical plane, a delay line, transmitters or receivers connected to different aerial elements and to different taps on the delay line and means for sending a high-frequency wave of cyclically varying frequency down the line whereby the polar diagram directivity varies cyclically with the momentary value of the frequency, there being no mechanical movement of the aerial system or its parts. Principle of operation (see Fig. 1).-Delay line L is connected at one end to saw-tooth frequency-modulated generator G and is terminated in its characteristic impedance at the other end by resistor K. Taps down the line feed successively horizontally-polarized vertically co-planar aerial elements l to n through corresponding amplifiers Al to An. If the aerial elements are equidistant and the line tappings are at adjacent intervals corresponding to an integral number of wavelengths at the generator's mean frequency fm, the polar diagram will sweep from the right, through the normal to the aerial plane and to the left as the generator frequency sweeps from maximum to minimum and its return sweep will be rapidly in reverse in correspondence with the saw-tooth frequency modulation " fly-back." Receivers Rl to Rn, coupled to the aerial elements by known directional couplers Cl to Cn (to avoid transmitter break-through), may simply be mixers connected as shown, their outputs being combined in output circuit BF; the polar diagram of reception is reciprocal with that of transmission. Application to frequency-modulated radar.- The aerial system (see Fig. 2) comprises horns a1 ... an, b1 ... bn, and c1 ... cn, each of aperture width l=# and height h=3# (where # is the wavelength corresponding to mean frequency fm); all horn mouths are in a common plane (see Fig. 3, not shown), whose normal is elevated by a small angle (for example, 10 to 15 degrees). The horns are connected as shown in Fig. 4 to transmitting amplifiers A and receivers R, both of which are connected in turn to mixers M2. To avoid inconveniently high delay necessary at the working mid-frequency of 1000 Mc/s. and maximum frequency deviation of 3 Mc/s., delay line LR is fed from generator G whose frequency varies, in a saw-tooth manner, from 7 to 10 Mc/s.; translation to the final frequency is accomplished with mixers M1 heterodyned at 90 Mc/s. from oscillator H1 and with further mixers M2 heterodyned at 900 Mc/s. from oscillator H2. In order to give three elevation coverages, the mixers M2 for lower aerial row a1, a2 ... are fed from oscillator H via phase-shifter D2 and the mixers M2 for upper aerial row C1, C2 ... via phase-shifter D1; in a first sweep (e.g. <3>/10 second) phaseshifter D1 introduces a phase advance and D2 a phase retard such that the polar diagram is depressed; in a second sweep, switches (not shown) cut out phase-shifters D1 and D2 and a medium elevation coverage results and in a third sweep, the sense of D1 and D2 phase shifts is reversed to achieve high elevation coverage. This cycle is repeated. Continuous variation of elevation coverage can be arranged by continuously varying the phase shifts in D1 and D2. All the receivers feed into common output circuit L for utilization in known manner. The three horns in a set (e.g. a1, b1, c1) may be replaced by a single inclined horn divided into three sections by partitions. Modifications.-A further arrangement (see Fig. 5, not shown) provides for non-reciprocal transmission and reception polar diagrams and simultaneously at separate output leads signals corresponding to reception with different polar diagrams. A further arrangement (see Fig. 6, not shown) provides for three elevation coverages with reciprocal polar diagrams and simultaneously two other different polar diagrams for reception; and includes means for obtaining two adjacent frequencies, one for transmission and the other for reception, thus raising the beat frequencies corresponding to nearby targets. And one common heterodyning frequency may be varied to avoid interference or jamming.