Patent GB-1003174-A (GB)
Title: Improvements in or relating to pulse radar apparatus
Inventor: SCHNEIDER ADAM BRONISLAW
IPC: G01S1/02
Filed: 1962-04-02
Abstract: 1,003,174. Pulse radar. DECCA Ltd. March 29, 1963 [April 2, 1962], No. 12618/62. Headings H4A and HAD. A pulse radar apparatus comprises two transmitters operating on two different frequencies and an aerial system for radiating signals on both frequencies wherein the aerial is fed by a transmission system capable of carrying both signal frequencies as TE01 waves with the electric vector in either of two orthogonal planes and the transmitters are coupled to the transmission system by means enabling the planes of polarization of the radiated signals to be varied. The system is arranged to accept only echo signals with the same type of polarization as the transmitted signals. In the embodiment of the invention shown in Fig. 1, signals are fed from transmitters 10 and 11, to either end of a waveguide 17, via duplexers 12 and 13 and waveguides 14 and 15, at respective frequencies of f 1  and f 2 . The waveguide 17 forms part of a frequency combining and separating means 16 which further comprises a second waveguide 18, coupled to waveguide 17 by a pair of directional couplers 19, such that a combined signal having frequency components of f 1  and f 2  passes out of the lefthand end of waveguide 18 into waveguide 20. The use of the frequency combiner means 16 allows the use of only one rotatable coupling 22 in the feed to apparatus rotating with the aerial. The combined signal is fed to a second frequency combining and separating means 25 comprising two waveguides coupled by two directional couplers, such that the frequencies are separated out into the f 1  signal which passes through waveguide 26 and the f 2  signal which passes through waveguide 27. The two signals are fed to a changeover waveguide switch 29 such that the two signals can be fed into a square waveguide 28 at orthogonal tapping points, with the frequencies interchangeable by means of the switch 29. The two signals thus travel in the TE01 mode along the waveguide 28, polarized in orthogonal planes, said planes being interchangeable, to a horn radiator 31 and reflector 32. Received echo signals having random planes of polarization are passed in the form of their orthogonal polarization components down the waveguide 28, to the switch 29 and the second frequency combining and separating means 25. The component of the f1 echo signal having the same plane of polarization as the transmitted f 1  signal will pass along waveguide 26. The orthogonal component will pass along waveguide 27. Similarly the polarization component of the f 2  echo signal having the same plane as the transmitted f 2  signal will pass along waveguide 27, with the orthogonal component passing along waveguide 26. The orthogonal components of the two signals are absorbed in load 33 whilst the wanted components are combined and fed along waveguide 20 to the first frequency combiner and separator 16 where the f 1  and f 2  components are separated out into waveguides 14 and 15, for display, via duplexers 12 and 13, and receivers 34 and 35, on individual displays 36 and 37 on combined display 38. In a modification of this embodiment, Fig. 2 (not shown), a triple pole double throw switch is provided, just after the rotatable coupling 22, which, in one position sets the apparatus to function as in the embodiment of Fig. 1, but in the other position by-passes the second frequency combiner and separator means 25 and feeds the combined f 1  and f 2  signals directly to one of the tapping points in the waveguide 28. The other tapping point being connected, for echo signals, to an absorbtion load. The two signals will thus be radiated with the same planes of polarization. In a third embodiment, Fig. 3, the f 1  signal is fed to a power divider 60, which comprises a pair of waveguides 62 coupled by a pair of directional couplers 63 with a phase shifter 69 in between the couplers on the output waveguide. The amount of signal crossing from the input waveguide to the output waveguide can be controlled by varying the phase shifter 69. The portion of the f 1  signal crossed over is fed to a frequency combiner and separator 65 where it is combined with a corresponding position of the f 2  signal, to produce a combined signal which is fed to one orthogonal tapping point on the waveguide 28. The portion of the f 2  signal left in the input waveguide is fed via a phase shifter 70 to a second frequency combiner and separator 72 where it is combined with a corresponding portion of the f 2  signal, likewise phase shifted by phase shifter 71, to produce a combined signal which is fed to the second orthogonal tapping point on the waveguide 28. Each of the resultant f 1  and f 2  signals in the waveguide 28 thus has two components, polarized at right angles to each other and having a phase difference determined by the respective phase shifter 70 or 71 and relative amplitudes determined by the respective phase shifter 69. The signals radiated from the horn 31 are thus elliptically polarized of controllable ellipticity and major axis inclination or, with the phase differences set to zero, linearly polarized of variable inclination. As in the simpler embodiments only echo signals or parts of echo signals, having the same polarization as the corresponding transmitted signal pass to the duplexers and receivers for displaying. Any unwanted components are absorbed in loads 75 and 76. By the above means interference due to rain echos may be avoided. The embodiment of Fig. 3 requires two rotatable couplings, either in waveguides 14 and 15 or in waveguides 66 and 73. To overcome this two frequency combiner and separator means may be added to the output of the duplexers in the same manner as means 16 and 26 in the embodiment of Fig. 1, the single rotatable coupling now being between the two said means. The pulses from transmitters 10 and 11 may be produced alternately or similtaneously or in closely spaced pairs, a delay line in one of the receivers bringing the echo signals into alignment for simultaneous display at 38.