GB1416620A - Microwave generating and receiving apparatus - Google Patents

Abstract

1416620 Doppler radar; aerials MULLARD Ltd 17 Oct 1973 48262/73 Headings H4D and In a microwave generating and receiving apparatus first and second adjacent waveguides respectively contain an oscillator device and first and second mixer diodes. RF energy generated in the first waveguide is partly transmitted through one end thereof, and is partly coupled by a coupling means into the second waveguide through a side wall thereof. RF energy is also received through one end of the second waveguide, and the spacing of the diodes and of the coupling means therealong is such that the coupling means and the first diode are each further from that end than the second diode. The apparatus is applicable to Doppler radar, and in one embodiment two contiguous rectangular waveguides 1, 2, Fig. 1, have a common narrow wall 3, are terminated at one end by a short-circuit 4, and are mounted at their other ends, which form aerial apertures, on a flange 5. The waveguide 1 accommodates a Gunn device 6 which is spaced #/2 (# = wavelength at the mean operating frequency) from the termination 4. The waveguide 2 accommodates two matched mixer diodes 7, 8. The coupling means is a circular iris 9 in the wall 3, with a diameter approximately two-thirds the width of said wall, and located approximately mid way between the Gunn device 6 and the termination 4. The iris 9 and the first diode 7 are each further from the open end of the waveguide 2 than the second diode 8, the two diodes being on opposite sides of the iris. By spacing the diode 8 a distance of #/8 from the iris a phase difference of 90 degrees results in its output relative to that from the diode 7, and from the sign of this (positive or negative) the sense of the velocity of a target may be ascertained. In another embodiment, the two diodes are both between the iris and the open end of the waveguide, and are spaced #/8 apart (Fig. 2, not shown). In a third embodiment, an additional receiving waveguide 10, Fig. 3, is provided, on the other side of the waveguide 1, containing mixer diodes 12, 13 and having a coupling iris 14 through its common wall 11 with the waveguide 1. The diodes 7, 8 and 12, 13 are located between their respective associated irises 9, 14 and the open ends of the waveguides. Each pair of diodes is spaced #/4 apart, which enables unwanted noise to be reduced by combining their outputs. A 90 degree phase difference between the two combined outputs, to enable velocity sense determination, is provided by spacing the irises #/8 apart.