GB883475A - Improvements in or relating to microwave modulators - Google Patents

Abstract

883,475. Amplitude modulation; frequency modulation. RAYTHEON CO. Oct. 29, 1958 [Oct. 30, 1957], No. 34669/58. Class 40(5). [Also in Group XL(b)] A microwave modulator comprises a ferrite circulator arranged to receive and produce deviation from a fixed polarization in microwave energy emanating from a microwave source, and to direct the deviated energy back to the source to frequency or amplitude modulate the energy emitted by said source in accordance with the reactive or resistive character of a load presented to the source. As shown a circulator comprising an input T section 16, a ferrite rotator 14 and an output T section 12 is connected between a microwave source 18, e.g. a magnetron or klystron oscillator, and an antenna 12 (shown to a reduced scale) or other load. The input T section 16 comprises a section of square waveguide 53 and a rectangular arm 54 provided with a matched termination 55 consisting of a section of rectangular waveguide filled with an absorbing material such as Polyiron. The rotator 14 includes a cylindrical ferrite element 36 supported in a section of circular waveguide 38 by two members 39 and 39a of low-loss dielectric material such as teflon. A coil 42 is connected through a choke 45 to a D.C. source 44 and through a capacitor 47. to an A.C. source 46. The output T section 12 comprises a section of square waveguide 26 rotated through an angle of 45 degrees with respect to the waveguide 53 and a rectangular arm 27 in which a plunger 32 can be moved by a screw 31. Microwave energy entering the waveguide 53 passes to the rotator 14, is rotated 45 degrees by the D.C. field and passes along the waveguide 26 to the antenna or load. Reflected energy is rotated a further 45 degrees and is absorbed by the termination 55. The A.C. field in the rotator 14 produces small deviations from the 45 degrees rotation so that some energy enters the arm 27 which presents a resistive or reactive load to the source 18 in dependence on the position of the plunger 32. With the plunger set at a distance of #/8 from a zero position, usually 8 occurring a short distance outside the outer wall of the waveguide 26, the load is resistive and produces amplitude modulation. Frequency modulation, at a rate depending on the frequency of the source 46, is obtained with the plunger set at a distance of #/4 to provide a reactive load. A mixture of frequency and amplitude modulation is obtained with an intermediate setting.