An automatic RF matching device

An automatic matching device has been designed in order to meet a specification of 1.2:1 in maximum VSWR for a high power S-band radar operating over a 15% frequency band, with a maximum load mismatch of 2.0:1. Two pairs of detectors coupled to the waveguide are used as the sensing elements; one pair responding to the real, the other to the imaginary component of the reflection coefficient. Their outputs are used as error signals and are amplified to drive motors controlling two tuning plungers which match the load to the transmitter. The paper describes the theory of operation of the system. Details are given of the detector probes, tuning plungers and waveguide stubs for high power operation. The servo control aspect of the equipment is discussed and details of an analog simulation are given. An experimental model, designed for a 4% bandwidth was tested. A residual VSWR of better than 1.09:1 was obtained for all phases of terminal VSWR up to 2.0:1. The automatic matching operation takes less than one second. The mechanical details of a prototype design are described.