Simplified phase-controlled television broadcast switching circuit and three-position coaxial LC phase shifter therefor

摘要

A noncontact switch couples power from A and B radio frequency sources to a load and an antenna in three modes. Mode I couples the A source to the antenna and the B source to the load; Mode III is B to antenna and A to load, and Mode II couples both A and B sources to the antenna. The structure includes a first 3dB, 90° coupler coupled to the sources and a second 3db, 90° coupler coupled to the load and the antenna. A third 3dB, 90° coupler is coupled in a first path between the first and second couplers. A pair of reflective terminations coupled to ports of the third coupler are mechanically controllable to one of three phase-shift conditions; 0° for mode I, 90° for mode II and 180° for mode III. A fixed phase shifter couples the first and second 3dB, 90° couplers by a second path. Each reflective phase shifter is a coaxial circuit including the parallel combination of first and second series inductance-capacitance circuits. A gap in the hollow center conductor is used to provide the capacitance. A conductive slug sliding in the hollow controls the capacitance.