IF Return-Loss Measurements in Microwave Radio Systems

The basic designs and several applications of a ferrite-core transformer bridge that realizes a directivity better than 60 dB are described. The bridge is intended for use in IF return-loss measurements of microwave and satellite systems operating from 50 to 100 MHz. The bandwidth of the unit extends from 5 to 200 MHz. The main feature of the balanced transformer is the use of a symmetrical primary winding in which the applied signal is tightly coupled into a reversed neutralizing winding. This method virtually eliminates capacitively coupled unbalance components that normally exist in such a transformer. The applications include an unusual approach to measurement of the source impedance of a generator on its own signal. It is referred to as the amplified double-reflection method and uses a second bridge with an amplifier to provide significant improvement in obtainable resolution over conventional cable-reflection methods.