A Broadband Tracking YIG-Tuned Mixer for a State-of-the-Art Spectrum Analyzer

A switched. YIG-tuned filter/mixer/discriminator has been developed for a microwave spectrum analyzer to eliminate tuning problems associated with magnetically tuned filters. Such problems arise from nonlinear hysteresis and eddy current delay. The new broadband component (2.7 to 22 GHz) contains a triple YIG sphere tuned preselector. a fundamental mixer using a GaAs monolithic diode IC. and a YIG-tuned discriminator. The output of the YIG discriminator is a voltage proportional to the difference between the RF signal applied to it and the ferrite resonant frequency. This voltage provides a feedback signal to the control circuits driving the main magnet of the YIG-tuned filter/mixer to correct for tuning error. The result is a microwave spectrum analyzer setting a new standard in amplitude accuracy and sensitivity.