A compact 100 MHz to 7 GHz frequency equalizer based on distributed passive circuits

A compact frequency equalizer based on distributed passive circuits is designed, analyzed and implemented for the front end circuit of a portable spectrum analyzer working between 100MHz to 7 GHz. The equalizer is based on a T-shape passive attenuator consisting of multiple distributed inductive and capacitive elements. As a test vehicle, a 3-stage broadband amplifier has been implemented, connected to the designed equalizer, and characterized in the targeted frequency range. Without the equalizer, the measured gain of the implemented amplifier varies from 34.7 dB to 46.97 dB showing a 12.27 dB roll off in the frequency range. After connecting the equalizer, overall gain variation is reduced to ± 1.1dB. Compared with other preexisting frequency equalizers, the implemented one features a small footprint of 6×8 mm² and a wide frequency bandwidth of 100MHz to 7GHz. Detail description on the equivalent circuit model and general design guidelines are given, and parametric analysis is performed. The implemented equalizer is suitable for the front end circuits of compact broadband test and measurement instruments, such as a portable spectrum analyzer and vector network analyzer.