An Ultra-Broadband Direct Demodulator for Microwave FM Receivers

A new broadband frequency discriminator is introduced for demodulating the frequency modulated signals in the microwave frequency range. Direct demodulation with no need for tuning the center frequency of the resonance circuits is the most important advantage of the proposed technique. This technique uses the in-phase/quadrature demodulation, in some manner, without using any additional local oscillator for down conversion. Simulation of the proposed demodulator has been done with Advanced Design System software to evaluate and predict the system behavior. A setup based on the proposed method was designed and implemented in order to verify the accuracy of the theory. We tested the proposed frequency discriminator for FM signals at different microwave frequencies with various waveforms of the modulating signal. We also measured the bit error rate of the demodulator when the modulating signal is pseudorandom binary sequences for some data rates. To the best of our knowledge, this structure demonstrates the widest bandwidth direct demodulator without any tuning circuits among published FM demodulators to date.