Substrate Integrated Waveguide Electrically Tunable Equalizer Based on Varactor and p-i-n Diodes/Transistors

In this article, a novel design method of substrate integrated waveguide (SIW) electrically tunable equalizer, based on varactor and p-i-n diodes/transistors, is proposed. It can operate in various frequency bands (up to millimeter-wave) and achieve dynamic adjustment, including center frequency and equalization value controlled by various analog control voltages, acting on varactor diodes and p-i-n diodes/transistors, respectively. In this work, the working principle and design method of SIW electrically tunable equalizer are discussed in detail. A hybrid distributed-lumped element equivalent circuit model is employed to thoroughly analyze SIW structure, providing detailed performance evaluation over a wide frequency band. The equalizer is composed of multiple resonant units, each of which can be regarded as a parallel RLC resonance circuit. For the prototypes of SIW equalizer based on varactors and p-i-n diodes, the measurement results show that the return losses are almost better than 18.8 and 10 dB, and the equalization values are up to 30.81 and 37.94 dB over the whole Ku-band and Ka-band, respectively. In order to reduce control voltage sensitivity, the transistors operating in the triode region are introduced as variable resistors to replace p-i-n diodes. For SIW equalizers based on varactors and transistors, the measurement results show that the equalization value can exceed 32.03 dB in Ku-band. Different from previous studies, this is the first report about electrically tunable equalizers with concave and monotonic characteristics on a single printed circuit board (PCB) in the research field.