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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i>-band and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i>-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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i>-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.