Design of Improved Quadruple-Mode Bandpass Filter Using Cavity Resonator for 5G Mid-Band Applications

Abstract

In this chapter, a compact and low-cost resonator bandpass filter for 5G mid-band applications is designed with four internal conductive poles in a single resonating cavity, which adds novel quad-resonating modes to the realization of bandpass filter. This chapter covers the design, creation and testing of the S-band combline coaxial cavity filter. The metallic cavity and high Q coaxial resonators offer the advantages of narrowband, low loss, better selectivity and high potential for power handling, as compared to microstrip filters. Furthermore, the tuning of coupling screws in the combline filter allows for frequency and bandwidth adjustment. Using the iris structure, the length of the inner square cavity is reduced. HFSS is used to build and simulate the quadruple-mode filter. At the resonance frequency, a fractional bandwidth of 12.8% (500 MHz impedance bandwidth) has been obtained with a return loss of more than 18 dB and an insertion loss of less than 2.5 dB over the targeted bandwidth. Four-pole resonating cavity filters have been developed and the center frequency is 4.5 GHz. Insert loss is 0 dB and the estimated bandwidth is 850 MHz and the quality factor is 4.3. A selection of frequencies that transmit between 4 and 8 GHz is seen in the simulated result. The insertion loss is 0 dB and the bandwidth of the resonating band measured is 850 MHz.