Quad Band Filter with Controllable Transmission Zeros using Vertical and Diagonal Coupling of Triple and Dual Step Impedance Resonators

Abstract

A quad-band pass filter using back-to-back Tri-State Step Impedance Resonator (TSSIR) for Wireless Applications is presented in this article. The achieved passband center frequencies are 2.45 GHz (for WLAN), 3.5 GHz (for WiMAX), 5.4 GHz (for WLAN), and 8.05 GHz (for Satellite Communications). A unique method of simultaneous vertical and diagonal coupling between TSSIR and conventional two-step SIR structures is introduced here to create Transmission Zeros (TZs) in the stop bands of a quad-band filter. The main objective is to produce controllable TZs through shunt capacitive coupling. In the overall filter design, there are a total seven TZs, and the minimum Insertion Losses (ILs) at the mentioned passband center frequencies are found to be −0.4, −0.6, −0.4, and −0.7 dB. The simulation results (using HFSS 13) are in good correlation with the measured prototype (using Arlon AD 250, height 0.76 mm, Dielectric Constant 2.5).