High-Order Fully-Reconfigurable Balanced Bandpass Filters Using Mixed Technology Resonators

This manuscript reports on high-order balanced bandpass filters that are continuously tunable in terms of frequency and bandwidth (BW) and can be intrinsically switched-off. They are based on a hybrid integration scheme in which capacitively-loaded coaxial and microstrip resonators are effectively combined within the same filter volume. Low in-band insertion loss and high out-of-band selectivity are obtained in its differential mode of operation through the realization of a quasi-elliptic transfer function. High levels of suppression are obtained in its common mode of operation through multiple transmission zeros and resistively-loaded resonators. The concept is presented through various synthesized examples. For practical validation purposes, a mixed-technology prototype was manufactured and measured. It demonstrated frequency tuning between 2.22 - 2.94 GHz, BW tuning between 104 - 268 MHz, and an intrinsically switched-off mode with isolation >50 dB. For all these states, the common mode suppression was > 35 dB.