High-order and tunable balanced bandpass filters using mixed technology resonators

Dakotah Simpson,Dimitra Psychogiou

doi:10.1017/s1759078721000453

Abstract

AbstractThis paper reports on high-order balanced bandpass filters (BPFs) that are continuously tunable in terms of frequency and bandwidth and can be intrinsically switched-off. They use a hybrid integration scheme based on two different types of capacitively loaded resonators—ceramic coaxial and microstrip—that reduce the filter size, enhance its out-of-band selectivity and common-mode suppression, and allow for multiple levels of transfer function tuning. High selectivity is obtained in the differential mode due to the high number of poles and transmission zeros present. The common mode is highly suppressed through the introduction of additional transmission zeros and resistively loaded resonators. Furthermore, the use of ceramic coaxial resonators results in supplementary transmission zeros that are used to lower the out-of-band transmission in the differential mode. Multiple levels of tuning are obtained by reconfiguring only the frequency of the BPF's resonators. For experimental validation, a tunable mixed-technology microstrip prototype was manufactured and measured at S-band. It exhibited frequency tuning between 2.22 and 2.94 GHz, bandwidth tuning between 104 and 268 MHz, and an intrinsically switched-off mode with isolation >50 dB in the differential mode. For all states, the common mode was suppressed by at least 35 dB at the center frequency and within a wide range.

Highlights

Balanced radio frequency (RF) transceivers offer the advantage of higher immunity, which is important in maintaining a high signal-to-noise ratio in the RF front-end, to electromagnetic (EM) interference, crosstalk, and other types of noise [1]
As a key component in such systems, tunable balanced bandpass filters (BPFs) that efficiently transmit the signals in the differential mode and effectively suppress signals in the common mode have been a focus of recent research efforts [2,3,4,5,6,7,8,9,10,11,12,13]
This paper reported on a new class of high-order fully reconfigurable balanced BPF that uses both coaxial and microstrip type resonators

Summary

Introduction

Balanced radio frequency (RF) transceivers offer the advantage of higher immunity, which is important in maintaining a high signal-to-noise ratio in the RF front-end, to electromagnetic (EM) interference, crosstalk, and other types of noise [1]. The balanced BPF in [3] was designed using substrate-integrated waveguide dual-mode cavity resonators and exhibits limited tunability (only tunable in frequency), low levels of common-mode suppression (30 dB), and poor differential mode selectivity (second-order response). Similar to the other filters, this design demonstrates low selectivity (second-order response), low levels of common-mode suppression (20 dB), and limited levels of tuning (only tunable in bandwidth (BW)). A variety of coupled microstrip line balanced BPFs are presented in [5,6,7,8,9] Their shortcomings include center frequency tuning only and low selectivity (first order in [5], second order in [6,7,8], and third order in [9])

Objectives

Conclusion