Multi-Functional Single/Multi-Band Bandpass Filters With Co-Integrated RF Isolator, Variable Phase Shifter or Variable Attenuator Functionalities

Abstract

This manuscript introduces a novel RF co-design methodology that allows to co-integrate the functionality of a single-/multi-band bandpass filter (BPF), an RF switch, a variable phase shifter (VP), a variable attenuator (VA), and an RF isolator within a single multi-functional RF component. It is based on a power reconfigurable rat-race coupler (RFRC), spatiotemporally modulated (STM) resonators and a switchable phase coupling element that controls three modes of operation. These include: 1) a co-designed single/multi-band reflectionless BPF, an RF isolator (enabled/disabled by turning ON/OFF STM) and a 360°-variable phase shifter (BPF/BPFI-VP), 2) an RF switching mode and 3) a single/multi-band BPF, an RF isolator (enabled/disabled by turning ON/OFF STM) and a variable attenuator (BPF/BPFI-VA). A detailed theoretical framework is provided alongside a variety of single-band and multi-band design examples. The methodology is validated through the implementation of a single-band prototype (Prototype 1) and a dual-band prototype (Prototype 2) at 700 MHz. Specifically, Prototype 1 features a single-band BPF/BPFI-VP mode with continuously tunable phase shift of 360° while having constant transfer function (TF), a wide reflectionless bandwidth (RBW) from 375 to 1093 MHz as well as uni-directional transmission with over 20 dB directivity (D). When reconfigured in its BPF/BPFI-VA mode, a wide attenuation tuning range of 15.8 dB can be obtained with a well-preserved TF, low phase imbalance (<5°) and D >20 dB. Furthermore, it can be intrinsically switched-off with an isolation >30 dB. Prototype 2 supports a third order dual-band TF with 360° tunable phase shift capability for both of its bands. Furthermore, it exhibits a RBW between 370-1200 MHz, switching-off capability with >30 dB of IS and with {D} gt 10 dB.