Reconfigurable Filter With Switchable Operating Frequency, Bandwidth, and Response Type Using RF Switches and Circulators

Abstract

This article presents a novel design approach of a reconfigurable filter with switchable operating frequency, bandwidth, and response type. Boolean-like operations, including intersection and complement, of frequency responses are defined, as the basic design principle. The switchable filtering responses are discussed in detail when utilizing one- or two-channel filters with overlapping passbands. It is easy to extend the properties to the N-stage case of a reconfigurable filter. Generally, for a cascaded N-stage reconfigurable filter, one can achieve $2N^{2}+ 2$ filtering responses, including $(3N-1) N/2$ bandpass responses, $(N+1)N/2$ bandstop responses, along with an all-pass (AP) response and an all-stop (AS) response. As the basic building block, a switchable filter unit consists of a channel bandpass filter (BPF), a circulator, and three RF switches, whose response type can be reconfigured by adjusting the states of the switches. A single-stage switchable filter unit and a three-stage reconfigurable filter prototype are developed with microstrip structures. The reconfigurable filter prototype offers 20 different filtering responses with only three channel filters, occupying an area of $1.21\times 0.69~\lambda _{g}^{2}$ . For the provided bandpass responses, the 12 passbands cover $1.17~\sim ~1.6$ GHz with selectable bandwidths of $60.6~\sim ~245.4$ MHz, with in-band insertion losses (ILs) of $5.1~\sim ~7.9$ dB. For the bandstop responses, the six suppression bandwidths are $227.6~\sim ~368.1$ MHz, with an in-band suppression of $16.3~\sim ~22.5$ dB. The IL is 3.5 dB for the AP response, and the suppression level is 63 dB for the AS response. Good agreement is obtained between the simulated and measured results to validate the proposed technique.