Frequency-agile field-programmable filter array (FPFA) with multiple functionalities

This paper demonstrates the concept of a field-programmable filter array which can be configured in the field after fabrication. The proposed array is composed of tunable resonators and can have multiple functionalities by rerouting signals from input ports to output ports. Signal rerouting can be achieved by controlling the inter-resonator coupling with a wide tuning ratio of coupling coefficients. The inter-resonator coupling structure presented in this paper is designed to have both positive and negative coupling values. The presented coupling structure has a large tuning ratio so that both large coupling and large isolation between two resonators can be obtained. A unit cell of the proposed field-programmable filter array was fabricated to prove the proposed concept. It is shown that the unit cell can be adjusted to have second-order bandpass responses, third-order bandpass responses, and fourth-order bandpass responses. The unit cell can also be operated as a switchable filter bank without a switch. All operation modes are verified by measurement.