Tunable 3-D Bandpass Frequency-Selective Structure With Wide Tuning Range

A new three-dimensional (3-D) tunable bandpass frequency selective structure (FSS) with wide tuning range is presented. The tunable FSS consists of a periodic array of printed circuit boards and a number of inserted metallic plates, where varactor-loaded λ/4 stepped-impedance resonators (SIRs) are constructed based on the propagation mode excited in the structure. By properly choosing the impedance ratio of the SIRs, a wide tuning range can be achieved. Detailed discussion is given to determine the key parameters involved in this tunable FSS, including varactor-loaded λ/4 resonators and coupling coefficient. Finally, a prototype tunable FSS is fabricated and measured. The results exhibit a 2:1 (65%) frequency tuning range from 1.4 to 2.75 GHz with an insertion loss of 4.5-1.0 dB within the passband.