Microstrip Four-Way Reconfigurable Single/Dual/Wideband Filtering Power Divider With Tunable Frequency, Bandwidth, and PDR

Abstract

In this paper, a microstrip reconfigurable four-way filtering power divider (FPD) with tunable center frequency (CF), bandwidth (BW), and power division ratio (PDR) is presented. A novel coupling scheme is proposed based on four stub-loaded quad-mode resonators (SL-QMRs), two three-line coupled structures, and two quarter-wavelength transformers, which can achieve tunable CF, BW, PDR, and wide isolation BW. Switchable single/dual/wideband filtering response and the CF and BW of a dual-band FPD can be tuned by controlling the varactor diodes loaded onto the open-ends of SL-QMRs. Meanwhile, the PDR is controlled by varying the coupling strength between the center line and sidelines of a three-line coupled structure. Compared with the conventional wideband FPDs, the capacitor loaded onto the parallel coupled line of two outputs enlarges the coupling, which can improve the return loss and, thus, relieve the limitation of the line space. Based on the coupled resonator theory, the parameters of the resonators and coupling sections are analytically determined. For the dual-band FPD, the measured results show that the 3-dB fractional BW of the lower passband can be tuned from 23.4% to 30.9%, while the one of the upper passbands is tuned from 12.3% to 18.5%. The measured CF for the upper passband can be tuned independently from 1.98 to 2.21 GHz, while the lower one remains fixed. Then, the measured PDR is controlled from 1:1:1:1 to 1:2:1:2. The proposed four-way reconfigurable FPD exhibits switchless single/dual/wideband filtering responses, high isolation level, wide isolation BW, and the control of CF, BW, and PDR.