Novel Reconfigurable Single-to-Balanced, Power-Dividing, and Single-Ended Filter With Frequency and Bandwidth Control

Abstract

In this paper, a novel tunable filter with reconfigurable single-to-balanced (SE-BAL), power dividing (PD), and single-to-single-ended (SE) filtering functionalities is proposed, for the first time, without any additional switching circuit. The proposed filter only consists of three stepped-impedance resonators, which are loaded and connected by varactors in between. With a very simple and compact configuration, the proposed filter achieves multiple reconfigurable functionalities between SE-BAL filtering, PD filtering, and conventional SE bandpass filtering. Moreover, the reconfigurable SE-BAL, PD, and SE bandpass filter can not only offer continuously frequency tuning over a wide tuning range but also have independent bandwidth tuning and maintain good phase/amplitude balance in each tuning state. The proposed filter is designed and fabricated with the microstrip line technology; the measured results show that the SE-BAL, PD, and SE filtering functions can be continuously tuned from 1.02 to 1.32, 0.96 to 1.27, and 1 to 1.28 GHz, with 1-dB bandwidth tuning from 30 to 60, 30 to 110, and 70 to 130 MHz, respectively. The amplitude and phase imbalances of the SE-BAL and PD bandpass filter are less than 0.4 dB, 1.3 degrees and 0.5 dB, 1.5 degrees, respectively, in the passband of each tuning state. Good agreement was obtained between simulated and measured results.