Simultaneous Phase- and Frequency-Tunable Hybrid Coupler

• Published in: IEEE transactions on industrial electronics (1982) Vol. 64; no. 10; pp. 8088 - 8097
• Main Author: Zheng, Shao Yong
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Branch line coupler; Capacitors; Couplers; Frequency control; frequency tunable; hybrid coupler; Mathematical model; Performance enhancement; Phase shift; Phase shifters; phase tunable; Ports (Computers); varactor loaded; Varactors
• ISSN: 0278-0046; 1557-9948
• DOI: 10.1109/TIE.2017.2698423

The existing tunable circuits mainly concentrate on the control of frequency and amplitude. The control of phase characteristics becomes more and more important in the modern system for further performance enhancement. But none of existing coupler configurations can achieve this tunability. A novel hybrid coupler with simultaneous phase- and frequency-tunable characteristics is presented for the first time. Varying the difference between the capacitances for two rows of tunable capacitors loaded on the branch lines can provide different phase differences between two output ports with equal magnitude. Based on the same circuit, a tunable operating frequency can be realized while maintaining the equal power division and desired phase characteristics. This is achieved by simply changing the capacitances for two rows of tunable capacitors in unison. The high flexibility to achieve tunability in phase and frequency simultaneously is implemented. For demonstration purposes, a hybrid coupler operating at 1 GHz is designed and measured to validate the concept. It exhibits a variable phase difference from 45° to 135° while maintaining equal power division. Meanwhile, the same circuit gives a tunable operating frequency extending from 0.8 to 1.1 GHz while maintaining good performance for a 3 dB coupler with a tunable phase difference from 50° to 130°.