Tunable frequency coupler with broad bandwidth and small size

In order to meet the demand of the small size and reconfigurable communication development, this paper presents a frequency reconfigurable hybrid with broad tuning bandwidth and small size. In order to reduce the circuit size, the π-type adjustable structure is adopted, and the adjustable part of the circuit is placed in the internal angle of the coupler. The open circuit microstrip line of the adjustable circuit has three parameters, the angle, the length and the width. The influence of three parameters on the center frequency is analyzed. The electric adjustment network is utlized with varactor diodes. In this paper, the structure of the circuit is analyzed, and the mechanism of the tunable center frequency can be revealed. The proposed hybrid is simulated, fabricated and measured. The measured results agree well with the simulated ones. Simulation and measurement results show that by varying biasing voltage of the varactor diodes, the center operating frequency can be tuned continuously from 705 to 1050 MHz. In the tuning range, it has phase orthogonality and amplitude balance of the output ports. The cause of output terminal insertion loss is analyzed.