Highly Reconfigurable Dual-Band Coupler With Independently Tunable Frequency and Coupling Coefficient at the Lower Band

To satisfy the stringent requirements of the emerging wireless communication system, the dual-band operation and reconfigurability are both desired for the front end. However, few works can realize them simultaneously. In addition, the flexibility of the implemented reconfigurability is limited. In this article, a reconfigurable dual-band quadrature coupler with independently tunable characteristics at the lower band is proposed. Based on the investigation of an ideal model, the design requirements to achieve the previous reconfigurability can be obtained. Thus, the coupled line loaded with varactor is proposed on a patch coupler to implement the desired functionality. By varying the voltages applied on the varactors, the frequency and coupling coefficient at the lower band of the proposed coupler can be tuned independently with the characteristics at the upper band fixed. For validation, a prototype was designed, fabricated, and measured. Measured results show that the frequency of the coupler at the lower band can be tuned from 2.9 to 3.2 GHz. Meanwhile, the corresponding coupling coefficient can be tuned from 3 to 10 dB. During the lower band tuning, 3 dB coupling coefficient and quadrature phase difference can be always maintained for upper band, which is fixed at 4.7 GHz.