Novel Dual-Band Branch-Line Coupler (Paper Submitted)

January 2010 - Present

Research Assistant, Center of Microwave and RF Technologies (CMRFT) in Shanghai Jiao Tong University, Shanghai, China

Advisor: Prof. Liang Zhou

Motivation:For future communication, more portable mobile terminals are desired. The size of a whole system can be reduced remarkablly if all microwave components in that system are multi-band. Coupler, one of the most popular passive microwave component, is the object in my research because dual-band couplers reported in various literatures are still too large compared with the traditional single-band one. So the objective in this project is to develop a high performance coupler with a more compact size. 

Outcomes:

• Designed a compact dual-band quadrature hybrid with a very broad achievable frequency ratio.

 Stepped-impedance stubs are added to two ends of the branch-line to achieve a dual-band property. Two free parameters are brought in with the stubs. Various different bandwidths and a very broad frequency ratio range can be acommpolished.

• Modeled the proposed coupler with lumped elements and extract the parameters' value from the model.

For the purpose of analyzing the mechanism of this dual band quadrature hybrid, a lumped elements model was built up, and the values of each parameters in the below figure are extracted.

• Validated the design by simulating with HFSS, ADS and fabrication. 

The measurement results are in a good accordance with the simulation one. The input return loss and the isolation factor achieves lower than -20dB in both two operating frequencies, two coupled ports get approximately 3dB coupling in two specific frequencies.

• Wrote and submitted a paper to describe this work

        One paper about this topic is under review.