Theoretical analysis and design optimization of wideband input/output branch waveguide couplers for a sheet beam traveling wave tube

Abstract

The branch waveguide coupler (BWC) with an intrinsically excellent microwave property in an extremely wide frequency range was proposed to build the input/output (I/O) structure for the sheet beam traveling wave tube. The odd and even mode theory is utilized to analyze the BWC. Based on the theory, a code is written to calculate its microwave performance parameters. The numerical calculation has a good agreement with the computation simulation. To improve the efficiency of developing the BWC, a novel design optimization approach based on the MATLAB optimization tool is proposed. A BWC with nine branch waveguides is optimized using multi-objective genetic algorithm. In addition to the excellent microwave property, a compact configuration is achieved. It is predicted that the I/O structure possesses a very good performance with coupling above −0.3 dB, port reflectivity under −19 dB, and isolation less than −15 dB in a broad frequency range of 37.4–51.0 GHz, corresponding to a bandwidth of 13.6 GHz (30.7%).

Keywords:

• sheet beam traveling wave tubes
• input/output structure
• multi-objective genetic algorithm
• odd and even mode theory
• branch waveguide coupler
• wideband coupler

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [grant number G0501040161101040].