Two novel broadband couplers in W band for sheet beam travelling wave tube

Two input/output couplers consisting of multiple apertures in E plane and H plane are designed and analyzed for a W-band broadband sheet beam traveling wave tube (TWT). Multi-apertures are adopted in the couplers to separate the electromagnetic field from the beam and extend the operating bandwidth. Simulation results optimized by HFSS indicate that the E-plane coupler can achieve a 1 dB transmission bandwidth of 45.3% and a -20 dB isolation bandwidth of 34.7% respectively. Similar results are obtained by adding two more apertures for the H-plane coupler, specifically, the 1 dB relative bandwidth and the port isolation under -15 dB can get improved to 45.3% and 30.6% respectively. Both novel couplers can achieve high isolation and low reflection in extreme broad bandwidth. In comparison with the E plane coupler, the H plane structure is easy to fabricate, cool and integrate with periodic permanent magnet in compact dimensions.