Design of Couplers incorporating fabrication limitations for Helix TWT

Input and Output couplers have been designed for Ka band 130 W helix Traveling Wave Tube (TWT) with return loss better than -20 dB throughout the frequency band of 17.7 GHz to 19.7 GHz. The fabrication limitations surrounding the junction of first helix turn and the RF window and the impact of such limitations on return loss have been presented. Re-design of SMA connector in input section and the door knob structure in output section of TWT for obtaining optimum return loss has been done by modifying the simulation model to include these limitations. The observed simulated and measured results are in good agreement. The design simulations have been carried out in CST.