Optimization and measurement of a smoothly profiled horn for a W-band gyro-TWA

In this paper, a smoothly profiled horn was designed and manufactured to replace a corrugated output horn for a W-band gyrotron traveling-wave amplifier with improved ultrahigh vacuum compatibility. It was optimized for high vacuum integrity, low reflection, high fundamental Gaussian mode content, low sidelobe levels, and high directivity over the frequency bandwidth of 90-100 GHz. Over this operating frequency band the reflectivity was better than -37 dB and the coupling to a fundamental Gaussian mode was above 97%. The far-field pattern showed a directivity of approximately 27 dB in the measurement with sidelobes lower than -30 dB.