THz Square Cross Section Smooth Spline Horns as a Competitive Alternative to Corrugated Horns

This paper describes a novel design of smooth wall spline horn with square cross section throughout its length instead of circular. The paper further describes the design philosophy of such horn along with its simulated parameters. The simulated results from WIPL-D tool suggests that this horn has very high Gaussian Coupling efficiency ( $\eta_{G}$ ) comparable to classical corrugated horns. As a case study the said horn is designed over frequency range of 110–170 GHz (D-band) with standard WR-06 rectangular waveguide as its input. The simulated results suggests a minimum $\eta_{G}$ of ≈ 95% over whole bandwidth with its value better than 98% over 140–150 GHz. Furthermore the said horn maintains a constant beam waist ( $\omega_{0}$ ) of 3.65 mm over full waveguide band. This feature shows the effectiveness of these horns as an alternative to classical corrugated horns for THz Quasi-optical systems. It is also worth to mention that with the absence of corrugations the fabrication of these horns using convectional split block technique as well as using modern additive manufacturing becomes very cost effective for mass production. The fabricated prototype of the said horn is also presented in this paper.