Near-constant beamwidth wideband horn antenna design

The use of horn antennas is increasing because of their need in wideband, and high gain antenna applications. Beamwidth constancy along the wideband becomes particularly important and necessary in applications such as direction finding (DF) and reflector antenna feeds. We propose a design methodology for near-constant beamwidth, wideband, corrugated double ridged horn antenna over 4:1 frequency band in this thesis. In this study, the beamwidth constancy is not restricted to a single-plane or to a symmetrical geometry antenna which has a limited bandwidth (BW) ratio of 2:1. Rather, we aimed to design a rectangular horn with constant beamwidths at both azimuth and elevation planes from 4.5 to 18 GHz. We first design X-band standard gain horn antenna (SGHA) to understand the characteristics of horns and a conventional double ridged horn antenna (DRHA) to use it as a reference for beamwidth variation of wideband horns through the operating band. We also investigate the root causes that impede the antenna from constant beamwidth along wideband, and the requirements to achieve the beamwidth constancy. We first modify the DRHA to design near-constant beamwidth wideband horn antenna (NCBWHA), and then use structures called "pinwall" and "stepped-shape corrugated slot", which are implemented in H-plane sidewalls and in E-plane walls, respectively. We derive the input admittance of a new step-shaped slot, and then determine the bandwidth by comparing to conventional corrugations. The proposed corrugation presents wideband characteristics with a BW ratio of more than 4:1. We also designed a broadband double ridged waveguide-to-coaxial (rwg-to-coax) adapter to match the antenna impedance to 50 Ω. After the design is completed in simulations, two different prototypes of antennas are built which are coax-fed curved pinwall DRHA and NCBWHA. The radiation pattern and other parameters of manufactured antennas are measured using a commercially available near-field system. We observe that the measurement results corroborate with simulation ones fairly well. The proposed antenna in this study has 4:1 wideband characteristics with 31.0o±2.5o in H-plane and 37.4o±5.2o in E-plane 3-dB beamwidths.