Design of a 3-20 GHz Broadband Quad-Ridged Horn Antenna with a Closed Boundary and a Partially Open Feeding Structure

This paper presents the design and experimental validation of a broadband quad-ridged horn antenna (QRHA) operating from 3 to 20 GHz. A partially open feeding structure is proposed to improve the voltage standing wave ratio (VSWR) performance, particularly in the low-frequency range of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3-4 \text{GHz}$</tex>. The proposed QRHA achieves a bandwidth ratio of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6.67: 1$</tex>, demonstrating broadband characteristics. In addition, the antenna exhibits high polarization purity, maintaining a co-tocross polarization difference of over 15 dB across the operating band. The measured results align with simulation data, confirming the feasibility and reliability of the proposed design.