Design of a New Monopulse Horn Antenna by Orbital Angular Momentum Generation

The aim of this paper is to design a novel compact and wideband feed for monopulse antenna using the Orbital Angular Momentum (OAM) modes of 0 and 1. The OAM mode 0 produce the sum pattern and the OAM mode 1 generate the difference pattern. Based on the correspondence between the OAM mode 0 and the circular polarized (CP) TE11 mode in circular waveguide, as well as between the OAM mode 1 and the circular polarized TE21 mode, the feed structure consists of two circular waveguides with different radius. In the waveguides with smaller and larger radius, the CP TE11 mode and TE21 mode are excited respectively, using the novel proposed mode coupler. Each mode coupler has two pairs of arms, one of which excites the TEi1 mode (i = 1,2) and the other the orthogonal ones (TE
$^{\bot }$
i1, i = 1,2) with 90-phase difference inside the circular waveguide. The frequency bandwidth of the proposed feed is from 9.65-10.85 GHz (11.7%) and the isolation between TE11 and TE21 mode couplers is -30 dB. The frequency bandwidth of the proposed structure is very higher than the state of the art references. Moreover, it has low side lobe levels as well as compact structure with high power handling. These specifications prove the ability and capability of the proposed structure in radar applications.