# Conceptual Design of a Semi-Dual Polarized Monopulse Antenna by Computer Simulation
## 1 Introduction  
Monopulse antenna technology can be employed to obtain the position and angle of a target using a single pulse. There have been many research efforts on the subject of accurate target or signal angle estimation using monopulse techniques, which can be called \"the monopulse theory\" [1, 2, 3, 4, 5, 6, 7]. High-gain monopulse reflector antennas are often used for tracking moving targets and signals at long ranges. Applications of monopulse reflector antennas include tracking radars [8], telemetry, tracking, and control (TT and C) of rockets, satellites, and space-crafts [9], missile seekers [10], and space object detection [11]. In some applications, it is desirable to use a monopulse antenna with an ability to operate with dual linear or circular polarization. Satellite signals are affected by the Faraday rotation, which alters the wave polarization from one form to another. The depolarization of radar signals occurs by multiple reflections from objects, so the cross-polarized component can become stronger than the co-polarized one. Therefore, it becomes necessary to design a monopulse antenna that can mitigate the polarization mismatch by using dual-linear or dual-circular polarizations. Dual-polarized monopulse methods have traditionally been used in tracking rockets [12] and satellites [13]. In recent years, there have been research efforts focused on the use of dual-polarized monopulse techniques for mitigating angle jamming in missile seekers [14]. There are several published results on dual-polarized monopulse feeds and dual-polarized reflector antennas. [PERSON] and co-workers investigated a dual-linearly polarized reflector antenna employing a crossed-dipole monopulse feed operating at 2.2-2.3 GHz [15]. With a reflector diameter of 1.8 m, they obtained a 32.3 dBi sum channel gain, 5.5\({}^{\circ}\) cross-over angle, and \(-\)17.5 dBi null gain. [PERSON] and co-workers presented a dual-circularly polarized feed for K/Ka-band satellite communication antennas operating at 17.7-20.2 GHz and 27.5-30.0 GHz. Their feed is based on waveguide components and consists of a conical corrugated horn, an orthomode junction, two low-pass filters, and two polarizers for Rx and Tx ports [16]. Their feed design shows a reflection coefficient of less than \(-\)30 dB, polarization isolation greater than 20 dB, and axial ratio of less than 0.4 dB. [PERSON] and co-workers presented a dual-polarized monopulse reflector antenna operating at W-band with a dual-linearly polarized sum channel and two single-polarized difference channels [17]. Their design is based on four square waveguide radiators with a waveguide-type monopulse comparator consisting of four waveguide-type orthomode transducers and four T-junction power dividers. With a reflector of diameter 135 mm, they achieved a 41 dBi sum channel gain, 34 dBi elevation difference channel gain, and 32 dBi azimuth difference channel gain at W-band (frequency not specified). The structures of a monopulse feed and a corresponding feed network for dual-polarized sum and dual-polarized difference channels are quite complicated and costly, and, thus, their use is justified only for sophisticated space and military applications. In this paper, we propose a simpler solution to the problem of the dual-polarized monopulse reflector antenna. Our solution consists of a dual circularly polarized sum channel, a horizontally polarized azimuth (AZ) difference channel, and a vertically polarized elevation (EL) difference channel. The proposed idea is applicable to radar target tracking antennas since backscattered sum channel circularly polarized waves can be received by linearly polarized difference channels with a maximum polarization loss of 3 dB. The 3 dB loss can be tolerated for the benefit of a very simple and cheap monopulse comparator network.