# Design of a Ku-Band Monopulse Antenna with a Truncated Reflector and an Open-Ended Waveguide Feed
## 1 Introduction  
The monopulse technique can be used to determine the target's position from a single pulse by comparing the received signals obtained concurrently from one or more antenna beams [1]. This makes it significantly better than other techniques as it delivers an unmatched accuracy of the target's position and angle. Reflector antennas have been a popular solution for delivering high-gain communications at high frequencies in areas such as satellite communications, radar, and astronomy.  
It is worth mentioning that researchers have developed different kinds of monopulse antennas for radar applications [1; 2; 3; 4; 5]. In [6; 7; 8], the monopulse feed was designed by leveraging a dielectric lens. In [9], researchers investigated a monopulse reflector antenna operating at 35 GHz for missile applications. In [10], a parabolic reflector with a compact monopulse feed was developed for earth observation use. The investigation of the monopulse antenna soars in [11] included researching a W-band tracker and using a monopulse feed parabolic antenna. In [12], a monopulse beam tracking system for UAV use was reported. Investigations advanced with [13] using the monopulse feed technique to address long-range communications from the air to the ground. A matched feed illuminating parabolic reflector was investigated in [14; 15; 16]. In [17], antenna feed with offset parabolic reflectors was studied. The electric field distribution of the fast and slow modes in the open-ended waveguide was reported in [18]. In [19], a parabolic antenna design for coastal radar surveillance was reported using a dual horn feed.  
In some applications, a monopulse antenna with a narrow beam in one plane and a wider beam in the other plane was required. However, investigations that achieved a concurrent sharp pencil beam at the elevation plane, an outspread beam at the azimuth plane, and a robust sum channel beam with minimum side lobes have not been sufficiently explored. Study [20] designed a truncated paraboloid reflector antenna, however, with a single antenna feed system.  
Monopulse feed design used to be very complicated because one needs to carefully combine four or five apertures to arrive at the symmetric and balanced sum and difference patterns. In this paper, we propose a very simple monopulse feed suitable for illuminating a truncated parabolic reflector. The proposed feed utilizes four rectangular waveguide apertures that are excited by a coaxial probe. It is easier to implement a monopulse comparator in a coaxial medium than in waveguide form. We employed four rectangular waveguide open-ends, which are compact and simple to realize.  
Few results have been published regarding monopulse reflector antennas with asymmetric beamwidths suitable for the tracking of flying objects. In this paper, we propose a design for an optimally illuminated truncated parabolic reflector antenna with well-balanced sum and difference patterns.  
First, a design is carried out for a monopulse consisting of four open-ended waveguide radiators, and the sum and difference gain patterns of the feed are analyzed to find an optimum reflector geometry. Part of a parabolic reflector surface is removed so that the feed optimally illuminates the reflector. Essentially, the purpose of our paper is to present an idea, not to show the result of development efforts. In this regard, we have used CST Studio Suite 2022, a well-proven simulation tool whose accuracy has been confirmed in many published papers so that the simulation alone is enough to prove the proposed concept.