# Rectangular Microstrip Array Feed Antenna for C-Band Satellite Communications: Preliminary Results
## 1 Introduction  
Satellite systems offer a wide coverage area for communication and other purposes, such as remote sensing applications. However, creating a satellite communication system is a challenging task. The design considers many parameters to meet acceptable requirements. One of the difficult circumstances is the high rainfall rate. Compared to other satellite communication channels, satellites using C-band frequencies, such as Himawari satellites, are more reliable in severe weather conditions such as heavy rain [1, 2]. An antenna is a crucial component of a satellite communication system. In particular, high-gain antennas are required to provide a good communication link between the satellite and ground stations. These days, earth stations frequently employ horn antennas and satellite dishes (parabolic reflectors). To meet the design requirements (i.e., high gain, directed radiation patterns, and polarization), a parabolic reflector can be used [1]. The reflector is necessary to obtain the expected gain of a receiving ground station antenna higher than 30 dBi. This value indicates that the radiation pattern is directional with a small beamwidth or close to a pencil beam pattern. Meanwhile, for the feeding antenna, the required gain is greater than 10 dB with a symmetric beamwidth of the E plane and the H plane to conform to a reflector. The microstrip antenna is one of several antennas that can be used as a satellite data receiver, particularly in the C-band frequency range [3, 4, 5]. Some types of microstrip antennas for satellite communications include microstrip antenna with slot [6], microstrip antenna with electromagnetic bandgap technique [7], microstrip antenna with inset feed technique [8, 9, 10], and microstrip antenna with E-shaped technique [11]. However, a reflector has commonly been integrated with a microstrip antenna to achieve the desired performance. In particular, it has been used in dual-band circular patch array [12], microstrip printed dipole [13], two-element microstrip array with Wilkinson power divider [14], 2 \(\times\) 2 microstrip array antenna [15], waveguide combined with 2 \(\times\) 2 microstrip array antenna [16], and dual-circularly polarized microstrip array antenna [17, 18]. Some critical issues may occur when trying to increase the gain of microstrip antennas using array techniques. The issues include the need for many elements of the array to achieve the high expected gain, which increases antenna size, losses, and complexities in the feeding system. The antenna also becomes mechanically fragile due to its large area. Therefore, another feasible solution is needed to obtain good performance from microstrip antennas for communication satellites. This paper proposes the design and fabrication of a rectangular patch array microstrip antenna for a geostationary ground station of the Himawari satellite communication system operating at frequencies of 3.8-4.2 GHz with more than 30 dBi gain and linear polarization. The proposed design is a combination of a multilayer microstrip array antenna, proximity-coupled feed, a coaxial probe feeding technique, and a parabolic reflector. Each technique of this combination contributes to improved antenna performance. The antenna array technique is selected as it can significantly increase the gain value proportional to the number of single antennas in the array [19; 20; 21]. The feed method considered is a proximity-coupled feed or an electromagnetically coupled feed [22; 23; 24]. This feeding method is suitable for planar feeding, as it provides less radiation than conventional microstrip feed (closer to the ground plane) and provides a wider bandwidth (no influence of inductance on the probe so the substrate can be thicker) [25; 26]. Another consideration is the coaxial probe feeding technique. It offers easy adjustment to the coaxial cable connected to the connector, and easy to obtain the matching conditions by adjusting the feed position [27; 28]. Those three parts construct the feeding antenna.