Microstrip Patch Antenna Design for Military Satellite Communication

http://dergipark.gov.tr/ejosat 142 Microstrip Patch Antenna Design for Military Satellite Communication Mustafa Koçer, Mustafa Emre Aydemir 1 Istanbul Esenyurt University, Engineering and Architecture Faculty, Electrical and Electronics Engineering Department, Istanbul, Turkey (ORCID: 0000-0003-45514788) 2 Istanbul Esenyurt University, Engineering and Architecture Faculty, Electrical and Electronics Engineering Department, Istanbul, Turkey (ORCID: 0000-0003-36341782)


Introduction
Microstrip antennas are compatible with MMIC designs with easy production and low cost using modern printing technology. Due to the need for low profile antennas in application areas such as satellites, aircraft, missiles, microstrip antennas with small dimensions are actively used in these areas (Pozar, 1992). However, microstrip antennas have narrow bandwidth and low gain compared to other antennas. In this study, it is aimed to design a broadband and high gain antenna that covers the entire downlink frequency 7.25-7.75 GHz and uplink frequency 7.9-8.4 GHz allocation for use in military satellite communication using optimization techniques. The designed antennas were optimized with genetic algorithm and simulated on the HFSS program.

Microstrip Patch Antenna
Microstrip antennas were first put forward by G. A. Deschamps in 1953 but patented by Gutton and Baissinot in 1955 (Deschamps, 1953;Warren & Gary, 1998). Nevertheless, the microstrip antennas, patented until the 1970s, were not taken seriously. The first microstrip antenna was demonstrated by the work done by Howell in 1972 and by Musson in 1974 (Munson).
There are substrate materials whose dielectric constants are generally in the range of 2.2≤ r≤12 for use in microstrip antenna design. A substrate with high thickness and low dielectric constants is often used to achieve good design performance. Thus, high bandwidth and good efficiency are achieved.
Microstrip Antennas are formed with substrate, patch, ground and radiation plane as seen in Figure 1.

Microstrip Patch Types
Microstrip antennas are named according to the patch shapes used at the top of the dielectric material during the design phase. The patches used in microstrip antennas are shown in Figure 2. Among these, the most common square and rectangular patch is used. In this project, a rectangular patch was chosen as the patch shape.

Microstrip Feed Types
There are many techniques used to feed microstrip antennas (Pozar, 1992). The most common of these are microstrip line, coaxial probe, aperture coupling and proximity coupling (Bahl & Bhartia, 1980;Carver & Mink, 1981;Katehi & Alexopoulos, 1984). In this design, a microstrip feed is preferred, which provides slightly more bandwidth and does not disrupt the planarity of the antenna. The antenna given in Figure 1 was made with the microstrip feeding technique.

Genetic Algorithm
The optimization algorithm used is a genetic algorithm based on the survival of individuals with high suitability value by transforming an evolutionary process into a computer environment. The idea of a genetic algorithm was introduced in 1975 by J. Holland. As a result, he developed this algorithm with his friends and published the book "Adaptation in Natural and Artificial Systems" (HOLLAND, 1975). There are individuals who represent the solution of the problem in genetic algorithms and there is a fitness function that controls whether these individuals are suitable for the solution of the problems. As a result of the fitness function, individuals with high values are introduced to the cross operator and produce new individuals called children. Individuals with low suitability value in a new population to be created as a result of this process are removed from the population. Flow chart of genetic algorithm is shown in Figure 3.

Antenna Design
In this design, the antenna's bandwidth is required to be at least 1.2 GHz for military satellite communication. In order to obtain high bandwidth, the materials used in the antenna design were examined, and as a result, Rogers RT / duroid 5880 material with dielectric constant 2.2 and 3.175mm height was selected. For the antenna whose resonance frequency is determined as 7.825 GHz, the dimensions of an ideal antenna were found with the formulas used in the microstrip antenna design. Designed with 50 ohms input impedance using the above formulas, the 1st antenna is optimized with genetic algorithm, then Wg = 34.19mm, Lg = 29.72mm, W = 15.14mm, L = 10.87799615mm, Wa = 0.125mm, La = 4.7925mm, Wb = 3mm, Lb = 4.7325mm results were found. In order to increase the bandwidth of the 1st Antenna designed, the patch dimensions of the 1st Antenna were optimized by keeping the search space wide and as a result Wg = 34.19mm, Lg = 29.72mm, W = 21mm, L = 10.45mm, Wa = 1.946mm , La = 9.635mm, Wb = 2.8mm, Lb = 3mm results were found. As a result of the changes made on the designed antenna, the 2nd Antenna operates in the frequency ranges of 6.73 -9.69 GHz. The 7.8 center frequency has -25.4 dB return loss, 6.63 dB gain and 1.11 standing wave ratio.

First Antenna
The 1st Antenna designed as a result of the studies, covers all the up and down frequency ranges allocated for military satellite communication and has a bandwidth of 1.35 GHz = 17.25%. The 2nd Antenna, designed as a result of the changes made on the 1st Antenna, operates in the frequency ranges of 6.74 -9.69 and has a bandwidth of 1.6 GHz more than the 1st Antenna.

Conclusions and Recommendations
In this study, it is aimed to design a microstrip patch antenna operating in the range of downlink frequency 7.25-7.75 GHz and uplink frequency 7.9-8.4 GHz allocated for military satellite communication.
Antenna dimensions have been optimized by using a genetic algorithm for the designed antenna to operate in suitable frequency ranges, and as a result, the antenna has been enabled to operate in the desired frequency ranges.
Antenna sizes were optimized to increase the bandwidth of the designed antenna, resulting in a bandwidth increase of 1.6 GHz compared to the first antenna. It is evaluated that the two antennas designed in this way can be used for military satellite communication.

Acknowledge
I would like to thank Assoc. Dr. Mustafa Emre Aydemir, who shared his valuable information with me and assisted me in the realization of this study.