# Rectangular Microstrip Array Feed Antenna for C-Band Satellite Communications: Preliminary Results
## 2 Antenna Design  
Figure 1 shows the structure of the proposed microstrip array antenna design. The top layer consists of 2 \(\times\) 2 array antennas considering the antenna area at an optimum size, which is as small as possible, as a feeding antenna to avoid blocking effect or power reflection, as some radiation reflects back from the surface of the parabolic reflector and touches the antenna area. The optimum number of radiating elements is four with a two-dimensional configuration to achieve the desired gain and symmetric beamwidth. The middle and bottom layers show the proximity-coupled feed and the coaxial probe, respectively. This combination obtains a wider bandwidth and easy matching conditions. The transmission line from the probe point to each array element on the middle layer has a similar path length to keep the linear polarization. The quarter-wavelength impedance matching technique is also applied to maintain the matching condition and avoid reflection loss. The parameter values for the top and bottom layers are given as follows: patch width, \(W_{p}=40.93\) mm, patch length \(L_{p}=20.76\) mm, substrate width, \(W_{s2}=120\) mm, and substrate length, \(L_{s2}=85\) mm. The widths of the microstrip line for the middle layer are \(W_{f}=6.69\) mm, \(W_{o}=0.32\) mm, \(W_{A}=1.71\) mm, \(W_{B}=0.26\) mm, \(W_{C}=0.75\) mm and \(W_{D}=0.78\) mm. The lengths of the microstrip line for the middle layers are \(L_{f}=15.71\) mm,\(L_{o}=27.15\) mm, \(L_{A}=3.78\) mm, \(L_{B}=38.59\) mm, \(L_{C}=8.37\) mm, \(L_{D}=7.46\) mm. These approximation values are simulated and characterized to reach the most optimum parameters. The designed antenna is fabricated using the RT/Duroid-5880 substrate material with a dielectric constant value (\(\epsilon_{r}\)) of 2.2, a thickness of 1.575 mm, a tangential loss (\(\tan\delta\)) of 0.0009, and a copper thickness of 0.035 mm. Figure 2 shows the fabricated microstrip array antenna from the upper, middle, and lower layers. Measurement was carried out using the Rohde & Schwarz ZVL Network Analyzer 9-13.6 GHz for the measurement of S parameters, the Hewlett Packard 8753E 32-6 GHz Network Analyzer, and the Schwarzbeck BBHA 9120A as a reference antenna when measuring radiation pattern and gain. The simulated and measured reflection coefficient for the designed antenna is shown in Figure 3. It can be seen that the designed antenna results in a good reflection coefficient (\(S_{11}\)) of \(-14.243\) dB at a frequency of 4.148 GHz. It also has a bandwidth of 703.7 MHz in a frequency range of 3.8-4.4 GHz. The gain of the antenna is 12.75 dBi. Furthermore, the measured reflection coefficient is in good agreement with the simulated one. Figures 4 and 5 show the radiation pattern for the simulation and measurement of the antenna in the E plane and the H plane, respectively. It can be seen that the measurement results verify the simulation results. Both show a directional radiation pattern in which the angle of 0\({}^{\circ}\) has the highest level compared to the other angles. Then the results of the radiation pattern measurement in the E plane show better characteristics in the sidelobe, where the received power level of the 40\({}^{\circ}\)-140\({}^{\circ}\) angle and the 220\({}^{\circ}\)-320\({}^{\circ}\) angle has a much lower value than the simulation results. Figure 6 shows the gain comparison between the simulation and the measurement in a frequency range of 3.0-5.0 GHz. The measurement shows that the gain value varies from 6.16 dBi at the 5 GHz frequency to a maximum of 12.074 dBi, which occurs at the 4.148 GHz frequency. There is a difference in the gain of 0.626 dB at the 4.148 GHz frequency, where the simulation result gain is higher than the measured gain. The difference in gain between simulation and manufacturing is still acceptable. The lower result could be due to defects in the fabrication process and measurement, such as poor sol  
Figure 1: The 2 \(\times\) 2 microstrip array antenna design. Figure 4: E-plane radiation pattern at 4.148 GHz.