# The Design and Implementation of a Phased Antenna Array System for LEO Satellite Communications
## 5 Design and Implementation of the Phased Antenna Array System for Leo Satellite Communications
Figure 6: Simulated radiation patterns of three-quarter wavelength phased uniform planar antenna array for \(0^{\circ}\) and \(150^{\circ}\) azimuthal beam steering angles. realization, including the dimensioning of the antenna elements corresponding to the frequency band of interest, which, in this case, is between 435 and 438 MHz (the band used by many LEO satellites). As the central frequency introduced in the simulations, the middle of this band was chosen, i.e., 436.5 MHz. The ground plane was made of aluminum sheet, so the values entered in in the simulation model for ground setup were \(\varepsilon=500\) (dielectric constant) and \(\sigma=100\),000 mS/m (conductivity). Since the antenna array was intended to be square uniform planar, the elements' spacing was the same (\(d_{x}=d_{y}\) in the context of Figure 1). Three-quarters of a wavelength vertical monopole antennas were chosen as antenna array elements, as shown above. We chose a half-wavelength spacing between array elements because the physical phenomena that occurred are easier to manage in the practical case using that distance. Compared to a larger spacing, the number of grating lobes is reduced, the gain is higher, and the HPBW is lower, which offers a much more accurate beam steering. If the distance is smaller than \(\lambda/2\), the gain decreases, and the unwanted effects of mutual coupling on impedance, resonant frequency, and SWR (Standing Wave Ratio) increase. Additionally, HPBW increases, leading to a decrease in beam steering accuracy [12; 29; 33]. Due to mutual coupling effects between array elements [12; 34], it is expected that the resonant frequency of the system of four antennas will be greater than that of a single element tunned on the same frequency and have the same length. Previous research [26] showed that in practice, for tuning a two-element three-quarter wavelength antenna array to the resonant frequency close to 434 MHz, each individual element needed to be dimensioned for 426 MHz (about 8 MHz lower) resonance. Then, after implementation into the two-element antenna system, fine-tuning of the elements was initiated while keeping the same length corresponding to 426 MHz. In the case of the four-element array, we initially dimensioned one of the identical elements to be three-quarters of the wavelength, corresponding to the frequency of interest of 436.5 MHz, resulting in a length of approximately 51.52 cm. Afterward, the other three elements were added to form the complete antenna array, and the resonant frequency of the array increased to approximately 460 MHz due to the mutual coupling effects. All elements were considered identical and spaced at \(\lambda/2\). Subsequently, we utilized the optimization feature available in MMANA-GAL to fine-tune the lengths of the elements incrementally until achieving the desired resonance frequency of the array to approximately 436.5 MHz. As a result, the length of each element increased to approximately 54.31 cm. This procedure was essential to provide us with a starting point in the physical construction of the array of elements and to evaluate the resonant frequency that each element should be tuned to. Following additional simulations, it was ultimately determined that each element should be tuned to approximately 406 MHz, with a length close to 54.31 cm. The simulation results showed that the impedance was close to the desired value of about 50 Ohms, and the SWR was nearly ideal (\(\approx\)1.0). Additionally, the simulation indicated that the gain of each individual element was approximately 6.5 dBi (decibels relative to isotropic), and the Front-to-Back ratio (F/B) was close to 0. Thus, considering the definition of the elements based on the simulation results, the next stage involves the practical implementation of the antenna array, which will be further elaborated. In order to minimize signal reflections in the entire array as a system, it was aimed to obtain a SWR as low as possible.