# 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  
The construction of an antenna array typically begins with selecting the frequency band and configuring the elements to be integrated into it, tailored to meet specific application requirements. In this case, these factors were elaborated upon in Section 2, where the rationale for choosing the (435-438) MHz frequency band and elements with favorable characteristics for medium elevation angles was described, leading to the proposal of utilizing the capabilities offered by elements configured at three-quarter wavelength. To emphasize this directivity characteristics favorability of the three-quarter wavelength element, we conducted an overlay comparison simulation between the proposed three-quarter wavelength and the commonly used quarter wavelength element configurations. As described in Section 2, during low elevations (below 25\({}^{\circ}\)), satellite reception is impacted by atmospheric absorption, interference, and reflections, particularly noticeable at considerable distances from the reception system. Furthermore, at high elevations (above 67\({}^{\circ}\)), the Doppler effect assumes significance due to the progressively higher velocities of the satellites. Additionally, it's noteworthy that satellite passes are rare. So, the medium elevation range offers a balance between good visibility of LEO satellites and the distance above the horizon, so signal reception can be done in more favorable conditions. Figure 5 shows the superimposed simulation results on widely used four-element quarter wavelength and three-quarter wavelength phased antenna arrays. We can observe that between 28\({}^{\circ}\) and 61\({}^{\circ}\) elevations, the three-quarter wavelength array's maximum gain is clearly higher (11.55 dBi) than that of the quarter-wavelength array (8.43 dBi). The representations are in the horizontal plane xOy (left) and in the vertical plane xOz (right), corresponding to 0\({}^{\circ}\) beam steering angle. Additionally, simulations show that the elevation angle limits corresponding to the maximum value of the main lobes vary between 42.5\({}^{\circ}\) (for 0\({}^{\circ}\) azimuth angle) and 43\({}^{\circ}\) (for 45\({}^{\circ}\), 150\({}^{\circ}\), and 210\({}^{\circ}\) azimuth angles). The simulated gain for the other beam steering angles different from 0\({}^{\circ}\) was about 11.97 dBi. Figure 6 shows the simulated radiation patterns of the proposed phased antenna array for azimuth beam pointing angles of \(0^{\circ}\) and \(150^{\circ}\). It can be observed the presence of secondary radiation lobes in the vertical plane, which have the greatest prominence for the azimuthal beam steering angle of \(0^{\circ}\), with the difference between the maximum gain corresponding to the main lobe and that of the secondary lobes being approximately \(-2.3\) dB. For the other azimuthal orientation angles, the levels of the secondary lobes are insignificant, having an average value of approximately \(-12.7\) dB. This leads us to conclude that the F/B is minimal at the \(0^{\circ}\) beam steering angle in the azimuth plane and much higher for the other beam steering angles. After selecting the configuration of the elements for the proposed antenna array, our next focus lies on exploring aspects concerning the definition of these elements. Commencing with preliminary observations derived from simulation results marks the initial step in the following discussion. Any antenna array is subject to mutual coupling effects between its elements. Taking these into account, it was considered necessary to carry out more simulations on the uniform planar antenna array in order to obtain certain starting points towards its practical  
Figure 5: Superimposed simulation results on a four\(-\)element quarter wavelength (in black) and three\(-\)quarter wavelength (in red) phased uniform planar antenna arrays in horizontal plane xOy (left) and in the vertical plane xOz (right), corresponding to \(0^{\circ}\) beam steering angle.