# 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 proposed phased antenna array has a ground plane as a mechanical base, which constitutes the border between its two main parts: the radiating part (which includes radiant elements placed above the ground plane) and the hardware part, placed beneath the ground plane and containing passive components and hardware electronics for the beam steering function. For the array radiating elements, four telescopic antennas, on which SMA (Amphenol) connectors were fixed by intning, resulting in four almost identical elements. The ground plane was made of an aluminum sheet with a thickness of 1.5 mm, processed in a discoidal shape with a diameter of 1 m, large enough for the distance from the elements to the edge of the plane to be greater than or equal to \(\lambda/4\) (minimalcondition for the ground plane). The metallic ground plane serves as a reflecting surface for electromagnetic waves and a reference for the antenna elements. It also plays a crucial role in the antenna array's overall performance. Before fixing all four elements, each one was fixed on the ground plane and tuned individually to about 406 MHz (as discussed above). The successive measurements on each element were performed with a VNA (Vector Network Analyzer), Anritsu MS8212E series (Atsugi-shi, Japan). The resonant frequency was approx. 406 MHz and the corresponding SWR was close to 1.00 (ideal) for each of the four elements. Additionally, the element impedances were very close to 50 Ohm, a very important fact for impedance matching with the other hardware components, which are designed to have 50 Ohm impedance as well. Once the procedures described above have been completed, for the array resonance fine-tuning, we moved on to fixing the elements on the ground plane to form the planar antenna array, which constitutes the radiant part of the phased antenna array. After the fine-tuning, a resonance frequency close to 436.5 MHz was obtained. A picture of the setup for preliminary measurements can be seen in Figure 7.  
To ensure good mechanical stability during the measuring process, the array was placed on the antenna positioner, which is part of the Lab-Volt equipment that will be used to obtain the radiation pattern. A Minicircuits power splitter/combiner (35) was used to combine the signals provided by the antenna elements. The transmission lines (RG058) had the same length of about 35 cm. The VNA was coupled at the combiner input. Figure 8 shows the VSWR measurement results obtained after the fine-tuning of the four-element array. A lower VSWR than that corresponding to the frequency of 436.6 MHz can be observed. This is due to the resonance of each individual element, close to 406 MHz. The effects of mutual coupling between the elements determine a resonance at a higher frequency. In this case, in the band of interest between 435 MHz and 438 MHz, the VSWR has a very good value of 1.06. The proposed design was thought of as a compact system prepared for LEO satellite reception applications, even in outdoor conditions for IoT application scenarios (36; 37). Thus, the entire hardware was fixed on the ground plane at the opposite part containing the radiating elements. The use of this concept offers the minimization of common mode currents and environmental influence factors. Figure 7: Setup for preliminary measurements on the four-element uniform planar antenna array (radiating part) during the process of fine-tuning the element lengths for the resonant frequency. Figure 9 provides a simplified block diagram of the proposed Phased Antenna Array System. The four elements of the antenna array (on the left side of Figure 9, numbered from 1 to 4) constitute the radiating part. The phase shifters (denoted with PS1 to PS4), Phase shifters control module, the splitter/combiner (used as a signal adder and marked with \"E\"), Battery pack, \"Low battery\" warning circuit, and Voltage stabilizer constitute the hardware part, these components being placed below the radiating part of the antenna array (below the ground plane).