# 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 phase shifters are denoted with PS1-PS4, and the corresponding phase shifts are introduced with \(W_{1}\)-\(W_{4}\). All components were electromagnetically shielded and electrically connected to the ground plane. An image from beneath the ground plane, opposite to the location where the vertical antenna elements of the array have been fixed, is depicted in Figure 10. This image  
Figure 8: VSWR measurement results were reached after the fine-tuning of the array. The markers 1, 2, and 3 indicate the same VSWR of 1.06 in the frequency band (435–438) MHz. Figure 9: Simplified block diagram of the proposed Phased Antenna Array. illustrates the positions of each hardware component within the proposed phased antenna array. Each component will be presented below. A module for controlling the shape and direction of the antenna array radiation pattern (also generally known as a beamforming module [12; 26; 33]) was designed and implemented and consists of a splitter/combiner, phase shifters, basic PCB and microprocessor-based control module. In the phased antenna array presented in this article, we have successfully integrated the original concept together with previously developed phase shifters that have already been tested for linear antenna arrays. The phase shifters utilized were equipped with AD8340 [27] integrated circuits produced using Analog Devices. This circuit, in order to achieve the desired phase shifts, requires two differential voltages to control the phase imposed on the RF input signal. Their values are normally included in the range of \(-500\) mV to \(500\) mV in common mode. To obtain those values with good accuracy, each of the phase shifters was equipped with a DAC8554 [28] that contains four digital-to-analog converters (DAC), each with a 16-bit resolution (65,536 stages of voltage variation for each DAC). The operation mode of the control module and phase shifters command software is presented below. Each of the four-phase shifters available and tested in previous research is equipped with the following essential components: a DAC8554 circuit, an AD8340 vector modulator circuit, and an LM4140 integrated circuit developed by National Instruments, with the role of voltage source used as a reference for DACs. To achieve a certain phase shift, the AD8340 circuit requires two differential voltages, which we denoted by \(V_{x}\) and \(V_{y}\). These voltages are functions of the phase shift that a phase shifter will achieve. For the orientation of the main lobe of the phased antenna array, we started from the results obtained in (10)-(13), which led to obtaining four values (w1, w2, w3, w4) for each chosen angle, denoted by \(\varphi_{0}\). Each of the \"wi\" values (\"i\" having integer values between 1 and 4) represents the phase shift that needs to be achieved using one of the four-phase shifters. Then, analog quantities \(V_{x}\) and \(V_{y}\) were obtained, and based on them, the software calculated the pairs of values that form the differential voltages. These were denoted by \(V_{x}\)+, \(V_{x}\)\(-\), \(V_{y}\)+, and \(V_{y}\)\(-\). Thus, the difference between \(V_{x}\)+ and \(V_{x}\)\(-\) is equal to the differential voltage \(V_{x}\), and the difference between \(V_{y}\)+ and \(V_{y}\)\(-\) is equal to \(V_{y}\). After converting those pairs of values to binary numbers, they were transmitted serially (via USB) from the computational system to the control hardware module, which in turn transmitted them to each phase shifter in order to be written on the four DACs. The same procedure was applied for each of the four-phase shifters that will feed each element of the antenna array. After the conversion from digital to analog, the differential voltages  
Figure 10: The hardware of the Phased Antenna Array System (passive components and hardware electronics which were fixed on the ground plane, at the opposite part with that containing the radiating elements). were obtained to command the AD8340 circuit to achieve the phase shift of the RF signal.