# Design of a SIW Variable Phase Shifter for Beam Steering Antenna Systems
## 4 Experimental Results  
The proposed SIW antenna system is fabricated on a single layer of RT/duroid 6002. The top and bottom views of the fabricated prototype and details of the phase shifter circuit are displayed in Figure 14. Two end launch K-connectors are used for exciting the ports. Four varactor diodes are soldered to the board between the microstrip and compensation stubs. Two inductors are placed in series with the varactor diodes and DC voltage supply which can be replaced by chip inductors.  
Figure 14: _Cont._  
Figure 13: Simulated gain pattern of the beam steering antenna system at 17 GHz for 5 different loadings while port 2 is excited.  
For performance verification, the antenna system is measured in a far-field anechoic chamber using an Anritsu 37397C vector network analyzer. Figure 15 presents both simulated and measured reflection coefficients of the beam steering antenna system for ports 1 and 2. The reflection coefficient is better than \(-10\) dB in the entire frequency range, and measurements show a fairly good agreement with simulation results.  
The far-field radiation pattern of this antenna system is measured for three different loadings for performance confirmation. \(V_{1}\) and \(V_{2}\) are the biasing voltages applied to the left and right phase shifters, respectively. First, \(V_{1}\) = 0 V and \(V_{2}\) = 20 V are applied, which steers the null to \(-8^{\circ}\), then \(V_{1}\) = 20 V and \(V_{2}\) = 10 V are applied, which steers the null to \(5^{\circ}\), and finally \(V_{1}\) = \(V_{2}\) = 20 V is applied, which has the null at \(0^{\circ}\) and the main lobes at \(\pm\) 25\({}^{\circ}\) which are shown in Figure 16.  
Figure 14: Beam steering antenna system prototype, (**a**) top view, (**b**) bottom view, (**c**) details of the phase shifter circuit.  
Figure 15: Measured and simulated reflection coefficients of the beam steering antenna system.  
The co and cross polarization of this antenna system are measured by exciting port 2, terminating port 1, and applying the 20 V biasing voltage to both phase shifters. Figure 17 demonstrates the comparison between the measured and simulated results. The measurements are in good agreement with simulations. This antenna system provides a cross polarization better than 20 dB in the entire beam steering range.  
Finally, Figure 18 demonstrates the scanning range of the antenna system. By increasing the biasing voltage of the varactor diodes from 0 to 20 V, a progressive phase shift is provided and applied to the antennas to steer the beam, resulting in 50\({}^{\circ}\) scanning ranges from \(-25^{\circ}\) to 25\({}^{\circ}\). Tables 3 and 4 present a comparison between seven recent antenna systems and our proposed design in terms of gain, phase shifter type, polarization, bandwidth, scan range, and number of antenna elements. As is shown, the proposed system in this paper provides a fairly wide scan range and good gain despite the fact that only two antenna elements are used when compared to other systems, which use four antennas.  
The antenna efficiency represents the ratio between the total co-polarized radiated power to the input power accepted by the system. This calculation provides an antenna efficiency of 78.89% at the mid-band frequency of 17 GHz which demonstrates a very good performance of the proposed beam steering system.  
Figure 16: Measured and simulated far-field radiation pattern of the antenna system while exciting port 1 with (**a**) \(V_{1}\) = 0 V and \(V_{2}\) = 20 V, (**b**) \(V_{1}\) = 20 V and \(V_{2}\) = 10 V, (**c**) \(V_{1}\) = \(V_{2}\) = 20 V.  
Figure 17: Co-pol and cross pol of the beam steering antenna system when exciting port 2 and applying \(V_{1}\) = \(V_{2}\) = 20 V at mid-band frequency of 17 GHz.