# Design of a SIW Variable Phase Shifter for Beam Steering Antenna Systems
## 1 Introduction  
Beam steering antenna systems have become progressively popular in modern communications. Transferring and receiving high rate data, scanning a large scale of the atmosphere, having compact structures with minimum losses--all are attributed to and achieved through electrical beam steering antenna systems. The main components in designing a beam steering antenna system are the phase shifters. Phase shifting in an antenna array can be achieved by using different methods. Included are variable phase shifters equipped with varactor diodes [1], PIN diode phase shifters (which have three types: switched line, loaded line, and reflection) [2], a Nolen matrix [3] or a Butler matrix [4] for constant phase shifts, complementary split ring resonators (CSRRs) [5], a tunable band-pass filter as phase shifter [6], a liquid crystal miniaturized phase shifter [7], some innovative vector-sum phase shifters by using CMOS technology [8; 9], and a continuously steered beam in a range of \(\pm 45^{\circ}\) through an array of vector controllers [10], to name only a few. Substrate integrated waveguide (SIW) has recently attracted a lot of attention because of its compactness, low loss, and its promising performance in mm-wave and microwave applications. Therefore, researchers started to not only use this technology for passive components, but also in active component areas like variable phase shifters. Reference [1] introduces two SIW phase shifters. First, an inline phase shifter using a varactor diode with a phase shift of \(25^{\circ}\). Secondly, a \(180^{\circ}\) SIW reflection-type phase shifter including a biasing circuit, four varactor diodes, and two open stubs. By changing the loading of a waveguide, a controllable phase shifter is achieved in [11]. The phase shift is controlled by four PIN diodes inserted in the substrate, and a maximum phase shift of \(45^{\circ}\) is obtained. An EM-wave coupling technique is proposed for achieving a wider bandwidth in a two layerSIW phase shifter design [12], and a phase shift of up to 180\({}^{\circ}\) is obtained by using eight PIN diodes. The combination of a 90\({}^{\circ}\) hybrid consisting of two waveguide layers and four varactor diodes, two on top and two on the bottom, results in a four layer structure. This phase shifter has nearly 360\({}^{\circ}\) phase variation [13]. The authors of [14] propose an SIW K-band phase shifter with minimum 105\({}^{\circ}\) phase tuning range and 4 dB insertion loss by using varactor diodes as tuning elements. Note that since varactor diodes and their connecting transitions add losses to the circuit and also affect the radiation pattern of the antenna due to radiations from the connecting microstrip lines, the use of fewer varactor diodes is desirable. A 2.8 GHz to 4.8 GHz beam steering microstrip antenna for radar applications is introduced in [15]. Beam steering is achieved with a pair of PIN diodes connecting the stubs to the ground and changing the state between On and Off. A single narrow bandwidth patch antenna is proposed in [5] which steers the beam by using complementary split ring resonators (CSRRs) as part of the ground plane. The antenna with double CSRR loading is able to steer the beam from \(-51^{\circ}\) to 48\({}^{\circ}\). A scan range up to 16\({}^{\circ}\) is obtained with an integrated 95 mm diameter lens antenna [16] in E-band. The beam is directed to different angles by switching between the feed elements of the array. Reference [2] presents a reconfigurable beam steering system comprising four patch antennas, three power dividers, and four phase shifters. A switched line PIN diode phase shifter is used for directing the beam between \(-30^{\circ}\) to \(30^{\circ}\). Reference [17] introduces a new approach to generate beam steering antenna systems without using phase shifters. A \(4\times 4\) planar circularly polarized spiral antenna array is designed and verified in a spherical coordinate system.