Design Of Miniaturized And Ultra-wideband Phase Shifters

Phased array radars have been widely studied and used because of its high-speed switching and efficient beamforming properties. Phase shifters are one of its key components, so methods of phase shifter miniaturization and ways to enlarge the bandwidth of the phase shifters are discussed in this dissertation.To lower the mutual coupling effect between adjacent antenna elements and to suppress side lobes, distances between adjacent antenna elements are usually between half wavelength to one wavelength. It often imposes difficulties and constraints when the size of phase shifter is larger than one wavelength. Therefore, miniaturization becomes of great interest in most of the applications where size of the Phase Array module is critical. In passive phased arrays, phase shifters based on planer or waveguide structure usually have a bandwidth less than 10%(mostly limited by the phase stability), leading to deteriorated frequency hopping ability and wideband imaging ability of the radar, which is the main disadvantage of passive phased array comparing to active phased arrays.This dissertation consists of three parts. The First part contains a brief introduction of the research conducted in this dissertation in Chapter 1 and Chapter 2. Furthermore, Phased Array theory and electronically controlled phase shifters are also covered in these two chapters.The second part consists of methods for phase shifter miniaturization discussed thoroughly in Chapter 3 and 4. Theory and equivalent circuit model of slow wave line is analyzed, meanwhile bias-tee network miniaturization method is also studied and proposed in the mentioned chapters. As a result, a miniaturized 4-bit digital phase shifter working in L band is presented. Measured results show that the return loss is better than 14 dB, insertion loss is less than 2.4 dB, phase error is less than 5% while the total size of the phase shifter is 30mm*80mm*17mm, which is very compact and suitable for most of the Phase array application.The third part consists of Chapter 5, where mainly ultra-wideband phase shifters are discussed. A generalized analysis method of a class of wideband loaded-stub phase shifters and a fast designing procedure is presented. Based on the procedure, a fixed-phase UWB 90° phase shifter is designed and fabricated. In the measured results the return loss is found to have better than 10 dB with excellent phase imbalance performance (90°±4°) over the 2.5 GHz-6 GHz frequency band. By combining this fixed-phase UWB fixed phase shifter with switching network, a tunable L-band 90° phase shifter is designed and fabricated, with a capability to switch between 0 and 90 phases electronically. Measured results reveal that 90°±4.2° phase shift is achieved with good return loss performance within 0.62 GHz-1.25 GHz frequency band is achieved. The proposed phase shifter has shown good UWB characteristics.