Research And Design Of Broadband Phase Shifter Applied In Base Station Antennas

Communication industry in our country is developing rapidly today, and personal com-munication is everywhere in people’s life since the number of mobile phone users in China ismore than1.2billion. As more and more communication systems and base stations come intouse, how to achieve good coverage has been a research hotspot. Electrically adjustableantennas is playing an important role in base station because its downtilt can be remotelycontrolled, which helps reducing cost. Phase shifter, as a key component of electricallyadjustable antennas, determines the effect of beam forming and thus its performance is vital.Although phase shifters have developed for several decades, there are still some problems inbandwidth, volume and weight. However, practical application demands smaller, lighter andmore broadband phase shifters. So research and design of such phase shifters is significant.This paper reviews the history of development of mechanical phase shifters since19thcentury and concludes how it evolved and its application in mobile communication. Bycomparing the advantages and disadvantages of different schemes, this paper aims to design aone input five outputs phase shifter with dielectrics moving longitudinally. Basic principles ofphase shifters are studied from the perspectives of transmission line theory and microwavenetwork theory. The phase shifter is simulated and designed from local to the whole and fromcircuit level to electromagnetic field level. Good results are achieved by means of impedancetransformation and step-by-step optimization. In addition, the performance of the phaseshifter is further evaluated and verified by applying it into antenna arrays.Measured results show that, in the bandwidth1.7GHz-2.7GHz, the VSWR is less than1.32, while the ripple of amplitude response between±1.5dB, the dispersion of phase lessthan10%, and the maximum phase shift is enough. Measured results match the simulatedquite well. Besides, the phase shifter is applied into electrically adjustable smart antennas andthe results of simulation and measurement indicate that the error of downtilts is not more than1°. The phase shifter proposed in this paper can satisfy the requirement of electricallyadjustable antennas and shows significance of engineering and application.