Design of Low-Cost Smart Antennas for Wireless Communications

Traditional smart antennas are complicated, bulky, power hungry and expensive, as they require a large number of radio frequency (RF)/microwave phase shifters, and trans-mit/receive (T/R) modules. For wide applications in civilian wireless communications, it is important to investigate novel designs of electronically beam-steerable smart antennas which feature compact size, low power, and low cost.

This dissertation presents novel designs and implementation of low-cost smart anten-nas for wireless communications. Four different designs of low-cost smart antennas have been presented, and these smart antennas can be categorized into two different types: The first type is electronically beam-switching antenna based on the concept of electrically steerable parasitic array radiator (ESPAR). The design utilizes the strong mutual coupling between the driven element and reconfigurable parasitic elements to electronically steer the beams. A polarization-reconfigurable square patch is employed as the driven element which is surrounded by reconfigurable parasitic dipoles. The antenna does not require any micro-wave phase shifters and is shown to be able to achieve electronic beam switching and polarization reconfigurability by electronically controlling the PIN diodes. The second type is an electronically beam-switching antenna using active frequency selective surfaces (FSS). Omnidirectional feeders are employed to illuminate reconfigurable FSS cylinders which consist of a number of unit cells loaded by PIN diode or varactors. By controlling the DC bias of individual columns of the FSS cylinder, directive beams can be swept across the entire azimuth plane. Based on different active FSS unit cells, three different low-cost smart antennas have been designed, including a dual-band electronically beam-switching antenna, a 3-D beam scanning antenna, and an electronically beam-switching antenna with continuous frequency tuning.

In this thesis, in order to evaluate the antenna performance, comprehensive full-wave electromagnetic (EM) simulations are carried out using commercial software. Furthermore, prototypes are fabricated and tested to validate the design concepts. Good agreement between the simulation and measurement results is achieved, and demonstrates that the smart antennas designed in this thesis have advantages of low cost and low power, thus rendering them promising for applications in wireless communications.