Design and Optimization Methods for Multiport Antennas

Modern wireless communications has evolved greatly within the past 30 years, and antennas are a significant part of the today's society. Almost everyone has a smartphone equipped with multiple antennas, and antennas are found in many everyday household objects and devices such as washing machines, coffee makers, and robotic vacuum cleaners. Furthermore, wearable antennas (such as those in medical devices, clothes, and watches) are becoming increasingly popular. In summary, antennas are placed in unconventional locations demanding new antenna design methods. Multiport antennas may provide benefits as compared to traditional single-port antennas. Therefore, this thesis discusses novel design methods for multiport antennas which requires new design methods. This thesis is divided into three parts. The first part studies using practical decoupling and matching networks (DMNs) in multiple-input-multiple-output (MIMO) antennas and antenna arrays. A DMN for a four-port MIMO antenna is realized with sufficient bandwidth, and a method is presented for optimizing a DMN of an antenna array with a commercial circuit synthesis tool by applying a unit cell model. The second part of the thesis discusses a method to optimize the radiation efficiency of a multiport antenna. The method provides an ultimate efficiency limit for a given multiport antenna in terms of its port characteristics. The developed method can be viewed as a design tool of sorts, and its practicality is demonstrated by designing a mobile MIMO antenna based on the results obtained with this method. The third part of the thesis focuses on extending the multiport antenna method discussed in the second part. The method is extended to optimize the partial radiation efficiency of multiport antennas and the realized gain of an antenna array comprising multiport elements. Although these methods are based on theoretical formulation, they enable a systematic way to realize practical multi-port antennas. The methods developed within this thesis provide a basis for developing multiport antennas. This hopefully advances the use of multiport antennas and enables the design of better and more complex antennas for future needs.