Multiple-Input Multiple-Output (MIMO) wireless communication can significantly increase capacity without requiring increases in transmission power or spectrum. MIMO wireless communication has many applications including Wi-Fi (IEEE 802.11n and 802.11ac), long-term evolution (LTE). With the rapid development of wireless communication systems, there is a demand for communication devices that provide multiple services over a wide range of frequencies but remain compact in volume. A critical aspect in the design of compact MIMO antennas for communications is providing sufficiently good antenna isolation. In this thesis, the focus is on the design of compact MIMO antennas to serve different systems and make efficient use of the volume available. The thesis provides four new contributions abo...[ Read more ]

Multiple-Input Multiple-Output (MIMO) wireless communication can significantly increase capacity without requiring increases in transmission power or spectrum. MIMO wireless communication has many applications including Wi-Fi (IEEE 802.11n and 802.11ac), long-term evolution (LTE). With the rapid development of wireless communication systems, there is a demand for communication devices that provide multiple services over a wide range of frequencies but remain compact in volume. A critical aspect in the design of compact MIMO antennas for communications is providing sufficiently good antenna isolation. In this thesis, the focus is on the design of compact MIMO antennas to serve different systems and make efficient use of the volume available. The thesis provides four new contributions about compact MIMO antennas.

The first contribution focuses on novel planar MIMO antenna designs, which are the foundation of high density array of MIMO antennas. The basic idea of the design is the development of a canonical 2-port antenna that can be replicated and concatenated together to form MIMO antennas with arbitrary even numbers of ports. To validate the design, results from 20-port planar printed MIMO antennas are presented, operating at 2.6 GHz with a bandwidth of 100 MHz. The 20-port antenna with size of 1.3λ₀×0.69λ₀ mm² provides an antenna density of 22 antennas in free space square wavelength (λ₀²).

The second contribution focuses on novel compact 4-port reconfigurable MIMO antenna design for IEEE 802.11 applications in the small area of 20×46 mm². In one configuration, the antenna provides 4-port operating from 4.9-5.75 GHz with isolation between antennas greater than 20dB. In another configuration, it provides a 2-port antenna operating at 2.4-2.5 GHz together with another 2-port antenna operating at 4.9-5.725 GHz all with isolations greater than 14 dB.

Third, we propose a new design for a dual-band dual-port MIMO antenna operating in the 2.4/5GHz WLAN combined with two single-band antennas operating at 5GHz WLAN. A major advantage of this design over the second design is that it does not require reconfiguration. In particular, the design provides a 2-port antenna operating at 2.4-2.5 GHz simultaneously with a 4-port antenna operating at 4.9-5.725 GHz, with isolations greater than 12 dB, size 46×20×1.6 mm³,with no need for switches and bias circuitry.

Fourth and finally, we describe a method for designing and optimizing MIMO antenna efficiently using a pixelated surface. In this approach, we focus on single and multi frequency/band MIMO antenna and the reflection coefficient (S_i,i) and isolation (S_i,j) are the necessary parameters we optimize. As an example, we design and optimize a 2-port MIMO pixel antenna for a 2.4/5GHz WLAN and a 4-port MIMO pixel antenna for a 5GHz WLAN using the proposed approach and genetic algorithm. The proposed antennas are investigated by simulation and measurement and they are printed on an FR-4 printed-circuit-board (PCB), which is a low-cost substrate and allows for straightforward prototyping.