MEMS-Enabled Smart Beam-Steering Antennas

MEMS-Enabled Smart Beam-Steering Antennas

Hadi Mirzajani (Sahand University of Technology, Iran), Habib Badri Ghavifekr (Sahand University of Technology, Iran) and Esmaeil Najafi Aghdam (Sahand University of Technology, Iran)
DOI: 10.4018/978-1-4666-4888-3.ch010
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Abstract

In recent years, Microelectromechanical Systems (MEMS) technology has seen a rapid rate of evolution because of its great potential for advancing new products in a broad range of applications. The RF and microwave devices and components fabricated by this technology offer unsurpassed performance such as near-zero power consumption, high linearity, and cost effectiveness by batch fabrication in respect to their conventional counterparts. This chapter aims to give an in-depth overview of the most recently published methods of designing MEMS-based smart antennas. Before embarking into the different techniques of beam steering, the concept of smart antennas is introduced. Then, some fundamental concepts of MEMS technology such as micromachining technologies (bulk and surface micromachining) are briefly discussed. After that, a number of RF MEMS devices such as switches and phase shifters that have applications in beam steering antennas are introduced and their operating principals are completely explained. Finally, various configurations of MEMS-enabled beam steering antennas are discussed in detail.
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1. Introduction

Wireless communication systems, like their wired counterparts, have some fundamental challenges (Vanderveen, 1997):

  • 1.

    Limited allocated spectrum which results some limitation on capacity.

  • 2.

    Because of uncertainty in radio propagation environment and the mobility of users signal fading and spreading in time, space and frequency increases.

  • 3.

    Power limitation which is the main constraint in any mobile and hand held device and system.

Moreover, interference due to frequency reuse in cellular wireless communication systems is another challenge. Many efforts have been done to investigate potential technologies in order to alleviate such undesired effects. Some of these potential methods that researchers find are multiple access schemes, channel coding and equalization and smart antenna employment.

Figure 1 shows the main problem with wireless communication systems that smart antennas are used to alleviate that effect (Winters, 1998).

Figure 1.

Disorder in the received signal in wireless communication systems

The main idea which smart antennas are working on, is sometimes referred to as human listening system by an intuitive example (Bellofiore, 2002). A person can determine the Direction-of-Arrival (DOA) of an acoustic signal by a three stage process as flow;

Firstly, the listener hears the acoustic wave by his/her acoustic sensors (ears), and then because the ears are separated with each other, the acoustic wave arrives at different times to each ear. Finally, the human brain, which is a sophisticated processor, does a lot of computations and determines the location of the source of the acoustic wave. In order to intuitively understand the above mentioned information, consider three persons in a room, which both of them are carrying on a conversation with the listener which is located between them, as shown in Figure 2.

Figure 2.

An example for understanding the concept of smart antennas

As the listener moves around the room, he/she receives the acoustic signals from two persons. His/her brain computes the difference of the acoustic signal received from each person and predicts their location. Then the brain can add the strength of acoustic signal from each ear in order to focus on the intended user in specific location. Moreover, if the number of speakers increases, the human brain can enhance the received signal from the intended user and tune out unwanted interferences. Therefore, the listener has the ability to distinguish the desired speaker from many speakers and only focus on it. Conversely he/she can respond the intended speaker by orientating his/her transmitter (mouth).

Transmitting the same idea into wireless communication systems, the antenna plays the role of ear and mouth and the signal processing unit immediately after the antenna works as human brain. A schematic diagram of a smart antenna system is shown in Figure 3 (Baltersee, 1998; Balanis, & Ioannides, 2007).

Figure 3.

A conceptional view of a smart antenna

The smart antenna is consists of three segments which are; antenna array, patternforming network, and adaptive processor.

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