Low-cost Smart Antennas

3Electronically Steerable Parasitic Array

3.1 Introduction

A parasitic array antenna consists of a driven element and several parasitic elements [1]. The driven antenna is the only active radiating element, and the RF energy is distributed from the driven element to parasitic elements by electromagnetic coupling. One of the well known parasitic arrays is the Yagi‐Uda antenna, which uses parasitic elements to obtain high directivity. There is another type of parasitic array antenna called the electronically steerable parasitic array (ESPAR). This type of parasitic array antenna applies tunable components to parasitic antenna elements to obtain reconfigurable radiation patterns. Figure 3.1 shows a typical example of a seven‐element ESPAR antenna.

Figure 3.1 Configuration of the typical seven‐element ESPAR antenna [2].

As shown in Figure 3.1, the element located at the center of the ESPAR antenna is the only active element connected to the RF front end. This active element is surrounded by a number of parasitic elements. The parasitic elements are loaded by electronically tunable components such as sliding loads, PIN diodes, varactors, and MEMS switches. The tunable loads can be adaptively controlled by a DSP. When performing the beamforming, the reactance loads of the parasitic array antennas are adjusted to perform the weighted signal synthesis. Since RF energy is distributed from the ...