To overcome the use of the PIN diodes and achieve directive beam from one low-gain source, Section 3 presents a simple and an efficient hexagonal SBA configuration based on Fabry-Pérot cavity leaky wave antenna (FPC LWA) arrays. However, this type of configuration requires a huge number of switchers such as PIN diodes that complicate the structure. After the introduction, an RPA is presented using as a technique to create SBA, which is obtained from an omnidirectional source surrounded by an active FSS, wherein active elements are mounted on its surface. Two SBA configurations, allowing 360° coverage, are presented in this chapter, which is organized as follows. Moreover, if the antenna element has an omnidirectional radiation pattern, such as monopole, the directivity will be divided into two opposed directions that are decreasing, which causes the radiated energy. In addition, these two classical smart antenna systems do not provide 360° of coverage due to the printed circuit broad (PCB) technique used on the design of antenna which radiates above the ground plane of the structure allowing only half-plane coverage. Thus, the SBA is less costly, but its complexity and losses increase when the number of beams is increased. When interference and useful signal are both located in the same beam, the SBA system is disabled to resolve this scenario compared to the adaptive antennas. In general, switching operation is assured by a fixed beamforming network, such as Blass matrix, Rotman lens, and Butler matrix, connected to a linear antenna array. The behavior of these systems consists in the detection of the user's position by measuring signal strength, selects one of the predefined fixed beams and switches from one beam to another when the user moves. On the other side, the SBA generates multiple fixed beams in a specific area. However, the physical implementation of this system is very complex and expensive and requires high-power consumption and a longer time period to compute the current weight’s values (amplitude and phase) for each antenna which is not suitable for high data rate communications. Moreover, these adaptive systems have the ability to distinguish between user signal and interferences and also to steer the main beam in the desired direction with insertion zeros, thereby increasing the signal-to-interferences ratio. Īdaptive antennas are able to adapt their radiation patterns by exploiting the wireless radio channel at both transmitter and receiver sides with high precision using digital signal processing. Depending on their architectures, these systems are divided into two categories based on transmit strategy: adaptive antennas and switched-beam antenna (SBA). īasically, a smart antenna system is based on the theory of phased antenna arrays wherein the differential phase between adjacent antennas permits the scan of radiation pattern. īeamforming is seen as a solution for the problems cited previously to ensure a high quality of service (QoS) and increased channel capacity using smart antenna systems. In fact, these requirements force the improvement of the immunity of base station in front of many constraints such as multipath fading and interferences created between wireless networks due to an omnidirectional radiation pattern. Wireless communications are evolving to offer new generations of services such as video, satellite broadcasting, Internet, and mobile networks, which require high throughput to transmit multimedia signals with a good reliability. As a conclusion, SBA based on FPC LWA is the most suitable solution for future wireless communications. To increase more sectorization level and channel’s capacity, the proposed sector in FPC LWA arrays can be divided into three subsectors by using an active high-impedance surface (HIS). A sector-directive beam is generated from a simple patch antenna embedded inside a resonant Fabry-Pérot cavity with specific dimensions which have an influence on beamwidth and radiation efficiency. However, a simple and an efficient SBA configuration based on a hexagonal Fabry-Pérot cavity leaky wave antenna (FPC LWA) arrays is proposed as a solution for RPA problems. Unfortunately for a sector antenna, a huge number of diodes are required which complicates the structure in terms of efficiency and complexity. The behavior of FSS is controlled by PIN diodes which are able to divide the Azimuth plane into six sectors from one common source. First, a reconfigurable pattern antenna (RPA), which is composed of an omnidirectional slot-antenna array surrounded by an active cylindrical frequency selective surface (FSS), is studied. The concept of switched-beam antenna (SBA) systems covering an area of 360° for wireless base station applications is presented.
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