**1. Introduction**

Present scenario of wireless communication system required compact and multiple band antenna design. Since many systems are operating at multiple frequency range, requiring dual and triple band antenna for various applications such as WLAN, WiMAX, RFID, satellite communication, etc. Presently, many printed monopole antenna are proposed. Serve for wireless applications to cover the wireless standards for Wireless local area network (WLAN: 2.4–2.48, 5.15–5.35, and 5.75–5.825 GHz) and worldwide interoperability for microwave access (WiMAX: 3.4–3.69 GHz) are two among the available wireless standards which allow interconnections of devices for communication. To achieve multi-functionality, various parameters of antenna such as polarization characteristics, resonant frequency, patterns and impedance bandwidth etc., are reconfigured as per requirements [1].

Presently wireless communication systems are adopting the concept of cognitive radio system where using a sensing antenna performing the monitoring of the spectrum, and can be reconfigured to operate over a desired frequency band. This system is required a frequency band reconfigurable antenna as a sensing element [2]. Most of frequency band reconfigurable antennas providing the band switching between narrowband modes [3–5].

Antenna obtained the quad-band switching by implementation of microelectromechanical systems (MEMS) switch [3]. Another frequency band reconfigurable patch antenna is proposed that operate in four different modes with the help of switching elements [4]. Recently, many microstip patch antenna have been designed that indicate the switching facility in narrowband as well as wideband modes [6–11]. In [6], a Vivaldi antenna is designed that provide the wideband and

narrowband mode switching facility. A frequency band reconfigurable antenna with four photoconductive switches is proposed that operating with switching between the three narrowband modes and UWB mode [7]. In [9], antenna has been proposed with narrowband and wideband functionality with reconfigurability characteristics is achieved with the implementation of p-i-n and varactor diodes. Tunable EBG structure are analyzed with active switching devices FET and obtained the transmission characteristics of the structure [12, 13]. Many techniques such as defective ground [14], etching slots [15, 16], metamaterial loading [17–23], dielectric resonator [24], fractal geometry [25, 26], etc., are applied to accomplish multiband reconfigurable operation to cover various wireless applications.

In this chapter, firstly design the octagonal shape patch antenna and implementing the inverted L shaped switchable slotted ground yielded switchable resonant modes such as, two narrowband modes (5.05–5.89 and 8.76–9.80 GHz), two dual band modes (2.21–2.52 GHz and 5.07–5.89 GHz and 2.18–2.52 GHz and 8.78–9.71 GHz) and UWB mode (2.87–16.56 GHz) for wireless applications. As per requirement to design antenna to frequency band reconfigurability introducing the five switching elements p-i-n diodes placed inside the slotted ground. The proposed design is compact in size as compared to antennas are discussed in published literature [6–11]. The simulation work of antenna is done by using CST Microwave Studio (CST MWS) software [27] and measurement is performed with the help of VNA (vector network analyzer-E5071C (300 KHz–20 GHz) ENA series Agilent Technologies). The fabrication of proposed structure is executed by using of PCB prototype machine (Caddo-71).

Following sections focused on the antenna designing with parametric study and switchable modes analysis with results in simulated as well as measurement modes.
