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<span>Wireless communication systems undergo tremendous growth these days and devices able to operate in a number of frequencybandsarehighlydemanded. Reconfiguration in antenna characteristic striggered the evolution of antennas that can workin multiple frequency, pattern<span> or polarization </span>environment.The frequency reconfigurable antennas thuse mergedarewell suited in Cognitive Radios which take part in the effective utilization of unused bands of frequencies by continuously interacting with the RF environment. Thus, Cognitive Radios enhancetheutilization of frequency spectrum and establish reliable communication. The most recent research works carried out in the arena of Frequency Reconfigurable Antennas for Cognitive Radio applications are reviewed and summed up in this paper to present the attributes and categorization. Four techniques adopted to attain frequency reconfiguration are extensively compared in this paper to find the advantages and constraints of each methodology. The applications of the works reviewed here are not only limited to Cognitive radios, but extended to a number of wireless communication services like, WLAN, WiMAX, etc</span>

We introduce a six-switch integrated ultra wideband (UWB)-frequency reconfigurable system for cognitive radio applications. With respect to the requirements of the cognitive radio, this proposed design incorporates a UWB section for sensing the frequency spectrum, and the same design is frequency reconfigured using switches to get narrow bands for communicating within the spectrum. The proposed design has a compact size of 40 mm × 40 mm × 1.6 mm and is printed on an FR4 substrate with relative permittivity 4.4. The first configuration of switches allows the antenna to have UWB characteristics from 3.10 to 12 GHz and beyond as per simulations and 3.13 to 12 GHz and beyond as per measurements. Configurations II to V cover the ultrawide band from 3.54 to 12 GHz through five narrow bands. Measured results match well with the simulated ones. The comparative analysis of the antenna in terms of frequency reconfigurability is also included in this work which proves that the proposed design is an effective candidate for Cognitive Radio applications.

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