# Hybrid Mode Reconfigurable Antenna with V-Shaped Extrudes for Cognitive Radio Applications
## 1 Introduction
By adjusting the phase difference amid the LHCP and RHCP waves by means of adjustable phase shifters made of a varactor diodes and a quadrature hybrid, the polarisation plane of the linear polarised wave is continually regulated [39]. This work proposes a dual-band quadrature coupler that is reconfigurable and has independent variable properties at the lower band. The design specifications required to achieve the prior reconfigurability can be found by investigating an ideal model. In order to accomplish the required functionality, a patch coupler with a coupled line loaded using a varactor was suggested. The suggested coupling coefficient and the coupler's frequency at the lower frequency band can be changed independently while keeping the features at the upper band static by adjusting the voltages applied to the varactors [40]. With the development of the DGS, the research and application of printed-circuit microstrip antennas are in a new era. A DGS is a purposefully created fault or slot in a patch antenna's ground plane that is used for a variety of applications. There may be one or more faults that are introduced into the metallic ground plane. The faults are introduced to lower the harmonics and decrease inter-element interaction. The defected ground structure (DGS), which is frequently utilised to modify the results of printed-circuit antennas, is a comparatively recent field of study. To introduce resonant qualities and alter the current distribution approximated using either single or many defects on the ground plane, an equivalent L-C combination is added [41]. The fundamental ideas of DGSs are covered in depth in [42]. Resonant and non-resonant forms of DGSs are distinguished. The resonant-type DGS (R-DGS) makes use of its defect's size and shape-dependent frequency selection property. R-DGSs can be applied in an extensive range of microstrip circuit applications, including rat-races, filters, Wilkinson power dividers, diplexers, branch-line couplers, and more. These applications are well described in [41; 42; 43; 44; 45]. Whenever the antenna is connected to the modules by p-i-n diodes, new radiation patterns may be easily formed by altering the conditions of the p-i-n diodes. Patch antenna designs are intriguing opportunities in frequency-reconfigurable systems with a low profile, cheap price, planar design, light weight, ease of manufacture, and simplicity of integration with other electronic components [46; 47; 48; 49]. [PERSON] was the first to propose the notion of microstrip radiators. A microstrip antenna consists of a metallic ground on either side of a dielectric substrate and a conducting patch on the another. Dielectrics are substances with insulating qualities. They are materials capable of transmitting electric force without conduction. The dielectric constant is defined as the capacitance ratio generated by two metallic plates in the presence of an insulator to the capacitance of the same location in the absence of a vacuum or air. The dielectric constant of a substrate material should ideally be small in order to improve the fringing fields responsible for radiation. Low-dielectric-loss substrates are costly. Through a low dielectric constant, a large loss tangent value is used. An increased loss tangent minimises impedance variation and increases patch loss, resulting in an increased BW and decreased efficiency. Radiation in a microstrip is characterised by the spreading of surface current over patch metallization. The radiating patch may have any shape, such as rectangular, square, circular, elliptical, or triangular. Cognitive radio (CR) provides a remedy for spectrum access that is dynamic [50; 51; 52; 53]. By allowing primary (licensed) and secondary (unlicensed) users to coexist together, CR seeks to increase spectrum usage. Primary user (PU) refers to the channel's owner, and secondary user (SU) refers to all other users (SUs). SUs are permitted to sporadically access the spectrum that is not being used by primary users (PUs). When a PU requests it, SUs exit the occupied spectrum.