# Hybrid Mode Reconfigurable Antenna with V-Shaped Extrudes for Cognitive Radio Applications
## 1 Introduction
Frequency- and pattern-reconfigurable antennae were discussed [32; 33]. This paper also discusses a simple Fabry-Perot antenna design with polarisation diversity. The suggested antenna consists of a planar metallic reflector, a partially reflective surface, and a repositionable microstrip patch. By electronically adjusting the ON and OFF conditions of a pair of p-i-n diodes, the polarisation of the antenna can be changed between dual-sense circular polarisation and single linear polarisation. This is significant because the proposed design does not demand the biassing wires that are generally used to build reconfigurable antennas. As a result, the negative effects of biasing wires on the antenna's operational parameters can be eliminated. The antenna offers resonance between 7.3 and 7.6 GHz. Moreover, the requisite radiation patterns have been produced with a maximum gain of 15.1 dBi [34]. The experimental testing of a revolutionary Ku-band, application-based, pattern-reconfigurable antenna array that can electronically create a variety of radiation patterns, such as a single-fan beam and single, dual, and quad beams was studied. There are four probe-fed O-slotted patch elements in total. Each element has two integrated p-i-n diodes, and the path of the excitation current can be changed by alternately activating one of the p-i-n diodes. The element can yield two-phase states with a 180\({}^{\circ}\) phase difference as a result. An L-shaped stub acting as a shunt capacitor has been further added to the O-slotted patch to provide better match port impedance to the stripline. The quasi-coaxial via transition, formed by four vias arranged around the probe, helps to increase the element's radiation efficiency. Therefore, a thin, planar restrained-feed antenna can be used in conjunction with reconfigurable array elements to fully integrate them. The entire antenna profile is substantially reduced to less than one wavelength [35]. The design of a wideband, unidirectional antenna with various LP/CP realisations is the main topic of this study. The major reconfigurable radiating source for the suggested antenna is a microstrip patch. In contrast to designs that use MS, MS is employed not only for circular polarisation BW augmentation but also to realise linear polarisation. It is important to point out that the antenna's polarisation-switching phenomenon can be easily implemented using just one switchable voltage and pair of p-i-n diodes. Moreover, a bias-T is used to bias the diodes in order to prevent dc biasing, which is often associated with the antenna via a biasing circuit that has an unfavourable impact on the RF performance of the antenna [36]. A reconfigurable antenna with shorting pins and a -varcator-loaded pattern is demonstrated. A square patch antenna was provided with null scanning and continuous beam reconfigurability by adding two groups of shorting pins with four varactors. With this study, the edge-shorting pins were positioned for various E-fields along the parallel edges of the square patch. For the purpose of improving the directivity and null depth, a second group of shorting pins was inserted symmetrically through the diagonal path of the patch. Varactors were linked through the edge-shorting pins to create a continuous configurable phase difference to perform continuous pattern reconfigurability. On the basis of a transmission-line model, the pattern reconfiguration mechanism and the impacts of the shorting pins were explored [37]. Pattern agility was achieved through three complementary split rings (CSRRs) on the ground plane in the patch antenna. The radiation beam of the proposed antenna is capable of steering the broadside pattern of the elevation plane at angles of 180\({}^{\circ}\), 15\({}^{\circ}\), and 0\({}^{\circ}\)[38]. Combining the left-handed circularly polarised waves and the right-handed circularly polarised waves emitted by a dual, circularly polarised (CP) antenna results the a linearly polarised (LP) wave with a random polarisation plane discussed herein.