# Hybrid Mode Reconfigurable Antenna with V-Shaped Extrudes for Cognitive Radio Applications
## 2 Antenna Design  
Beginning with the design depicted in Figure 2, a rectangular patch antenna element with dimensions of 16 \(\times\) 18 mm\({}^{2}\) on a substrate board with a size of 32 \(\times\) 36 \(\times\) 1.6 mm\({}^{3}\) was chosen, as shown in Table 1.  
For the intended frequency, appropriate impedance matching is necessary to attain the lowest probable return loss. The 50 \(\Omega\) microstrip feedline as deployed to excite this rectangular patch element and was moved around to increase the impedance match between the transmission line and patch. The substrate material FR-4 was used to fabricate the design, with a dielectric constant of 4.4 and a tan \(\delta\) of 0.0018. In the first stage of designing the antenna, a complete ground of copper material was adopted beneath the dielectric material. The microstrip feedline \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Symbols** & **Dimensions (mm)** \\ \hline Substrate Width & Gx & 32 \\ Substrate Length & Gy & 36 \\ Ground Width & Gx & 32 \\ Ground Length & Gy & 36 \\ Patch Width & Wp & 16 \\ Patch Length & Lp & 18 \\ Feedline Width & Wf & 3 \\ Feedline Length & Lf & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dimensions of rectangular antenna. Figure 2: (**a**) Rectangular patch antenna design; (**b**) Return loss plot. was used to provide the excitation to the antenna with a Wf of 3 mm and an Lf of 10 mm in which the Wf is the width and Lf is the length of the feedline, as depicted in Figure 2a. Figure 2b shows the return loss plot for the designed antenna. This rectangular antenna resonates at 7.7 GHz with a return loss of \(-\)35 dB. The antenna has a bandwidth of 800 MHz from 7.5 GHz to 8.3 GHz to match the 50 ohm impedance feedline with the Wf optimized at 3 mm. In this next step, as shown in Figure 3, two V shapes were extruded from the rectangular patch, one by one, from both top corners of the patch to enhance the bandwidth. On the patch, the slot was interpreted as a capacitive reactance. At a particular slot length, it was discovered that the resonance frequency decreased as the slot width increased. With longer slot lengths, the resonance frequency reduction was on the upper side, whereas for shorter slot lengths, it was on the lower side. In Figure 3a, one V-shaped slot with a length Lf of 8 cm and a width of 4 cm is cut from one side of the patch. Another V-shaped slot is cut out from another side of the patch with the same dimensions of 8 \(\times\) 4 cm\({}^{2}\). It is slotted as shown in Figure 3b. This antenna shows a return loss plot of less than \(-\)10 dB in which it covered the bandwidth of 1100 MHz from 7.8 GHz to 8.9 GHz. The frequency range of 7.8 GHz to 8.9 GHz falls within the microwave frequency spectrum and has a variety of applications in different fields, including radar systems for tracking and detecting objects, such as aircraft, ships, and missiles; for wireless communication applications, including the point-to-point and point-to-multipoint communication systems used in various ISM applications such as microwave ovens, medical diathermy machines, and industrial heating equipment; and global navigation satellite systems (GNSS), such as GPS. With one V-shaped extrude, it demonstrated resonance at 8 GHz, with a return loss of \(-\)36 dB, while with two extrudes, it demonstrated resonance at 8 GHz and 8.6 GHz, with a return loss of \(-\)21 dB and \(-\)29 dB, as explained in Figure 4.  
For a decrease in size and improved isolation among the antenna elements, a DGS is employed in the ground plane of the antennas, as shown in Figure 5b. A DGS is a very effective way to expand the performance of patch antennas by addressing common issues such as narrow bandwidth and unwanted radiation. By etching a precise shape or aperture on the ground plane beneath the patch, a DGS can create a resonant structure that can widen the bandwidth of the antenna. This is achieved by introducing additional resonances in the frequency response of the antenna.