# Hybrid Mode Reconfigurable Antenna with V-Shaped Extrudes for Cognitive Radio Applications
## 2 Antenna Design
Figure 3: (**a**) Rectangular patch antenna design with single V\(-\)shaped extrudes; (**b**) Rectangular patch antenna design with two V-shaped extrudes. The resonance frequency of typical patch antennas, depicted in Figure 6, is around 3.8 GHz, from 3.1 GHz to 7.7 GHz for the improved ground dimensions of \(32\times 7\) mm\({}^{2}\). A parametric analysis was performed for ground length Gl of 5 mm to 8 mm in which the antenna showed a wideband for Gl = 7 mm. In the next iteration, an element is connected to a patch with two p-i-n diodes, D1 and D2, which provide the radiator switching for different frequency bands. The rectangular element had dimensions of El \(\times\) Ew mm\({}^{2}\), as shown in Figure 5a, in which El is the length of the element, 20 mm, and Ew, the width, is 2 mm. The designed antenna uses the Infineon BAR 50-02V as a p-i-n diode for the switching actions. It has a resistance of 3 \(\Omega\) in forward bias operations, whereas it has 5 K\(\Omega\) of resistance and a parallel capacitance of 0.15 pF in reverse biased switching with an internal inductance of 0.6 nH, as shown in Figure 7. In a patch antenna, p-i-n diodes are applied to achieve reconfigurability, allowing the antenna to switch between different operating frequencies or radiation patterns. The p-i-n diodes are usually placed at the corners or along the edges of the patch. When the p-i-n diodes are switched off, the patch antenna acts like a conventional microstrip patch antenna, with a fixed operating frequency and radiation pattern. However, when the diodes are biased with a voltage, they act as switches, creating a short circuit between ground plane and the patch. This changes the effective  
Figure 4: Return loss plot for rectangular patch antenna with two V\(-\)shaped extrudes. Figure 5: Design of frequency-reconfigurable rectangular patch antenna with two V-shaped extrudes using DGS: (**a**) with p-i-n diodes as a switch; (**b**) bottom view. dimensions of the patch, causing a shift in the radiation pattern and operating frequency. By selectively biasing the p-i-n diodes, different radiation patterns and operating frequencies can be attained. For example, by biasing different combinations of p-i-n diodes, the antenna can switch between directional and omnidirectional radiation patterns. The antenna displays various frequency bands with the switching of the diodes. The simulated and measured outcomes provide good agreement, as presented in Figure 8. With both diodes in the ON condition, the antenna illustrates a resonance at 5.1 GHz, with an S\({}_{11}\) of \(-\)24 dB from 2.7 to 5.9 GHz with a bandwidth of 3200 MHz, as shown in Figure 8a. Switching Diode-D1 OFF and Diode-D2 ON provides three bands, defined in Figure 8b, from 1.4 to 1.5 GHz, 2.7 to 4.2 GHz, and 4.6 to 5.9 GHz. With Diode-D1 turned ON and Diode-D2 turned OFF, there are three bands from 1.4 to 1.5 GHz, 2.7 to 4.4 GHz and 4.6 to 5.8 GHz, as depicted in Figure 8c. With both diodes in the OFF situation, as shown in Figure 8d, it shows three frequency bands from 2.3 to 3 GHz, 4.1 to 5.8 GHz, and 7.8 to 8.3 GHz. Figure 6: Parametric analysis of rectangular patch antenna with two V\(-\)shaped extrudes using DGS: return loss plot. Figure 7: Equivalent circuit of p-i-n diode in ON\(-\)OFF condition. Figure 9 confirms the radiation pattern for the designed antenna, which demonstrates directivity from 3 dBi to 4 dBi with a main lobe direction of 155 degrees and an angular width from 70 degrees to 75 degrees. Figure 9a shows the radiation pattern in which the main lobe is at 155\({}^{\circ}\) at 5.5 GHz, with a directivity of 3.59 dBi in the D-1 ON and D-2 ON state. Again, when D-2 is turned ON and D-1 is turned OFF, the main lobe is at 155\({}^{\circ}\), as shown in Figure 9b. Changing the modes of D-1 on and D-2 off provides the same results observed for the radiation pattern depicted in Figure 9c.