## 5 Reconfigurability
In [33], in the first stage, the simple patch antennas is modified to a right-angle triangle and then two stubs are introduced on the top angle of the triangle in an inverted L-shape for enhancement of bandwidth. Two diodes, D1 and D2, were placed between the two stubs and the radiator. The antenna offers the broadside radiation pattern when both the diodes D1 and D2 are in the OFF state in H-plane while in the E-plane a small tilt is observed in case D1 is OFF and D2 is ON. On the other hand, when D1 is ON and D2 is OFF, it provides pattern radiation in 30 GHz and 32 GHz, respectively. When both diodes (D1 and D2) are in the ON state, then a little tilted beam is achieved by the antenna. The tilt scenario is due to the truncated ground. When both diodes are in the ON state, the impedance bandwidth offered by the antenna is 6.3 GHz, ranging from 29.95 to 32.25, which covers the potential spectrum from 26-29 GHz for 5G applications. When both diodes are in the OFF state, there is a bandwidth of 6.75 GHz ranging from 27.81-34.560 GHz, where S11 \(<\) 10 dB. In case (01), when one diode D1 is ON and the second one is OFF, the impedance bandwidth is of 6.42 GHz (27.81-42 GHz), where S11 is \(<\) \(-\)10 dB. The design is shown in Figure 19.  
Figure 17: Evolution steps of antenna presented in Figure 17. Different geometrical shapes (**a–d**). Figure 18: Final geometry of antenna element. (**a**) Top view, (**b**) bottom view, and (**c**) side view [73]. After generalizing the view of the reconfigurability scenario, the frequency and pattern reconfigurability must be explored. In [27], lumped elements as a switching component for hexaband switching capability is presented. Lumped elements are used to achieve tunable capacitance responsible for frequency reconfigurability of hexaband frequency spectrum, i.e., 2.10 GHz, 4.11 GHz, and 2.4 GHz and 5.2 GHz on affordable, compact geometry capable to be integrated with ease in modern communication systems. Pattern reconfigurable antenna is presented in [72]. For 5G, there are new radio frequency bands -N77(3.3 GHz-3.8 GHz). The structure of the radiating element is modified by a swastika-shaped structure. Around the radiator, four parasitic arc-shaped elements are loaded and each parasitic element is loaded with a pin diode to control the antenna radiation field pattern. Table 3 is the comparison of different antennas using pin diodes for switching. A UWB antenna [80] with improved gain and omega structure loaded in the radiating patch is presented. In omega structure, a lumped capacitor is inserted for tuning the notched frequency spectrum 5.7 GHZ to 3.8 GHz for both WLAN and WIMAX bands, respectively. For gain improvement, a 3 \(\times\) 2 single layer array with a unit cell of metamaterial in L-shape is used for UWB and gain improvement. Lumped capacitors have an effective role for the mitigation of interference of WiMAX and WLAN spectrum. Antennas with reconfigurable techniques through electronic switching components such as PIN diodes, Varacter diodes, and RF MEMS are reported in [33; 73; 74; 81; 82]. Each technique has some supremacy or advantages as well as some weaknesses/disadvantages. A comprehensive study on many kinds of electronics switching components used for gaining reconfigurability are also reported in [33; 73; 74]. Photoconductive switches are composed up of the famous semiconductor materials silicon and gallium arsenide [29; 30]. Biasing lines are used instead of electrical wire, obviating large sizes and offering high isolation along with fewer interference. The details of different switching techniques are summarized in Table 4.  
Figure 19: A reconfigurable antenna [33]. (**a**) Front view and (**b**) side view.