_applied_  
_sciences_  
_Article_  
**Design and Realization of a Frequency Reconfigurable**  
**Multimode Antenna for ISM, 5G-Sub-6-GHz, and**  
**S-Band Applications**  
**[PERSON] 1,*2,**3,**4,**5,**5,**6,**7,**8,**9,**10,**11,**12,**13,**14,**15,**16**,**17**,**18,**19,**10,**11,**12,**13,**14,**15,**16**,**17**,**18,**19,**20  
reconfigurability. In [6], a compact wideband monopole antenna is converted into tri-band antenna for ISM and 5G-sub-6-GHz applications. Although the antenna offers a compact size with the advantages of flexibility, it does not support frequency reconfiguration. Similarly another antenna by using the proximity-coupling feed to cover the WLAN and 5G-sub-6-GHz was presented in [7]. However, the proposed antenna has complex antenna structure that is the combination of two substrate separated by air gap. Several single band frequency reconfigurable antennas are proposed to operate in frequency band spectrum ranges 2-4.5 GHz [8; 9; 10; 11; 12]. Although the antennas reported in [8; 9; 10] are offering very high gain characteristics, they have multiple layered structures, which resulted in increased thickness and structural complexity. Although the work reported antennas in [11; 12] offer compact size, they cover very limited bandwidth, making them not suitable for modern-day devices operates in wideband frequency spectrum.  
Antennas with frequency reconfigurable characteristics for LTE and Wireless Local Area Network (WLAN) applications are presented in [13; 14]. A conventional rectangular patch antenna was modified by using Defected Ground Structure (DGS) for wideband operation, and three PIN diodes were incorporate to switch the operation [13]. In [14], various slots and asymmetric feed is utilized along with two pin diodes, to achieve frequency reconfigurability. Although these antennas have compact and simple geometry, the operational bandwidth in single and dual band is narrow. A dual to tri-band and a dual-band to quad-band frequency reconfigurable antenna were presented in [15; 16], respectively. Although, these antenna designs cover many bands, however, both works have impediment of narrow bandwidth, complex geometrical structures and lesser number of operational modes. In addition, the antenna presented in [15] suffers from the draw back of larger dimensions. A flexible frequency reconfigurable antenna was presented in [17] for sub-6-GHz applications. The presented work offers wideband and two dual-band operational modes with relatively simple structure. However, it has larger dimensions and limited operational bandwidth.  
To overcome the aforementioned challenges, a compact frequency reconfigurable antenna is proposed in this paper. The antenna radiator is composed of a triangular radiator with V-shaped slots and two PIN diodes are utilized to achieve frequency reconfigurability. The presented work shows a good combination of compact size, multimode operation, simple geometrical configuration, wide operational region, and reasonable gain. The rest of the paper is organized as follows. Section 2 presents the theoretical analysis and design methodology of the proposed antenna. Section 3 illustrates the discussion on various performance parameters of the presented work, while the paper is concluded in Section 4.