On demand band rejection through the use of PIN diodes, wide impedance matching (2-12 GHz), high isolation amongst the radiators, compactness achieved by angular placement of the radiators, low gain variation over the entire bandwidth, band rejection control achieved by adjusting the gap between stub and ground plane, and low total active reflection coefficient (TARC) values make the proposed design very suitable for commercial handheld devices. [PERSON] [7] presents a reconfigurable 3D slot antenna for 4G and sub-6G smartphones with a metallic casing. The antenna is located at the bottom of a smartphone and is integrated with the metallic casing. PIN diodes are loaded at the dual-open slot and the folded U-shaped slot, respectively, which realize four working states. The antenna has a compact volume and covers the long-term evolution (LTE) bands of 698-960 MHz and 1710-2690 MHz, and the sub-6G bands of 3300-3600 MHz & 4800-5000 MHz. The design is fabricated together with the measured performance and a comparison to other state-of-the-art antennas that shows the proposed design has multiband characteristics with small size. [PERSON] et al. [8] presents a novel combo-reconfigurable antenna architecture for the frequency and pattern reconfiguration of a novel antenna system for 5G millimeter-wave mobile communications. The tuning system independently controls the frequency and radiation pattern shifts, without letting them affect each other. The proposed antenna consists of two patches, radiating at 28 GHz and 38 GHz. A negative-channel metal-oxide semiconductor (NMOS) transistor is used as an ON/OFF switch. Frequency reconfiguration is controlled by two switches that vary the patch dimensions. Pattern reconfiguration is achieved by the remaining 16 that connect and disconnect parasitic stubs to the ground to control the surface currents. Results are shown for 18 different combinations of the switches' states. The optimal design of an aperiodic reconfigurable microstrip antenna array for broadcasting applications is introduced by [PERSON] et al. in [9]. The array is designed to serve as a DVB-T base station antenna operating in a single broadcasting channel (optimized at 698 MHz, center frequency of DVB-T channel 49). This allows the array to concurrently achieve a particular radiation pattern shaping with high forward gain, main lobe tilting, and null filling inside the service area, as well as low sidelobe level outside the service area. To concurrently satisfy all the above requirements, the geometry dimensions and the array feeding weights (amplitudes and phases) are optimized, thus leading to a complex multi-variable and multi-objective problem. The problem is solved by applying a recently developed particle swarm optimization (PSO) improved variant, called PSO with velocity mutation (vm), in conjunction with the CST electromagnetic simulation software, which is employed by the PSOvm every time a full-wave analysis is required. Furthermore, all the optimization methods found in the CST environment are compared with the PSOvm. The results show that the PSOvm is capable of producing an antenna array geometry that is closer to the predefined requirements than the geometries derived by the rest of the optimizers in the least amount of computational time. Last but not least, [PERSON] et al. [10] present a highly compact frequency-selective surface (FSS) that has the potential to switch between the X-band (8 GHz-12 GHz) and C-band (4 GHz-8 GHz) for RF shielding applications. The proposed FSS is composed of a square conducting loop with inward-extended arms loaded with curved extensions. The symmetric geometry allows the RF shield to perform equally for transverse electric (TE), transverse magnetic (TM), and 45\({}^{\circ}\) polarizations. The unit cell has excellent angular stability up to 60\({}^{\circ}\). The resonance mechanism is investigated using equivalent circuit models of the shield.