Gain Improvement of Bidirectional Substrate‐Integrated Waveguide‐Based Circular Cavity‐Backed Hexagonal Split Ring‐Shaped Slotted Antenna Using Metamaterial as Superstrate

A low profile substrate‐integrated waveguide (SIW)‐based circular cavity‐backed slotted antenna is proposed at an operating frequency of 5.42 GHz for wireless applications in U‐NII‐2B band in the TM 010 fundamental mode. Two hexagonal split ring‐shaped slots of 7 and 4 mm radius are placed on the patch as well as on the ground plane, resulting in bidirectional radiation. The reflection coefficient ( S 11 ) and gain for the single split ring‐shaped hexagonal slotted antenna (Antenna‐I) resonating at a frequency of 5.52 GHz is obtained as −23.4 and 6 dBi, respectively, having impedance bandwidth of 5.48–5.57 GHz while −29.8 dB and 7.2 dBi values of reflection coefficient and gain are obtained for double split ring hexagonal‐shaped slotted SIW cavity‐backed antenna (Antenna‐II) operating at 5.42 GHz. Furthermore, a band pass metamaterial operating in the frequency band of 5.19–5.57 GHz is used as a superstrate to augment the characteristics of the antenna and it is found that the gain is improved by 3.8 dBi as compared with Antenna‐I and 2.6 dBi as compared with Antenna‐II. The antenna–metamaterial composite structure is designed and fabricated on Arlon AD270 and Arlon AD320 substrate, respectively. Parametric studies are performed on the composite structure with respect to reflection coefficient, gain and metamaterial layer placement on the antenna to achieve the best results. Simulations are performed on HFSS v19.0 and show resemblance with the measured results.