New uniplanar electromagnetic bandgap (EBG) element is designed in this work for the superstrate of highly directive planar antenna and microwave filter design. The layout of the EBG is conceived of four arms spiral resonators (FASRs) and four corner square patches as a part of interdigital capacitor (IDC). The unit cell has dimension of only 3 mm, and the structure is engineered on a grounded dielectric substrate Taconic TLC-32 of thickness 0.79 mm. The designed EBG exhibits a wide bandgap property between the frequencies of 9.6-12.48 GHz ( 26.1 %). This work focuses on two different applications of the EBG - one as a superstrate of the microstrip antenna and the second as EBG loaded microstrip filter. The EBG loaded patch shows gain enhancement of 7.1 dB and bandwidth (BW) improvement of 330 MHz as compared to the reference antenna. A novel EBG based wideband filter is proposed for the C-band application. The passband BW of the filter covers the frequencies of 4.76-7.29 GHz (42 %) having insertion loss (IL) in the structure is below 1.2 dB over the operating range. © 2022 IEEE.