Capacitively Fed Cavity-Backed Slot Antenna in Carbon-Fiber Composite Panels

A new form of a conformal load-bearing antenna structure that consists of a cavity-backed slot in a carbon-fiber reinforced polymer (CFRP) panel is presented. The antenna is fed via a coaxial cable and patches that capacitively couple energy into the highly conductive carbon fibers without the requirement to abrade off the nonconductive epoxy resin layer on the surface. Computational simulations, which are validated by experiments, show that this feed configuration is as effective as soldering in a brass slot antenna. Backing the slot with a CFRP cavity enhances gain and front-to-back ratio by 2 and 13 dB, respectively. Gain is increased further by orienting the inner surface ply of the CFRP cavity to the same direction as the local E-field. Finally, the dimensions of the slot and cavity are optimized to minimize the antenna size. The resultant low-profile cavity is 14% of the volume of the original antenna design, but maintains similar gain and resonant frequency.