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This work proposes a novel way to reduce overall volume of reflectarray antennas while maintaining aperture efficiency relatively high. Different from conventional approaches, a feeder antenna is placed very close to the proposed reflectarray ground plane. In order to prevent expected degradation in antenna performance, which is mainly because the feeder is very close to the reflectarray, we impose an additional condition maximizing constructive interference between direct and reflected waves. Consequently, we can show that our antenna can provide relative high antenna gain and aperture efficiency even the antenna is remarkably reduced. Excellent agreement between simulation and experiment proves the validity of our proposal.

A printed circuit board (PCB) based electrically tunable absorber (ETA) providing good absorption rate at much higher frequencies than conventional ones is proposed. In conventional ETAs, the highest absorption frequency is mainly limited by very large capacitance of commercial varactors. In order to overcome the high-frequency limit, small parasitic capacitance is intentionally introduced by narrow slits inserted in a rectangular metallic patch printed on top of a substrate. Hence, overall capacitance of the proposed ETA can be remarkably reduced according to series connection between the capacitance from the slits and varactors. Consequently, we can continuously scan absorption frequencies in any target frequency band with almost no high-frequency limitation. In addition, by changing the number of slits, we can unrestrictedly select any target absorption frequency band. Good agreement between simulation and experiment proves the validity of our approach.