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We propose a new way to enlarge gain bandwidth of a miniaturized reflectarray antenna (MRA), a new type of reflectarray antenna (RA) with significantly reduced volume. To extend the gain bandwidth, we have used meander-line based sub-wavelength elements as reflectarray cells, which can fully cover a required reflection phase range ideally, 360°. As a result, we have accomplished a three times wider gain bandwidth than that of our previous MRAs. In addition, the proposed MRA can also provide high gain with good aperture efficiency even though a main beam directs toward a tilted direction. Furthermore, remarkably reduced electrical volume, which is 700 times smaller than the smallest conventional RAs, is still maintained. Measured aperture efficiency of the proposed MRA is 41.1% which is comparable with conventional RAs. And the measurement results show that the main lobe direction is very stable around the target direction within the given −1 dB gain bandwidth without any degradation in other performances. As a result, the proposed MRAs with wide gain bandwidth stands out as a good alternative of the conventional RAs.

We propose an electrically frequency tunable absorber (EFTA) with varactor diodes, which can provide good absorption properties even in much higher frequency bands than conventional EFTAs. In general, conventional EFTAs cannot guarantee high absorption rate beyond a certain frequency limited by high capacitance of commercial varactor diodes. In this letter, however, we suggest a simple but fairly effective way to overcome the high frequency limit by intentionally inserting parasitic capacitance introduced from multiple slits. The parasitic capacitance connected to the varactor diodes in series can decrease overall capacitance to an optimum value. Consequently, we not only can maintain good absorption rate in a very high frequency region, but also freely select a target absorption frequency band by modifying the number of slits. Experiments for normal and oblique incidence have been carried out to validate the proposed method. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:145–148, 2017

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.