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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