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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

A frequency reconfigurable dipole antenna based on a silicon radiator is presented. The silicon radiator is activated with the aid of highly dense solid-state plasma by injecting carriers into the intrinsic region of p-i-n diodes. The fabrication and design guideline of the reconfigurable dipole antenna with this plasma radiator are described. When the plasma radiator is activated or deactivated, the length of the dipole arm changes, which means that the operating frequency of the dipole antenna is reconfigurable. When all the channels in the plasma radiator are activated, the operating frequency is tuned from 6.3 GHz to 4.9 GHz. The measured tunable bandwidth of our fabricated dipole antenna is approximately 31%, which is a practical value in comparison to conventional frequency reconfigurable antennas whose tunable bandwidth is in a range from 20% to 50%. To further support the validity of our results, we provide the well-matched simulation results from an antenna simulation. These results demonstrate that silicon with its commercial technology, which has not attracted attention in comparison to a metal antennas, is a promising tunable material for a frequency reconfigurable antenna. This plasma-based reconfigurable antenna has great potential for use in the dynamic communication environment.

For the first time, this study demonstrates a reconfigurable antenna with electrical beamforming that is entirely integrated by semiconductor microfabrication technology. In this paper, a vertical structured array of solid‐state plasma which acts as a reconfigurable conducting wall to control the main beam direction of an antenna is proposed. In many conventional works, insufficient electrical conductivity of turned‐on plasma channels at the planar surface of PIN diodes causes an inherent large loss and low radiation efficiency of silicon‐based antennas. However, in this study, the overall performance of the antenna is notably enhanced by adopting the vertical plasma channels which solve the lower electrical conductivity problem of the surface‐type plasma structure. Accordingly, the proposed antenna achieves a high realized gain of more than 5 dBi over a frequency range of 27.5–29.6 GHz, even though it is comprised of lossy silicon with high permittivity. In addition, the low cost and electrically reconfigurable antenna, which benefits from the highly precise semiconductor fabrication process, is applicable to sub‐THz applications with a lightweight and compact sized feature. This work paves the way to make silicon antennas with commercial microfabrication technology a next‐generation antenna.