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Microstrip antennas inherently have a high input impedance at resonant frequency. This may not be convenient for some applications. For active integrated antennas, moreover, the radiated power of microstrip antennas needs to be very low at harmonic frequencies. The main goals of this study are impedance matching and harmonic suppression of microstrip antennas. In order to meet these requirements, two one-dimensional (1-D) photonic bandgap (PBG) structures, namely, the defected ground structure (DGS) and the compact microstrip resonant cell (CMRC), are applied to the feed line of microstrip antennas. The characteristic impedance of the microstrip line is controlled by the additional effective inductance of the PBG structure. Without any matching circuits, microstrip antennas can be easily fed by a simple 50Ω microstrip line with a PBG structure at the operating frequency. Additionally, the second harmonic of the proposed antennas is properly suppressed compared to a conventional antenna. Measured results Indicate that the two PBG structures are quite effective for harmonic suppression. Therefore, the proposed antennas are suitable for active integrated antennas. [ABSTRACT FROM AUTHOR]

InGaN quantum-well (QW) green laser diodes (LDs) with an emission wavelength of 483.7 nm were characterized by controlling the injection pulsewidth. The emission wavelength of LDs showed a large blueshift (> 20 nm) of spontaneous emission peak with increasing injection current below the threshold current. The huge blueshift was ascribed to the deep In localization states and the strong piezoelectric field in the green InGaN QW structure with higher In contents than conventional violet/blue InGaN QWs. However, the lasing wavelength of LDs was slightly redshifted by increasing the injection pulsewidth due to the thermal heating effects. [ABSTRACT FROM AUTHOR]

A novel technique for designing a tunable dual-band microstrip patch antenna is proposed. Dual-band operation is easily achieved by loading a microstrip patch antenna with one varactor diode placed on a small gap between a square patch and a parasitic strip. It is observed from the measured result that the proposed antenna shows a wide tuning range at the two resonant frequencies. [ABSTRACT FROM AUTHOR]

Abstract-A novel design of patch antennas with polarization diversity is proposed and experimentally studied in this letter. A pair of L-type slits is embedded into the edge of square patch and the shape of the slit is changed according to ON- or OFF- state of PIN diode. Therefore, the proposed patch antenna has different polarizations. The novel structure we describe here enables the optimization of the input match for both polarizations. From the measured result, low cross-polarization levels in the linear state and good axial ratios in the circular state are observed. [ABSTRACT FROM AUTHOR]