In this paper, a light-controlled frequency reconfigurable antenna is presented for 5 G, WLAN, and radio altimeter applications. The given (44 × 28) mm2 antenna consists of a radiating V-shaped structure and three stub arrangements. The main λ/2 length stub is used to feed the antenna and the two λ/4, λ/8 length open-circuited stubs are located perpendicular to the main feeding stub for tuning the frequency of the antenna. The length of the stubs can be adjusted by placing (4 × 1.2) mm photodiode switches on the perpendicular stubs. Four experiments are carried out to analyze the performance of the antenna. When light and DC bias voltage is not applied (Experiment-1) to the photodiodes the proposed antenna radiates from 4.1 to 4.63 GHz with 12% bandwidth. When light is applied to the photodiode without DC bias voltage and DC bias voltage is applied without light (Experiment-2,3) the antenna reconfigures its frequency band from 3.43 to 3.6GHz and 4.8 to 5.4 GHz with 4.85% and 12% bandwidth respectively. The antenna shifts the radiation from 4.8 to 5.5 GHz with 14% bandwidth when the light and DC bias voltage is applied to the antenna(Experiment-4). The measured gain of the proposed antenna is greater than 3.8dBi in all the experiments.

In order to restrain the prepulse of a high energy fluence diode, a flash-over switch made of a nylon cylinder was inserted in between the cathode stalk and the cathode. Secondary prepulse technique was developed to lower the flash-over voltage of the switch. It was found that the surface resistivity of the nylon insulator changes considerably after each shot and this resistivity on the order of 107 Ω/m is most suitable for a 20-mm long flash-over switch to operate stably at a lower flash-over voltage.

An electron-beam accelerator based on spiral water pulse forming line which consists of a primary storage capacitor system, an air core spiral strip transformer, a spiral pulse forming line of water dielectric, and a field-emission diode, is described. The experimental results showed that the diode voltage is more than 500 kV, the electron beam current of diode is about 24 kA, and the pulse duration is about 200 ns. The main parameters of the accelerator were calculated theoretically. The distributions for electrical field in the pulse forming line were obtained by the simulations. In addition, the process of the accelerator charging a spiral pulse forming line was simulated through the Pspice software to get the waveforms of charging voltage of pulse forming line, the diode voltage and diode current of accelerator. The theoretical and simulated results agree with the experimental results. This accelerator is very compact and works stably and reliably.

An electron-beam accelerator, which consists of a primary storage capacitor system, an air core spiral strip transformer, water Blumlein line of water dielectric, and a field-emission diode, is described. The experimental results show that the diode voltage is more than 400 kV, electron beam current is about 40 kA, and the pulse duration is more than 80 ns. This accelerator is very compact and works stably and reliably.

Mg has been widely used as p-doping species despite its intrinsic difficulties. It is nowadays well established that during the growth process of Mg doped GaN, atomic H is generated from the decomposition of NH3 and Mg-H complexes are formed in the layer. This has been for instance shown by the occurrence of LO mode in IR absorption, and by the observation of the Mg-H local vibration modes. This H passivation limits the electrical activity of Mg, therefore an activation process is required to get full activation of the Mg atoms. In the present study, bismethylcyclopentadienyl magnesium [(MeCp)2Mg] was used as precursor. However, this precursor reacts in the gas phase with NH3 to produce tiny solid particles as evidenced by a very bright diffuse emission visible along the laser beam used for reflectometry measurements. This simplest obvious product would be [(MeCp)Mg(NH2)]m(m≥2). To limit this drawback, Ga and Mg precursor lines have been separated. With proper in situ heat treatment, doping densities up to 1.5×1018 cm−3 have been obtained. PL spectra of lightly Mg doped samples (1016 cm−3) are dominated by shallow donor-acceptor pairs whereas for higher doping densities ( 1018 cm−3), the luminescence is dominated by a broad band in the 2.7-2.9 eV range. GaN LEDs were fabricated from Si doped (n-type) and Mg-doped (p-type) GaN, these LEDs emit in the blue-UV range.

Room temperature (RT) pulsed operation of blue (420 nm) nitride based multi-quantum well (MQW) laser diodes grown on c-plane sapphire substrates with lifetimes exceeding 6 hours have been demonstrated. Threshold current densities as low as 12.7 kA/cm2 were observed for 10×1200 μm lasers with uncoated reactive ion etched (RIE) facets. The emission is strongly TE polarized and has a sharp transition in the far field pattern above threshold.