In this study, we have fabricated the high-power GaNbased vertical light-emitting diodes (VLEDs) by exploiting a thermally stable nano-scaled Ni-Ag-Ni-Au mirror. After being treated at 600 C for 1 min in air ambient, the nano-scaled Ni-Ag-Ni-Au (5/2000/1000/2000 Å) mirror shows the specific contact resistance of cm and its reflectivity has increased from 89.5% to 93.0%. The increment in the reflectivity is due to the diffusion of Ni contact layer into Ag layer. Moreover, the reflectivity of the mirror has hardly deteriorated even after the wafer was thermally bonded with graphite substrate at 320 C for 5 min, meaning that the proposed mirror is thermally reliable. The light output power of the nano-scaled VLED (Chip size: 1 1 mm ) with thermal treatment at 600 C for 1 min is enhanced by 8% as compared to one without thermal treatment at an injection current of 350 mA. To our knowledge, our nano-scaled mirror has the highest reflectivity among other Ag-based multilayered reflectors, and thus it is a promising candidate for high-performance VLED.
Index Terms-GaN, light-emitting diodes (LEDs), light output power, thermally stable mirror, wafer bonding.
It is essential for the near-field receiving measurement to make beam pattern and check the performance of a active phased array antenna system. Also, we could obtain compensation value for mono-pulse function through the near-field receive test, however, if the radar has many frequency channel, the test would take long time and hard effort. So it is needed that frequency channels are selected for measurement and calculates the values for other frequency channels to improve efficiency in development and manufacture. In this case, the phase variations in sum and del channels would be checked. The phase measurement includes un-linear characteristic because of wrapping effect. Generally, radars have similar path length in sum and del channel, but if a radar has a electrical length gap between sum and del channel, errors could occur by phase's wrapping effect. In this paper, the interpolation method's error caused by electrical length gap is checked and the effective method for frequency channel selection to avoid wrapping effect is introduced.
An 3D radar system can detect the distance, azimuth, and altitude of targets. The radar acquires target information using an electronic or mechanically steered narrow antenna pattern. It calculates the target altitude using the detected information. In addition, angular accuracy is improved by applying various methods such as monopulse. The radar angular accuracy is affected by external factors such as multipath effects that are caused by various factors such as the radar installation environment and the flight altitude of the target. Radar systems apply various methods to improve the detection accuracy degradation caused by multipath effects. The squinted sum monopulse method can reduce the detection errors of the radar in a marine environment with a high frequency of multipath effects. The radar utilizes a different monopulse pattern that calculates an angular error with a sum pattern steered upwards of the detection beam. This is a method of minimizing the influence of the multipath received signal incident downward through a difference pattern in which the gain falls sharply below the detection beam. In this study, the effect of the squinted sum monopulse method was verified through simulation, and the effect was confirmed by applying it to an early warning radar installed in a sea environment condition.
It is necessary to check the fault of phased array antenna, when the active phased array radar installed in the site is suspected performance degradation due to external impact or long-term operation. However, the near -field test should be performed in anechoic chamber in order to measure the phased array antenna, so that much time and cost must be applied for radar disassembly and transportation, and the operational availability of the radar system is deteriorates. Therefore, we propose a near-field scanner with mobility to check the fault of the phased array antenna at the site, and the effectiveness of the proposed scanner was verified with ±0.5dB magnitude and ±1.5°phase in comparison with measured data in anechoic chamber.
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