Shuji Kobayakawa

A blind calibration method for an adaptive array antenna in DS-CDMA systems using an MMSE algorithm

A new blind calibration method is proposed to compensate for the amplitude and phase errors in the antenna branches of DS-CDMA base stations with adaptive array antennas. The proposed method calibrates these errors using the MMSE (minimum mean square error) algorithm, requiring only the received (or transmitted) signals at the array antenna and not requiring any additional reference signal to be inserted for calibration. The proposed method and structure can be applied to both the downlink and uplink. The fast convergence property of this method ensures a tracking capability against amplitude-phase variances. In an uplink, using the proposed calibrator, a beam steering adaptive array antenna based on a directional finding algorithm of a desired signal has a BER performance that improves by about 2 dB at the BER of 10/sup -3/ when a non-linear RF amplifier is used. We have also evaluated the downlink performance of this method when a non-linear RF amplifier is used and have confirmed its robustness against that of the amplifier.

Simple retractable monopole antenna with small mismatch loss and high radiation efficiency for cellular portable phones

We studied a simple retractable monopole antenna for cellular portable phones using computational and experimental analysis. This antenna configuration uses an antenna element, consisting of a straight conducting wire in both the extended and retracted positions, by changing the feed point on the element. We found that the optimization of some parameters, such as the element length and the feed point, enable the input impedance of the retracted position to be adjusted to that of the extended position. This characteristic guarantees a low mismatch loss in both the extended and retracted positions. We also discuss the effect of the terminal height and the gap width between the element and the terminal. The numerical simulations and experiments using a simplified model prove that this antenna configuration has an excellent return loss characteristic above 20 dB, even in the retracted position, and that also it has a high efficiency of 85% in the extended position including the matching circuit loss. Since this antenna configuration also provides a spatially efficient and mechanically durable structure, we used it in a cellular portable phone.