A monolithic linear power amplifier IC operating with a single low 2.7-V supply has been developed for 1.9-GHz digital mobile communication systems, such as the Japanese personal handy phone system (PHS). Refractory WNx/W self-aligned gate GaAs power MESFETs have been successfully developed for L-band power amplification, and this power amplifier operates with high efficiency and low distortion at a low voltage of 2.7 V, without any additional negative voltage supply, by virtue of small drain knee voltage, high transconductance and sufficient breakdown voltage of the power MESFET. An output power of 23.0 dBm and a high power-added efficiency of 30.8% were attained for 1.9-GHz π/4-shifted QPSK (quadrature phase shift keying) modulated input when adjacent channel leakage power level was less than -60 dBc at 600 kHz apart from 1.9 GHz.

Space division multiple access (SDMA) is an attractive technique to increase the channel capacity of wireless communication systems. In this paper, we first propose a new process to accomplish SDMA using an adaptive array at a base station receiver of broadband fixed wireless access (FWA) systems. Unlike other methods, the proposed process does not need highly accurate direction-of-arrival (DOA) estimation and is suitable to Directionally Constrained Minimization of Power (DCMP) algorithm in order to serve multiple fixed terminals. A newly modified DCMP with phase only control is proposed as well. The algorithm to control phase weights, uses only the array output power and does not require the complex baseband signals from individual array elements. The pattern measurement results in an anechoic chamber show that the proposed algorithm can direct a null to an interference while maintaining the gain to the desired signal.

This paper proposes a multiband automatic tunable antenna system for wide frequency bands of 704-2690MHz for cellular wireless communication systems. The proposed system controls variable capacitors connected between the antenna and a transmitter based on the received power of a probe. Locating the probe near the tip of the antenna enables frequency-a operation. The antenna is a multiband two-arm monopole antenna printed on a 60mm × 10mm area of a 60mm × 100mm FR-4 printed circuit board (PCB). The probe is a small dipole antenna capacitively coupled with the antenna. Fine-tuning based on simple hill-climbing optimization compensates the mismatch due to the surroundings, e.g., a user's hand/head or desk assuming channel-informed rough-tuning beforehand. A prototype consisting of varicap diodes and some other devices demonstrates automatic tunability.

Broadband fixed wireless access (FWA) systems offer significantly higher bit rates than current cellular systems to which adaptive arrays are partly applied. Digital beam forming is being eagerly explored on account of its flexibility, but it will be difficult to apply to the high-speed systems, because its digital signal processing requires huge resources and power consumption. Conventional phased arrays, on the other hand, utilize phase shifters through RF or IF signal lines, but the phase shifters are usually both bulky and expensive. The authors propose an adaptive array steered by IF local signal phase shifters in this paper. The phase shift and the frequency shift of the signal from each antenna element can be simultaneously accomplished at the down conversion stage by the phase-controlled local signal. A prototype receiver operated in the K-band with the proposed configuration and its beam pattern measurement results are also described.

Multi-path propagation structure in the urban mobile communication environment of 25 GHz band has been measured by means of newly developed "multi-path propagation parameter measurement equipment," which is capable of estimating coupled DOA (Direction Of Arrival), TOA (Time Of Arrival) and relative field strength by super resolution techniques. Before measurement, basic performance of the equipment has been evaluated in the anechoic chamber in order to ascertain limitation on measurement. For practice and verification of outdoor propagation characteristics, basic data have been collected in a works where accurate buildings and road layout is known. Sub-sequently, data have been collected in the urban mobile communication environment and following characteristics have been confirmed. 1) DOA and TOA of wave reflected by the side of building almost follow the ray-trace. 2) Street trees make 25 GHz band wave attenuate. 3) There are such unusual cases that it is possible to communicate in spite of out of line-of-sight by multi-path propagation. 4) Narrow streets have very complicated propagation structures. Finally, technologies that should be developed for the high-speed digital mobile communication are proposed based on the measurement results.