Osamu Shibata

Spatial optical beam-forming network for receiving-mode multibeam array antenna - proposal and experiment

This paper proposes an array antenna for multibeam reception with a beam-forming network (BFN) that uses spatial optical signal processing and also presents experimental results. In this antenna, signals received at individual antenna elements are converted to optical signals, and are optically divided from the directions of signal arrival by means of optical spatial Fourier transformation, and then the optical signals are reconverted into microwave signals at the BFN. In this BFN, to maintain optical path-length conditions, an optical integrated circuit is employed. We have experimentally investigated the optical signal processing performances of the BFN for multibeam reception. The experimental results show that optical beam direction is changed according to the signal arrival direction of an array antenna. Two multiple RF signals with different phase distributions are separated. The sidelobe level of the optical signal is reduced when amplitude distributions of optical signals are Chebyshev distributions. We also present the signal transmission behavior of this BFN. The measured carrier-to-noise-ratio degradation of this BFN is 2 dB at BER=10/sup -6/ when 118.125-Mb/s QPSK modulated signal is input into the BFN.

Receive mode of optical signal processing multibeam array antennas

A receive mode of the optical processing array antennas is presented. In this receive mode, the transmitting radio frequency (RF) signals generated by optical processor will be shifted as local oscillator (LO) signals, and the received RF beams will be discriminated in the downconverted intermediate frequency (IF) frequency domain by a mixer array between the optical processor and antenna elements. A proof-of-concept experiment for a two-beam and four-element array antenna is demonstrated, and the received IF power distributions for each beam have very good agreement with the calculated antenna patterns.

Spatial optical processing array antenna for multibeam reception

We propose a multibeam receiving antenna using spatial optical processing technique in a beam forming network. Also we experimentally investigate the basic performance of optical-microwave conversion, a key technology for achieving this antenna.

An adaptive array for high speed wireless local loops steered by local signal phase shifters

We propose an adaptive array steered by local signal phase shifters for high-speed wireless local loops. An adaptive array used as a radio receiver usually requires one or more frequency conversion sections to achieve acceptable sensitivity performance. The phase shift and the frequency shift of the signal from each antenna element can be accomplished simultaneously at the down-conversion stage by phase-controlled local signals. The configuration can avoid the additional loss or noise in the received signal due to the phase shifter itself, and ordinary commercial quadrature modulator ICs for mobile communications can be utilized for the CW local phase shifter. The adaptive array does not require high speed digital signal processing sections with fast AD converters for all of the array elements. In this paper, we describe the practical configuration of the array as well as pattern measurements in the S-band for a prototype including the essential elements.

A multibeam receiving array antenna by means of spatial optical signal processing

A multibeam receiving array antenna requires a beam-forming network (BFN) to separate signals according to the direction of signal arrival. When compared with conventional techniques which use a microwave BFN or the digital beam-forming array antenna, spatial optical signal processing has advantages with respect to the bandwidth, circuit complexity, size and weight. Spatial optical signal processing is a technique that uses optical spatial Fourier transform characteristics. ATR has proposed a beam shaping, beam scanning and multiple beam transmitting array antenna that uses spatial optical signal processing. In addition, we have proposed the concept of a receiving mode spatial optical signal processing array antenna. We show the configuration of our receiving mode spatial optical signal processing array antenna and also experimental results for the optical radiation patterns of a spatial optical signal processing BFN. The results for the radiation patterns are in good agreement with theoretically calculated values.

Beam formation by using optical signal processing techniques

We discuss the array antenna beam forming and multibeam operation controlled by an optical processor which performs signal processing by means of Fourier optics. We also give the antenna radiation pattern analysis, antenna system parameter evaluation, as well as a comparison with measured data.

Periodical intermittent interference suppression algorithm for 2.4-GHz-band adaptive array

The intermittent interference periodically radiated from a microwave oven degrades the performance of 2.4-GHz-band wireless LANs. We discuss the intermittent interference suppression technique using an adaptive array. We have proposed a low-cost analog beamformer called an adaptive array steered by local phase shifters (AA-LPS) which is suitable for high data rates. A null forming algorithm for the AA-LPS has also been proposed. This algorithm suppresses incoming interferences by minimizing the output power of the array. The advantage of the algorithm is that the weights are calculated using the output level of the array instead of the array input vector. To apply the algorithm against an intermittent interference, we modify the sampling timing of the algorithm. The modified algorithm samples only during the microwave active periods. A beam pattern measurement using the AA-LPS with 6 elements shows that the proposed algorithm directs a null to the microwave oven, and a throughput measurement based on the cyclic transmission of a 1500-byte packet shows that the AA-LPS can significantly improve the throughput.

Optical SCM transmission multiplexing IF and local signals for adaptive array

There has been much interest in the application of adaptive array antennas to wireless communication systems. To keep base station (BS) requirements simple, it is advantageous to separate the array antenna in a BS from a signal processing unit in a central station (CS) and link them by optical fiber. Several approaches have been proposed. In these approaches, due to ambient temperature changes, phase differences among antenna branches cannot be kept constant between a CS and a BS so that the antenna radiation pattern changes. We introduce a new configuration for optical subcarrier multiplexing (SCM) radio-on-fiber (ROF) transmission, which can avoid the above difficulties. In this system, the SCM signal comprises all antenna branch signals and all local signals for original frequency conversions. While the proposed system is simple, the phase difference among antenna branches can be maintained to be constant in spite of fiber length fluctuation. Furthermore, only a pair of optical transceivers and optical fibers for downstream and upstream lines is required between a CS and a BS. We show the results of several experimental investigations.