Yousuke Tajima

Improvement of Beam Scanning Characteristics of a Dielectric Lens Antenna by Array Feeds

In the Intelligent Transportation System, millimeter waves are used and antennas are required beam scanning ability. In the millimeter wave operation, a lens antenna is one of the prominent candidates which achieves wide angle beam scanning. Wide angle scanning can be achieved by introducing Abbe sine condition to lens surface shaping. Authors designed the shaped lens antenna that could achieve beam scanning ±30°. The narrow beam widths were maintained on the scanning plane. However, the beam widths were broadened on the transverse plane and large gain reduction was appeared. It was clarified that the reason of this beam deterioration was due to the phase delay on the antenna aperture. In this paper, an array feed composed of a group of rectangular horns is employed to compensate the phase delay on the antenna aperture. In designing the array feed, because there were no examples of phase radiation pattern synthesis, a new radiation pattern synthesis method is studied. Ability of the weighting matrix contained in the Least Mean Square synthesis method is paid attention. Adequate weighting matrix is found out. Satisfactory phase radiation pattern that can compensate the phase delay and an adequate amplitude radiation pattern are achieved. As a result, the improvement of scanned beam widths and antenna gains through the array feed are ensured. And adequate horn arrangements of the array feed for improving scanned beam are clarified. Moreover, in order to examine the realization of an actual array feed, the exact electromagnetic simulation is conducted. The validity of the radiation pattern synthesis is clarified.

Radiation pattern synthesis of an unequally spaced array antenna

The IMT 2000 mobile communication system uses the 2 GHz band so the base station antennas are expected to operate in the frequency band of the conventional systems (800 MHz, 1.5 GHz) and the new system (2 GHz). In the multi-frequency operation, an unequally spaced array antenna has the advantage of suppressing grating lobes produced in the higher frequency bands. This paper proposes a radiation pattern synthesis method for an unequally spaced array antenna. The LMS (least mean square) method is employed. As an initial study, the ability of designing low sidelobe patterns is shown. In order to improve the design accuracy, a matrix that enables weighting of the radiation pattern is introduced. Adequate value of weighting is studied and excellent low sidelobe patterns are achieved.

Design of dielectric lens antennas producing sharp caustics

Important design components of achieving wide angle beam steering are pursued. Wide angle beam steering antennas must have sharp caustics over all steering angles. Lenses satisfying Abbes sine condition can maintain sharp caustics even though the beam is scanned. Design methods of lens surfaces achieving this condition were developed. Numerical examples of lenses satisfying and not satisfying Abbes condition are shown.

RCS Measurement of a Scale Model Rocket

In this paper, measured results of RCS characteristics of a scale model rocket are obtained and are compared with the theoretical results. In order to determine the relation of received level unit [dBm] and the RCS unit [dBsm], circular disks are employed for calibration. Exact measurements method of RCS is confirmed.