The radiation pattern of a car antenna is evaluated with the power received by its antenna in mobile communication environments. In the evaluation, the horizontal radiation pattern is assumed to be omnidirectional; the vertical one is expressed in terms of the main beam direction θ1 and the half-power beamwidth θBW. The received power is calculated from such a radiation pattern and an angular probability density distribution of wave arrival. The distribution is estimated using a propagation model to simulate radio propagation paths and surroundings of them in urban areas. The tendency of the estimated distribution is in good agreement with that of the measured one. It is clarified from the estimated results that the angular probability density distribution of wave arrival strongly depends on the street angle ψ. Since the received power calculated from the distribution also depends on ψ, the minimum value (minimum received power) in the received power for ψ=5, 10, 15, , 85 is used to evaluate the radiation pattern. From the view that the radiation pattern for which the minimum received power is highest is suitable for mobile communications, it is revealed that θ1 and θBW in the suitable radiation pattern of the car antenna are roughly 20 and 15, respectively.

Theoretical and experimental studies are made in the UHF band on a quarter wavelength monopole and a half wavelength dipole located on a trunk-hood of a car. To calculate vertical radiation patterns, the theoretical model of the car body and the GTD approach are adopted. It is confirmed from a comparison between calculated and measured results that the theoretical model is very useful to analyze the trunk mount antenna performance and the effect of the body can be well examined with it. The results of pattern calculation for two type of antennas show that vertical radiation patterns, especially the pattern in the front direction of the car, depend largely on the car body. That is, many sharp lobes appear in the vertical pattern, and further, the shape of the lobe and the gain vary largely with the change of the antenna height and location. An approach of this kind can be effectively utilized as a design tool to estimate the radiation performance of mobile antennas.

This paper presents a method for simply estimating characteristics of signals received by a millimeter wave car radar. In this method, the substitution of a radar target with a set of scattering points is introduced to take account of the phenomenon that only a part of the target is irradiated with the radio wave from the radar antenna with a sharp beam; the phenomenon is peculiar to the car radar which operates in a compact range. The positions of these scattering points and the RCS values for the scattering points are appropriately determined on the basis of a measured RCS image for the target. The RCS image means a spatial distribution of RCS values on the surface of the target. In addition, influence of the ground, which is a dominant clutter in car radar environments, and characteristics of the car radar hardware can be included in the estimation method. The estimated characteristics of the signal received by the car radar are compared with the measured ones under typical cases in the car radar environments. The comparison verifies not only that the received signal characteristics are well estimated even when the range is rather short but also that the substitution of the target with scattering points is valid. The proposed method can realize the estimation of the received signal characteristics. Furthermore, the method can be developed into a computer simulation for evaluating the target detection performance of the car radar.

We propose a method for accomplishing accurate RCS (Radar Cross Section ) images of a car in a compact range. It is an improved method based on an ISAR (Inverse Synthetic Aperture Radar) technique. To obtain accurate RCS values, an idea of an image correction function for the Fourier transform used in the ISAR processing is introduced. The role of the image correction function is to compensate the difference of the propagation loss as to the different scattering points on a target. As a result, `sensitivity' of imaging in the compact range is kept uniform. Hamming window is suitable for the Fourier transform to accomplish RCS images because of its low sidelobe level and the sharpness of a mainlobe. When hamming window is adopted, the spatial resolution is approximately twice the size of granularity which is determined by the ISAR parameters. To verify the improvement of the RCS images obtained by means of our method, several numerical target models are employed. The results of the investigation show that uniformity of `sensitivity' for obtained RCS images is achieved in the compact range and accurate images with the resolution of twice the size of granularity are accomplished without blurs or distortions in the unambiguous area. RCS images for rear aspects of a passenger car are investigated with the spatial resolution of 50 mm in the 60 GHz band. The RCS image varies with the aspect angle of the car and the specular reflection occurs for the millimeter wave. When the curvature on the car edge is small, a blurred RCS image is observed. The reason is that a scattering center of the specular reflection moves so widely that it can't be regarded as a fixed point. This causes elongation of the RCS image. A peak value in the dominant area for each aspect angle is less the 0 dBsm and no remarkable areas where the RCS value exceeds-20 dBsm is found any more on the car except such the dominant area.