Study of Traveling-wave Series-fed Microstrip Array with a Low Sidelobe Level for Vehicle Radar

Abstract

A microstrip array antenna design technique suitable for vehicle radar applications has been studied, and its effectiveness has been verified. The vehicle radar is operated close to the ground and there are many clutters in the vicinity. Thus, array antennas are needed to achieve high directivity, and the radiated power of each radiating element must be controlled to achieve low side lobe characteristics. In addition, broadband characteristics are desired to increase the radial resolution, and traveling wave series feeding is preferred to reduce the radiation loss. In order to satisfy all these characteristics, it is desired to be able to control the radiated power and matching of the individual radiating elements at the same time In this research, three types of microstrip devices are used to solve the problem of controlling the radiated power and matching of the individual radiating elements at the same time. The element type is selected according to the desired ratio of radiating power to input power for each element on the series feed line. The specific design parameters and element spacing have been studied. Based on the proposed technique, the 1x8 1-dimensional traveling wave array was designed, fabricated and measured to show the low side lobe characteristics over broad bandwidth. The proposed technique has been implemented as a design automation program. A high-gain 32x20 two-dimensional array antenna for front radar was designed using the proposed design technique. Through actual fabrication and measurement, the designed array antenna has been shown to have high gain and narrow beam width, low sidelobe level and wide band operation characteristics. In addition, radar tends to evolve to have the ability to scan elevation and azimuth direction in real time, so we designed a two-dimensional array antenna capable of elevation and azimuth scan. The antenna is designed to control the elevation of the main beam by changing its center frequency and to control the azimuth through the phase change. Near-field radiation characteristics were collected through near-field measurements of the designed antenna, and it was confirmed that the elevation and azimuth control of the main beam according to the center frequency and phase change were possible through data processing. In vehicle radar applications, it is usually mounted behind the bumper or fascia. At this time, the electromagnetic wave radiated from the antenna forms a pattern different from the pattern in free space due to interference by a bumper or fascia. It is unrealistic to use a full-wave-based commercial electromagnetic wave simulator, which requires huge computation time and memory resources to simulate such interference effects. We have developed an interference effect analysis algorithm based on the near-field-to-far-field transformation technique and ray tracing method. A two-dimensional array antenna with high gain and reference fascia was used to analyze the effects of the fascia and was experimentally verified by measurement.