Narrow-band microstrip antenna array for a robust receiver for navigation applications

Abstract

The design of navigation receivers for safety-of-life (SoL) applications requires the system to be robust against interference coming from several different sources, such as hand-sets and base stations for mobile communications, and radars. One way to minimize the effects introduced by such interferers is to place a filter with low insertion loss between the antenna and the low-noise amplifier (LNA). In order to increase robustness, the antenna itself can be designed to be narrow-band, so that only low power levels in the out-of-band region are received.

In order to receive only the L1 band of the Galileo system (1.565 – 1.585 GHz), a narrow-band antenna may be used. This paper describes the design of an active microstrip antenna array that is under development with this frequency-selective characteristic. The geometry of the single antenna is composed of a square patch, which is located at the top of the multilayer structure, the slots, which are in the middle, and the feeding system, which is at the bottom. During the design process of this antenna, several parameters can be used to obtain a good matching inside the band of interest and a strong reflection (low gain) outside of it. A 90°-hybrid has been integrated in order to generate circularly polarized waves. The variation of the gain in the band of interest is about 0.6 dB. At the region of GSM, the rejection is at least 14 dB, which is higher than it would be obtained with an ordinary microstrip antenna.

The antenna described above will be used in a 2x2 array, where each patch will be connected to an LNA. In order to compensate for the differences of the S-parameters of the used amplifiers, a calibration is necessary. For this purpose, a directional coupler has been integrated at the output of the 90°-hybrid. It will be used to couple the calibration signal to the input of the active part. The structure described above is under construction at the moment and a better description will be given in the final version of this paper and in the conference. Also, a study of the radiation properties of the 2x2 array under different beamforming conditions will be presented.