The paper presents a way of narrowing the width of the sensitive area of radio-wave Doppler sensor. This is important when the sensor is used for oscillating measuring or biomedical research to eliminate the influence of extraneous moving objects that are in the process of getting into the lateral region of the antenna radiation and cause false positives or errors in the measurements. As a form of radio-wave Doppler sensitive area of the sensor is determined by the pattern of the antenna, in this paper, for its narrowing decided to use a special antenna system. This antenna system provides formation of two different shape patterns - basic and compensation, followed by the formation of difference signal information in the processing circuit.
To implement antenna system two microstrip radiators rectangular shape are used - basic and additional connected by an electronic switch on p-i-n diodes. When the switch is disconnected, only the main radiator is involved in the radiation. It forms a radiation pattern with maximum normal to the plane of the radiator but with a high level of lateral radiation. This is the basic mode of operation of the sensor.
In the closed state of electronic switch additional radiator is connected to the main. Options of antenna system chosen so that high-frequency energy is distributed about equally between the emitters, but the phase of the emitted waves are opposed. As a result, compensation radiation pattern appears that provides lateral radiation level comparable to the level of radiation the primary side of the radiator. However, in the normal direction is a minimum of energy. By subtracting signals obtained during open-loop and closed states of the electronic switch narrowed sensitive area is formed.
The paper presents the equivalent circuit of the antenna sensor that allows for the simulation of its basic parameters. Modeling of the sensitive areas in different states of the electronic switch was carried out. The causes that affect the distortion of sensitive areas determined.
Experimental model of radiowave sensor with designed antenna system was made. The material used foiled fluoroplastic. Operating frequency is 2.63 GHz. Experimental studies in the laboratory showed a narrowing of the width of the sensitive area. Suppression of the side information signal lines over 10 times, compared to the conventional mode of operation of the sensor. In this case, the amplitude of the information signal from the main direction merely reduced by 40%.