Development of Microstrip Decimeter Antennas with Circular Polarization

Modern design variants of microstrip antennas with circular polarization are considered, in which circular polarization is created using single-point and two-point power supply. To manufacture the studied antenna model with circular polarization, the simplest form of the antenna was chosen; the one with a radiator in the form of a continuous circle, which is powered by a two-point scheme. With regard to use in intra-object telemetry systems, the frequency of operation range of 640 ... 650 MHz was chosen. Two options for a two-point power supply of such an antenna were studied - with the help of a symmetrical and asymmetric square strip bridge. Calculation, coordination and tuning simulation of power divider variants were performed. As a result, the manufactured layout of the first antenna design turned out to be three-layered, the second - two-layered. The technique for creating antennas includes an estimated calculation of geometric dimensions, which was further refined using computer simulation in the CST Microwave Studio program. Frequency tuning of the completed antenna layouts is carried out using adjusting teeth along the contour of the round radiator. The study of the created antenna layouts showed better manufacturability and stability of the characteristics of a two-layer structure compared to a three-layer one. Therefore, a two-layer round antenna with a point-to-point power supply was chosen for production. It is designed for telemetric radio channels inside enclosed spaces. The measurements performed showed that the manufactured antenna operates in right-hand circular polarization with an ellipticity factor of 1.2 dB. The standing wave ratio in the operating frequency band of 640…650 MHz did not exceed 1.32, the gain was at least 5 dBi, the width of the radiation patterns in two planes was 95 and 93 angular degrees, respectively. The antenna provides for an operation mode as a transceiver, since the decoupling of the receiving and transmitting paths is carried out due to different polarization, for which it is necessary to connect the second input of the power divider instead of a balanced resistor to the receiving device.