Design And Research On Circularly Polarized Periodic Microstrip Leaky-Wave Antenna

As the front terminal of communication system,antenna has an indispensable role.With the continuous development of communication system,the traditional antenna with large scale and sole performance can no longer satisfy the requirements for application in modern communication system.Circularly polarized antennas are good candidates for present communication systems because of unique propagation characteristics of handed orthogonality.Meanwhile,the microstrip leaky-wave antenna is a kind of traveling-wave antenna,which has been extensively investigated in recent years because of its superiority with high gain and frequency sweep characteristics.In this paper,it is proposed that a method to achieve circular polarization by rotating and arranging right-angle triangular metal patches in parallel in a unit on the transmission line by series feeding to obtain a circularly polarized leaky wave antenna.Based on this method,three models are fabricated,which will be presented in three parts as follows:Firstly,it is designed a circularly polarized leaky wave antenna based on an isosceles right-triangle metal patch operating in the frequency band of 15.9 GHz-28GHz(with a relative bandwidth of 54%).The antenna structure is periodically to introduce isosceles right triangle metal patches on both sides of the transmission line.By loading the slot,the antenna axial ratio bandwidth is improved.It is shown that the proposed antenna achieves a beam scan of-30°-18°,a 3 dB axial ratio bandwidth of22.5%(18.5 GHz-23 GHz),a circular polarization scan angle of-8°-16°,and a maximum gain of 17.32 dBic.Secondly,a circularly polarized leaky wave antenna with a right-angle triangular metal patch arranged in a single-row is designed.The antenna is connected with four right-angle triangular patches for units,and the internal reflections are eliminated by rotating and arranging them in parallel on one side of the transmission line,thus achieving an no attenuation circularly polarized scan of the antenna main beam in the broadside.The operating band of the antenna is 18.6 GHz-34 GHz(58.6% relative bandwidth),the beam scanning angle is-56°-40°,the 3 dB axial ratio bandwidth is 30.5%(21.4 GHz-29.1 GHz),and the circular polarization scanning angle is-19°-22°.The average gain of the antenna is 13.41 dBic,and the average radiation efficiency is 68%.Finally,a circularly polarized leaky-wave antenna with a double-row arrangement of right-angle triangular metal patches is designed.To improve the radiation efficiency,circular polarization is achieved by introducing a pair of right-angle triangular metal patches on both sides of the transmission line to form a pair of vertical radiation apertures.Its operating band is 21 GHz-33.8 GHz(relative bandwidth is 46.72%),and the antenna has stable high gain scanning in its operating band range,achieving a coverage range of-30°-34°.The 3 dB axial ratio bandwidth is 20%(22.5 GHz-27.5GHz),circular polarization scanning angle is-18°-13°,and the average gain of the antenna is 14.85 dBic.The average efficiency is 79%,which is 11% higher than the efficiency of single-row antenna.