Study On Key Technology Of The Wideband Endfire Antenna

Antenna, as an electromagnetic signal transceiver device, is a critical component in wireless communication systems. Antenna performance directly determines whether the whole system can achieve the design goals. Specifically, endfire antenna can directly determine the effectiveness of the anti-radiation missile in the processes of missile acquisition, target tracking and radiating target attacking. With the increasingly fierce competition in military equipment and technology, the anti-radiation missile technology has been rapidly developed. The anti-radiation missiles, however, have limited space and diversification, so the antennas must have better performances such as compact size, high gain, wide bandwidth, easy to install and so on. Generally, it is a challenge to design the end-fire antenna with an ultra-wide bandwidth, while maintaining end-fire antenna radiation characteristics with low sidelobe. When the endfire antenna is installed on the missile surface, it is important to reduce the influence of the metallic surface on the antenna performance. Therefore, these issues of the end-fire antenna need to be addressed. However, it is highly challenging to solve these issues in the design of end-fire antennas and very difficult to solve these problems using traditional methods. In this dissertation, through combining the end-fire antennas with other broadband electromagnetic structures, several wide-band end-fire antennas have been designed and analyzed in details. This dissertation explores and develops the bandwidth expansion, gain promotion and miniaturization mechanism of Yagi-Uda antenna, Quasi-Yagi antenna, log-periodic antenna and wideband end-fire conformal antenna array, based on the radiation mechanism of original end-fire antenna and antenna array. In the dissertation, the main achievements are as follows.1. The dissertation proposes a novel monopole log-periodic antenna and end-fire monopole log-periodic antenna array operating at 2GHz-18 GHz. Through the study of classical monopole log-periodic antenna rigorous theoretical derivation for the radiation pattern was carried out. The theory of eliminating the stop-band of classical monopole log-periodic antenna array is also analyzed. The novel log-periodic monopole antenna uses the novel microstrip-to-slot transition as feed network, which has simple structure, wide band and easy to fabricate. The novel log-periodic monopole antenna array structure can achieve 100% band width. The proposed log-periodic antenna has wide band, simple structure, easy to fabricate, and exhibits good endfire radiation characteristics. The dissertation used two types of novel log-periodic monopole antennas(2GHz-6GHz, 6GHz-18 GHz novel log-periodic antennas) to constitute an end-fire log-periodic monopole antenna array that cover 2GHz-18 GHz. As the proposed log-periodic monopole antennas are conformal to missile surface, therefore the aerodynamic layout of the missile remains unchanged after antenna installation. The dissertation analyzed the wave diffraction characteristics with limited bottom, radiation characteristics of novel log-periodic monopole antenna with limited bottom and provide theoretical analysis for the design of the novel log-periodic monopole antenna.2. The dissertation studies the theory of the Yagi-Uda end-fire antenna. The structure and working principle of Yagi-Uda end-fire antenna is reported. Through the theoretical analysis of the traditional Yagi-Uda antenna, the radiation formula of the current in the half space is obtained. At the same time, the theoretical analysis of the far field radiation characteristics of Yagi-Uda antenna is also carried out. Based on the theoretical research of Yagi-Uda antenna, the dissertation illustrates the design method of Yagi-Uda end-fire antenna. A Yagi-Uda antenna with 15 dipoles was designed to verify the design method of Yagi-Uda antenna. Because of good end-fire radiation characteristics, easy to fabricate and low cost, the microstrip Quasi-Yagi antenna is widely used in electronics equipment. In this dissertation, the classical wideband microstrip Quasi-Yagi antenna is studied. The feed network of the microstrip Quasi-Yagi antenna is very important for its wideband characteristics. So the design method of f the broadband feed structure is studied, and a variety of feed structures were compared and analyzed. The radiation efficiency of Quasi-Yagi is studied. Through theoretical analysis, the radiation efficiency of the classical microstrip Quasi-Yagi antenna was found to be 93%.3. A novel double half rhombus Quasi-Yagi antenna with stable end-fire radiation patterns is proposed in this dissertation. The achieved bandwidth of the proposed double half rhombus Quasi-Yagi antenna is 96.6%. The bandwidth of the Quasi-Yagi antenna is hence increased by 45%, compared to the classic Quasi-Yagi antenna. The proposed double half rhombus Quasi-Yagi antenna overcomes shortcomings of classic Quasi-Yagi antenna such as narrow bandwidth, deterioration of radiation pattern in high frequency. The proposed design used six double half rhombus Quasi-Yagi antennas to constitute an end-fire Quasi-Yagi antenna array that covers 5.5GHz-17.3GHz. Because of the influence of the metal column, the radiation pattern of proposed end-fire Quasi-Yagi antenna array was tilted upward by an angle of about 3 0 ?. However, according to the requirements of the end-fire Quasi-Yagi antenna array, the radiation pattern still satisfies the requirement of the anti-radiation missile.4. A novel wide band balun structure is proposed in this dissertation. A wide band Quasi-Yagi antenna with balun and log-periodic directors is proposed in this dissertation. The proposed antenna uses the novel balun as the feeding network, and adds the log-periodic directors. The bandwidth of the proposed Quasi-Yagi antenna is increased by 65%, compared with the classic Quasi-Yagi antenna and exhibits good end-fire radiation characteristics. The gain of the proposed Quasi-Yagi antenna in the endfire direction is increased by 2dBi, as compared to the classic Quasi-Yagi antenna. The maximum gain of the proposed Quasi-Yagi antenna was found to be 7.5dBi.5. A Quasi-Yagi antenna with electromagnetic metamaterial is proposed in this dissertation. A "I" electromagnetic metamaterial structure is proposed to replace the conventional structures. The proposed "I" electromagnetic metamaterial structure has simple structure and easy to fabricate. In this dissertation, the Quasi-Yagi antenna with ”I” electromagnetic metamaterial structure covers wide band from 4.5GHz to 9.5GHz, and has 4-8dBi gain in the end-fire direction. The gain of the proposed Quasi-Yagi antenna is increased by 2d Bi, as compared to the unloaded Quasi-Yagi antenna. The Quasi-Yagi antenna with electromagnetic metamaterial structure has good end-fire radiation pattern, and it can be widely used in electronic equipment such as wireless communication, guidance and direction-finding systems.These results can provide theoretical guidance and performance evaluation method for the design of the end-fire antenna element and array loaded on the missile.