Pattern Reconfigurable Planar Antennas

Antenna is an indispensable part of a communication system. As modern wireless communication systems are developed towards large capacity, multi-function, and ultra-wide band, the antenna performance needs great enhancement. Due to the advantages of small size, versatility, and easy to achieve diversity, reconfigurable antennas have received great attention. By adjusting the electronic components integrated in the antenna aperture, the performance of the antenna can be reconfigured. As a reconfigurable antenna has a variety of operating modes, it becomes a superposition of multiple antennas. This approach not only meets the needs of the development of modern wireless system, but also reduces the number of antennas on the communication platform, simplifying the electromagnetic environment. Depending on the different reconfigurable purposes, reconfigurable antennas can be divided into frequency reconfigurable antenna, polarization reconfigurable antenna, pattern reconfigurable antenna. As pattern reconfigurable antennas can change the direction of the radiation pattern according to the operating environment, they can avoid signal interference, improve safety and save the power of system. Therefore, pattern reconfigurable antenna has become a hot research topic in recent years. However, there are still many problems that need to be resolved in this field, such as the complicated structure, poor directivity, narrow bandwidth. In this paper, we mainly study the antennas with planar structures. The main contributions of this work include:1. A brief introduction of research background, significance and the state of art of pattern reconfigurable antennas is presented. Then we introduce the basic knowledge of antenna and pattern reconfigurable antenna. On this basis, a pattern reconfigurable antenna based on monopole ring is designed, which works in 2.3-2.5 GHz. The antenna gain is 4.6 dBi on average. By changing the states of switches, it can switch the radiation patterns in two opposite directions. It is shown that the antenna has the characteristics of simple structure and stable performance.2. A folded dipole with a planar structure and good directivity is studied. The theory of good directivity and pattern reconfigurable mechanism is investigated. A pattern reconfigurable antenna based on folded dipole is proposed. The antenna has a planar structure. A balun is used to feed the antenna. It is shown that the antenna can realize its radiation pattern reconfiguration in two opposite directions by changing the states of switches. But the relative bandwidth of the antenna is only 5.4%, which is not enough to meet the requirements of broadband. So it needs further improvement.3. As the pattern reconfigurable antenna based on the folded dipole has a narrow band, the methods of bandwidth enhancement are investigated. By adding a pair of parasitic elements and a pair of straight dipoles, a broadband pattern reconfigurable antenna based on folded dipole is obtained. The broadband pattern reconfigurable antenna features a simple configuration and good directivities. It is shown that the pattern reconfigurable antenna achieves a pattern bandwidth of 16.3%(2.25-2.65 GHz) for front-to-back ratio(F/B) >15 d B. Experimental results show that the reconfigurable antenna achieves an impedance bandwidth of 32.6%(1.98-2.75 GHz)for return loss(RL)>10 dB, a pattern bandwidth of 20.8%(2.15-2.65 GHz) for F/B>10 dB, and a gain of 5 d Bi on average.