The concept of reconfigurable antennas was first proposed in the 1983 patent "Frequency Agile, Polariza TIon Diverse Microstrip Antennas and Frequency Scanned Arrays". According to its reconstruction function, it can be mainly divided into frequency reconfigurable antenna and pattern reconfigurable antenna. The frequency reconfigurable antenna can change the operating frequency, and the pattern remains basically unchanged; the pattern reconfigurable antenna can reconstruct the radiation pattern while maintaining the frequency stability, so that one antenna has the function of multiple antennas. When the pattern reconfigurable antenna is applied to the antenna array, the beam direction of the unit can be changed to concentrate the beam directions of different units in a certain direction to provide higher array gain; or it can be applied to a wireless communication system. Improve signal quality by changing the beam direction to align the signal to the user who needs to communicate, or to avoid interference sources. Therefore, reconfigurable antennas are still a research hotspot in the field of antennas.
As we all know, Yagi antenna has a good directionality and has a good application in direction finding and long-distance communication. The microstrip patch antenna is small in size, light in weight, low in profile, and conformable to the carrier, and is simple to manufacture and low in cost. By combining the microstrip patch with the Yagi antenna, a microstrip rectangular patch Yagi antenna and a microstrip vibrator antenna can be constructed. A switch is mounted on the microstrip oscillator to change the length of the parasitic oscillator to form a reconfigurable microstrip Yagi antenna. By performing slot loading on the microstrip patch and introducing a switch, a reconfigurable Yagi antenna of a rectangular patch is constructed. The triangular microstrip patch antenna has a similar field structure and resonant frequency as the rectangular microstrip patch antenna, but the patch area is relatively small, and can meet some special performance requirements such as miniaturization of the antenna patch in practical applications. . In this paper, a triangular patch is used as the Yagi antenna unit to form a pattern reconfigurable antenna. The antenna radiation pattern is deflected in three different directions by etching a simple rectangular groove on the parasitic patch and installing a switch. Compared with the Yagi antenna of the rectangular patch structure proposed in the literature, the structure of the groove is simpler and the number of switches is smaller.
Antenna design
The structure of the antenna is shown in Fig. 1. The array elements of the reconfigurable Yagi antenna of the triangular patch are formed by three triangular patches placed in the same straight line. A slightly larger triangular patch in the middle is used as an excitation element, and is fed by a coaxial probe. Two identical but smaller triangular patches are placed on both sides as parasitic elements. A rectangular slit is etched at the same location on both parasitic patches, and a switch is placed in the middle of the rectangular slit. The distribution of the surface current on the parasitic patch can be changed by changing the state of the switch, and finally the reconstruction of the antenna radiation pattern is achieved.
The size of the dielectric substrate of the antenna is 34 & TImes; 17 mm, the thickness of the dielectric plate is 0.76 mm, and the relative dielectric constant is 2.94. The side lengths of the triangular patches are 10 mm and 8 mm, respectively. The size of the rectangular slit etched on the parasitic patch is 5.0 & TImes; 0.4 mm, the size of the switch is 0.4 & TImes; 0.4 mm, the distance between the rectangular slit and the apex of the triangle b =4.9647mm.
Etching a rectangular slot on the triangular parasitic patch can cut the surface current on the patch, thereby changing the surface capacitance and inductance of the patch, so that the parasitic patch plays different roles in the radiation process. The HFSS simulation shows that in this antenna, when the switch on the parasitic patch is broken, the parasitic patch acts as a director, which can deflect the beam radiation direction of the antenna toward the direction in which the parasitic patch is located. The state of the patch is D; when the switch on the parasitic patch is closed, the parasitic patch has little effect on the radiation beam direction of the antenna. We call the state of the parasitic patch N at this time, so the antenna has at least three modes. , mode DN, ND and NN. The mode DN means that the switch on the left parasitic patch is disconnected as a director, and the switch on the right parasitic patch is closed, and the antenna pattern is deflected to the left (Y-axis negative direction); the mode ND is opposite to the mode DN. It means that the switch on the parasitic patch on the right side is broken, as the director, and the switch on the left parasitic patch is closed, the direction of the antenna is deflected to the right (Y-axis positive); the mode NN refers to the parasitic patch on the left and right sides. The upper switch is closed, and the beam direction of the antenna is radiated directly above the patch.
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