Research And Design Of Shaped Antennas In Complex Environments

With the continuous development of modern microwave hyperthermia,near-field detection and energy transmission,the array antenna working in the near-field environment has become a hot research topic.In these near-field application environments,the near-field distribution of antenna needs to be adjusted according to different application environments.Due to the complex radiation characteristics of the antenna in the near-field region,the research on the focusing and shaping of the near-field region has been a research hotspot in recent years.This paper will study the method to maximize the power transmission efficiency between the two arrays to solve the problem of electromagnetic field shaping in the near-field region.The method is to place multiple test receiving antennas in the near-field target region,and realize the electromagnetic field shaping in the target region by optimizing the power transmission efficiency between the transmitting array antenna and the test receiving antenna.Firstly,the scattering parameters between the transmitting and receiving antennas are obtained by using the high-frequency electromagnetic simulation software Ansys HFSS,and then the scattering parameters are brought into the formula to maximize the power transmission efficiency to calculate the optimal excitation distribution of each port of the transmitting array antenna.Finally,the optimized excitation distribution is realized by designing the corresponding feed network.Because the scattering parameters in this method include the arrangement mode of array elements,the coupling between array elements and the environmental factors around the array antenna,this method can also be used in the antenna design of practical applications with complex environment.The specific work of this paper includes:Firstly,an eight-element near-field ultra-high frequency(UHF)radio frequency identification(RFID)read-write array antenna is designed in the retail metal cabinet environment,and its center frequency is 922.5MHz.By placing the test receiving antenna in the target recognition area,using the power transmission optimization theory to adjust the energy intensity received by each receiving antenna at the corresponding position,the optimal excitation distribution of the transmitting array antenna is obtained,and the uniform electric field distribution in the target reading and writing area is realized in the general metal cabinet of retail industry.The simulation and measurement results show that the electric field fluctuation range in the target reading and writing area in the metal cabinet is no more than3 d B.Then,based on the extended maximum power transmission efficiency method(MMPTE),a transmitting array antenna with 36 elements operating at 2.45 GHz is designed.Based on MMPTE,the electric field energy method is introduced.By adjusting the electric field energy value of the target area,adding a weighting matrix to adjust the energy distribution of the target area,and then maximizing the ratio of the received power to the input power,the optimal excitation distribution of the array antenna is obtained.Compared with the traditional MMPTE,the method of adjusting the electric field energy completely omits the receiving antenna,greatly reduces the operation time,and can be applied in more complex environments.In this paper,it is verified that the target shapes in the near-field region of the antenna are X-shaped,Y-shaped,T-shaped and L-shaped in the liquid environment,and the results are ideal.