Study On Frequency Reconfigurable Antenna Based On Barium Strontium Ti-tanate Materials And Metasurfaces

Antennas are the important parts of communication and radar systems. In recent years, developments in the field of digital circuit design, signal processing, computer chip manufacture, and multi-functional software technology, make the wireless communication systems transit from analog to digital mode. Today, back-end and middle processing parts of the communication system have basically upgraded into digital signal processing. However, microwave antennas, as the front-end module of the communication system, have retained their analog operation modes due to technology limitations. This arises a significant mismatch between analog front and the digital operation mode in modern communication systems. In order to improve the performance of modern communication systems, antenna modules should be more versatility and multifunctional. Recently, four directions on frequency reconfigurable antennas have attracted a lot of attention, such as miniaturization, reconfigurable multifunctions, reconfigurable instantaneous wideband, large tunable ratio. In this paper, theories of frequency reconfigurable antenna based on novel materials have been studied to improve the instantaneous bandwidth and the reconfigurable ratio. Some reconfigurable antenna samples were manufactured and measured, and the measured results are consistent with the theoretical results.Barium strontium titanate(BST) films have good dielectric tunability and very low dielectric loss. However, the relative permittivity of BST films are extremely high, which causes serious electromagnetic impedance mismatch between air and BST layer. Moreover, high dielectric constant also generates significant surface wave that worsens the antenna radiation performance. For overcoming the impedance mismatch, an aperture coupled slot structure has been adopted to balance the input resistance. Also, a microstrip filter has been designed to reduce the negative effect of the bias current. In theoretical details, this paper proposed an accurate equation to describe the frequency reconfiguration process, and a good agreement has been obtained between the theory and the experiment. Meanwhile, under the guidance of the theory established above, the operation band of our antenna samples can be tuned over 10%, and radiation gain levels are greater than 6 d B.On the basis of the previous research, in order to broaden the instantaneous bandwidth of the frequency reconfigurable antenna, the longitudinal parasitic coupled structure has been proposed to solve this problem. In this structure, an individual FP resonant cavity has been introduced to generate an extra resonant band, which can extend the instantaneous bandwidth of the frequency reconfigurable antenna. Meanwhile, this broadened instantaneous band can also be reconfigured by the bias electric field. This article gives an accurate design formula to calculate the center resonant frequency, and the theoretical results agree well with the experimental results. Finally, with the help of the theoretical analysis and the simulation model, the antenna sample has 26% instantaneous bandwidth, which is much greater than 7% level of other conventional reconfigurable antenna. What’s more, the frequency tuning range of our antenna has remained around 10%.The third part in this paper is the exploration for obtaining larger tunability. Until now, functions of most frequency reconfigurable antenna are based on the change of the effective resonant length. Although this idea can be implemented to realize the continuous coverage in the tuning range, the tunability is still limited by dielectric tunable level of most materials. To solve this problem, a new concept of frequency reconfiguration based on abrupt electricmagnetic phases was proposed. At the same time, transmission phases of metasurfaces were studied to obtain precisely theoretical description. Also, metasurface samples were manufactured and measured to verify our design. After this work, frequency reconfigurable microstrip antenna based on abrupt phases was explored and studied. Theoretical formulas of frequency reconfiguration were given under the perfect assumption. A theoretical antenna model was designed to achieve 122% tuning range of center frequency.Due to the profile limitation, metasurfaces cannot be utilized practically in the microstrip antenna. Hence, frequency reconfigurable waveguide antenna based on metasurfaces was studied. According to our research on the metasurface, arbitrary abrupt phase at arbitrary frequency can be designed suitably. Finally, the desired phase dispersion was designed in our reflection metasurfaces, and over 26.7% frequency tunable range was obtained for our antenna samples with different metasurface states.