Design Of Trans-directional Coupler And BST Phase Shifter

Reflection-Type Phase Shifters based on BST ferroelectric thin film and trans-directional coupler has the advantages of fast phase shift,high phase shift precision,small insertion loss and large power capacity,making it a competitive choice for the new tunable microwave devices.It has a great prospect in modern microwave systems.Therefore,the design and application of the trans-directional coupler and BST phase shifter are studied in this paper.Based on the intensive study of the characteristics of trans-directional coupler and BST phase shifter,the structural parameters of trans-directional coupler and phase shifter are extracted by full wave electromagnetic simulation software.In order to improve isolation of trans-directional coupler,a new type of trans-directional coupler with open-stub and short-stub is designed and measured and reasonableness of the design scheme is verified.The coplanar waveguide ferroelectric phase shifter is applied to the antenna array to steer the array beam,the characteristics of the phased antenna array are realized.The main contents of this paper are as follows:1.The principle and key technology of transdirectional coupled-line coupler have been studied.The effect of patch size on coupler performance is analysised.A method to improve the isolation of the coupler is proposed.The TRD coupler was fabricated and measured,the experimental results are consistent with the simulation results,thus the experimental research verified the validity of the designing scheme.2.The influence of different structures loaded with BST on performance have been significantly studied.The CPW ferroelectric phase shifter is simulated by HFSS,and the influence of substrate thickness,film thickness,gap between ground wire and transmission line on the performance of phase shifter is studied.Then,the phase shifter periodically loaded with interdigital structure is simulated.The effects of the length of interdigital,the number of cycles and the thickness of the film on the phase shift,insertion loss,and return loss of the phase shifter are studied.3.Focus on the application of BST phase shifter in antenna array.Each radiating element loads CPW ferroelectric phase shifter.Different combinations of dielectric constant can steer the main beam of antenna array.The antenna array can realizecontinuous scanning by a reasonable bias voltage network,and the phased array antenna can be realized.