Researches On Microwave Key Device Based On Complementary Split Ring Resonator And Nematic Liquid Crystal

With the rapid development of electronic technique, modern electronic information system not only had high performance but also became more cost-effective, lighter, smaller, reliable and functional. As a result, the researches of miniature and high-performance microwave components have been important in modern microwave systems, which have been one of the most critical, difficult and popular areas in the microwave fields also. In the perspective of further miniature of microwave passive components, this dissertation investigates the band-notched ultra-wideband(UWB) antennas, SIW/HMSIW evanescent mode filters and microwave broadband phase shifters by using miniature resonator, metamaterial and nematic liquid crystal, separately. The main works of this dissertation are concluded as following:1. Firstly, the monopole antenna radiation patch and the contribution of ground to radiation characteristics are analyzed. It analyzes how radiation patch changes the impedance bandwidth in details. It also analyzes the contribution of ground to the radiation characteristics, and proposes the importance of the structure and size of ground on improving the impedance bandwidth of printed UWB antennas and robustness of radiation patterns. By studying the surface current distribution of miniature UWB antennas, a design method of miniature co-direction complementary split-ring resonator(CSRR) loaded UWB antenna are illustrated. The designed methods of one/two/multiple notch and controllable center frequency are validated by combining one/two/multiple CSRRs with similar structures on UWB antennas. By qualitatively analyzing the equivalent circuits of UWB trap antennas, together with the analysis of the distribution of antenna surface notched current, the operating principle of the notched is illustrated and the operability and accuracy of the antenna design are proved. The dimension of notched antenna based on trapezoidal ground is only 25×27.9mm. The experimental results show that the impedance bandwidth is 2-15 GHz, and three notch frequencies could cover 3.7-4.25 GHz, 5.12-5.48 GHz, 5.66-5.98 GHz can be realized. The lowest notch frequency radiation efficiency as low as 3%. The gain of notch frequencies are lower than pass-band about 12 d B while the far-field radiation pattern is omnidirectional in 2-12 GHz.2.Based on the operating principle and transmission characteristics of SIW and HMSIW, it shows that CSRR can be applied to SIW transmission line so as to achieve the functionality of filtering. By loading CSRR metamaterial on the surface metal of SIW, it is experimentally validated that the planar integrated transmission line with electromagnetic resonance type superconducting medium can amplify the evanescent modes and thus achieve the characteristics of filtering. In addition, the principles of pass-band filter and band-stop filter are illustrated by extracting the equivalent magnetic permeability and dielectric constant from the simulated S-parameters. Then, a HMSIW evanescent mode filter based on CSRR amplifying evanescent modes is designed, and the filter can achieve good out-band rejection while significantly reducing device size. Using the principles of transmission line and equivalent circuits, accurate modeling analysis has been done to the new load structure. The miniature filter is eventually fabricated and measured. The results show that its center frequency is 5.017 GHz, 3dB bandwidth is 944MHz(4.52GHz-5.464GHz), relative bandwidth is 19%, return loss is more than 15 d B in the pass-band frequency range from 5.06 GHz to 5.29 GHz and the overall dimension is 20mm×9mm. The experimental results show that the evanescent mode filter has smaller size compared to the conventional filters while maintaining high performance.3.By theoretical derivation, the vector principle of nematic liquid crystal is discussed and the relationship between nematic liquid crystal and refractive index is analyzed. A phase shift by using nematic liquid crystal with inverted microstrip line structure is proposed for the first time. By simulating the critical parameters of inverted microstrip line structure and nematic liquid crystal(height of nematic liquid crystal and substrate), the basic principles of choosing material when making liquid crystal phase shifter are obtained. A liquid crystal phase shifter with copper as the floor is fabricated with size 125mm×20mm by optimizing the device structure. The proposed phase shifter can achieve 0-150 degree relative phase shift when 10MHz-6GHz with bias voltage 0-10V(56 g in weight). In order to further realize the miniaturization of phase shifter and small weight, the smaller nematic liquid crystal phase shifter with aluminum floor combined with inverted microstrip structure of serpentine. Measurement r esults show that the size of nematic microwave phase shifter is only 30mm×35 mm, when the bias voltage of 0-10 V can achieve 0-200 relative degree shift vector(10MHz-6GHz), the weight only 26 grams so that the phase shifter while significantly reduce the volume and weight, proved high perform significantly. By fabricating and measuring the device, the aims of making microwave phase shifter miniature, cost-effective, operate at low voltage and possess high degree of phase shift are achieved.