| EBG loaded waveguides are generally synthesized by loading metal EBG planes in waveguide housings. They possess the similar properties to the periodical photon crystals, such as compact physical configurations, stable pass-band/stop-band characteristics, good slow-wave effect on out-band of band-gap. On the other hand, they take the advantages of good mechanical intensity, large power capacity and small transmission attenuation as well as those of the traditional waveguides. Therefore, EBG-loaded waveguides can be well applied in the design of high powered systems, components and their miniaturization at microwave band. This dissertation focuses on the electro-magnetic characteristics of EBG-loaded waveguides and their applications in broadband filters and antennas designs with detailed considerations as follows.(1) The classical Mode-Matching Technology (MMT) is adopted to establish a model of dual-plane discontinuousness of the quadruple-ridged square waveguide, with which the characteristics parameters of quadruple-ridged square waveguide, such as eigenvalues, cutoff frequency, characteristic impedance, single-mode operation band and complex propagation constant, can be accurately obtained. Then Multilayer Perceptron Neural Network Model (MLPNN) and Back Propagation Algorithm (BP) are employed to improve the design efficiency. Corresponding results in this dissertation show good agreement with those deduced by MFIE, FEM in existing references. The model provides theoretical foundation for the design of the EBG loaded waveguide filters.(2) Double-array-loading in parallel is adopted to achieve apparent improvement of the stop-band characteristics referring to those of traditional single-array EBG loaded waveguide BPF. Generalized scattering matrix, equivalent circuit analysis and software simulation are employed to perform parametric optimization. Variation rules of BPF performances have been acquired with various structural parameters, such as inserts height, loading period and parallel distance. An EBG-loaded BPF with center frequency of 9GHz is fabricated. Measured results show 6GHz～12GHz pass-band with in-band insert attenuation less than 1dB and 12.5GHz～16GHz stop-band with the largest out-band attenuation 55dB has been obtained. The filter can be used for out-band high-ordered harmonic suppression.(3) Regarding the symmetrical structure and dual-polarization trait of regular square waveguide, a symmetrically quadruple-loaded BPF is designed. Influences of inserts height and loading period on the overall BPF characteristics are considered. The inserts shape is chose to be round-crown and rectangular-bottom, which can reduce the EM coupling between the two sets of distributed LC resonant planes in perpendicular position. An experimental filter is designed and measured results show good agreement with the predicted results. 7.5GHz～14GHz pass-band with insert attenuation less than 1dB and 14.5GHz～16.8GHz stop-band with largest out-band attenuation 45dB can be obtained. Good dual-polarization isolation, larger than 25dB, is achieved on the entire band. The BPF can be used for the high-ordered harmonic suppression of dual-polarized systems.(4) An EBG loaded square pyramidical horn antenna is designed to improve the performances of ordinary unloaded horn. Simulations of ordinary unloaded horn, symmetrically quadruple-ridged horn and EBG-plane symmetrically loaded horn are performed to compare their characteristics of return loss, modal isolation, E-plane and H-plane radiation patterns. A practical EBG loaded horn is fabricated and the measured results show good agreement with the predicted ones. On the condition of same dimensions, EBG-loaded horn can achieve larger directivity than quadruple-ridged horn and lower side lobes than ordinary unloaded horn.(5) A design of microwave broadband coaxial to waveguide transition is proposed for the measurement of EBG loaded filters and horn antenna. Designs of several components are presented, including the wideband coax to double ridged waveguide transition, double ridged waveguide to arbitrary sized rectangular waveguide transition, rectangular-square waveguide transition. Double ridged waveguides are used to obtain lower cutoff frequency and better impedance matching with standard coaxial 50Ω. Tapered waveguide and ridges are employed to provide the best transition between different waveguides with different cross-sections. Two sets of microwave broadband measurement loops are established respectively for the measurement of the EBG loaded waveguide BPFs and horn antenna.
|
PDF Full Text Request