| With the rapid development of science and technology, some requirements on the microwave devices are critically required, such as low profile, wide band, high reliability, miniaturization and high integration etc. The main researches of this work are about the folded substrate integrate waveguide (FSIW) and the inverted microstrip (IMS). Actually, FSIW is an improved planar waveguide structure with more compact size and higher integration than SIW.The main advantage of this structure is lower dielectric loss especially in millimeter wave; meanwhile it takes the features of simple structure, easy in fabrication and convenience in connection with solid microwave devices. The dielectric loss characteristic of inverted microstrip has been investigated in this paper. A simple formula of the dielectric loss for inverted microstrip has been derived using Fuzzy EM method; numerical verifications by HFSS and IE3D have been carried out, demonstrating the accuracy of the derived formula.Based on the theory of ordinary FSIW, a special structure of FSIW with different dielectric constants for upper and lower substrate layers has been investigated. The effects of some parameters on the cut-off frequency and the transmission constant are addressed and discussed, such as the tendency of cut-off frequency with the gap, the change of the cut off frequency with different dielectric constant and different height etc.In addition, three kinds of transitions from this special FSIW to inverted microstrip have been designed and investigated, such as the orthogonal trapezoid transition, taper transition and cone-shaped transition.Finally, three kinds of bandpass filters based on FSIW are designed and discussed. One type filter is realized by introducing plane septa in the middle metal layer as a K-inverter. Another one is realized by inserting slot in metal vane as J-inverter. The last one utilizes the combinations of above two different structures and demonstrates good performances. |
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