Research On High Selective Frequency Selective Structure Based On Non-Resonant Mode

The traditional frequency selective surface(FSS)is usually realized by microstrip resonators(with low-quality factor).Although it has the advantage of a low profile,it is difficult to improve its selectivity.The metal-cavity based frequency selective structure has a high-quality factor,so it has high selectivity,but its disadvantage is high profile and large volume.In this paper,the substrate integrated waveguide(SIW)technology is applied to the frequency selective structure,which not only has the advantages similar to the traditional frequency selective surface with a low profile,but also has the high selectivity of the metal cavity structure.A SIW frequency selective structure based on non-resonant mode is proposed,and transmission zeros are generated on both sides of its passband by using the non-resonant mode,which makes its selectivity higher than that of conventional SIW frequency selective structure.The in-depth study of this structure not only has a high theoretical value,but also has a very good practical engineering application value.The main research work of this paper consists of the following parts:1)Starting from the realization of the high selectivity of frequency selective structure,the basic concept of non-resonant mode and the theory,and method of realizing high selectivity are introduced.The step angle in the frequency selective structure is used to disturb the degenerate modes,so that the degenerate modes are separated and a certain frequency passband characteristic is achieved.The cross-coupling in high selectivity is introduced and analyzed.The theory of SIW based frequency selective structure is introduced in detail.2)The design method and theoretical analysis of a high selective single-layer SIW frequency selective structure are described.A high selective single-layer SIW frequency selective structure with a working frequency of 10.4 GHz and two transmission zeros is designed,with a relative bandwidth of 1.5% and a transmission loss of 1.0dB.A single-layer SIW frequency selective structure of 10×10 cells is fabricated and measured.It is shown that,the measured and simulated results agree very well,which shows the correctness of the design method.3)Based on the single-layer SIW frequency selective structure,a double-layer SIW frequency selective structure with a working frequency of 10.4 GHz and higher selectivity is designed,and its structure is analyzed theoretically.Because of its double-layer structure,the energy is transmitted through the coupling slot in the middle,and it has four transmission zeros.The relative bandwidth of the structure is 1.1%,and the transmission loss is 2.5dB.A double-layer SIW frequency selective structure of 7×7 cells is fabricated and measured.The measured results are in good agreement with the simulation ones.