Application Of Sub-Wavelength Structure In Microwave Circuit

As wireless communication technology's swift development, the electronic systems have become increasingly demanding on the performance of microwave circuits. Its type is getting more and more, and new craft and design methods are also emerging. The microstrip circuit becomes a kind of important component because of its unique characteristic, and its related technology has also obtained extensive and in-depth research and considerable development, especially the size of the circuit turns toward miniaturization. In particular the introduction of sub-wavelength structures, the microstrip circuit has presented unprecedented features, such as slow-wave characteristics, left-handed properties and so on. This paper explores the characteristics of the microstrip circuit based on sub-wavelength structure; simultaneously the author proposes several novel sub-wavelength structures and designs a new kind of microstrip branch-line directional coupler with sub-wavelength structure.Firstly, introduces the development and prospects of the microstrip circuits, and narrates the basic theory of microstrip transmission line, network theory and testing technology, as well as the basic concept of sub-wavelength structure. Secondly, studies a kind of novel sub-wavelength structure, and makes a detailed analysis of the integral part of the structure, and very good pass-band characteristics of the structures have been obtained. At the same time, the left-handed properties are discussed in this part. And makes this structure cyclical arrangement, and has analyzed transmission characteristic of the periodic structure, and the measured results and simulated results match well. The third part of the paper, several novel sub-wavelength structures are discussed in detail which are composed with compensated split-ring resonators (CSRR), split-ring resonators (SRR), defected ground structure (DGS). Finally, the author introduces some basic knowledge of the directional coupler, and designs a novel microstrip branch-line coupler with sub-wavelength structure. The new coupler is smaller than the traditional one, and has wider passband, and the simulation and measurement prove that the coupler has a good transmission characteristic.Researches on the subject contribute to the achievement of the miniaturization of microstrip, and are helpful for improving the performance of microstrip transmission.