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Broadband stripline directional coupler design

Author: HuZhuMing
Tutor: GongYuBin；WangWenXiang
School: University of Electronic Science and Technology
Course: Physical Electronics
Keywords: Stripline Coupled stripline Odd mode impedance Multi-section coupled line Gradient coupled lines
CLC: TN622
Type: Master's thesis
Year: 2008
Downloads: 951
Quote: 7
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Abstract

Modern electronic warfare systems, measuring instruments, systems, and other microwave systems increasingly wide band coverage, this trend presents a variety of microwave devices broadband requirements. Microwave system is widely used as a directional coupler has also been a challenge in this area, so the development of broadband as well as ultra-wideband directional coupler has an urgent practical significance. Directional coupler can have a variety of ways, coaxial, rectangular waveguide, circular waveguide, stripline and microstrip directional coupler can be constituted, this use of the strip lines to achieve directional coupler. Described in more detail herein, two broadband stripline directional coupler design method, the frequency bandwidths of 2 ~ 18GHz and 0.5 ~ 18.5GHz, respectively,-20dB coupling and-10dB. For the first wideband coupler using asymmetric multi-section side coupled stripline technology, the latter using a gradient of asymmetric bias coupled stripline technology. Two kinds of broadband stripline coupler base are single section coupled stripline, while the single-section coupled stripline is constructed on the basis of the stripline, so this paper describes in detail a variety of stripline nature. As stripline transmission TEM mode, the paper special attention stripline TEM properties. Analysis coupled stripline is the primary means odd mode method. Based on the analysis of the odd mode coupled stripline three commonly used, namely the side-coupled, broadside coupling and bias coupled stripline. For these three structures, even and odd mode impedance is the most important problem to solve, because the odd mode impedance of the coupler determines the size parameters. For broadband coupler, its odd mode impedance solution is a more complex process, but also the design of the difficulty lies. Therefore, this paper discusses two wideband stripline directional coupler design method, it will focus on the odd-mode impedance on solving. For non-symmetric multi-section coupled transmission lines, the analysis method is based on the parity is still molding. The multi-section coupled transmission lines is equivalent to the multi-section stepped impedance filter cascade, according to the microwave network theory can get multi-section coupled line attenuation function L_A and reflection coefficient Γ. In order to achieve such as corrugated transformation, select the attenuation function or reflection coefficient of Chebyshev polynomials, and the introduction of Richard transformation, you can Chebyshev polynomials for solving the reflection coefficient Γ, the use of the root can be solved to obtain the corresponding even mode impedance. In the fourth chapter will see that this is a complex and comprehensive process that requires the use of computer to complete. This paper chooses the side coupled to achieve 2 ~ 18GHz, coupling degree of 20dB wideband stripline directional coupler. Scalar network analyzer test results show that the use of multi-section coupled line coupler is designed to meet the needs of a wide band range of technical indicators. In order to further expand the bandwidth, you need to use a gradient coupling line technology. Gradient coupled line core approach is to take a small section of the gradient line coupled lines, be regarded as parallel coupled lines, using the integral method to obtain the corresponding coupling response curve, this happens to be an integral Fourier transform its inverse Fourier transform can be obtained Find a coupling coefficient corresponding to the expression k (x), then obtain the corresponding odd-mode impedance. However, the response is often very complex coupling function directly solve its inverse Fourier transform is very difficult, so many ways to get a polynomial approximation coupling coefficient k (x). We use a high-pass Chebyshev form of gradient coupling line technology, the design of 0.5 ~ 18.5GHz, the degree of coupling is 10dB wideband stripline directional coupler. Vector network analyzer test results show that using the gradient coupled line coupler designed to meet the needs of a wide band range of technical indicators.

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