关键词: 二项式响应, 切比雪夫响应, 宽带定向耦合器

Abstract: The paper analyses the coupled-transmission-line directional coupler. For the symmetric, the universal expression of multi-element directional coupler is obtained and then the couple coefficient of every element by the condition that the forward (n-1) steps derivative of Binomial response(the most flat response) is calculated. For the asymmetric, normalization impedance of step-impedance filter by Chebyshev polynomial and Richard transform are synthesized. This is the same as theeven mode impedance of multi-element asymmetric directional coupler, because the 1/4 wavelength coupler and 1/4 wavelength step-impedance filter are equivalent. Then the couple coefficient of Chebyshev response can be obtained. In thepaper, the two kinds couplers are designed, whose frequency is from 4 GHz to 20 GHz. The frequency response of Binomial response coupler is the most flat. The bandwidth ratio of Chebyshev response coupler is larger than Binomial response coupler. Finally, two-element micro-strip coupler made with Rogers 5880 micro-strip, 0.254 mm thickness, is applied in module.

Key words: binomial response, Chebyshev response, wideband directional coupler