Abstract
A modal analysis for the directional coupler is presented in this paper. The analysis is based on the mode-matching technique. The theory is verified by Ansoft HFSS software at a directional coupler with standard X-band (WR 90) rectangular waveguide ports. Element values of equivalent circuit model are computed by using the S-parameters obtained from the presented method in this paper. In addition this paper has corrected two formulations used in two previous works which have been published.
Highlights
Duo to its equal power splitting, high isolation, low VSWR and accurate 90 phasing, the directional coupler [1] is a very attractive microwave circuit element for many applications such as in the duplexer, balance mixers, broad band-band switches, and H-plane magic tee[2,3]
The structure of a narrow wall directional coupler is shown in Fig. 1, the two waveguides are coupled through the slot in the narrow wall
The geometry of the narrow wall directional coupler is shown in Fig. 1, the two waveguides are coupled through the slot in the narrow wall
Summary
Duo to its equal power splitting, high isolation, low VSWR and accurate 90 phasing, the directional coupler [1] is a very attractive microwave circuit element for many applications such as in the duplexer, balance mixers, broad band-band switches, and H-plane magic tee[2,3]. The key to designing the coupler is to obtain the width of the slot and the width of the coupling region [4, 5], so a large number of directional coupler simulated to find out the best one which realizes a -3dB coupler. The topology of the model is the same as that introduced by Marcuvitz [11] This method calculates the admittance matrix of the directional coupler from its scattering matrix that is obtained by the modematching technique
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