MoM Analysis and Design of a Compact Coaxial-to-Microstrip Directional Coupler
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Abstract
In order to overcome the main drawbacks of coaxial, waveguide, and stripline couplers, the analysis and the design of a compact coaxial-to-microstrip directional coupler convenient for power and antenna control application, are presented using the method of moments (MoM) in two dimensions. This technique is adapted to study the complex configuration of the line’s system, which does not have a simple analytical solution. The modeling of this structure consists in analyzing the primary inductive and capacitive matrices ([L] and [C]). When these matrices are determined, it is possible to calculate the inductive and capacitive coupling coefficients (<i>k<sub>L</sub></i> and <i>k<sub>C</sub></i>) and estimate the resulting scattering parameters of the coupler using an adapted numerical model. The coupler can be integrated into a printed circuit board (PCB) and operates over 17 to 35 dB coupling coefficients and is always compensated. The compensation is achieved by the proper displacement of a tuning ground plane with respect to the edge of the PCB from 0.1 to 3.3 mm. As an application, we present the design of a compact coupler with 7.5 × 4.8 × 25.8 mm of size and having approximately 20 dB of coupling coefficient at 2 GHz and a minimum directivity of 23.3 dB in the frequency range [0.1 - 4] GHz. In order to check our numerical calculations by the MoM we made simulations in 3D by using CST MICROWAVE STUDIO software for the same geometrical and physical parameters of our designed coupler. The results obtained by the two numerical models (MoM and CST) show a good agreement of the frequency responses of the coaxial-to-microstrip directional coupler. The studied structure represents a great improvement for high power measurement systems, since it has broad-band, good directivity, and can be easily designed and fabricated.
- A. Sawicki, “A New Class of Asymmetrical Directional Couplers for Power/Antenna Control Applications,” Microwave Journal, Vol. 48, No. 11, November 2005, pp. 102-112.
- S. Uysal and H. Aghvami, “Synthesis, Design, and Construction of Ultra-Wide-Band Nonuniform Quadrature Directional Couplers in Inhomogeneous Media,” IEEE Transactions on Microwave Theory and Techniques, Vol. 37, No. 6, June 1989, pp. 969-976. doi:10.1109/22.25398
- R. E. Collin, “Foundations for Microwave Engineering,” 2nd Edition, McGraw-Hill, New York, 1992.
- H. Schmiedel and F. Arndt, “Field Theory Design of Rectangular Waveguide Multiple-Slot Narrow-Wall Couplers,” IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-34, July 1986, pp. 791-798. doi:10.1109/TMTT.1986.1133442
- L. T. Hildebrand, “Results for a Simple Compact Narrow- Wall Directional Coupler,” IEEE Microwave and Guided Wave Letters, Vol. 10, No. 6, June 2000, pp. 231-232. doi:10.1109/75.852425
- A. H. McCurdy and J. J. Choi, “Design and Analysis of a Coaxial Coupler for a 35-GHz Gyroklystron Amplifier,” IEEE Transactions on Microwave Theory and Techniques, Vol. 47, No. 2, February 1999, pp. 164-175. doi:10.1109/22.744291
- A. R. Djordjevic, M. B. Bazdar and T. K. Sarkan, “LINPAR for Windows: Matrix Parameters of Multiconductor Transmission Lines, Software and User’s Manual,” Artech House, London, 1999.
- N. Benahmed and N. Benmostefa, “Design Directional Couplers for High Power Applications,” Microwaves & RF, Vol. 45, No. 10, October 2006, pp. 90-98.
- R. F. Harrington, “Field Computation by Moment Methods,” Macmillan, New York, 1968.
- W. Cao, R. F. Harrington, J. R. Mautz and T. K. Sarkar, “Multiconductor Transmission Lines in Multilayered Dielectric Media,” IEEE Transactions on Microwave Theory and Techniques, Vol. 32, No. 4, April 1984, pp. 439- 450. doi:10.1109/TMTT.1984.1132696
- J. Venkataraman, S. M. Rao, A. R. Djordjevic, T. K. Sarkan and N. H. Yang, “Analysis of Arbitrary Oriented Microstrip Transmission Lines in Arbitrary Shaped Dielectric Media over a Finite Ground Plane,” IEEE Transactions on Microwave Theory and Techniques, Vol. 33, No. 10, October 1985, pp. 952-960. doi:10.1109/TMTT.1985.1133155
- M. B. Bazdar, “Evaluation of Matrix Parameters of Multiconductor Transmission Lines by the Galarkin Method,” M.Sc. Thesis, School of Electrical Engineering, University of Belgrade, Belgrade, 1991.