Advances in Radio Science www.adv-radio-sci.net 1684-9965 1684-9973 6 Kleinheubacher Berichte 2007 2008 10.5194/ars-6-9-2008 http://www.adv-radio-sci.net/6/9/2008/ http://www.adv-radio-sci.net/6/9/2008/ars-6-9-2008.html http://www.adv-radio-sci.net/6/9/2008/ars-6-9-2008.pdf 9 17 2008-05-26 Compact mode-matched excitation structures for radar distance measurements in overmoded circular waveguides G. Armbrecht armbrecht@hft.uni-hannover.de E. Denicke I. Rolfes N. Pohl T. Musch B. Schiek Inst. für Hochfrequenztechnik und Funksysteme, Leibniz Universität Hannover, Appelstraße 9A, 30167 Hannover, Germany Lehrstuhl für Integrierte Systeme, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany Institut für Hochfrequenztechnik, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany This contribution deals with guided radar level measurements of liquid materials in large metal tubes, so-called stilling wells, bypass or still pipes. In the RF domain these tubes function as overmoded circular waveguides and mode-matched excitation structures like waveguide tapers are needed to avoid higher order waveguide modes. Especially for high-precision radar measurements the multimode propagation effects need to be minimized to achieve submillimeter accuracy. Therefore, a still pipe simulator is introduced with the purpose to fundamentally analyze the modal effects. Furthermore, a generalized design criterion is derived for the spurious mode suppression of compact circular waveguide transitions under the constraint of specified accuracy levels. According to the obtained results, a promising waveguide taper concept will finally be presented. Barrow, W.: Transmission of electromagnetic waves in hollow tubes of metal, Proceedings of the IEEE, 72, 1064–1076, 1984. Brumbi, D.: Measuring process and storage tank level with radar technology, Radar Conference, 1995., Record of the IEEE 1995 International, pp. 256–260, \doi10.1109/RADAR.1995.522555, 1995. Brumbi, D.: Low power FMCW radar system for level gaging, Microwave Symposium Digest., 2000 IEEE MTT-S International, 3, 1559–1562 vol.3, \doi10.1109/MWSYM.2000.862273, 2000. Fernandez~Casares, S. and~Balle, S. M.-V P.: Mode beating and spontaneous emission noise effects in a variable-waveguide model for the dynamics of gain-guided semiconductor laser arrays, IEEE J. Quantum Electronics, 30, 2449–2457, \doi10.1109/3.333695, 1994. Hartog, A.: Influence of waveguide effects on pulse-delay measurements of material dispersion in optical fibres, Electronics Lett., 15, 632–634, \doi10.1049/el:19790450, 1979. Katsenelenbaum, B. Z. and~Mercader, L. P. M. S. M. T M.: Theory of Nonuniform Waveguides: The Cross-Section Method, vol 44, ser. IEE Electromagn. Waves. London, U.K., IEE Press, 1998. Kielb, J. A. and~Pulkrabek, M.: Application of a 25 GHz FMCW radar for industrial control and process level measurement, Microwave Symposium Digest, 1999 IEEE MTT-S International, 1, 281–284, \doi10.1109/MWSYM.1999.779475, 1999. Le~Huerou, J.-Y. and~Gindre, M. A. A. U. W. W M.: Compressibility of nano inclusions in complex fluids by ultrasound velocity measurements, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 50, 1595–1600, \doi10.1109/TUFFC.2003.1251143, 2003. Musch, T.: A high precision 24-GHz FMCW radar based on a fractional-N ramp-PLL, Instrumentation and Measurement, IEEE Trans., 52(2), 324–327, doi:10.1109/TIM.2003.810046, April 2003. Narasimhan, M. S. and~Balasubramanya, K.: Transmission Characteristics of Spherical TE and TM Modes in Conical Waveguides (Short Papers), IEEE Trans. Microwave Theory and Techniques, 22, 965–970, 1974. Parker, S.: Diverse uses for level radar, InTech, ISA International Society for Measurement and Control, May 2002. Pohl, N. and~Gerding, M. W. B. M. T. H. J. S B.: High Precision Radar Distance Measurements in Overmoded Circular Waveguides, IEEE Trans. Microwave Theory and Techniques, 55, 1374–1381, \doi10.1109/TMTT.2007.896784, 2007. Rusch, W.: Scattering from a hyperboloidal reflector in a cassegrainian feed system, IEEE Trans. Antennas and Propagation, 11, 414–421, 1963. Sai, Bin and~Kastelein, B.: Advanced High Precision Radar Gauge for Industrial Applications, International Conference on Radar, 2006. CIE '06., pp. 1–4, \doi10.1109/ICR.2006.343173, 2006. Shum, M. L P.: Effects of intermodal dispersion on short pulse propagation in an active nonlinear two-core fiber coupler, Photonics Technology Lett., IEEE, 16, 1080–1082, \doi10.1109/LPT.2004.824994, 2004. Stolle, R. and~Heuermann, H. S B.: Novel algorithms for FMCW range finding with microwaves, Microwave Systems Conference, 1995. Conference Proceedings., IEEE NTC '95, pp. 129–132, \doi10.1109/NTCMWS.1995.522875, 1995. Tang, C.: Mode Conversion in Tapered Waveguides At and Near Cutoff, IEEE Trans. Microwave Theory and Techniques, 14, 233–239, 1966. Weiss, M.: Low-cost, low-power nanosecond pulse radar for industrial applications with mm accuracy, 2001 International Symposium on Electron Devices for Microwave and Optoelectronic Applications, pp. 199–204, \doi10.1109/EDMO.2001.974307, 2001. Weiss, M. and~Knochel, R.: A Highly Accurate Multi-Target Microwave Ranging System for Measuring Liquid Levels in Tanks, 27th European Microwave Conference, 1997, 2, 1103–1112, \doi10.1109/EUMA.1997.337945, 1997.