8. T. Hinata, H. Hosono, and H. Ono, ‘‘Scattering of Electromag- netic Waves by an Axially Slotted Conducting Elliptic Cylinder in Homogeneous Medium,’’ IEICE Trans., Vol. E79-C, Oct. 1996, pp. 13641370. 9. M. Abramowitz and I. A. Stegun, Eds., Handbook of Mathemati- cal Functions, Dover, New York, 1972. 10. V. P. Chumachenko, ‘‘Modified Method of Calculation of E-Plane Waveguide Mode Having a Polygonal Boundary,’’ Radiotekh. Ž . Elektron., Vol. 34, July 1989, pp. 15811587 in Russian . 11. J. Minor and D. Bolle, ‘‘Propagation in Shielded Microslot on Ferrite Substrate,’’ Electron. Lett., Vol. 7, No. 17, 1971, pp. 502504. 12. J. Ramakrishna, ‘‘Even-Mode Characteristics of the Bilateral Slot Line,’’ IEEE Trans. Microwa  e Theory Tech., Vol. 38, June 1990, pp. 760765.  1997 John Wiley & Sons, Inc. CCC 0895-247797 A COMPACT, HIGH-POWER, LOW-LOSS, L-BAND COAXIAL 18-WAY POWER DIVIDER / COMBINER Robert Lehmensiek 1 and P. W. van der Walt 2 1 Radar Division Reutech Systems P.O. Box 686 Stellenbosch 7599, South Africa 2 Faculty of Engineering University of Stellenbosch Stellenbosch, South Africa Recei  ed 12 June 1997 ABSTRACT: The design, construction, and measured performance of a compact, low-loss, L-band 18-way coaxial power di  ider is presented.  1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 241243, 1997. Key words: power di  ider; high power, coaxial structure I. INTRODUCTION An n-way power divider generally splits a signal into n equiphase, equal amplitude parts. Power divider structures may be loosely categorized into the following three groups: the corporate Wilkinson, the fork, and the radial power dividers. The corporate Wilkinson divider and the fork di- vider are suitable for small n. For large n, these structures become large, especially for a larger bandwidth, and the   efficiency drops rapidly 1 . The radial divider 2 is suitable for larger n and higher input power levels. However, it becomes an electrically large structure, and is therefore prone  to unwanted modes 3 . We have developed a more compact and much simpler structure, where the output connectors are strapped together symmetrically around the coaxial structure. Figure 1 illustrates the divider construction, and a schematic of the circuit model is shown in Figure 2. The center pins of the 18 output connectors are directly connected to the center conductor of the coaxial structure, and lie in a plane perpen- dicular to the axis of the coaxial system. Since all 18 outputs are strapped together symmetrically around the coaxial struc- Ž ture, the impedance level at the output plane is 50   . 18 ports  2.78 . This impedance level is transformed with a quarter-wave impedance transformer to the 50  impedance level at the input port, with the order dependent on the required bandwidth. The two short transmission lines to the left of the output plane in Figure 1 realize a short-step short-circuit stub, which presents a high reactance at the output ports. The total length of the stubs is reduced to less than a quarter wavelength by the stepped design. Because of the divider’s compact size, no higher order resonant modes can exist provided that the number of output ports is smaller than 20. Reciprocity allows the divider to also function as an  equal power combiner 3 . In general, isolation between the output ports of a power divider is achieved with isolation resistors between the output ports. Due to the physically large isolation resistors required for higher power levels, the capacitance between these resis- Ž. tors and the earth plane s causes currents to flow through Figure 1 Construction of the coaxial 18-way power divider MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 16, No. 4, November 1997 241