1. ‘Guided Wave Concept in Electromagnetic Theory’, Research Report, R-269-52, Polytechnic Institute of Brooklyn, Microwave Research Institute, 14, May, 1952 p. 1 P.I.B.-208, ONR
2. Sommerfeld, A.: Partial Differential Equations in Physics, (Academic Press, New York 1949), p. 246
3. Stratton, J.A.: Electromagnetic Theory, (McGraw-Hill, New York 1941), p. 573
4. Frank-Mises: Differentialgleichungen der Physik, (Friedrich Vieweg und Sohn, Brunswick, Germany 1935),2, Chapter 19, Sec. 5