M. D. Prouty and S. E. Schwarz, "Hybrid couplers in bilevel microstrip," IEEE Transactions on Microwave Theory and Techniques, vol. 41, no. 11, pp. 1939-1944, Nov. 1993.
S. E. Schwarz and W. G. Oldham, Electrical Engineering: An Introduction, 1st ed., HRW Series in Electrical and Computer Engineering, New York, NY: Holt, Rinehart, and Winston, 1984.
G. Eckhardt, R. W. Hellwarth, F. J. McClung, S. E. Schwarz, D. Weiner, and E. J. Woodbury, "Stimulated Raman scattering from organic liquids," Physical Review Letters, vol. 9, no. 11, pp. 455-457, Dec. 1962.