1. L. A. Vainshtein, Open Resonators and Waveguides [in Russian], izd. Sov. radio, Moscow, 1966.
2. V. S. Averbakh, S. N. Vlasov, and V. L. Talanov, Radiotekhnika i elektronika11, 943, 1966.
3. B. Z. Katsenelenbaum, Theory of Irregular Waveguides with Slowly Varying Parameters [in Russian], izd. AN SSSR, Moscow, 1961.
4. L. D. Landau and E. M. Lifshitz, Quantum Mechanics, Addison-Wesley, New York, 1958.
5. P. M. Morse and H. Feshbach, Methods of Theoretical Physics, Chap. 12, Sec. 3, McGraw-Hill, Englewood Cliffs, New Jersey, 1953.