1. P. D. Kalachev and A. E. Salomonovich, Radiotekhnika i elektronika,6, no. 3, 43, 1961.
2. V. I. Zagatin, G. S. Misezhnikov, and V. B. Shteinshleiger, Radiotekhnika i elektronika,12, no. 3, 539, 1967.
3. L. D. Bakhrakh, Modern Problems in Antenna and Waveguide Technology [in Russian], Nauka, Moscow, 1967.
4. C. M. Wade, Phys. Rev. Letters,17, no. 20, 1061, 1966.
5. E. William, Howard III, and Stephen P. Marar, Astrophys. J. Suppl. Ser.,93, 159, 1965.