Microwave Antennas and Dielectric Surfaces

Abstract

For a plane dielectric sheet near a receiving antenna the power varies sinusoidally with distance, having a half-wave period and an average proportional to the transmission coefficient. This is explained by assuming an equivalent antenna reflection, an assumption checked by special experiments. The theory includes phase and arbitrary incidence, for which the wave may be elliptically polarized. The reciprocal of received amplitude vs. polarization then gives a similar ellipse with 90° shift in orientation. Corresponding theory for transmitters shows that the reflection varies sinusoidally with half-wave period and with average proportional to the reflection coefficient. For a distant sheet there is inverse-distance attenuation. The effect of initial antenna mismatch is fully investigated. For any cylindrical surface, including corrugations or a plane, amplitude reflection varies with angle as the secondary power pattern. With a paraboloidal antenna of radius a at wave-length λ, the reflection from a circular cylinder of radius ρ and reflection coefficient R is 6R(λp)½/13a; that from a narrow strip of width 2aq is (7Rq/80)(15−10q2+3q4); that from a narrow strip distant aq′ from the axis is proportional to R(1−q′2)4. If the initial mismatch gives a reflection r, and if the surfaces make an angle θ with the axis, the above are multiplied by (1−r2) exp (4θ2 ln2/w) where w is the antenna pattern half-width. Corresponding results are given for corrugated surfaces and series of strips. Applications to radomes are discussed, and to pressurizing seal design and tolerances. All results are extensively verified experimentally.