C. W. Horton

The Radiation Patterns of Dielectric Rods—Experiment and Theory

A theory is developed describing the electromagnetic radiation from dielectric rods used as terminations to rectangular wave guides. The radiation patterns are computed from the fields due to equivalent magnetic and electric currents on the surfaces of the rods. These equivalent currents are determined by use of Schelkunoffs equivalence principle applied to approximate fields within the dielectric. Specific calculations are carried out for rods whose average dimensions are 0.9″×0.25″ and whose lengths vary from three to ten wave‐lengths. Experimental patterns are obtained for eight polystyrene rods, some of which are variable in length. Agreement with theory is found for rods from three to six wave‐lengths long; differences between experiment and theory are discussed.

Convection Currents in Porous Media: II. Observation of Conditions at Onset of Convection

Small‐scale experiments have been carried out for determining the minimum vertical thermal gradient which is required to cause convection in liquids entrapped in porous media. Observations relative to the onset of convective flow in unconsolidated sands indicate that the present theories predict minimum gradients which are excessive by considerable amounts, possibly because they neglect the temperature‐dependence of viscosity. The ratio of theoretical to observed gradients is found to be roughly R=(Kh2μAV/kρα)0.51, where h2 is the thermal diffusivity, μAv is average viscosity, k is flow‐permeability, ρ is density of liquid, α is the coefficient of cubical expansion of the liquid, and where K = 10−3 sec.2 per cm2 °C for c.g.s. units. By extrapolation, it is possible to strengthen the earlier conclusion that convection occurs in the Woodbine sand near the Mexia fault zone.

On the Calculation of Radiation Patterns of Dielectric Rods

A previous paper described the radiation field of a dielectric rod used as a termination for a wave guide. The theory therein made use of a standing wave distribution of equivalent currents over the surface of the rod to describe its radiation effect. It is shown in this paper that the equivalent currents may be expressed in terms of traveling waves without appreciably changing the computed radiation patterns.

On the Diffraction of Radar Waves by a Semi‐Infinite Conducting Screen

The diffraction patterns of radar waves about a semi‐infinite copper screen have been measured. The measurements were made by revolving a bisectoral horn in a circle of radius 15″ or 30″ about the diffracting edge. Measurements were made at three positions along the edge, one of which coincided with the corner of the screen so that the pattern obtained was actually that of a quarter‐infinite plane. Measurements were made for two orientations of the screen corresponding to angles of incidence of 0° and −22½°. Theoretical patterns have been calculated for the entire 360° of rotation and these agree well with the experimental patterns. A comparison is made between the theory, measurements, and the equivalent optical measurements.

An Experimental Investigation of the Dielectric Rod Antenna of Circular Cross Section Excited in the Dominant Mode

The radiation pattern and the gain were measured for four series of dielectric antennas of circular cross section. These antennas were excited by a TE11 mode in a circular metallic wave guide at a frequency of 9275 mcps. Only one parameter was changed in each series of rods so that the effect of this parameter on the pattern and gain could be studied. Measurements of gain are presented for two further series of rods in which the length is varied. The measurements showed that a polystyrene rod of length 6λ0 and constant cross section has maximum gain and best pattern for a diameter of approximately 2λ0. On the other hand when the taper of a Lucite rod was varied while the length and the maximum diameter were held constant at 6λ0 and 0.87λ0, respectively, the gain and the pattern behavior improved as the minimum diameter was decreased to zero. It is shown that losses in the dielectric produce a significant decrease in the gain.

On the Radiation Patterns of Dielectric Rods of Circular Cross Section— the TM0,1 Mode

The radiation patterns have been measured for five dielectric rods of circular cross section which were excited in the TM0,1 mode. These rods were each 0.870λ0 in diameter, and the lengths were 2λ0, 4λ0, 6λ0, 8λ0, and 10λ0. The theoretical radiation patterns have been computed by means of equivalent surface electric and magnetic currents. Excellent agreement is obtained when it is assumed that the diameter of the surface on which these currents are distributed is 0.65 of the diameter of the dielectric rod. Representative experimental and theoretical patterns are shown for the full 360°.

On the Diffraction of a Radar Wave by a Conducting Wedge

Diffraction patterns of radar waves have been measured about the edge of a perfectly conducting wedge. Theoretical patterns have been calculated using an asymptotic solution suggested by Pauli. Good agreement is observed between experimental and calculated patterns. The thin wedge tested showed much similarity in diffracting properties to a suitable semi‐infinite conducting screen. The results may have application to diffraction effects about wedge‐shaped wings on high speed aircraft and missiles.

On the Diffraction of a Plane Electromagnetic Wave by a Paraboloid of Revolution

The problem of the diffraction of a plane electromagnetic wave by the convex surface of a paraboloid of revolution is examined. Expressions for the components of the incident wave, the scattered wave, and the refracted wave are obtained and are written in such a form that boundary conditions can be satisfied over a paraboloidal surface ξ=ξ0. The analysis is then restricted to the case of a perfectly conducting paraboloid and a wave whose wave front is perpendicular to the axis of rotation. The amplitude of the scattered wave is plotted as a function of the distance along the axis of rotation for three paraboloids. One of these curves is compared with the scattered field produced by a sphere whose radius is equal to the radius of curvature of the paraboloid at the nose.