Polarization tracking of antennas

In Part I of this paper, the polarization characteristics of antennas using "geographical" analogies are reviewed. From the longitude polarization of a dipole and the latitude polarization of a loop, a vector description is given to the radiation from these basic elements. Combinations of dipoles, loops, or dipoles and loops can then be readily analyzed from simple complex vector formulas describing the amplitude, phase, and polarization of the far fields. In particular, turnstile-type combinations providing nominal circular polarization are discussed. The vector technique is also applied to aperture antennas. It is shown that the obliquity factor of aperture antennas ( ) is a scalar constituent of an obliquity vector characterizing the radiated field, whether associated with linear or circular polarization. The vector antenna pattern for a linearly polarized horn antenna is derived and applied to the problem of the square horn fed by orthogonal TE modes in quadrature. Strong left circularly polarized lobes are radiated by a nominally right circular horn. The reduction of cross-polarization by providing a square horn with polarized teeth is described. The paper contains "geographical" drawings and sketches of 3 D contour plots of right and left circular component antenna patterns. In Part II of this paper, "Punch-Through" problems associated with sidelobe suppression systems are discussed. The effectiveness of side-lobe suppression systems at any given angle of incidence can be determined by the measurement of punch-through probability for all possible polarizations of the input signal. For systems where only random linear polarizations need be considered, a rotating linearly polarized test signal is used, and the punch-through probability can be measured directly as a percentage of a complete rotation that produces an acceptable response. For side-lobe suppression systems that must consider response to completely random polarized signals, - rotating linearly polarized source can again be used as the test signal. In this case, however, ellipticity measurements are obtained on each of the antennas separately, and this data can then be used to complete the punch-through probability by either analytic or plotting techniques. Typical results obtained for an S-band circularly polarized side-lobe suppression system are presented which support the conclusion that in a multiantenna side-lobe suppression system, careful selection of antenna types with regard to polarization tracking characteristics must be used in order to minimize the amount of unwanted signal reception or punch-through.