Occurrence of concurrent `orthogonal' polarization modes in the Lienard-Wichert field of a rotating superluminal source

We evaluate the Lienard-Wiechert field of a rotating superluminal point source numerically and show that this radiation field has the following intrinsic characteristics. (i) It is sharply focused along a narrow, rigidly rotating spiral-shaped beam that embodies the cusp of the envelope of the emitted wave fronts. (ii) It consists of either one or three concurrent polarization modes (depending on the relative positions of the observer and the cusp) that constitute contributions to the field from differing retarded times. (iii) Two of the modes are comparable in strength at both edges of the signal and dominate over the third everywhere except in the middle of the pulse. (iv) The position angle of the total field swings across the beam by as much as 180$^\circ$. (v) The position angles of its two dominant modes remain approximately orthogonal throughout their excursion across the beam. Given the fundamental nature of the Lienard-Wiechert field, the coincidence of these characteristics with those of the radio emission that is received from pulsars is striking.