The broadening of pulses due to multipath propagation of radiation

Observations of pulsars at low radio frequencies (ca. 100 MHz) show that the pulses received are broadened in time presumably because of multipath propagation in the interstellar medium. Uscinski’s recent analysis of this effect, by means of a diffraction theory, is here reworked into a form which is readily compared with the results of a stochastic ray-path theory, and the two approaches are found to agree exactly. The reasons for this are investigated. The ray approach suggests a Monte Carlo method of calculating the pulse shape at points deeper into the scattering medium than is possible by the method Uscinski used. Pulse shapes are calculated in this way both for the configuration discussed by Uscinski, and also for the case in which a statistically uniform medium extends along the whole length of the line of sight. Deep inside the medium the pulse shapes calculated agree well with the asymptotic solutions derived previously by the present author. The general problem for a non-uniform medium is also discussed.