Origin of the circularly polarised sub-bands

Explain the origin of the two frequency sub-bands (near approximately 800 MHz and 1 GHz) that exhibit 100% circular polarisation in the Relay 2 burst, given that neither an electrostatic discharge nor a micrometeoroid impact mechanism accounts for this feature.

Background

Polarisation analysis shows the event is predominantly linearly polarised across most of the band but becomes fully circularly polarised at two narrow frequency regions near 800 MHz and 1 GHz. The authors evaluate both ESD and micrometeoroid impact scenarios as plausible burst origins but note that neither mechanism explains these circularly polarised bands.