| Description: | This last spring, Sergey Matrosov pointed out that the Circular Depolarization Ratio
measurements on the SGP radar indicated the isolation between the co and cross channels was
only about 15 dB. Typically isolation of 25-30 dB is expected for polarization measurements
to be useful.
We set about to see if we could identify the source of the poor isolation. Kevin Widener
had purchased a custom built orthomode transducer and polarizer that hadn't gone through
any previous testing and we decided to swap it out with an ETL unit that had shown good
isolation in the past. Kevin performed the swap a couple of weeks back and this week the
latest archive data was available to compare results between the OMTs.
Results from two precipitating cloud conditions, where we looked below the melting layer,
where we expect to find domination of spherical water droplets and therefore maximum
values for cdr - the maximum isolation (CDR) appears to be about 17 dB. The results showed
that the poor isolation is probably not due to the OMTs but rather to the antenna itself. |