DQRID : D050714.4
Start DateStart TimeEnd DateEnd Time Data Quality Metric
SGP/MMCR/C1 - Poor cross polar isolation
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.
Users of cross polarization data should be aware the cross polar isolation is only 17 

dB and not the 25-30 dB it should be.
  • CircularDepolarizationRatio

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