# Difference between revisions of "Polarization Calibration"

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== Linear to Circular Conversion == | == Linear to Circular Conversion == | ||

At EOVSA’s linear feeds, in the electric field the linear polarization, X and Y, relates to RCP and LCP (R and L) as: | At EOVSA’s linear feeds, in the electric field the linear polarization, X and Y, relates to RCP and LCP (R and L) as: | ||

− | |||

− | |||

− | |||

− | :<math> | + | :<math> |

+ | \begin{align} | ||

+ | R = X + iY | ||

+ | L = X - iY | ||

+ | \end{align} | ||

+ | </math> | ||

+ | |||

+ | In terms of autocorrelation powers, we have the 4 polarization products XX*, YY*, XY* and YX*, where the * denotes complex conjugation. The quantities RR* and LL* are then | ||

− | :<math> LL^* = (X - iY)(X - iY)^* = XX^* + iXY^* - iYX^* + YY^* </math> | + | :<math> |

+ | \begin{align} | ||

+ | RR^* = (X + iY)(X + iY)^* = XX^* - iXY^* + iYX^* + YY^* | ||

+ | LL^* = (X - iY)(X - iY)^* = XX^* + iXY^* - iYX^* + YY^* | ||

+ | \end{align} | ||

+ | </math> | ||

One problem is that there is generally a non-zero delay in Y with respect to X. This creates phase slopes in XY* and YX* from which we can determine the delay very accurately. As a check, | One problem is that there is generally a non-zero delay in Y with respect to X. This creates phase slopes in XY* and YX* from which we can determine the delay very accurately. As a check, |

## Revision as of 20:19, 24 September 2016

## Linear to Circular Conversion

At EOVSA’s linear feeds, in the electric field the linear polarization, X and Y, relates to RCP and LCP (R and L) as:

In terms of autocorrelation powers, we have the 4 polarization products XX*, YY*, XY* and YX*, where the * denotes complex conjugation. The quantities RR* and LL* are then

One problem is that there is generally a non-zero delay in Y with respect to X. This creates phase slopes in XY* and YX* from which we can determine the delay very accurately. As a check,

For completeness:

When I plot the quantities I, V, R and L as measured (Figure 1) for geosynchronous satellite Ciel-2, the results look reasonable, except that there are parts of the band where R and L are mis-assigned, and others where they do not separate well.

The problem is that residual phase slope of Y with respect to X, caused by a difference in delay between the two channels. This can be seen in the upper panel of Figure 2, which shows the uncorrected phases of XY* and YX*. To correct the phases, the RCP phase was fit by a linear least-squares routine, and then the phases were offset by π/2 for both XY* and YX* according to:

## Polarization Mixing Correction

Due to relative feed rotation between az-al mounted antennas and equatorial mounted antennas