Circular polarization in radars: an assessment of rain clutter reduction and likely loss of target performance

Fixed circular polarization has been used for rain clutter reduction for over thirty years,1¿3 but a proper understanding of the inter-relationship of radar propagation path and target parameters is still not widely known. The paper sets out to provide a basic analysis, together with a set of `universal curves¿ from which expected rain clutter reduction and target loss may be obtained for any particular set of circumstances. The paper then provides a guide to current literature from which the nearest reported results may be used to provide realistic performance estimates. These are supported with a limited number of experimental results obtained with an X-band radar fitted with dual aerials. Comments on the use of the propagation factor F for rain in the special case of surface search radars are offered for criticism. An alternative method of rain rejection using orthogonal linear polarization for transmission and reception is also covered in less detail.