On mathematical and physical principles of transformations of the coherent radar backscatter matrix

TL;DR

This paper clarifies the correct mathematical principles behind polarization basis transformations in radar backscatter matrices, emphasizing the role of conjugation and dual spaces, and introduces spinor formalism for consistency.

Contribution

It corrects misconceptions about the congruential rule, derives it from fundamental principles, and proposes a spinor-based formalism for accurate polarization transformations.

Findings

The congruential rule is justified through proper conjugation considerations.

A dual space framework for antenna and wave states is established.

Spinor formalism provides a consistent approach to polarization basis transformations.

Abstract

The congruential rule advanced by Graves for polarization basis transformation of the radar backscatter matrix is now often misinterpreted as an example of consimilarity transformation. However, consimilarity transformations imply a physically unrealistic antilinear time-reversal operation. This is just one of the approaches found in literature to the description of transformations where the role of conjugation has been misunderstood. In this paper, the different approaches are examined in particular in respect to the role of conjugation. In order to justify and correctly derive the congruential rule for polarization basis transformation and properly place the role of conjugation, the origin of the problem is traced back to the derivation of the antenna hight from the transmitted field. In fact, careful consideration of the role played by the Green's dyadic operator relating the antenna height to the transmitted field shows that, under general unitary basis transformation, it is not justified to assume a scalar relationship between them. Invariance of the voltage equation shows that antenna states and wave states must in fact lie in dual spaces, a distinction not captured in conventional Jones vector formalism. Introducing spinor formalism, and with the use of an alternate spin frame for the transmitted field a mathematically consistent implementation of the directional wave formalism is obtained. Examples are given comparing the wider generality of the congruential rule in both active and passive transformations with the consimilarity rule.