The Existence of a Zero-Cross-Polarization Mode Through Rain

In this paper, it is shown that there exists a zero-cross-polarization mode through rain in which no cross polarization will be induced when orthogonally polarized signals are transmitted. This mode is derived based on a matrix model of the rain-induced depolarization effect for the linear case suggested by Chu [12]. It is also assumed that when the canting angles θ of the raindrops are treated as a random variable, the received signal will have an amplitude equal to its expectation value weighted by the probability density of θ, f (θ). The zero-cross-polarization mode through rain will then be two orthogonal linear polarizations at an angle ϕ away from the conventional vertical and horizontal directions. The magnitude of ϕ can be determined if the statistical distribution of the canting angles is partially known. In fact, ϕ is determined by only two parameters, ϵ and θ
_eff
, which can be obtained from measured data. It is also shown that when f (θ) is sysmetric about its mean value, the magnitude of ϕ will be exactly that mean value. Some data reported by Chu [12] for ϵ and θ
_eff
provide an example. The results are also extended to the cases of circular polarizations and satellite communications.