## 1 Introduction
### Classification of the Received Signals  
The signal model in Equation (4) or (5) has a similar form with those in [26; 28]. However, models in the references do not consider the restriction of the signal amplitudes in LHCP antenna. If we use the typical AR values of signals and antennas, i.e., \(R_{\text{LOS}}=1.8\) dB [35] and \(R_{\text{L}}(\psi_{0},\varphi_{0})=2\) dB [34] and then substitute Equations (1) and (2), into \(B_{0}\) in Equation (6), the power of the LOS signal (\(B_{0}^{2}\)) received by the LHCP antenna ranges from \(-39.0\) dB (\(\Delta\tau_{0}=90^{\lx@math@degree}\)) to \(-13.3\) dB (\(\Delta\tau_{0}=0^{\lx@math@degree}\)) as \(A_{0}^{2}\) is normalized to \(0\) dB. Palamartchouk also reports that their receiving antenna provides cross-polarization selectivity at the level of approximately \(15\) dB or better for the reception of a signal coming from the zenith [33], which corresponds with our calculation. Before determination of \(B_{1}^{2}\), we assume that the power of the MP signal is no higher than that of the LOS signal, and the AR of the MP signal before reflection is the same with the LOS signal, i.e., \(1.8\) dB, and \(R_{\text{L}}(\psi_{1},\varphi_{1})=4\) dB (different AR values from \(2\) dB to \(10\) dB alter little to the range of the received MP signal power in LHCP antenna). By substituting Equations (1)-(3), the typical parameters of antennas as assumed above, and the electrical properties of the reflective materials given in [1] into \(B_{1}\) in Equation (6), Figure 2 illustrates the relative power of the MP signal (\(B_{1}^{2}\)) received by the LHCP antenna. When the reflected material is wet ground, the received MP signal in the LHCP antenna will not exceed \(-3\) dB as the red circle lines in Figure 2 illustrates; if it is reflected by concrete, this upper bound is approximately \(-9\) dB as the blue lines show. Based on the results of the reflection of these two typical materials, generally we assume that the power of \(B_{1}^{2}\) ranges from \(-40\) dB to \(-3\) dB as \(A_{0}^{2}\) is normalized to \(0\) dB (it is worth noting that if there is no multipath, the lower bound of \(B_{1}^{2}\) can be minus infinity and if it is reflected by a metal surface, the received power can reach as high as about 0 dB in theory). Similar with the determination of \(B_{1}^{2}\), the range of \(A_{1}^{2}\) is from \(-40\) dB to 0 dB. To sum up, the relative power of LOS and MP signals received by a dual-polarization antenna can be concluded in Table 1 below. In this paper we investigate how the additional LHCP antenna in a dual-polarization antenna contributes to mitigating the multipath that interferes with the LOS signal in RHCP antenna, thus, the relative power of the MP signal (\(A_{1}^{2}\)) in the RHCP channel is set constantly to \(-6\) dB for evaluation. Concerning the variation of both \(B_{0}^{2}\) and \(B_{1}^{2}\), we choose the maximum receivable power of the LOS signal in LHCP channel, i.e., \(-15\) dB, as the primary factor to discuss the possible received signal cases:  
* Weak LHCP signal case: \(B_{1}^{2}\) is lower than \(-15\) dB. * Strong LHCP signal case: \(B_{1}^{2}\) is higher than \(-15\) dB. We choose some typical values to cover the range of the power of \(B_{0}^{2}\) and \(B_{1}^{2}\). Table 2 shows the specific power level of \(B_{0}^{2}\) and \(B_{1}^{2}\) with which we continue our analysis in the next section. For convenience, we define the dual-polarization gain (\(DPG\)) of a multipath as \(DPG=\frac{A_{1}^{2}+B_{1}^{2}}{A_{1}^{2}}\), which is the ratio of the total power of the MP signal received by a dual-polarization antenna over that by an RHCP antenna, particularly to describe the contribution of the LHCP antenna in increasing the received power of the multipath signal over an RHCP antenna. \(DPG=2\) is equivalent to \(B_{1}^{2}=A_{1}^{2}\), which means the LHCP antenna receives as much of the MP signal power as that of the RHCP antenna.