Bias Analysis and Correction for Wideband Polarimetric Phased Array Radar

Abstract

There exhibit some challenges for the wideband fully polarimetric phased array radar (PPAR) in order to meet the requirement for highly accurate polarimetric measurements. Specifically, the electric field radiated from the horizontal $(H)$ port is not necessarily orthogonal to that from the vertical $(V)$ port when the beam is directed away from the normal of the antenna plane. The cross-polar components are produced, and this is where the polarization biases yield from. Meanwhile, the parameters of electronic equipment, such as transmitter and receiver, are frequency-dependent. The polarimetric characteristics of the practical wideband PPAR antenna vary with frequency, and the polarization non-orthogonality are also frequency-dependent. Therefore, the wideband characteristics and the frequency-dependent polarimetric properties are mutually coupled. All the above factors will cause the polarization measurement bias, and they can also be considered as the frequency response (FR). In this paper, a bias correction method for the wideband PPAR is proposed. Firstly, the fully polarization measurement bias model based on the transmitting and receiving process of the electromagnetic wave is built, and the effects of frequency response on the polarization scattering matrix (PSM) are analyzed. Then, the proposed frequency band division method for measurement parameter bias is detailedly derived to eliminate the effect of the bandwidth. A wideband microstrip patch array element is conducted to demonstrate the effectiveness of the proposed method. The effects of bandwidth and beam direction for the polarimetric variables, such as differential reflectivity $(Z_{DR})$ and linear depolarization ratio $(L_{DR})$ , are analyzed. The simulation results show that the biases of $Z_{DR}$ and $L_{DR}$ can be decreased to less than 0.1 dB and −40 dB, respectively. The proposed method can maintain a favorable measurement accuracy with widening the frequency band.