计算雷达的信噪比，其中pt表示峰值功率，freq表示雷达中心频率，g表示天线增益，sigma表示目标截面积，te表示有效噪声温度，b表示带宽，nf表示噪声系数，loss表示雷达损失，range表示目标距离，snr表示信噪比-Calculate the radar signal-to-noise ratio, wherein PT represents the peak power, freq said radar center frequency, g represents the antenna gain, Sigma represents the target cross-sectional area, te effective noise temperature, b represents the bandwidth, nf represents the noise factor, loss represents a radar losses, The range represents the target distance, SNR represents the signal to noise ratio