雷达数字中频接收机需要一个线性中频预放大电路和一个监测用的对数中频放大器。采用射频变压器形成输入匹 配网络,采用高性能低噪声宽带差分放大器AD8350作为线性放大器件,采用双调谐回路作为选频网络,采用魔T电路构 成功率分配网络,采用高动态范围宽带对数放大器AD8309作为对数放大器件,设计了一个兼具线性和对数特性的中频放 大器。实验表明,该放大器中频输入输出阻抗50 Ω,中心频率30 MHz,带宽4 MHz。线性通道增益为18 dB,输出动态范 围达98 dB(1 dB压缩点-90 dBm 和+8 dBm)。对数通道中,在输入功率为-68 dBm ~ -8 dBm 时,对数放大器输出电压范 围对应为0.19 V ~2.06 V。

An IF pre-amplifier is necessary in the digital IF receiver for radar. A logarithmic amplifier for radar echo monitor is needed too. RF (Radio Frequency) transformer is employed for constructing input impedance match network. High-performance, low-noise and wide band differential amplifier AD8350 is carried on the linear amplification circuit. Double resonance band pass network acts as IF filter. Power splitter is consisted of ‘Magic T'structure. High dynamic range, wide band logarithmic amplifier AD8309 is made up the major logarithm channel chip. So, radar IF amplifier with linear and logarithmic Characteristics has been designed. Experiments show that, the amplifier operates at 50 Ωinput impedance, 30 MHz center frequency and 4 MHz band width. It possess 18 dB gain and 98 dB (1 dB compression point -90 dBm and +8 dBm) output dynamic range in linear channel. Its output voltage range is 0.19 V to 2.06 V when input power is at -68 dBm to -8 dBm in logarithm channel.