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Besides the electrode-pair antenna,the magnetic antenna is also used for the extremely low frequency (ELF) submarine communication.To receive the weak ELF signals,the structure of a small sized magnetic antenna determines its specific electrical characteristics.The ELF magnetic antenna shows high internal resistance, alternating-current impedance,and a resonance frequency near the operating bandwidth.In accordance with the electrical characteristics of ELF magnetic antenna,a low noise preamplifier and frequency compensation circuit were designed and realized.The preamplifier is a three-stage negative feedback circuit,which is composed of parallel JFET,common-emitter amplifier with a Darlington structure and a common-collector amplifier in push-pull connection.And a frequency compensation circuit is cascaded to compensate the characteristic in low frequency range.In the operating bandwidth f = 30-200 Hz,the circuit has a gain of 39.4 dB.The equivalent input noise is 1.97 nV/Hz~(1/2) and the frequency response keeps flat in operating bandwidth.The proposed preamplifier of the ELF magnetic antenna performs well in receiving ELF signals.
Also the electrode-pair antenna, the magnetic antenna is also used for the extremely low frequency (ELF) submarine communication.To receive the weak ELF signals, the structure of a small sized magnetic antenna determines its specific electrical characteristics. The ELF magnetic antenna shows high internal resistance, alternating-current impedance, and a resonance frequency near the operating band. In accordance with the electrical characteristics of ELF magnetic antenna, a low noise preamplifier and frequency compensation circuit were designed and realized. The preamplifier is a three-stage negative feedback circuit, which is composed of parallel JFET, common-emitter amplifier with a Darlington structure and a common-collector amplifier in push-pull connection. And a frequency compensation circuit is cascaded to compensate the characteristic in low frequency range. f = 30-200 Hz, the circuit has a gain of 39.4 dB. The equivalent input noise is 1.97 nV / Hz ~ (1/2) and the frequency response keeps flat in operating bandwidth. The proposed preamplifier of the ELF magnetic antenna performs well in receiving ELF signals.