Calibrating the super low frequency （SLF） magnetic antenna in magnetic free space or an outdoor environment is difficult and complicated due to the large size calibration instruments and lots of measurement times. A...Calibrating the super low frequency （SLF） magnetic antenna in magnetic free space or an outdoor environment is difficult and complicated due to the large size calibration instruments and lots of measurement times. Aiming to calibrate the SLF magnetic antenna simply and efficiently, a calibration system comprised of a multi-frequency source, an A.C constant-current source and a solenoid is proposed according to the characteristic of an SLF magnetic antenna. The static magnetic transfer coefficient of the designed solenoid is calibrated. The measurement of the frequency response characteristics suggests the transfer coefficient remains unchanged in the range of the SLF band and is unaffected by the magnetic antenna internally installed. The CORDIC algorithm implemented in an FPGA is realized to generate a linear evenly-spaced multi-frequency signal with equal energy at each frequency. An A.C constant weak current source circuit is designed in order to avoid the impact on the magnetic induction intensity of a calibration system affected by impedance variation when frequency changing, linearity and the precision of the source are measured. The frequency characteristic of a magnetic antenna calibrated by the proposed calibration system agrees with the theoretical result and the standard Glass ring calibration result. The calibration precision satisfies the experimental requirement.展开更多
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 dete...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.展开更多
This article proposes a new type of antenna which allows getting rid of certain limitations of classic monopole antenna. Like a normal monopole, this antenna belongs to a class of radio antenna consisting of a straigh...This article proposes a new type of antenna which allows getting rid of certain limitations of classic monopole antenna. Like a normal monopole, this antenna belongs to a class of radio antenna consisting of a straight rod-shaped conductor. But unlike a classic monopole, this antenna can operate at all frequencies of a very wide range. In addition, it does not require grounding. The article considers the wide possibilities of antenna applications.展开更多
基金supported by the Defense Pre-Research Foundation of China(No.51401020503)
文摘Calibrating the super low frequency （SLF） magnetic antenna in magnetic free space or an outdoor environment is difficult and complicated due to the large size calibration instruments and lots of measurement times. Aiming to calibrate the SLF magnetic antenna simply and efficiently, a calibration system comprised of a multi-frequency source, an A.C constant-current source and a solenoid is proposed according to the characteristic of an SLF magnetic antenna. The static magnetic transfer coefficient of the designed solenoid is calibrated. The measurement of the frequency response characteristics suggests the transfer coefficient remains unchanged in the range of the SLF band and is unaffected by the magnetic antenna internally installed. The CORDIC algorithm implemented in an FPGA is realized to generate a linear evenly-spaced multi-frequency signal with equal energy at each frequency. An A.C constant weak current source circuit is designed in order to avoid the impact on the magnetic induction intensity of a calibration system affected by impedance variation when frequency changing, linearity and the precision of the source are measured. The frequency characteristic of a magnetic antenna calibrated by the proposed calibration system agrees with the theoretical result and the standard Glass ring calibration result. The calibration precision satisfies the experimental requirement.
基金Project supported by the Defense Pre-Research Foundation of China(No.51401020503)
文摘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.
文摘This article proposes a new type of antenna which allows getting rid of certain limitations of classic monopole antenna. Like a normal monopole, this antenna belongs to a class of radio antenna consisting of a straight rod-shaped conductor. But unlike a classic monopole, this antenna can operate at all frequencies of a very wide range. In addition, it does not require grounding. The article considers the wide possibilities of antenna applications.
