The third obstacle is the general lack of research on NFC noise and SNR performance Sussman-Fort and Rudish and Jacob and Sievenpiper provided conflicting results on SNR performance in HF. Previous researchers have presented methods in ultrahigh frequency (UHF) and did not address the matching process between the antennas and the tunable NFCs. The second obstacle is the lack of a negative tunable inductor suitable for VLF receive antenna matching. This matching circuit can only function at a single frequency or in a small bandwidth as opposed to the whole bandwidth. To the best of the authors’ knowledge, the only NFC design in VLF was described by Albee from 14 to 38 kHz, where a variable capacitance was matched passively to the antenna and the antenna’s reactance was canceled by a negative reactance generated by a single NFC. The bandwidth of the signal is limited by using this type of antennas, so improving the bandwidth and SNR of the received signal is very necessary. Now, the receive antennas equipped on the submarine are passive antennas, such as trailing wire antennas (about 200 m long) or loop antennas. Submarines under water usually receive VLF signal which is transmitted by large VLF transmitting stations although the VLF signal could go through the water, the signal bandwidth and rate received by the submarine are relatively low. VLF receive loop antennas, which are common in submarines as a signal reception component, are a good example of this. First, little is known about the antennas’ operation frequency band enlargement process, especially below HF. There are three main obstacles to the practical realization of NFCs.
#Vlf receiver schematic series
Also, negative non-Foster impedances are not absolutely stable circuits which could be a serious problem in practical application the stability of negative impedances in several circuits was analyzed, including series C-C tank circuit, parallel C-C tank circuit, and series- parallel C-C tank circuit. Different NFCs, including CMOS based NFC, diode based NFC, and amplifier based NFC have been matched to various types of antennas, including the monopole antenna, loop antenna, Egyptian axe dipole antenna, microstrip leaky-wave antenna, and parasitic array, with mostly favorable results. Earlier researchers mainly concentrated studies on the high frequency (HF) band. Several NFC topologies have been reported to date, most of which were designed for enhanced stability and bandwidth performance. These negative elements exist only theoretically an equivalent circuit, for example, negative impedance converter (NIC) or negative impedance inverter (NII or NIV), is necessary to invert the passive capacitor to a negative capacitor or inductor. The limit can be overcome by adding active elements to the antenna’s matching circuit and “non-Foster” elements are particularly effective due to their “negative capacitance” or “negative inductance” characteristics. Wheeler and Chu provided very useful descriptions of this fundamental tradeoff limit.
ESAs infamously suffer from high radiation quality factor ( ) value and a corresponding efficiency-bandwidth tradeoff when using passive impedance matching. IntroductionĮlectrically small antennas (ESAs) are a popular research subject because they are the enabling technology for wireless communication applications.
The noise and received signal-to-noise ratio (SNR) of the matching network were assessed to find that, with a low noise floor level (4 dB) receiver, the SNR of the passive loaded antenna performs better than the non-Foster loaded antenna in VLF. A loop antenna was matched to the designed NFC with −10 dB fractional bandwidth, marking a 383% improvement as well as enhanced transducer gain ( ) compared to most bands in passive matching (over 15–30 kHz). The NFC can be applied to different VLF loop antennas by adjusting the number and inductance of the cells in the tunable inductor.
A 1 1 m VLF receive loop antenna was designed with a CMOS switch-based tunable inductor built into the NFC. This paper presents a non-Foster matching circuit (NFC) for very low frequency (VLF) receive loop antennas.
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