Wideband Response Of Non-Foster Element And Its Applications

With the development of modern communication, the advanced technology such as modulation techniques and spread spectrum have been widely used. Moreover, the improvement of large scale integrated circuit and space technology lead to the miniaturization of the electron device. Therefore, people demand more on the miniaturization and broadband of the communication devices. At the same time, antenna, which is the front terminal component in the communication equipment, whose miniaturization and broadband become a hot topic in the field of antenna research.In the recent years, small antenna is often applied to VHF or lower frequency. However, for the balance of high quality factor and bandwidth efficiency the passive matching would be restricted by the Bode-Fano gain bandwidth product. According to the Foster reactance theory, the Non-Foster element has the opposite properties of frequency response compared to the normal inductance and capacitance. Thus it could be applied to the small antenna to offset the high reactance and make the antenna no longer limited to Bode-Fano limit. Then we could increase the bandwidth, signal to noise ratio and gain of the small antennas.We investigate for the first time the full-range radio frequency response of a Non-Foster element. Our research indicates that the de-embedded input impedance of an NE co-existing with a properly designed stabilization network has an inverted Lorentzian absorption resonance that satisfies the Kramers-Kronig relations. This thesis discusses two kinds of Non-Foster circuits, one is based on operational amplifier and the other is based on transistors. According to calculation, simulation and experiment, we analyze the properties of the Non-Foster element well.Moreover, we applied the Non-Foster element into the electrically-small antennas. One is a coplanar waveguide (CPW) fed monopole antenna, and the other is dipole antenna design using balanced microstrip balun feed. Two kinds of antennas are connected in parallel with the Non-Foster elements. We measure the S parameter by using the vector network analyzer and standard antenna. Compared with the passive match, we could observe the advantages of Non-Foster match.