Characterisation and Design of Novel Non-Foster Circuits for Electrically Small Antennas
Publisher
Metadata
Show full item recordAbstract
There is a demand for broadband electrically small antennas that cover
large frequency bands without any requirement of reconfiguration techniques.
This is particularly true at low frequencies (VHF/UHF), where
wavelengths are long and antennas are physically large. The fundamental
gain-bandwidth limitation was related to the electrical size of passive
electrically small antennas by Wheeler and Chu; their result implied that an
electrically small antenna exhibits high quality factor which limits the bandwidth.
Additionally, the gain-bandwidth limitation was related to impedance
matching conditions by the Bode-Fano criteria, which restricts available
bandwidth using conventional reactive elements. A non-Foster circuit approach
has been presented which delivers a broadband input impedance
match and also overcomes the aforementioned fundamental limits. These
non-Foster impedance circuits can be realised by negative impedance converters
(negative inductance and/or capacitance). The thesis also explores
the advantages and challenges of antenna impedance matching using negative
impedance circuits based on two topologies: (1) conventional transistorbased
circuits, and (2) a novel resonant tunnelling diode approach. The
advantages of non-Foster circuits in the implementation of broadband small
antennas include wideband performance around one-tenth of the self-resonant
frequency and overcoming of the fundamental limits associated with passive
antennas. Diode-based circuits are more compact, easily configurable, less
sensitive to stability, have low power consumption and are less complex as
compared to the transistor based designs. These features makes it a potential
candidate for array and meta-material applications. However, there
are few challenges for non-Foster circuit integration with an antenna due
to high noise figure, which affects the system channel capacity and receiver
performance in a communication system. A detailed design procedure has
been developed to mitigate the effects of noise and instability and also, the
system performance and measurement of the non-Foster circuit integrated
antennas have been discussed.
Authors
Nagarkoti, Deepak SinghCollections
- Theses [4235]