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Browsing by Author "Loghmannia, Pedram"

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    Time-Variant Components to Improve Bandwidth and Noise Performance of Antennas
    Loghmannia, Pedram (Virginia Tech, 2021-01-18)
    Without noise, a wireless system would be able to transmit and receive signals over an arbitrary long-distance. However, practical wireless systems are not noise-free, leading to a limited communication range. Thus, the design of low-noise devices (such as antennas, amplifiers, and filters) is essential to increase the communication range. Also, it is well known that the noise performance of a receiving radio is primarily determined by the frontend including the antenna, filter, and a low-noise amplifier. In our first design, we intend to reduce the noise level of the receiving system by integrating a parametric amplifier into the slot antenna. The parametric amplifier utilizes nonlinear and/or time-variant properties of reactive elements (capacitors and/or inductors) to amplify radio frequency signals. Also, the parametric amplifier offers superior noise performance due to its reactive nature. We utilize the parametric amplifier to design a low-noise active matching circuit for electrically small antennas in our second design. Using Chu's limit and the Bode-Fano bound, we show a trade-off between the noise and bandwidth of the electrically small antennas. In particular, to make the small antenna wideband, one needs to introduce a mismatch between the antenna and the amplifier. Due to the mismatch, the effect of the low-noise amplifier becomes even more critical and that is why we choose the parametric amplifier as a natural candidate. As a realized design, a loop antenna is configured as a receiver, and the up-converter parametric amplifier is connected to it leading to a low-noise and wideband active matching circuit. The structure is simulated using a hybrid simulation technique and its noise performance is compared to the transistor counterpart. Our simulation and measurement results show more than 20 times bandwidth improvement at the expense of a 2 dB increase in the noise figure compared to the passive antenna counterpart.