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. / Doctor of Philosophy / Nowadays, there is a high demand for compact and high-speed electronic devices such as cellphones, tablets, laptops, etc. It is therefore essential to design a miniaturized wideband antenna. Unfortunately, a trade-off exists between the bandwidth and gain of small antennas. The trade-off is based on some fundamental limits and extends to all small and passive antennas, regardless of their shape or structure. By using an active component such as an amplifier, the gain-bandwidth trade-off can be improved. However, we show that the active component adds noise to the receiving system leading to a new trade-off between noise and bandwidth in the receiving structures. In other words, utilizing the active component does not solve the problem and just replaces the gain-bandwidth trade-off with the noise-bandwidth trade-off. To improve the noise-bandwidth trade-off, we propose a new receiving structure in which we use the parametric amplifier instead of a commercially available transistor amplifier. The noise performance of the parametric amplifier is extremely better than the transistor amplifier leading to lower noise for the specified bandwidth. In particular, we improved the noise performance of the receiving system by 3 dB leading to doubling the communication distance.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/111228 |
| Date | 18 January 2021 |
| Creators | Loghmannia, Pedram |
| Contributors | Electrical Engineering, Manteghi, Majid, Earle, Gregory D., Yang, Yaling, Safaai-Jazi, Ahmad, Emori, Satoru |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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