Design of High-Performance Antennas and Novel Electromagnetic Radiation Measurement Techniques for Biological Cells

Abstract

The pursuit of compact wireless communication systems has been a major force driving research efforts toward miniaturization. Antennas, as one of the key components, are of no exception. At low frequencies, the prohibitively large size of conventional antennas constitutes a major hurdle in the realization of compact systems. In the first part of this dissertation, an extremely low-profile frequency-tunable composite antenna with enhanced gain and operational bandwidth is designed for wireless mobile systems in the very high frequency band. The antenna is based on a recently developed miniaturized two-legged monopole antenna. By introducing 8 parasitic elements and utilizing the mutual couplings between them, we are able to enhance the antenna gain by about 10 dB. The design is further modified for frequency tunability. It achieves an operational bandwidth of 3.32%, which is about 20 times greater than the bandwidth of the original monopole. The total dimensions of the composite antenna are 470 mm×470 mm×50 mm (λ_0/16×λ_0/16×λ_0/150, where λ_0 is the free-space wavelength at 40 MHz). In addition, a new method for measuring the performance of a monopole antenna with an electrically small ground plane using cascaded transformers is developed and presented.

The second part of the dissertation is focused on high-performance miniaturized millimeter-wave (mmWave) antennas for 5G smartphones. To address various system requirements, three antenna arrays are proposed for mmWave 5G smartphones. The first design is a 28 GHz differential dual-polarized antenna array. The array element is composed of two discrete sub-elements, a folded dipole and a substrate integrated waveguide cavity-backed slot antenna, to provide two orthogonal linear polarizations. The array can cover the entire 28 GHz band allocated for 5G applications. The second design is a low-profile dual-band dual-polarized phased array that can simultaneously cover 26-30 GHz and 38-40 GHz. A prototype of a 1×4 phased array is designed, fabricated and tested. Good agreement against full-wave simulation is achieved. In the last design, a very compact dual-polarized array topology consisting of four sub-arrays is presented. The array can support multiple 5G bands, including the 26 GHz, 28 GHz, 37 GHz and 39 GHz bands. The overall dimensions of the array are 25 mm×6 mm×0.97 mm. This dissertation addresses many design challenges associated with implementing low-cost mmWave antennas in smartphones, and provides practical solutions to mmWave 5G mobile devices.

In the last part of this dissertation, novel measurement techniques are developed to explore the existence of electromagnetic (EM) radiation from bacterial biofilms. Several special measurement systems capable of measuring extremely weak signals are designed and implemented, including a wideband near-zone radiative system, a spiral antenna system and a regenerative RF sensing system. We successfully identified EM radiation from Staphylococcus aureus biofilms in the 3-4 GHz frequency range. Furthermore, long-term and short-term cycles of the total radiation intensity are observed over the course of a 70-day experiment. This is the first time that EM radiation from bacterial biofilms has been detected in the gigahertz frequency range. This work confirms the existence of EM radiation within bacterial communities, which is a key requirement to demonstrate EM signaling among bacterial cells.