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<p> Recently, there has been a strong trend in medicine to use implanted electronic devices for diagnostic and/or therapeutic purposes. These devices usually involve a one- or twoway communication link, allowing communication with the implant. One revolutionary implanted system that was recently launched into the healthcare market is the wireless imaging capsule for monitoring the gastrointestinal tract. Among the application-specific design challenges of such a wireless system are the severe constraints on low power and on small physical size. Besides, the allowed power levels of signals due to in-body radiating devices are restricted to very low values due to human safety concerns. To meet the requirements of such a wireless system, highly efficient, small-size, low-power transmitting radio frequency (RF) blocks are needed. </p> <p> This thesis focuses on the design, implementation and measurements of the last two blocks in the transmitter, namely the antenna and the power amplifier (PA). Three PA circuits have been designed and measured, all of class AB topology. The first two PAs operate at 2.4 GHz, while the third is designed for 405-MHz operation. All designs are fully integrated and realized in a standard mixed-signal 0.18 ~m complementary metaloxide- semiconductor (CMOS) process. Measurement results show that at a supply voltage of 1.4 V, the circuits have a maximum drain efficiency of 32% and 40.7% for the 2.4-GHz and the 405-MHz designs, respectively, while providing an output power of 7.2 and 8 dBm to the load. These results greatly outperform similar designs in the literature, proving that class AB PAs, if properly designed, are well-suited for low-power biotelemetry application. </p> <p> A simple layout design approach was developed to minimize the parasitic effects of on-silicon interconnections that cause significant degradation in the performance of RF integrated circuits (RF ICs ). This approach was used to design the layouts of the three PA circuits presented in this work, and the approach was tested on a low-noise amplifier (LNA) operating at 5 GHz, since at such a high frequency the parasitics become more pronounced. Measurements on the LNA circuit show good agreement with simulations. </p> <p> Thus, next to allowing for optimized circuit performance, this approach can shorten the design time of RF ICs by providing very good predictions of performance characteristics. </p> <p> The last part of this thesis deals with the analysis and design of efficient in-body antennas. A study of the use of loop antennas in medical implants was conducted. Simulations and measurements have been used to characterize the radiation performance of loop antennas in terms of their radiation resistance, transmitting bandwidth and biocompatibility. At 405 MHz, the antenna has proven to be efficient in the dissipative biological tissues, to have a wide transmitting bandwidth, and a specific absorption rate (SAR) distribution that is well below the safety limits. To further verify its suitability for in-body operation, a miniature loop antenna was fabricated and measured at 405 MHz and 2.4 GHz. For measurement purposes, two body simulating chemical solutions were prepared in-house to provide the necessary radiation environment. Measurements show that small loop antennas are well matched in the medium and are thus good in-body radiators. </p> / Thesis / Master of Applied Science (MASc)

This dissertation reports results of an investigation into the performance of adaptive beamforming and diversity combining using antenna arrays that can be mounted on handheld radios. Handheld arrays show great promise for improving the coverage, capacity, and power efficiency of wireless communication systems. Diversity experiments using a handheld antenna array testbed (HAAT) are reported here. These experiments indicate that signals received by the antennas in two-element handheld antenna arrays with spacing of 0.15 wavelength or greater can be combined to provide 7-9 dB diversity gain against fading at the 99% reliability level in non line-of-sight multipath channels. Thus, peer-to-peer systems of handheld transceivers that use antenna arrays can achieve reliability comparable to systems of single-antenna handheld units, with only one-fifth the transmitter power, resulting in lower overall power consumption and increased battery life. Similar gains were observed for spatial, polarization, and pattern diversity. Adaptive beamforming with single- and multi-polarized four-element arrays of closely spaced elements was investigated by experiment using the HAAT, and by computer simulation using a polarization-sensitive vector multipath propagation simulator developed for this purpose. Small and handheld adaptive arrays were shown to provide 25 to 40 dB or more of interference rejection in the presence of a single interferer in rural, suburban, and urban channels including line-of-sight and non line-of-sight cases. In multipath channels, these performance levels were achieved even when there was no separation between the transmitters in azimuth angle as seen from the receiver, and no difference in the orientations of the two transmitting antennas. This interference rejection capability potentially allows two separate spatial channels to coexist in the same time/frequency channel, doubling system capacity. / Ph. D.

In the field of antenna design and analysis, often the need arises to numerically extrapolate the far-zone performance of a radiating structure from its known (or assumed known) near-zone electromagnetic field. Mathematical processes developed to accomplish such a task are known in the literature as near-zone to far-zone transformations (NZ-FZTs) as well as near-field far-field (NF-FF) transformations. These processes make use of sampled near-zone field quantities along some virtual surface, viz., the transformation surface, that surrounds the radiating structure of interest. Depending upon the application, samples of the required near-zone field quantities are supplied via analytical, empirical, or computational means. Over the years, a number of NZ-FZT processes have been developed to meet the demands of many applications. In short, their differences include, but are not limited to, the following: (1) the size and shape of the transformation surface, (2) the required near-zone field quantities and how they are sampled, (3) the computational methodology used, and (4) the imbedding of various application-driven features. Each process has its pros and cons depending upon its specific application as well as the type of radiation structure under consideration. In this dissertation we put forth a new and original NZ-FZT process that allows the transformation surface along which the near-zone is sampled to be spheroidal in shape: namely a prolate or oblate spheroid. Naturally, there are benefits gained in doing so. Our approach uses a formulated eigenfunction expansion of spheroidal wave-harmonics to develop two distinct, yet closely related, NZ-FZT algorithms for each type of spheroidal transformation surface. The process only requires knowledge of the E-field along the transformation surface and does not need the corresponding H-field. Given is a systematic exposition of the formulation, implementation, and verification of the newly developed NZ-FZT process. Accordingly, computer software is developed to implement both NZ-FZT algorithms. In the validation process, analytical and empirical radiation structures serve as computational benchmarks. Numerical models of both benchmark structures are created by integrating the software with a field solver, viz., a finite-difference time-domain (FDTD) code. Results of these computer models are compared with theoretical and empirical data to provide additional validation. / Ph. D.