This work seeks to supplement the work previously done on the Ultra-Wide Band SSDL Circulator. The technique, Sequentially-Switched Delay Line (SSDL), is applied in this circuit to achieve non-reciprocal behavior using only classical, reciprocal integrated circuit elements. Previous iterations of this project have yielded successful results; showing the ability to achieve wide band circulator performance from on-chip measurements. The control element essential to the performance of the circuit is the appropriate biasing of the gates of the Gallium-Nitride (GaN) Field Effect Transistor (FET) switches. These high-power, high-channel breakdown devices require gate bias ranges spanning 10 V to 0 V. Driving such large gate voltages causes the circuit to draw a large amount of power, on the order of watts. In this work, resonant Inductor-Capacitor (LC) sections were used at the gate drive to boost the switching signal through the resonant gain effect. The resultant work showed that a small input gate drive signal could be boosted by the LC section to the required voltages to drive the GaN FETs. On-chip measured results showed close to a ten-fold reduction in circuit power consumption with no impact on performance. Realistic implementations of this technique are fundamentally limited by the quality factor of the LC section components. Two circuits were fabricated, a 1.25 GHz variant and a 2.5 GHz variant, and are described in this work.

Power efficiency, bandwidth, and signal fidelity are critical specs of wireless transmitters, which are often traded off in transmitters with conventional analog circuit and antenna design. For example, high quality factor antennas and components help to achieve high efficiencies but often suffer bandwidth limitations. Switched-mode amplifiers and antennas have been proposed to achieve both high efficiency and broad bandwidth but the quantization noise issues prevent those techniques from being practically deployed.

In this research, digitally enhanced techniques are proposed to enhance the design of switched-mode RF transmitter toward higher data rates, better power efficiency and lower quantization noise. Two specific research projects will be discussed. In the first project, an active noise filtering technique called Channelized Active Noise Elimination (CANE) is used to actively suppress the quantization noise in the bitstream modulated transmitter by employing the delaying and combining structure of multiple power amplification channels. The power efficiency of each of the power amplifier is preserved by a load modulation mechanism in the power combining operation. The proposed technique is implemented in a transmitter with a FPGA based signal processing module and the experimental results prove that the CANE technique can be a software-controlled, robust and flexibly tunable filter solution.

The second project is utilizing the Direct Antenna Modulation (DAM) technique to surpass the physical bandwidth limit imposed by the high radiation quality factor of the electrically small antenna. The DAM concept has been proposed with various types of digital modulations, such as On/Off Keying, BPSK and QPSK, etc. A newly proposed DAM frequency shift keying (FSK) is developed to synthesize the parasitic components of switches with the matching circuit to improve the switching quality and signal integrity in the switched-mode electrically small antenna system.

A near-field power transfer equation for an inductively coupled near-field system is derived based on the equivalent circuit model of the coupled resonant loops. Experimental results show that the proposed near-field coupling equation is trustworthy as it correctly predicts the transferred power versus distance relationship for different values of loaded quality factors at the transmitter and the receiver.

Capacity performance of near-field communication (NFC) links is analyzed for noise limited and interference limited scenarios based on information theory. The analytical results provide guidelines for design of inductively coupled antenna systems as the power and capacity budget of the link is carried out. Examples of inductively coupled VLF NFC links are evaluated for different operating scenarios, demonstrating the efficacy and importance of the proposed near-field link budget.

However, in a conventional setup of inductively coupled NFC link, the power coupled through and the bandwidth must be traded off. Direct Antenna Modulation (DAM) is a feasible scheme to break this dilemma. With DAM utilized in NFC link, the power and bandwidth product limit in a high Q system can be circumvented because the non-linear/time-varying nature of the operation allows high speed modulations decoupled from the charging and discharging process of the high-Q resonator. In this work, the theory of NFC link with DAM on the transmitter is presented and validated with an experimental setup. Improvement in reception of the high-speed modulation information is observed in the experiment, implying that a superior capacity performance of a NFC link is achieved through DAM versus the traditional scheme.

The resonant coupling efficiency is limited by the product of the quality factors Q, of the transmitter and receiver and the coupling coefficient k. We observe that in order to achieve maximum efficiency, the ratio of the load-to-loss impedances at both the source and load should be equal to a prescribed value. This is the same condition that yields simultaneous impedance matching at source and load. The efficiency limit is then calculated for single transmitter and two uncoupled receivers. In that case, optimal efficiency is obtained when the load-to-loss impedance ratio is equal to the same prescribed value for all devices simultaneously. However, this condition does not provide for simultaneous matching at the source and loads, which turns out to be impossible. The analysis is then generalized for a single transmitter and N uncoupled receivers and we find that as the number of receivers increases, the total efficiency limit also increases. Finally, we present the efficiency limits and optimal conditions for a system consisting of single and multiple repeaters between transmitter and receiver, which have been shown previously to relay power to larger distances.

Switched-mode RF power amplifiers (PAs) under bitstream modulations such as bandpass or envelope delta-sigma modulations have received increasing attentions over the past years. They have been proposed to overcome a trade-off between linearity and efficiency with an idea to discretize analog envelope from a complex modulation signal into discrete driving points for high efficiency operation. Such amplifiers offer enhanced efficiency under power back-off conditions with pulse train waveforms yet maintain linearity in amplification through digital coding and modulations. The quantization noise generated during a discretization process, however, is a challenge to be rejected properly and restore desired signal.

This work presents a switched-mode PA based on the pulsed load modulation (PLM) technique with multi-level envelope delta-sigma modulation (EDSM) to realize broadband efficient amplification of non-constant-envelope signals. PLM technique modulated load impedance to be optimized for dynamic power range and maintained optimum efficiency over 6 dB back-off. Multi-level EDSM introduced additional transition levels and reduced quantization noise power with improved signal to noise ratio.

In addition, active noise filtering scheme is proposed with a potential to replace an external high-Q passive bandpass filter in delta-sigma modulation. Multiple PA units were driven by identical signal with different phase. Challenged quantization noise power was suppressed by multi-path combining filtering.

The proposed transmitters were demonstrated at X-band using GaN devices. Both 2-level and 3-level EDSM techniques were tested and compared. Two channel active noise filtering is also presented with regard to their quantization noise levels and power efficiencies.

With the development of modern wireless communications, interference has become a primary challenge for spectrum utilization and coexistence. High frequency-selectivity, tunable, low-noise, and high-linearity RF front-end components can greatly help the reception robustness under heavy interference scenarios. In this work, we propose to utilize the parametric mixing and amplification behavior of the time-varying transmission lines (TVTL) to design and implement such devices.TVTLs are reactance-based circuits consisting of passive transmission lines whose inductance or capacitance is modulated by an electromagnetic wave called the “pump”. The single-sideband operation of a TVTL is especially favorable in that it can provide low-noise parametric amplification and frequency conversion with a moderate amount of gain. Moreover, TVTLs are compatible with modern IC technologies and can be realized with small form factors. In this work, an in-depth theoretical study on the time-varying transmission lines (TVTL) in the single-sideband operation is presented. The theory then serves as a guideline to design three configurations of TVTLs on commercially available monolithic microwave integrated circuit (MMIC) processes. These MMIC TVTLs are then applied to design the RF correlator with either the frequency translational approach or the tunable peak amplifier approach to overcome the interference issues faced by modern receivers. Measurements results showed that 0 dB conversion loss was realized in the directly-pumped TVTL frequency translational correlator prototype. >25 dB correlation suppression was also achieved by the same prototype when comparing the reception of the correlated signal with the reception of the uncorrelated (orthogonal) signal. For the tunable peak amplifier approach, experiments indicated that the peak gain of the tunable peak amplifier was >25 dB with a bandwidth <5MHz, and the measured frequency tuning range was >100 MHz. The noise figure of the tunable peak amplifier in both simulation and measurement was <1.8 dB. Lastly, the tunable peak amplifier also exhibited good linearity in the measurement, which was -11.5 dBm in-band IIP3 and 30 dBm out-of-band IIP3.

The finite difference time domain method has long been one of the most widely used numerical methods for solving Maxwell’s equations due in part to its accuracy, explicit nature, and simplicity of implementation. Modern research interests have created a need for this method to be extended to handle multi-scale multi-physics problems where numerous physical phenomena are coupled with classical electrodynamics. These phenomena typically occur on vastly different spatial scales; however, the conventional finite difference time domain method requires a uniform spatial discretization across the entire simulation space. Additionally, the maximum time evolution that may be solved in a single iteration of the algorithm is proportional to the smallest discretization length. Consequently, properly resolving the smallest feature of a multiscale problem causes phenomena of a larger scale to be over-resolved, resulting in an unnecessarily large amount of memory and often an impractical number of computations required for simulation. The development of a capability for sub-gridding, where local domains of fine resolution may be incorporated into a simulation space of coarser resolution, is imperative to treat this issue. This thesis proposes a new algorithm to implement sub-gridding. The results of comprehensive numerical evaluations show promise for this algorithm to be of general use in solving multi-scale multi-physics problems.

First responders navigating compromised environments, such as burning buildings, often face obstructed fields of view, making navigation challenging. Alleviating these difficulties is crucial for providing essential aid to individuals at risk. Quasistatic electromagnetics serve as an effective tool for real-time position sensing and tracking within non-line-of-sight, steel-reinforced structures. The quasistatic regime is characterized by electromagnetic waves that vary slowly over time, allowing for deep penetration into structures with minimal signal loss. We propose a multiaxial system architecture that couples magnetoquasistatic and electroquasistatic waves radiating from collocated loop antennas and piezoelectric field emitters. Our research into the radiation characteristics of these devices revealed that piezoelectric emitters cannot produce fields strong enough for effective coverage in single-story buildings. Consequently, we adjusted to a magnetoquasistatic sensor fusion system which predicts positioning with meter-level accuracy. The efficacy and accuracy of our system operating within a single-story structure were verified and presented in a live demonstration.