Quantum Barrier Devices for Sub-Millimetre Wave Detection

Resonant-Tunnelling Diodes (RTDs) are a specific class of Quantum Barrier Devices, which offer a lot of potential for customisation through careful engineering of their semiconductor layer structure. They exhibit characteristics that make them good candidates for use in both subharmonic mixers and signal amplifiers, that operate at millimetre and sub-millimetre frequencies. In this thesis RTDs fabricated at the University of Leeds from three different layer structures are investigated. Initially, device measurements are presented along with a device model for use in circuit simulation software. Planar transmission media circuits were designed for subharmonic mixers and two types of amplifiers, all using these devices. Additional circuits, implemented in waveguide technology, were also studied in preparation for realising the RTD based amplifiers at sub-millimetre and terahertz frequencies. The sub-harmonic mixer circuits were simulated at microwave, millimetre, and sub-millimetre frequencies. Best predicted conversion loss performance is on the order of 20 dB. It was found that amongst the devices used an optimum size exists, offering best trade-off between junction capacitance and current density. The amplifier circuits are divided into two groups, reflection based amplifiers and active transmission line. Their purpose would be to complement the mixers towards eventually building a receiver with low power requirements and low overall conversion loss. The former were found to either exhibit high narrow-band gain, while the latter had low wide-band gain, with an additional, resonant peak at frequencies in the sub-millimetre wave region. The project was primarily a parametric design study, rather than a build and test project. Therefore, the simulation results are used to determine what characteristics of the devices studied would make them suited for use in circuits at high frequencies; and to come up with recommendations for future optimum RTD layer design

Substrate Integrated Bragg Waveguide: an Octave-bandwidth Single-mode Functional Transmission-Line for Millimeter-Wave and Terahertz Applications

We demonstrate an air-core single-mode hollow waveguide that uses Bragg reflector structures in place of the vertical metal walls of the standard rectangular waveguide or via holes of the so-called substrate integrated waveguide. The high-order modes in the waveguide are substantially suppressed by a modal-filtering effect, making the waveguide operate in the fundamental mode over more than one octave. Numerical simulations show that the propagation loss of the proposed waveguide can be lower than that of classic hollow metallic rectangular waveguides at terahertz frequencies, benefiting from a significant reduction in Ohmic loss. To facilitate fabrication and characterization, a proof-of-concept 20 to 45 GHz waveguide is demonstrated, which verifies the properties and advantages of the proposed waveguide. A zero group-velocity dispersion point is observed at near the middle of the operating band. This work offers a step towards a novel hybrid transmission-line medium that can be used in a variety of functional components for broadband millimeter-wave and terahertz applications.Comment: 11 pages, 9 figures, journal articl

Substrate integrated Bragg waveguide: an octave-bandwidth single-mode hybrid transmission line for millimeter-wave applications

We demonstrate an air-core single-mode hollow hybrid waveguide that uses Bragg reflector structures in place of the vertical metal walls of the standard rectangular waveguide or via holes of the so-called substrate integrated waveguide. The high-order modes in the waveguide are substantially suppressed by a modal-filtering effect, making the waveguide operate in the fundamental mode over more than one octave. Numerical simulations show that the propagation loss of the proposed waveguide can be lower than that of classic hollow metallic rectangular waveguides at terahertz frequencies, benefiting from a significant reduction in Ohmic loss. To facilitate fabrication and characterization, a proof-of-concept 20 to 45 GHz waveguide is demonstrated, which verifies the properties and advantages of the proposed waveguide. A zero group-velocity dispersion point is observed at near the middle of the operating band, which is ideal for reducing signal distortion. This work offers a step towards a hybrid transmission-line medium that can be used in a variety of functional components for multilayer integration and broadband applications

Data associated with ‘Multi-modal millimeter-wave sensors for plastic polymer material characterization’

This paper presents, for the first time, a multimodal sensor for characterizing relative permittivity of plastic polymers by integrating in a single sensor (1) frequency-reconfigurable resonance technique at 98 and 100 GHz, and (2) 80-100-GHz broadband modified transmission-line technique. The sensor is designed based on a custom-made WR-10 waveguide featuring dual rectangular Complementary Split-Ring Resonators (CSRRs). By loading the CSRRs with a Material-Under-Test (MUT), the reflected and transmitted electromagnetic waves propagating inside the waveguide are changed depending on the dielectric properties of the material. Various plastic polymer materials, e.g. Polytetrafluoroethylene (PTFE), Polymethylmethacrylate (PMMA) and High-Density Polyethylene (HDPE), are characterized. The sensor in this paper offers various key advantages over any state-of-the-art material characterization techniques at millimeter-wave frequencies, e.g. multiple characterization techniques integrated in a single device, miniaturization, much higher tolerance to changes in the measurement environment, ease of design and fabrication, and better cost effectiveness