Chris D. Gamlath

Bio: Chris D. Gamlath is an academic researcher from University of Bristol. The author has contributed to research in topics: Microwave & Microstrip antenna. The author has an hindex of 5, co-authored 17 publications receiving 77 citations.

Microwave Properties of an Inhomogeneous Optically Illuminated Plasma in a Microstrip Gap

Abstract: The optical illumination of a microstrip gap on a thick semiconductor substrate creates an inhomogeneous electron–hole plasma in the gap region. This allows the study of the propagation mechanism through the plasma region. This paper uses a multilayer plasma model to explain the origin of high losses in such structures. Measured results are shown up to 50 GHz and show good agreement with the simulated multilayer model. The model also allows the estimation of certain key parameters of the plasma, such as carrier density and diffusion length, which are difficult to measure by direct means. The detailed model validation performed here will enable the design of more complex microwave structures based on this architecture. While this paper focuses on monocrystalline silicon as the substrate, the model is easily adaptable to other semiconductor materials such as GaAs.

An Optically Controlled Coplanar Waveguide Millimeter-Wave Switch

Abstract: This letter demonstrates an optically controlled coplanar waveguide switch operating in the millimeter-wave region. Full-wave electromagnetic analysis used a multilayer model to simulate the photoinduced plasmas and a good agreement between measured and simulated results has been achieved. The insertion loss is less than 4 dB and isolation is greater than 15 dB from 32–50 GHz. This approach requires the use of 175 mW of optical power at a wavelength 980 nm, but it removes the need for bandwidth limiting electrical bias networks.

Investigation of an optically reconfigurable plasma for silicon based microwave applications

Abstract: This paper investigates the use of photoconductive plasmas for controlling microwave circuits and antennas on semiconductor substrates. Initial experiments show that significant changes in the reflection coefficient characteristics can be obtained by varying the length of a photo-illuminated plasma region from 0 to 2mm. The resulting structure forms the basis for further experiments involving tuneable microwave devices.

Experimental evaluation of 3D printed spiral phase plates for enabling an orbital angular momentum multiplexed radio system.

Abstract: This paper evaluates the performance of three-dimensionally (3D) printed spiral phase plates (SPPs) for enabling an orbital angular momentum (OAM) multiplexed radio system. The design and realizati...

Emerging Hardware Enablers for More Efficient Use of the Spectrum

Abstract: Tunable and reconfigurable radio frequency (RF) technologies have the potential to aid a more efficient use of spectrum through increased bandwidth efficiency, increased flexibility in operating frequencies, more efficient spectrum authorization models, and more efficient spectrum sharing mechanisms. Spectrum sharing mechanisms are already deployed in some countries (e.g. television white-space), however a lack of low-cost tunable RF technologies for user equipment applications has contributed to slow adoption of the technology. To exploit the benefits of spectrum sharing, frequency agile transceivers are required in the low and mid frequency ranges (e.g. 600 MHz to 6 GHz), making tunable and reconfigurable RF technologies a key enabler for spectrum sharing in 5G.This paper reviews recent advances in tunable RF technologies in the context of spectrum use. This work covers power amplifiers, acoustic filters/duplexers, self-interference canceling duplexers, and receivers, discussing the subsystem performance requirements and potential benefits. Various technology challenges are identified at device, subsystem, and transceiver system level, and current research directions and progress are reviewed. Substantial progress is forthcoming in this field. The uptake of spectrum sharing technology is likely to accelerate, with the the development and deployment of 5G and IoT devices, however further work is required to address performance enhancements in RF front-ends through sub-system co-design in the next generation of devices.

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Next generation wireless cellular networks: ultra-dense multi-tier and multi-cell cooperation perspective

Abstract: The next generation wireless cellular network is aimed to address the demands of users and emerging use cases set by industries and academia for beyond 2020. Hence, The next generation 5G networks need to achieve very high data rates, ultra-high reliability, extremely low latency, energy efficiency and fully connected coverage. To meet these demands, ultra-dense networks (UDN) or ultra-dense heterogeneous networks (UDHetNet), millimeter wave (mmWave) and multicell cooperation such as coordinated multipoint (CoMP) are the three leading technology enablers. In this paper, we have made an extensive survey of the current literature on 5G wireless communication focusing on UDN, mmWave and CoMP cooperation. We first discuss the architecture and key technology enablers to achieve the goals of the 5G system. Subsequently, we make an in-depth survey of underlying novel ultra-dense heterogeneous networks, mmWave and multicell cooperation. Moreover, we summarize and compare some of the current achievements and research findings for UDHetNet, mmWave and CoMP. Finally, we discuss the major research challenges and open issues in this active area of research.

Time-Modulated Reconfigurable Antenna Based on Integrated S-PIN Diodes for mm-Wave Communication Systems

Abstract: This paper concerns the study of the mm-wave reconfigurable antennas based on S-PIN diodes suitable for using in mm-wave communication systems The investigated antennas were designed, fabricated, and subjected to the measurements in both steady and transient states One selected antenna was incorporated into a wireless system to determine its suitability for operating in such a system as a time-modulated linear array By means of appropriate switching of the antenna, multiple radio frequency (RF) chains were simulated in a receiver having only one RF chain This allowed applying a combining technique for improving the system performance in a presence of a strong interfering signal

Full control of dual-band vortex beams using a high-efficiency single-layer bi-spectral 2-bit coding metasurface.

Abstract: Vortex beams (VBs) carrying orbital angular moment (OAM) modes have been proven to be promising resources for increasing communication capacity. Although considerable attention has been paid on metasurface-based VB generators due to the unprecedented advantages of metasurface, most applications are usually limited at a single band with a fixed OAM mode. In this work, an emerging dual-band reflection-type coding metasurface is proposed to mitigate these issues by newly engineered meta-atoms, which could achieve independent 2-bit phase modulations at two frequency bands. The proposed coding metasurface could efficiently realize and fully control dual-band VBs carrying frequency selective OAM modes under the linearly polarized incidence. As the first illustrative example, a dual-band VB generator with normal beam direction is fabricated and characterized at two widely used communication bands (Ku and Ka bands). Moreover, by encoding proper coding sequences, versatile beams carrying frequency selective OAM modes can be achieved. Therefore, by adding a gradient phase sequence to the first VB generator, the second one is designed to steer the generated beams to a preset direction, which could enable diverse scenarios. The measurement results of both VB generators agree very well with the numerical ones, validating the full control capability of the proposed approach.