No description available.

No description available.

No description available.

No description available.

No description available.

Yes / This paper proposes a new solution to improve the performance parameters of on-chip antenna designs on standard CMOS silicon (Si.) technology. The proposed method is based on applying the metasurface technique and exciting the radiating elements through coupled feed mechanism. The on-chip antenna is constructed from three layers comprising Si.-GND-Si. layers, so that the ground (GND) plane is sandwiched between two Si. layers. The silicon and ground-plane layers have thicknesses of 20μm and 5μm, respectively. The 3×3 array consisting of the asterisk-shaped radiating elements has implemented on the top silicon layer by applying the metasurface approach. Three slot lines in the ground-plane are modelled and located directly under the radiating elements. The radiating elements are excited through the slot-lines using an open-circuited microstrip-line constructed on the bottom silicon layer. The proposed method to excite the structure is based on the coupled feeding mechanism. In addition, by the proposed feeding method the on-chip antenna configuration suppresses the substrate losses and surface-waves. The antenna exhibits a large impedance bandwidth of 60GHz from 0.5THz to 0.56THz with an average radiation gain and efficiency of 4.58dBi and 25.37%, respectively. The proposed structure has compact dimensions of 200×200×45μm3. The results shows that, the proposed technique is therefore suitable for on-chip antennas for applications in system-on-chip for terahertz (THz) integrated circuits. / Innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424; UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E0/22936/1.

The increasing demand for high data rate services necessitates the adoption of very wideband waveforms. In this case, the channel is frequency-selective, that is, a large number of resolvable multipaths are present in this environment and fading is not highly correlated across the band. Orthogonal frequency division multiplexing (OFDM) is well-known to be effective against multipath distortion. It is a multicarrier communication scheme, in which the bandwidth of the channel is divided into subcarriers and data symbols are modulated and transmitted on each subcarrier simultaneously. By inserting guard time that is longer than the delay spread of the channel, an OFDM system is able to mitigate intersymbol interference (ISI). Deploying an adaptive antenna array at the receiver can help separate the desired signal from interfering signals which originate from different spatial locations. This enhancement of signal integrity increases system capacity. In this research, we apply adaptive array algorithms to OFDM systems and study their performance in a multipath environment with the presence of interference. A novel adaptive beamforming algorithm based on the minimum mean-squared error (MMSE) criterion, which is referred to as frequency-domain beamforming, is proposed that exploits the characteristics of OFDM signals. The computational complexity of frequency-domain beamforming is also studied. Simulation results show employing an adaptive antenna array with an OFDM system significantly improves system performance when interference is present. Simulations also show that the computational complexity of the algorithm can be reduced by half without significant performance degradation. Adaptive array algorithms based on the maximum signal-to-noise ratio (MSNR) and the maximum signal-to-interference-plus-noise ratio (MSINR) criteria are also applied to adaptive vector OFDM systems (AV-OFDM). Simulation results show that the adaptive algorithm based on the MSNR criterion has superior performance in the multipath environment but performs worse than the one based on the MSINR criterion under the flat fading channel. / Master of Science

A unique property of spherical and hemispherical helical antennas is that they provide very broad half-power beamwdiths and circular polarization over a narrow bandwidth. In this thesis, new designs for hemispherical helical antennas are introduced that provide significant improvement in bandwidth, while maintaining the directivity and half-power beamwidth of the basic design. In the basic design, a simple wire of circular cross section is wound on the surface of a hemisphere, whereas in the proposed new designs a metallic strip forms the radiating element. Furthermore, the metallic strip may be tapered and tilted relative to the hemispherical surface, allowing wider bandwidth to be achieved. The antenna is fed by a coaxial cable with the inner conductor connected, through a matching section, to the radiating strip and its outer conductor connected to a ground plane. Radiation properties of the proposed hemispherical helical antennas are studied both theoretically and experimentally. A commercial software, based on the method of moments, is used to perform the numerical analysis of these helices. Three-dimensional far-field patterns, axial ratio, directivity, and voltage standing-wave ratio (VSWR) are calculated for several designs. The impacts of tapering as well as tilting of the metallic strip on radiation characteristics are examined. Also, matching of the proposed hemispherical antennas to 50â ¦ transmission lines is addressed. A 4.5-turn hemispherical helix with tapered radiating element and zero degree tilt angle, (metallic strip is perpendicular to the hemisphere axis of symmetry) provides the largest overall bandwidth. A nonlinearly tapered matching section is incorporated into the design in order to reduce the VSWR. For this design, an overall measured bandwidth of about 24% at a center frequency of 3.35 GHz is achieved. Over this bandwidth, the axial ratio remains below 3 dB, the VSWR is less than 2, and the directivity is about 9 ±1 dB. A half- power beamwidth of 70° is also obtained. A prototype of the best design was fabricated and tested using the VT indoor antenna range. Radiation patterns, the scattering parameter S₁₁, and the axial ratio were measured. The measured and simulated results agree reasonably well. In particular, agreements between measured and calculated far-field patterns and VSWR are quite remarkable. This compact, low profile antenna might find useful applications in avionics, global positioning systems (GPS), and high data rate wireless communication systems. / Master of Science

In order to accurately describe the behavior of an antenna, one needs to understand the radiation mechanisms that govern its operation. One way to gain such an insight is to view the fields and currents present on a radiating structure. Unfortunately, in close proximity to an antenna empirical techniques fail because the measurement probe alters the operation of the radiating structure. Computational methods offer a solution to this problem. By simulating the operation of an antenna, one can obtain electromagnetic field data near (or even internal to) a radiating structure. However, these computationally intense techniques often generate extremely large data sets that cannot be adequately interpreted using traditional graphical approaches. A visualization capability is developed that allows an analysis of the above-mentioned data sets. With this technique, the data is viewed from a unique, global perspective. This format is well suited for analytical investigations as well as debugging during modeling and simulation. An illustrative example is provided in the context of a rectangular microstrip patch antenna. A comparison is performed between the visualized data and the theory of operation for the microstrip patch in order to demonstrate that radiation mechanisms can be obtained visually. An additional analysis tool is developed using Gabor filters and image-processing techniques. This tool allows one to detect and filter electromagnetic waves propagating with different velocities (both speed and direction). By doing so, each mode of an antenna can be analyzed independently. The fields of a multi-moded, open-ended rectangular waveguide are analyzed in order to demonstrate the effectiveness of these techniques. / Master of Science

Yes