Performance Analysis of Novel Multi-band Monopole Antenna for Various Broadband Wireless Applications

Wireless Personal Communications - This study investigates a novel concept of using slot and Coplanar Waveguide fed antenna to obtain multiband operation. The compact antenna includes a star...     

Impact of Waveguide Filling Material on Near-Field Microwave Inspection of Carbon-Loaded Composites

The advent of carbon loaded composite materials gave a boost to many industries. This is because of their light weight, durability and strength. As new structures utilizing carbon loaded composites are built, the need for a reliable nondestructive testing technique increases. A carbon-loaded composite testing poses a challenge to most nondestructive testing and evaluation (NDT&E) techniques. Microwave NDT&I techniques main challenge is the lossy nature of carbon, especially at high microwave frequencies. Lower frequencies penetrate deeper in carbon-loaded composites, however, to operate at lower frequencies the size of the waveguide probe increases significantly which degrades the resolution rapidly. Open-ended rectangular waveguide sensors filled with a dielectric material will be used to inspect carbon-loaded composites. The filling of the waveguide reduces the frequency of operation and keeps the small size of the waveguide (i.e. increases the penetration depth and maintains the resolution). However, varying the waveguide filling material dielectric properties will have an impact on the measurement parameters optimization process and consequently on the detection sensitivity. In this paper, the use of the waveguide filling material as an optimization parameter will be investigated. Carbon-loaded composites with disbonds will be inspected and the variation of the dielectric properties of the loading material of rectangular waveguide probes for carbon loaded composites inspection will be assessed.     

A Cat-Shaped Patch Antenna for Future Super Wideband Wireless Microwave Applications

Wireless Personal Communications - Compact super wideband (SWB) monopole antenna with a novel Cat-shaped patch is proposed and investigated for wireless applications in this article. The...     

Performance Analysis of Soft-Bit Maximal Ratio Combining in Cooperative Relay Networks

In digital cooperative relaying, signals from the source-destination and relay-destination links are combined at the destination to achieve spatial diversity. These signals may not necessarily belong to the same modulation scheme due to the varying channel qualities of the two links. Recently, we have proposed the "soft-bit maximum ratio combiner" (SBMRC) as a low complexity diversity combining scheme for signals with different modulation levels. SBMRC exhibits BER performance that is very close to the optimal maximum likelihood detector (MLD), but with much reduced complexity. In this paper, we revisit SBMRC and provide tight lower bound for the BER performance. Since SBMRC has BER performance slightly inferior to MLD, the derived lower bound can also be used as a good approximation for the BER performance of MLD.     

Near-field microwave image formation of defective composites utilizing open-ended waveguides with arbitrary cross sections

Many nondestructive testing techniques fail to detect the presence of defects inside composite materials due to their complex nature. Microwave near-field nondestructive testing utilizing open-ended rectangular waveguides showed promising results in detecting defects inside these composite structures. Carbon-loaded composites are lossy materials, which, in general, reduce the range of frequency that can be used to inspect these kinds of composites due to the high attenuation. Thus far, open-ended rectangular waveguide based probes have been used to inspect the structural integrity and homogeneity of these structures. These probes were found to be suitable for detecting defects in these composites. However, due to the linear polarization of the fields radiated out of open-ended rectangular waveguide probes and the linear nature of the carbon fibers, high attenuation of the radiated signal is inevitable. Consequently, only close to the surface defects were detected. Circular waveguides have not been used in near-field NDT. Circular waveguides offer many attractive features such as the circular polarization of the radiated waves. This fact might be used in penetrating deeper in high-loss composites. In this paper, the potential of utilizing rectangular and circular waveguides in inspecting defects in carbon-loaded composites will be theoretically investigated. An air void will be introduced inside both types of composites and theoretical images will be formed. Interpretation of the captured images will be done through power patterns in different planes.