Antenna Beamforming for Energy Harvesting in Cognitive Radio Networks

In this paper, a cooperative cognitive radio network (CRN) with energy harvesting capabilities of its secondary users is considered. Specifically, cooperative spectrum sensing and multi-antenna beamforming are employed to improve the sensing performance and the energy transfer efficiency, respectively. In our approach, a homogeneous CRN scenario is studied where the optimal sensing probability of each second user (SU) is obtained to maximize the control center (CC) throughput while satisfying the energy causality and primary user (PU) collision constraints. An iterative algorithm is proposed to obtain the optimal charging time. Numerical results depict that in an energy constrained scenario, cooperative spectrum sensing with beamforming performs much better than cooperative spectrum sensing without beamforming in terms of increased system throughpu

Mobile device antenna design & isolation technologies

Mobile device antenna design and isolation technologies are thoroughly investigated in this thesis. The antenna design parameters for mobile devices are quantified using practical restraints by analyzing almost 60 mobile handsets and the effect of materials, human tissue, manufacturing, and antenna type/placement on antenna design and then mapped into Wheeler-space that correlates the spherical wave modes with the antenna performance. The isolation technologies with mutual coupling anti-resonances are unified by a single performance parameter to distinguish them from the more traditional isolation technologies. This unifying performance parameter is the group delay between two antennas where high group delay indicates the presence of a bandstop filter in the form of either a PCB or an antenna modification. This thesis analyzes both PCB and antenna modifications with high group-delay and demonstrates these types of antennas can be placed in close proximity without affecting other performance parameters. It is also shown that both the PCB and antenna modifications contain two isolation methods where each isolation method is a mirror complement of the other method. Some antenna geometries can also increase the mutual coupling in order to improve the antenna performance using a phenomena called over-coupling. These over-coupled antenna systems can result in lower SAR for the cellular antennas and decreased array sizes for NFC/RFID/wireless-power antennas, resulting in better performance of antennas inside mobile devices.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph

Compact low-profile antennas for mobile communications

In recent years, countries throughout the world have agreed to allocate the frequency band 1.7 → 2.1 for future personal communications systems (PCS). Handsets are expected to decrease in size and cost as the circuits and antenna components scale down. The size of the handset is primarily limited by the antenna length and the battery. The ability of multiple antennas on the handset to improve data transfer reliability increases the need for compact antennas. Although the PCS system will reduce the antenna length by a factor of 2 from the current 9OOMHz cellular system, the handset will also scale down and the need for small antennas remains. In the past, cellular handsets employed a (shielded) monopole for transmitting and receiving data. Recently, efforts have been focused on several new designs, including the planar inverted F antenna (PIFA) with a resonant wavelength of λ/4. There exist a variety of techniques to reduce the physical length of the antenna. Dielectrics can increase the electrical length of the antenna by [square root]εr, therefore decreasing the physical length by [square root]εr. Increasing the dielectric constant to reduce the antenna's physical length, however, is cost-prohibitive. Another method involves the use of strategically placed inductive and capacitive loads on the antenna structure. An inductive load is difficult to manufacture as the resonance properties are sensitive to the pitch and spacings between the coils. A capacitive load increases the resonant resistance and reactance, decreasing the probability of achieving a 50ω match. In this thesis, we design a new antenna with length λ/8 for PCS applications. The Finite Difference Time Domain method is used in the design process and results from a prototype are used to verify the findings

Capacitively loaded PIFA

A planar inverted-F antenna is described that is provided with a capacitive load that allows the dimensions of the antenna to be reduced from a conventional λ/4 to λ/8. To maintain good bandwidth and impedance matching in spite of the presence of the capacitive load, a capacitive feed is also provided