Morteza Shahpari

An Investigation Into the Gustafsson Limit for Small Planar Antennas Using Optimization

The fundamental limit for small antennas provides a guide to the effectiveness of designs. Gustafsson et al., Yaghjian et al., and Mohammadpour-Aghdam et al. independently deduced a variation of the Chu-Harrington limit for planar antennas in different forms. Using a multi-parameter optimization technique based on the ant colony algorithm, planar, meander dipole antenna designs were selected on the basis of lowest resonant frequency and maximum radiation efficiency. The optimal antenna designs across the spectrum from 570 to 1750 MHz occupying an area of 56 mm × 25 mm were compared with these limits calculated using the polarizability tensor. The results were compared with Sievenpipers comparison of published planar antenna properties. The optimized antennas have greater than 90% polarizability compared to the containing conductive box in the range 0.3 <; ka <; 1.1, so verifying the optimization algorithm. The generalized absorption efficiency of the small meander line antennas is less than 50%, and results are the same for both PEC and copper designs.

The Impact of Reduced Conductivity on the Performance of Wire Antennas

Low cost methods of antenna production primarily aim to reduce the cost of metalization. This might lead to a reduction in conductivity. A systematic study on the impact of conductivity is presented. The efficiency, gain and bandwidth of cylindrical wire meander line, dipole, and Yagi-Uda antennas were compared for materials with conductivities in the range

Point Contacts in Modeling Conducting 2-D Planar Structures

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Novel Biconical Antenna Configuration with Directive Radiation

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Dual band dual polarized antenna with high efficiency for base transceiver stations

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Generalised absorption efficiency of Yagi-Uda antennas

S/m. In this range, the absorption efficiency of both the dipole and meander line changed little, however the conductivity significantly impacts on radiation efficiency and the absorption cross section of the antennas. The extinction cross section of the dipole and meander line antennas (antennas that Thevenin equivalent circuit is applicable) also vary with radiation efficiency. From the point of radiation efficiency, the dipole antenna performance is most robust under decreasing conductivity. Antennas studied in this study were fabricated with brass and graphite. Radiation efficiency of the antennas were measured by improved Wheeler cap (IWC) method. Measurement results showed a reasonable agreement with simulations. We also measured the extinction cross section of the six fabricated prototypes.

Exploring the fundamental limits of planar antennas using optimization techniques

Use of an optimization algorithm to improve performance of antennas and electromagnetic structures usually ends up in planar unusual shapes. Using rectangular conducting elements, the proposed structures sometimes have connections with only one single point in common between two neighboring areas. The single-point connections (point crossing) can affect the electromagnetic performance of the structure. In this letter, we illustrate the influence of point crossing on dipole and loop antennas using method of moments (MoM), finite-difference time domain (FDTD), and finite-element method (FEM) solvers. Current distribution, radiation pattern, and impedance properties for different junctions are different. These solvers do not agree in the modeling of the point crossing junctions which is a warning about uncertainty in using such junctions. However, solvers agree that a negligible change in the junction would significantly change antenna performance. We propose that one should consider bridging and chamfering of the conflicting cells to find optimized structures. This reduces the simulation time by 40% using FDTD modeling; however, no significant reduction is obtained using the MoM and FEM methods.

Q-factor and efficiency of carbon nanotube antennas

In this paper a novel biconical antenna geometry has been proposed that has directive radiation pattern, higher gain and enhanced front to backratio. Wide band performance is another characteristic of this new antenna.

An Investigation of the Performance Limits of Small, Planar Antennas Using Optimisation☆

In this paper new array element for use in dual band dual polarized antenna will be introduced that has high efficiency (more than 95%) and has high isolation in both 900 MHz and 1800 MHz bands. Also radiation pattern of this antenna is according to IEC recommendation.

Polarizablity of 2D and 3D conducting objects using method of moments

The generalised absorption efficiency is the ratio of the all-spectrum absorbed to scattered energies. Although often estimated as 0.5, it should be rigorously calculated for the accurate estimation of fundamental limits. Many antennas, as tuned in the resonant frequency, absorb as much power as they scatter. One of the interesting properties of the Yagi-Uda antennas is more absorption rather scattering. Absorption, scattering, and extinction cross sections of a typical Yagi-Uda antenna are reported in this paper to study the generalised absorption efficiency for this antenna type.