Alessandro Garufo

Radiation of Logarithmic Spiral Antennas in the Presence of Dense Dielectric Lenses

In this paper, the performance of logarithmic spiral antennas as feeds of dense dielectric lens are investigated in detail. The performances are evaluated in terms of clean symmetric radiation patterns, high polarization purity, antenna efficiency, and radiation dispersivity. A logarithmic spiral antenna placed in the dielectric-air interface can provide high aperture efficiencies over large bandwidths if coupled to a synthesized elliptical lens. The use of an air gap increases the directivity of the spiral radiation inside the dielectric allowing for lens directive patterns without sidelobes and reducing the dispersivity of the radiated pulse. The directivity enhancement of the fields inside the dielectric is validated by the measurement of a prototype. The highest frequency at which these antennas can be fed by a planar microstrip line is limited by the thickness of the microstrip substrate.

A Quasi-Analytical Tool for the Characterization of Transmission Lines at High Frequencies [EM Programmer's Notebook]

In this article, we present a freely accessible software tool that allows for fast characterization of dynamic phenomena in a wide variety of transmission lines that include characteristic impedance, effective dielectric constant, and losses, such as radiation into space and surface waves. For printed transmission lines, the radiation effects are of particular importance when the transverse dimensions of the transmission lines become significant in terms of wavelength. Generally, dispersion and losses of the line due to these dynamic phenomena are predicted by full-wave simulations as quasi-static formula do not suffice. The presented software tool, freely downloaded from http://terahertz.tudelft.nl, is capable of accurately analyzing the most widely used transmission lines at high frequencies.

Improvement of the radiation efficiency in a logarithmic spiral lens antenna

This paper shows a comparison a comparison in terms of gain of a lens fed by a standard logarithmic spiral antenna, and its enhanced version including an air gap.

Enhanced radiation properties of spiral lens antennas

Spiral antennas have been widely used in the THz regime as ultra wide band-width feeds for dielectric lenses. Indeed, the impedance behavior of such antennas is very flat over the frequency band, especially when logarithm spirals are used. Even so, these feeds generate a relatively wide field inside the lens and this results into a poor illumination of the lens. In this contribution, we will demonstrate how the performances of these lens antennas can be considerably improved by using a small air gap between the spiral and the dielectric material.