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

Abstract

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.

Norton Equivalent Circuit for Pulsed Photoconductive Antennas—Part II: Experimental Validation

“…The logarithmic spiral and the bow-tie lens feeds present a quite constant efficiency behaviour over the operative bandwidth. The spiral lens antenna is slightly more efficient than the bow-tie lens antenna because of the broadside radiation of the spiral feed inside the lens [16], as it is shown in Fig. 8(e)-8(f), which decreases the reflection losses with respect to the bow-tie antenna, which indeed illuminates consistently the lateral part of the lens [14], see Fig.…”

“…The highest spillover efficiency is from the reflectors system fed by the logarithmic spiral lens antenna over the entire bandwidth due to the better lens illumination. The broadside field radiated by the spiral lens feed illuminates more homogeneously the upper part of the lens [16], resulting in more directive beams radiated by the lens, as it is shown in Fig. 9(e)-9(f).…”

“…The H-dipole and the bow-tie have standard design features. The logarithmic spiral has been designed according to [16] with the limitation of designing a gap of length W y = 10 µm. The geometrical features of the antennas are listed in the caption of Fig.…”

Incoherent Detection of Orthogonal Polarizations via an Antenna Coupled MKID: Experimental Validation at 1.55 THz

“…Using (8), we can extract the value of the measured normalized optical throughputs for different source temperatures. The values of the measured optical throughputs per source powers and their average values are shown in Fig.…”

“…The aforementioned observatories will require detectors operating in the 1-10 THz frequency band, and, for SPICA-SAFARI, an input bandwidth of about one octave: for example, the low frequency band from SAFARI is defined from 1.4 THz to 2.7 THz [7]. For such wide bandwidths, log spiral [8] or sinuous antennas [9] based lenses, [10] have been proposed, but they are difficult to fabricate with distributed feeding lines at such high frequencies. Recently a leaky slot based antenna solution was proposed providing a bandwidth up to 1:10 at a frequency range of 0.15 -1.5 THz with a very good agreement between the simulated and measured antenna beam patterns [11].…”