Unai Beaskoetxea

Terahertz Corrugated and Bull's-Eye Antennas

The radiation and temporal properties of one-dimensional and two-dimensional (Bulls-eye) corrugated antennas are investigated numerically and experimentally at terahertz. The thickness of the antenna is miniaturized, within the fabrication limits, by using the transverse slot resonance rather than the longitudinal resonance. Square and triangular corrugations are discussed. The comparison between these two profiles shows that, in terms of return loss and gain, the antenna is robust to the corrugation shape, which alleviates the fabrication complexity. The temporal analysis of the Bulls eye antenna is also shown to demonstrate the contributions coming from the leakage of the surface wave at each groove. This insight allows us to engineer the temporal shape of the output pulse by varying independently the depth of each groove. The antennas presented here hold promise for manipulating with very low profiles pulse- and beam-shapes of THz radiation.

Zoned near-zero refractive index fishnet lens antenna: Steering millimeter waves

A zoned fishnet metamaterial lens is designed, fabricated, and experimentally demonstrated at millimeter wavelengths to work as a negative near-zero refractive index lens suitable for compact lens antenna configurations. At the design frequency f = 56.7 GHz (λ0 = 5.29 mm), the zoned fishnet metamaterial lens, designed to have a focal length FL = 9λ0, exhibits a refractive index n = −0.25. The focusing performance of the diffractive optical element is briefly compared with that of a non-zoned fishnet metamaterial lens and an isotropic homogeneous zoned lens made of a material with the same refractive index. Experimental and numerically-computed radiation diagrams of the fabricated zoned lens are presented and compared in detail with that of a simulated non-zoned lens. Simulation and experimental results are in good agreement, demonstrating an enhancement generated by the zoned lens of 10.7 dB, corresponding to a gain of 12.26 dB. Moreover, beam steering capability of the structure by shifting the feeder on...

77-GHz High-Gain Bull’s-Eye Antenna With Sinusoidal Profile

A high-gain Bulls-Eye leaky-wave horn antenna working at 77 GHz with sinusoidal profile has been designed, fabricated, and experimentally measured. The influence of the number of periods on the gain and beamwidth is numerically investigated. Experimental measurements show a high gain of 28.9 dB, with low sidelobe level and a very narrow beamwidth in good agreement with results obtained from simulations.

3-D-Printed 96 GHz Bull’s-Eye Antenna With Off-Axis Beaming

Reducing the profile, footprint and weight of antennas embarked on aircrafts, drones or satellites has been a long pursued objective. Here we tackle this issue by developing a millimeter-wave 96 GHz elliptical Bulls-Eye antenna with off-axis radiation at 16.5° that has been fabricated by low cost 3-D printing stereolithography, followed by metal coating. The theoretical basis for optimum off-axis operations is explained. Measurement results show an overall good agreement with simulations, displaying a gain of 17 dB and a 3.5° beamwidth (E-plane) at the operational frequency. The off-axis beaming enlarges the potential applicability of this technology with respect to the broadside beam solution.

Broadband frequency and angular response of a sinusoidal bull’s eye antenna

This work was supported by the Spanish Government under contract TEC2014-51902-C2-2-R. MN-C is supported by University of Birmingham (Birmingham Fellowship). MB acknowledges support by the Spanish Government under contract RYC-2011-08221.

High Aperture Efficiency Wide Corrugations Bull’s-Eye Antenna Working at 60 GHz

A full metallic Bull’s-eye antenna operating at 60 GHz is numerically and experimentally analyzed. The antenna presents wide grooves, rather than narrow ones, which support higher order resonances that lead to a large gain enhancement with just a pair of corrugations, achieving an overall miniaturization and increase of its aperture efficiency. In addition, an annular soft surface (SS) of five grooves is placed on the edge of the antenna, giving rise to a slight increase of the gain, reduced sidelobe level as well as reduced end-fire and backward radiation, when compared with an antenna without SS and another antenna with narrow corrugations. A narrow beam antenna with a gain of 19 dBi and nearly −16 dB sidelobe level and 10.8° beamwidth is numerically obtained at the operating frequency. Measurements and numerical results show overall good agreement, with an experimental gain of 20.2 dBi, −13.2 dB sidelobe level, 10.4° beamwidth, and 32% of aperture efficiency.

Flat Corrugated and Bull’s-Eye Antennas

This chapter is focused on a family of antennas recently proposed, whose common denominator is that they consist in a flat metallic plane with a central narrow aperture surrounded by corrugations. This new family of antennas has occupied a very important place in the development of communication technologies and solutions for several communication applications since, compared to higher volume structures, as horn or parabolic antennas, they present equal or even higher radiation characteristics. An introduction, which also serves as an historical overview, is presented in the first place, emphasizing the relation with both extraordinary transmission structures demonstrated initially at optical wavelengths as well as with leaky-wave antennas, developed mainly in microwaves. Afterwards, the physical mechanism for radiation and the main guidelines for the design of these antennas are discussed. Next, an overview of some of the most appealing designs and results related with this technology is presented, putting special emphasis in terahertz-band applications. Finally, tips on foreseen future trends are summarized to conclude the chapter.

Millimeter wave Bull's-Eye antenna frequency and angular response

In this work, the two-sided frequency beam scanning property of a millimeter-wave leaky wave Bulls-Eye antenna is numerically, analytically and experimentally demonstrated. The pointing angle for n = -1 and n = -2 space harmonics in terms of frequency is first extracted and the operation at different frequencies is analyzed. Finally, the gain and beamwidth as a function of frequency is studied, showing the latter one interesting low values in a fractional bandwidth of 4% around the operation frequency.

High gain leaky wave antenna operating at 0.566 THz

Metallic structures consisting of a central λ0/2 slot surrounded by straight parallel wedge corrugations present high transmission enhancement for an impinging EM beam, compared to that given by a single central slot with no grooves. Here, a 0.566 THz low profile leaky-wave antenna (LWA) with triangular corrugations is numerically and experimentally analyzed. Negligible differences are observed between triangular and typical square corrugation profiles. A manufactured prototype is also numerically and experimentally studied. LWAs are of high interest in several frequency ranges, including the expanding range of the THz.

Extraordinary-transmission-inspired Bull's eye antenna for automotive radar

Summary form only given. Leaky wave antennas have been studied since 1940s (C.H. Walter, Traveling Wave Antennas, Peninsula Pub., 1990). They have become a promising type of antenna for applications requiring low-profile antennas such as automotive radars (M. Ettorre, R. Sauleau, L. Le Coq, and F. Bodereau, IEEE Antennas Wirel. Propag. Lett. 9, 859, 2010). Unfortunately, pure broadside radiation cannot be achieved due to the open stopband effect.In this communication we will look at a leaky wave antenna that mimics broadside radiation by combing the radiation of two counter-propagating leakywaves (D. R. Jackson, A. A. Oliner, T. Zhao, and J. T. Williams, Radio Sci., 40, 1, 2005). Although neither of the leaky-waves radiates broadside, the angle of radiation is close enough to normal that the radiation pattern appears as a single beam. The antenna is based on a central resonant slot surrounded by corrugations in the form of Bulls Eye (M. Beruete, I. Campillo, J. S. Dolado, E. Perea, F. Falcone, and M. Sorolla, IEEE Antennas Wirel. Propag. Lett., 4, 365, 2005), and is originally inspired by the extraordinary optical transmission (F.J. Garcia-Vidal, L. Martin-Moreno, T.W. Ebbesen, and L. Kuipers, Rev. Modern Phys. 82, 729, 2010). The proposed antenna is completely metallic, unlike other leaky wave antennas proposed for millimeter-waves applications. Hence, dielectric losses, that cannot be disregard at these high frequencies, are completely removed, allowing higher gains. We will analysis the effect that the profile of the corrugations has in the radiation characteristics. In particular, we will demonstrate that sinusoidal rather than square corrugations are preferable if high directivity is required. We will link this to the different properties of the leaky-waves supported. Measurements of an all-metallic prototype with 20 sinusoidal corrugations shows at 77 GHz an input reflection coefficient of -20 dB, a 28 dB gain and side lobe level of -21.4 dB, in agreement with the numerical modelling.