Bidimensional Phase-varying Metamaterial for steering beam antenna
Abdelwaheb Ourir, Shah Nawaz Burokur, André de Lustrac Institut d’Electronique Fondamentale, Univ. Paris-Sud, UMR 8622 ; CNRS, Orsay, F-91405
ABSTRACT
Dielectric substrates supporting planar periodic subwavelength metamaterial-based metallic arrays and presenting frequency dispersive phase characteristics are applied to ultra-compact high-gain and high-directivity planar antennas. In
this paper, different models of metamaterial-based surfaces introducing a zero degree reflection phase shift to incident waves are firstly studied numerically using finite-element method analysis where the bandwidth and operation frequency
are predicted. These surfaces are then applied in a resonant Fabry-Perot type cavity and a ray optics analysis is used to design different models of ultra-compact high-gain microstrip printed antennas. Firstly, a cavity antenna of thickness
λ60 based on the use of a microstrip patch antenna and two bidimensional metamaterial-based surfaces, the first one acting as a High Impedance Surface HIS and the second one acting as a Partially Reflecting Surface PRS is designed.
This cavity is then optimized for easier fabrication process and loss reduction by the use of only one bidimensionnal composite metamaterial-based surface acting as a PRS. Secondly, another surface presenting a variable phase by the use
of a non periodic metamaterial-based metallic strips array is designed for a passive low-profile steering beam antenna application. Finally, a switchable operation frequency cavity by the implementation of varicap diodes is designed and
fabricated. All these cavity antennas operate on subwavelength modes, the smallest cavity thickness being of the order of λ60.
Keywords: metamaterial, high-gain antennas, ultra-compact antennas, Fabry-Perot cavity, High Impedance Surface, Partially Reflecting Surface, variable phase, steering beam antenna, switchable operation frequency, varicap diodes.
1. INTRODUCTION
There has been a lot of study published in literature on the improvement of the performances of microstrip patch antennas [1-3]. Most of the solutions proposed in the past were to use an array of several antennas. The particular
disadvantage of this method comes from the feeding of each antenna and also from the coupling between each element. Other interesting solutions have been suggested: the first one was to make use of a superstrate of either high permittivity
or permeability above the patch antenna [1] and the second one proposed recently by Nakano et al., is to sandwich the antenna by dielectric layers of the same permittivity [2]. The numerical study of a patch antenna where a Left-Handed
Medium LHM is placed above has also been done and in this case a gain enhancement of about 3dB has been observed [3]. However, these solutions are all based on non-planar designs which are bulky for novel telecommunication systems
requiring compact low-profile and environment friendly directive antennas.
Concerning the design of compact directive electromagnetic sources based on a single feeding point, different interesting solutions have also been proposed recently. At first, resonant cavities in one-dimensional 1-D dielectric photonic
crystals were used [4]. Afterwards, three dimensional 3-D structures rather than 1-D were used, leading to better performances [5]. Another interesting solution proposed by Enoch et al. is to use the refractive properties of a low
optical index material interface in order to achieve the directive emission [6]. We shall note that these solutions are all also based on the use of a bulky material. Otherwise, the most common method to reach directive emission is obviously
based on the Fabry-Perot cavity. Such cavities can be considered quite bulky too since a thickness of half of the working wavelength is required [7]. But recently, Feresidis et al. showed that the half wavelength restriction in a Fabry-Perot
cavity can be reduced to a quarter wavelength by using a novel type of metamaterial-based resonant cavity together with a microstrip patch antenna [8]. The latter requires the use of Artificial Magnetic Conductor AMC surfaces introducing
a zero degree reflection phase shift to incident waves. The AMC surfaces have been first proposed by Sievenpiper et al. in order to act as the so called High Impedance Surface HIS [9]. This HIS is composed of metallic patches periodically
nawaz.burokurief.u-psud.fr; phone +33 01 69 15 41 22; fax +33 01 69 15 40 90
organized on a dielectric substrate and shorted to the metallic ground plane with vias, appearing as “mushroom” structures. In a particular narrow frequency band, this surface creates image currents and reflections in-phase with the
emitting source instead of out of phase reflections as the case of conventional metallic ground plane. The HIS allows also the suppression of surface waves which travel on conventional ground plane. New applications of improved
performances in the field of reflectors and antennas have then been proposed. However, the HIS of Sievenpiper needs a non-planar fabrication process, which is not suitable for implementation in lots of microwave and millimetric circuits.
Other models of planer AMC surfaces have then been proposed for antenna and circuit applications [10, 11]. The cavity proposed by Feresidis is composed of two planar AMC surfaces. The first one is used as a HIS so as to replace the
Perfect Electric Conductor PEC surface for the antenna and hence, to avoid the
λ4 limit distance between the source and the ground plane. The second one acts as a Partially Reflective Surface PRS with a reflection phase equal to 180°.
This idea has been pushed further by Zhou et al. by taking advantage of the dispersive characteristics of metamaterials, designing a subwavelength cavity with a thickness smaller than a 10th of the wavelength [12]. Compared to Feresidis,
Zhou made use of a non-planar mushroom structure with a dipole acting as the feeding source.
In this paper, using a novel composite metamaterial, made of capacitive and inductive grids, we review our works in the fields of low-profile and high-gain metamaterial-based cavity antennas. We will show how our group has lately further
reduced the cavity thickness by λ60 for applications to ultra-thin directive antennas using two bidimensional
metamaterial-based surfaces, one as a HIS and the other as a PRS [13]. An optimization of the cavity has also been undertaken in order to facilitate the fabrication process and also to reduce the metallic losses by using a PEC surface as
the antenna’s ground plane and only one subwavelength metamaterial-based composite surface as the PRS [14]. We will then present the modeling and characterization of an optimized resonant cavity for a reconfigurable directive beam
antenna near 10 GHz. The cavity is composed of a PEC surface and a new unidimensional composite metamaterial made of metallic strips composing a non uniform capacitive grid and a uniform inductive grid, acting as the PRS [15]. Finally,
we will present our first results obtained with an electronically active metamaterial-based subwavelength cavity for a frequency reconfigurable low-profile and high-gain antenna application. A numerical analysis using the finite-element
method software HFSS [16] together with discussions on the fabrication process and the characterization results will be presented for the cavities mentioned above.
2. ANALYSIS OF THE PLANAR SUBWAVELENGTH METAMATERIAL-BASED
