This paper outlines a new polarization reconfigurable EBG (Electromagnetic Band Gap) antenna in the 60 GHz millimeter waves band. The proposed hybrid antenna is composed of a multilayer pyramidal DRA (Dielectric Resonator Antenna) exciting source covered with a FSS (frequency Selective Surface) superstrate. The device can switch between circular and linear polarization by a simple 45° mechanical rotation of the pyramidal DRA. This structure has the advantage that it maintained stable bandwidth, gain, efficiency and radiation properties when switching between the two configurations of circular and linear polarization.
The fast development of wireless communication systems involves the development of new equipment and devices to meet the requirements of the new multimedia applications. These modern devices are essential for the improvement of communication performance in harsh environments where the interferences due to multipath wave propagation limit significantly the data rates. Reconfigurable antennas, either in frequency, radiation patterns or polarization are potential candidates to fulfill the requirements with a minimum of clutter and complexity. The basic advantage of such antenna over conventional ones where the parameters are fixed, is that the application of electrical, mechanical or optical switching technology extend the capabilities and improve the performance of these wireless devices with a minimum impact on the complexity and cost of these systems [
Many studies have been made to obtain polarization configurability, for example, in [
Due to their physical and geometric properties, an EBG structure is a very good candidate to realize reconfigurable functions [
In the first part of this paper, a new hybrid approach to enhance both the gain and the frequency bandwidth of the EBG antenna simultaneously is introduced, which uses the concept of FSS superstrate for enhancing the gain. Furthermore, a wider bandwidth can be achieved by exciting the EBG structure with multilayer cylindrical dielectric resonator antenna (MCDRA) and a parametric study has been carried out to optimize the design properties of the multilayer DRA covered with a FSS superstrate. A prototype has been fabricated using printed circuit technology and results are reported. In the second part, a reconfigurable polarization EBG antenna excited with a multilayer pyramidal DRA is studied in view of achieving a double polarization device. It will be shown that two polarization configurations are achievable by a simple mechanical rotation of the DRA source, being linearly polarized when the angle of rotation θ = 0 and circularly polarized when θ = 45˚.
The design reference EBG antenna, shown in
Initially, a design method based on a detailed parametric study is presented. Two main points are described, the characterization of the appropriate excitation source as well as the development of the upper surface with the characteristics necessary to achieve the desired gain over a given bandwidth.
Superstrate | Lsup = 14 mm, Wsup = 14 mm, Hsup = 0.381 mm, ds = 2.5 mm |
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Intermediate substrate | L = 25 mm, W = 25 mm, h3 = 0.127 mm |
Dielectric resonators MCDRA | D = 3.5 mm (diameter), h1 = 0.254 mm, h2 = 0.254 mm |
Slot | Ls = 1.27 mm, Ws = 0.2 mm |
Substrate | L = 25 mm, W = 25 mm, h = 0.127 mm |
Fed microstrip line | Lfeed = 12.5 mm, Wfeed = 0.4 mm |
In order to obtain a compact EBG structure, thin and easy to manufacture while achieving an acceptable gain, a parametric study, using CST Studio Suite 2014, is performed on the geometric properties of the superstrate FSS.
antenna decreases. At the frequency of 60 GHz, the gain is reduced from 17.75 to 14.75 dBi, when the width changes from 1.1 to 2.2 mm.
In order to deduce its influence on the gain realized, the variation of the spacing between the rods must be carefully studied.
Our choice for the excitation of the EBG antenna is a multilayer cylindrical dielectric resonator (
The aim of this experiment is to show the increase in bandwidth when passing from the excitation of the BEG structure by a conventional cylindrical DRA to an excitation by a multilayer cylindrical DRA.
thickness h1 = h2 = 0.254 mm. Finally
Numerical results in
The width of the adaptation band is therefore improved by 2.4% when changing the homogeneous cylindrical DRA by two elements MCDRA, and also improved by 4.5% when passing from two elements to three. It is clear that the bandwidth of the three elements MCDRA will be higher than that of the homogeneous cylindrical DRA.
After the nature and geometry of the upper interface of the EBG resonator and its source of excitation were chosen for the three elements multi-layer cylindrical DRA, the proposed antenna has been fabricated and measured. The final structure of the proposed EBG antenna is shown in
The EBG antenna’s measured and simulated reflection coefficient (S11) is depicted in
simulations and the experimental ones. It is obvious that those results show a bandwidth that meets the design goal.
The antenna gain as a function of frequency is illustrated in
In addition to the improvement of bandwidth necessary for the development of the EBG structures associated with the antennas, the challenge is to obtain reconfigurable structures. Currently, there is now a strong demand for antennas offering polarization diversity, that is to say switching between linear and circular polarization. In the previous section, a high EBG reference antenna excited with multilayer DRA has been designed to generate a wideband linear polarization. In this section, it will be demonstrated that by changing the multilayer cylindrical source by a pyramidal one and rotating it by θ = 45˚ (
The geometry of the proposed source of excitation DRA is optimized numerically so that the radiated fields are equal in amplitude and 90˚ out of phase.
Superstrate | Lsup = 14 mm, Wsup = 14 mm, Hsup = 0.381 mm, ds = 2.5 mm |
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Multilayer pyramidal DRA | l1 = 1.7 mm, w1 = 0.89 mm, l2 = 0.98 mm, w2 = 0.51 mm, l3 = 0.88 mm, w3 = 0.46 mm, Htot = 0.762 mm |
Slot | Ls = 0.75 mm, Ws = 0.2 mm |
Fed microstrip line | Lfeed = 12.5 mm, Wfeed = 0.4 mm |
the multilayer pyramidal DRA. The optimum AR ratio is found when the length l to width w ratio is 1.9, corresponding to l1 = 1.7 mm, w1 = 0.89 mm, l2 = 0.98 mm, w2 = 0.51 mm, l3 = 0.88 mm, and w3 = 0.46 mm.
Simulation results such as a reflection coefficient S11, gain, efficiency, radiation patterns, and axial ration for both linear and circular configurations shown here has been performed within CST Studio Suite 2014 and prove to be very attractive.
Three resonance frequencies were discerned at 57, 60 and 64 GHz, for both configurations with a few hertz offset. It can be concluded that the effect of switching between the linear/circular polarizations, does not greatly affect the operation of the antenna, such as bandwidth and resonance frequencies.
The maximum gain simulated for both linear and circular configurations is shown in
Switching between the linear and circular configurations has no major influence on the radiation of the proposed antenna. Indeed, the main lobes of the radiation patterns in the E plane for both configurations are almost identical (see
One can conclude that the proposed antenna switches between two linear circular polarizations, while maintaining stable radiation (
In this paper, a performant EBG reconfigurable polarization antenna based on multilayer DRA for millimeter-wave has been proposed. By applying a mechanical rotation of 45˚ on the DRA source, the structure is able to switch between linear and circular polarization. In the first part of this paper, the aim was to design a reference antenna characterized by a wide bandwidth and high gain, which can be modified subsequently to have a reconfigurable structure able to switch between linear and circular polarization. For this purpose, a new approach for enhancing gain and bandwidth has been successfully developed. The technique is based on the combination of two techniques in order to benefit from the individual advantage of each of them, namely, FSS superstrate structures and multilayer DRA. The simulation and measured results showed a good agreement, with an obtained bandwidth of 9 GHz corresponding to an enhancement of 6.9% compared with homogeneous cylindrical DRA. Also a gain value of 18 dBi is obtained, an increase of 12 dBi compared to a DRA without FSS superstrate.
The second part of the paper has shown that by optimizing the length to width ratio of the multilayer pyramidal DRA source and applying a rotation to the pyramidal sides by θ = 45˚ with the central axis of the microstrip line, it is possible to generate two configurations of polarization. The linear polarization is obtained when θ = 0˚ while circular polarization is achieved when θ = 45˚. The advantage is that, when switching between a circular and linear polarization, the structure maintains stable radiation characteristics such as bandwidth, resonant frequencies, gain, efficiency and radiation patterns. The proposed antenna can be used for transmission and reception simultaneously with the aim of combating the multipath effect. Further efforts must be pursued to manufacture the antenna and develop the numerical control system in order to make the device more flexible and smart.
Using a 60 GHz reconfigurable antenna polarization offers many new potential applications, especially in the next generation 5G mobile systems. Following this work, futures studies may be proposed like multiplying the number of dielectric resonators used as an excitation network, in the perspective that it would be possible to exploit the proposed antenna in the “Massive-MIMO” technologies dedicated for 5G.
Elkarkraoui, T., Delisle, G.Y. and Hakem, N. (2016) 60 GHz Polarization Reconfigurable DRA Antenna. Open Journal of Antennas and Propagation, 4, 176-189. http://dx.doi.org/10.4236/ojapr.2016.44014