Superdirective dimers of coupled self-resonant split ring resonators: Analytical modelling and numerical and experimental validation

Abstract

Superdirective antennas developed over the last century have received renewed interest in recent years from the development of metamaterials. these arrays of electromagnetic resonators (or meta-atoms) carrying short wavelength electro-and/or magneto-inductive waves support current distributions with very high spatial frequency as required by the classical conditions for superdirectivity. As meta-atoms can have both electric and magnetic dipole characteristics (and hence radiation properties), developing antennas exploiting these distributions can challenge conventional intuitions regarding the optimal configurations required. In this work we are reporting the development of a genuinely superdirective array using split ring resonators (SRRs). We provide a comprehensive analytical model characterizing the radiation from SRR dimers in which excitation of only one split ring leads to superdirective radiation via mutually coupled modes. our model exploits simple circuit descriptions of coupled resonant circuits, combined with standard radiation formulae for curvilinear current distributions. Using this simple model we are able to map directivity against possible SRR locations and orientations in two dimensions and identify the unique optimal configuration which meets the requirements for superdirective emission. We validate the theoretical findings by comparison to both full wave simulations and experiments showing that our SRR dimer achieves endfire directivity very close to the maximum theoretical value. Directional and smart antennas are one of the approaches that could be used to increase the capacity and flexibility of wireless systems in future integrated gigabit communications (5G and beyond). The advantages of a steerable antenna system include the possibility of tracking a terminal signal and mitigating interference between network nodes, thus improving network capacity. Directional antennas can also improve power efficiency 1. The most common technique to realize a directive antenna consists in assembling a multiple-antenna array in which the radiation pattern can be reinforced in a particular direction and suppressed in undesired directions. By individually controlling each array element in phase and amplitude, the direction of radiation can be electronically steered (phased arrays) 2. Multi-element arrays are by now widely used in based stations of cellular networks, but simple implementation for mobile devices is severely constrained by the need for small antennas, the conventional phased array techniques for enhancing the directivity leading to a significant increase of the antenna size and requiring a separate RF chain for each antenna element. On the other hand, antenna miniaturization is usually achieved at the expense of efficiency, bandwidth, directivity and gain, but especially miniaturized antennas tends to present a practically omnidirectional radiation pattern. However, future regulations might require the use of adaptive directional antennas also for mobile terminals, due to the invaluable role...

The Statistics of Superdirective Beam Patterns

“…Thus, the NBP results to be (11) Because it was assumed that   f l   0, the real and imaginary parts of the ABP, can be expressed, respectively, as…”

“…The possibility of considerably increasing the directivity makes superdirectivity a topic of great interest and current research [8][9][10][11], in view of numerous applications, including microphone array [12,13], sonar [14,15], radar [5,16] and radio communication [6,17]. The main research aim is to combine the increase in directivity with the reduction in robustness against spatially uncorrelated noise and random errors.…”

Homogenization of the vertically stacked medium frequency magnetic metamaterials with multi-turn resonators

“…Despite the low and high frequency structures, the medium frequency magnetic field metamaterials were discussed as well. Their topology is similar to the high frequency metamaterials, for example the split-ring resonators 27 , 28 , hence unit cells consist of an inductive element (in this case a planar coil) made of a conductive material and connected with capacitance (parasitic, or in a form of the lumped capacitor), which are then arranged periodically to form the structure with effective properties. Aside from the classical horizontally stacked unit cells, some examples of vertically stacked resonators were shown 1 , 11 , 29 – 31 , to create a composite possessing identical outer dimensions but able to interact with other component of an external field.…”

3D Printing of Functional Metal and Dielectric Composite Meta‐Atoms

“…For example, there are reports of solely dielectric resonator antennas produced using FDM, [5,6] however the permittivity of these thermoplastics is generally too low to be of much value for such applications, unless loaded with fillers that can raise their dielectric constant. [7] In order to construct useful radio frequency (RF) devices, such as filters [8] and antennas, [9] conductors are essential to couple feeds, create antennas and form resonant structures. Many examples of conductive filaments have been demonstrated using thermoplastics loaded with particles, including carbon fiber, copper, and silver.…”