2017 A Proposed Design of Unit Cell of Metamaterial for 5G Mobile

jamalmrasool@yahoo.com. Abstract In this manuscript a design of metamaterial unit cells which are new artificial materials made of periodic arrangement much smaller than the guided wavelength, are proposed which are suitable to work for 5G mobile communication working with millimeter frequency band at 28 GHz due the high demand for the frequency spectrum for mobile networks .The structures of unit cells were simulated using High Frequency Structure Simulator HFSS software. The design starts with the metamaterial structure which is composed of double rectangular (DRR) and circular split ring resonator (DSRR). The results of simulation showed very good results such as wide operating frequency band which is 1.34 GHz with very law radiation losses the unit cell designed to overrun the radiation losses which are appear with the work of


Introduction
Metamaterials MTM are new artificial materials made of periodic arrangement of unit cells much smaller than the guided wavelength with some unique properties. Such properties include a simultaneous negative permittivity and permeability that translates into a negative refractive index; these structures are commonly referred as left-handed materials (LHM). By using LHM in the design of a structure, its properties can be tailored in a broader manner than with classical materials [1,2].
The increasing demand of applications in terms of throughput and latency explains the evolution of telecommunication standards. The next generation of telecommunication standards such as the 5th-generation (5G) wireless communication networks are expected to considerably accommodate larger number of wireless connections to better support existing and evolving applications including social media high definition video streaming, full-featured web browsing,and real-time gaming. This can be made possible thanks to new features utilized in 5G wireless access networks as presented in [3]: massive MIMO (Multiple Input Multiple Output), beamforming, small dense networks, millimeter wave frequency, and movable base stations Millimeter-wave frequencies often refer to the frequency range from 30GHz to 300GHz, the wavelength of which is between 10mm to 1mm. There are several motivations for wanting to use mm-wave frequencies in radio links such as the radio spectrum at mm-wave frequencies is still rather undeveloped and more bandwidth is available at these frequencies and Because of higher attenuation in free space and through walls at mm.
Frequencies [4], the same frequency can be reused at shorter distances. The physical size of antennas at mm-wave frequencies becomes so small that it becomes practical to build complex antenna arrays and/or further integrate them on chip or PCB. The antenna performance will be dropped significantly due to the atmospheric attenuation.
Therefore, selecting the right band for 5G mobile networks is very important to overcome this significant issue. Hence, the millimeter frequency band has great advantages which can be used in modern communication networks because of their very high channels for communication and very wide frequency band so the 28 GHz has been carefully selected due to its optimal characteristic respecting on their small loss due to the atmospheric absorption characteristics of millimeter waves propagation for that this frequency band was chosen to 1146 design metamaterial unit cell which can be used antennas and electromagnetic band gap filters [5].
To overrun the losses which are appear with the work of metamaterials a new structure of unit cell was proposed which will be explain in section III.

Design of Metamaterial Unit Cell
Here the description on the selected metamaterial structure, the design calculation of the unit cell structure and includes the design and simulation results which being performed on the metamaterial unit cell with different dimensions to see the effect of the variations on the frequency region and the LHM propertie [6].
After obtaining the optimum dimensions for the unit cell structure, the array of unit cell is designed for the target working frequency 28GHz to see the effect of the metamaterial structure.
The designed structure is then simulated using High Frequency Structure Simulator (HFSS), this standard software uses a 3D full-wave Finite Element Method (FEM) to compute the electrical behavior of high-frequency and high-speed components, calculate the Sparameter for the metamaterial unit cells.
The structure can be designed in many ways. The fundamental concept and theory of the structure and its properties is very important since it will determine the ability to produce the LHM behavior in the required frequency band. As shown in Figure1 the design starts with the metamaterial structure which is composed of double rectangular (DRR) and circular split ring resonator (DSRR), the DRR & SRR consists of two metallic microstrip rings with a slit (or gap) which may be different in shape. However, with the same linear dimension, metal characteristics and gaps, in general the circular DRR and DSRR printed on both sides of the substrate shows higher value of the magnetic response which is due to the smaller area and the smaller side length.
There are several parameters that need to be tuned including width of each ring (w1=w2), separation between two rings (s), size of the gap (g), material properties of the rings, but in this work these parameters are kept constant because the important parameters such as radius of the microstrip rings (r1, r2), dimension of substrate (d) and surrounding medium are adjusted in order to get the desired negative permeability property at certain frequency range [7,8].

Simulation of Unit Cell and Analysis
The Simulation of Metamaterial unit cell is offered in this section. The suggested DRR and DSSR unit cell operate at 28 GHz band which is the candidate band for 5G mobile network applications. In Figure 2 the scattering parameters S 11 of the unit cell is shown. As seen from the Figure  Obviously as it is seen in the literature explaining the work of metamaterial that MTM is suffering from radiation losses for that in this paper a composed metamaterial unit cell had been used to overrun the radiation loss by using retrieval and transmission analyses.
The technique of the radiation loss reduction was done by using the induced surface current and retrieval analysis. Figure 4 expose the induced surface current on the both sides of the DRR unit cell at 28 GHz which produces circulating current in the front and back sides of the unit cell leading to the magnetic dipole response, from that the electric dipole response is induced by the turfs that expand to middle of X1 on the front and back countenance s of the unit cell of metamaterial structure as it very clear in Figure 4   The dipole response produces large radiation losses. However, by modifying the metamaterial structure to apply an opposite currents, the induced currents cancel out each other thus repressing the radiation loss.

Conclusion
Several types of metamaterial unit cells are discussed which are working in frequency band near millimeter band in 28GHz for mobile 5G communication. These types are DSSR and DRR printed on both sides of the substrate fulfill frequency bandwidth of 1.34 GHz.
Metamaterial unit cell had been used to overrun the radiation loss by using retrieval and transmission analyses.