DESIGN OF A SMALL PATCH ANTENNA AT 3.5 GHZ FOR 5G APPLICATION

In this paper a low profile patch antenna has been designed for 5G communication application. The resonating frequency has been chosen as 3.5 GHz for 5G application. FR4 epoxy material with permittivity of 4.3 has been chosen for the substrate material which has fire redundant property. The size of the substrate is 25.2×48 mm2. The main radiating patch is in a shape of ellipse and the line feed technique is used. The simulation is done by CST microwave studio software. Different parameters like S-Parameter, Antenna Gain, Directivity, Efficiency has been observed. The antenna has a gain of more than 5 dB which is very useful for communication applications. The antenna is designed for 5G communication applications.


Introduction
The fifth generation (5G) communication has been widely discussed to provide high data-rate communications in the future. The design and testing of the 5G communication system hinge on the understanding of the propagation channels [1], and a large body of channel measurements is thus required. Currently, 5G mobile systems are broadening their spectrum to support a high data rate. In the World Radio Communication Conference (WRC) in 2015, the 5G candidate frequency bands below 6 GHz have been widely discussed, and the following frequency ranges have been suggested: 470-694, 1427-1518, 3300-3800, and 4500-4990 MHz. Among them, 3.5 GHz has been widely considered, as it can be accepted for most of countries. Therefore this paper was focused on the propagation channel characterizations at 3.5 GHz band.
In the past, 3.5 GHz propagation channel has been studied mainly for the Worldwide Interoperability for Microwave Access (WiMAX) with limited bandwidth [2]- [3] [4] or the Broadband Fixed Wireless Access [5]- [6] [7]. Few works has been conducted for the 5G wireless propagation channels Elliptical dipoles were first investigated by N. P. Agrawall et al. in 1998. Elliptical elements offer even better matching than circular elements due to their more oblong from factor and more gradual taper [1]. Dipoles with elliptical elements offer good dipole performance over nearly two octaves. They also exhibit −10 dB return loss for 0.40 λ elliptic dipole height (2 h) in comparison with traditional dipoles whose height must equal approximately half-wave length [2]- [3].
The objective of the study is to design a small antenna for using at 3.5 GHz frequency for 5G application. The antenna has to be small enough to fit inside any small communication devices from new technology. Aim will be to have high gain and efficiency to ensure maximum data transfer.

Antenna Design
In Microstrip Patch antenna has three main parts namely Substrate, Patch, Ground Plane. An elliptical Microstrip patch antenna was designed for using in 3.5 GHz band for 5G applications. Substrate is designed using a box having material FR4 EPOXY with dielectric constant (εr) =4.3. The height(h) of the substrate is 1.6mm with respect to z-axis. The ground plane is made at the bottom of the substrate which results in the coplanar waveguide structure. The outer box is designed using air material and assigned with radiation.

Results and Discussions
This paper was intended to design an antenna which works at 3.5 GHz resonant frequency. Copper has been used as the radiating material and FR-4 (Ԑr =4.3, tanδ =0.015). CST microwave studio has been used to design and simulate the antenna. The performance of the antenna has been observed accurately and then they have been compared.

S Parameter
Scattering parameter which generally describes the electrical behavior of linear electrical system, this undergoes various steady state stimulation by electrical signal. S parameter describes the input and output relation between ports in an electrical system. As it is known that the resonant frequency(fr) and the return loss can be calculated from the S11 curve of the patch antenna respectively. So the obtained resonating frequency is 3.5 GHz and return loss is -30 dB. This shows that the antenna has very low return loss when it operates at 3.5 GHz frequency. That means a good amount of the signal will be transmitted by the antenna.

Radiation Pattern Directivity
Directivity is a fundamental antenna parameter. It defines the radiation intensity in a specific direction. Directivity plays a very vital role when the antenna is designed to radiate in a specified direction. The directivity of the main lobe of the antenna is 5.15 dBi at 81 degrees in theta direction. The side lobe level is -10.5 dB.

Conclusion
In this paper a small elliptical antenna has been designed for using at 3.5 GHz for 5G application. The antenna has a physical size of 25.2 X45 mm 2 . It has a return loss of -30dB at 3.5 GHz. Antenna gain is 5.01 dB. The antenna has a very high efficiency of 96.67%.