Dual Band Slotted Printed Circular Patch Antenna With Superstrate and EBG Structure for 5G Applications

Slotted circular printed layered patch antenna is designed, simulated and fabricated for 5G (Fifth Generation) wireless communication applications. The antenna consists of slots in the main radiating circular patch element for miniaturizing the size of the radiating element and providing dual band radiation characteristics. The feed line is separated on bottom substrate layer with EBG (Electromagnetic Band-Gap) embedded for enhancing the gain characteristics of the antenna. Superstrate layer is also used for improving the gain of the antenna where the distance from the radiating antenna element is optimized for maximizing the impedance bandwidth and radiation characteristics. The feed realization and impedance matching of the radiating slotted circular patch antenna is done by inducing slot at the middle ground plane of the slot embedded circular patch antenna system. The proposed configuration provides power radiation gain values of more than 5 dB for the Ka band of communications, whereas the impedance bandwidth of the antenna is verified for the dual resonances at 27.5 and 28.5 GHz. Dual band radiation characteristics are attained by embedding and optimizing the slot length and width in the circular patch radiator element that is placed on the upper face of the substrate RT Rogers Duroid 5880 layer. The length of the microstrip feed line embedded in the lower layer of the substrate is optimized for providing required bandwidth characteristics for the dual frequency point radiations. The antenna configuration is designed, modeled and simulated in CST (Central Standard Time) Microwave studio. The antenna is fabricated and measured vs simulated frequency response, gain patterns and current density plots are presented for the verification of antenna operation in the desired frequency bands.

. Wide band radiation characteristics can be achieved for 5G systems by using tapered slot radiating element fed by substrate integrated feeding line with multiple beam characteristics for MIMO (Multiple Input Multiple Output) communications [2].
High gain printed antennas provide suitability for the 5G systems for compensating path losses by using four element arrays that are designed by triangular shaped slots embedded in substrate fed by integrated feeding microstrip feeding lines [3]. Antenna systems can be designed for simultaneously supporting both 4G and 5G standards by combining MIMO antenna systems with array of slot radiating elements covering the 2100 MHz frequency band for 4G and 28 GHz for 5G systems respectively [4].
ANN (Artificial Neural Networks) allows calculations of the antenna dimensions for accurately modeling the slot antenna radiation and polarization characteristics that provides suitability for MIMO systems for the 5G networks [5]. Low side lobe antenna arrays are designed for achieving low cross polarization levels by substrate integrated feeding lines and tapered T junction dividers suitable at 28 GHz for 5G systems [6]. Electromagnetic exposures for radiations at higher frequencies that are required for the fifth generation systems can be analyzed by the power density function instead of specific absorption rates and using various configurations of array antennas [7]. Wideband antenna with reduced losses and high gain is designed by using dipole antenna based on magneto electric properties and excited by waveguide integrated coupled slot line where the gain is enhanced by stacking additional substrate layers [8].
Side lobe levels of more than -18 dB can be achieved that are suitable for fifth generation communication systems by using linear array of 7 elements and parasitic patch elements coupled through stacked substrate at 28 GHz frequency band [9]. Phased array beam steering antenna for three dimensional radiations coverage can be design for 5G applications at 28 GHz by using three arrays of slot radiator based elements and switching between the arrays provides larger coverage area along with enhanced bandwidth [10].
Wireless Communications provides many challenges for the designers in terms of lower cost systems, greater coverage area and high gain requirements. EBG structures provide various benefits in providing enhancement in antenna characteristics for wireless communication. EBG can be used for providing reduction in radar cross section by using layered configuration based on checkboard structures [11]. Gaussian beam is utilized for concentration the radiation along a direction which is achieved by coupling EBG and periodic slow structures [12]. The high mutual coupling between monopole radiating elements for MIMO systems is reduced by incorporating layered EBG for UWB (Ultra-Wide Band) applications [13]. Dielectric resonator an tennas are used in wireless commun ication applications by different researchers due to high efficiency and low loss characteristics with comparison to conventional metallic patches. For exciting HEM11 mode of Dielectric resonator antenna, the dielectric resonator can be placed above a metallic bottom ground plane with some dielectric substrate and it can also be placed without any substrate. For exciting the mode of TM11 other than HEM11 dielectric resonator mode, the excitation is done in the region between the copper ground plane and the circular dielectric resonator. The antenna is not categorized as dielectric resonator antenna Dual Band Slotted Printed Circular Patch Antenna With Superstrate and EBG Structure for 5G Applications family but rather considered as dense dielectric patch antenna when it is excited in this mode and reflected as part of the patch antenna category. Apart from retaining a low profile trait, the efficiency of this type of antenna at higher frequencies is estimated to be better than normal traditional metallic patch antenna as the efficiency of the conventional patch antenna becomes less at higher frequencies [14]. Gain enhanced antenna array system is essential at Millimeter wave frequency ranges for overcoming the degradation in the signal strength due to oxygen molecular absorption. One of the main techniques for gain enhancement is by using efficient antenna array system where radiation from the feed network can be isolated form the main radiating antenna elements [15]. In addition, for additional gain augmentation superstrate technology can be used [16][17]. Coplanar waveguide fed slotted three arms for achieving bandwidth from 5.75-14.51 GHz using artificial magnetic conductor for wideband applications [18]. EBG is used for achieving reconfigurability in terms of polarization and frequency tuning at broadband by using metallic patch arrays [19]. For improving the width of the band gap, an EBG structure is presented in [20], consisting of tapered Koch fractal structures.
EBG can be employed for achieving lower pass band attenuation and stopband below -20 dB [21], where the pass band ripples are reduced by Chebyshev tapering and defected ground plane structure is used for enhancing stopband bandwidth characteristics. EBG structures can be used for millimeter wave wireless communication applications [22] for reduced mutual coupling for array antennas based on miniaturized EGB cells at 60 GHz. Circularly polarized antenna is designed by using linearly polarized EBG antenna with layer of meander line polarizer from 29.5-30 GHz with less than 1 dB axial ratio is achieved [23]. Matching devices can be incorporated for compensating degraded axial ratio [24], by using iris based matching system and self-polarized EBG structure centered at 9 GHz providing 20 dB gain.
The radiator can be embedded within EBG for better efficiency and characteristics [25]. Multimode and multibands can be simultaneously attained by using mushroom like EBG [26], where omnidirectional as well as patch like radiation patterns are achieved for the various bands and modes are realized by tuning various parameters of EBG. The comparison summary for various antenna designs suitable for 5G systems is shown in Table 1.
In this paper a novel layered slotted antenna is     shown in the Fig. 2(b). The slotted line is cut in the ground place with its placement for feeding the radiating element at the middle. The length and width of ground plane is the same as that of the substrate of 20 mm.

FIG. 1. LABELED DIAGRAM OF THE PROPOSED SLOTTED CIRCULAR PATCH ALONG WITH THE EBG GROUND PLANE AND SUPERSTRATE LAYER
The slot line length and width is optimized at 5.6 and 0.2 mm respectively. The bottom substrate layer with EBG structure and microstrip feed line dimensions layout is shown in Fig. 2(c).  Table 2.
And the current densities are given by: Where a e is the effective radius of the circular patch and k 0 is the propagation constant.

SIMULATION AND ANALYSIS
The proposed slotted circular printed patch radiator is designed and optimized in CST Microwave Studio. The dual band measured vs simulated S11 frequency response of the slotted circular EBG based antenna is presented in    Thus by using the proposed layered configuration the antenna exhibits an increase in the gain characteristics.
The 3D gain pattern plots of the proposed circular printed slotted printed layered patch radiator are demonstrated in Fig. 7. As seen from the four plots over the frequency band covering the frequency points of 27.48, 27.76, 28 and 28.48 GHz, the shape of the radiation pattern remains directional with a gain of more than 7 dB throughout the frequency band. The surface current plots of the proposed slotted circular printed layered patch antenna along with the microstrip transmission feed line and EBG at the bottom of the ground plane is shown in Fig. 8. The surface currents are plotted for the frequencies of 27.48 and 28 GHz as shown in Fig. 8(a-b) respectively. As seen from the surface currents, for the antenna to be effectively