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Department of Communication, Canadian International College (CIC) Cairo, Egypt

- *Corresponding Author:
- Ashraf Sayed Abdel Halim

Department of Communication, Faculty of Engineering

Canadian International College (CIC) Cairo, Egypt

**E-mail:**[email protected]

**Received date:** 06/08/2019; **Accepted date:** 20/08/2019; **Published date:** 27/08/2019

**Visit for more related articles at** Research & Reviews: Journal of Engineering and Technology

A low-profile wideband linear polarized patch antenna using meta-surface is suggested for the wideband procedure at 5-GHz Wi-Fi bands. The antenna consisted of a rectangular patch interceded between a grid of 3 3 periodic meta-surface and the ground plane. The accepted coaxial probe feed is uncomplicated to manufacture and match. Characteristic Mode Analysis (CMA) is used to evaluate and study the mechanism of action of the suggested antenna. We found that 2 main distinctive modes are effectively excited causing the broadband procedure and linearly polarized radiation. The suggested dielectric-filled antenna with a low profile of 0.057 λ0 (λ0 is the working wavelength at 5.7 GHz in free space) gains about 30% calculated -10 dB impedance bandwidth (4.89-6.62 GHz) with 7.28 dBi median achievement. Over the bandwidth, the antenna performance is >90%, and cross-polarization levels are <18 dB.

Low-profile antenna, Wideband patch antenna, Linearly polarized patch antenna

Micro-Strip Antennas (MSAs) are prevalent and favored in wireless communication systems, mobile, GPS, armed goals, satellite communication, for its attractive characteristics of low profile, less complicated, lightweight, simple manufacture, and definite assurance. But micro-strip antennas also have drawbacks like a small achievement, limited effectiveness, small bandwidth because of its innate feature. Many researches have been carried out on elevating the bandwidth of various microstrip antennas [1-4]. But, it is complex to attain wide bandwidth when sustaining low profile. Metasurface (MTS) as an encouraging resolve has been investigated to exaggerate the bandwidth and several patch antennas utilizing metasurface have been introduced for low profile and broadband procedure [5-8]. A lot of techniques involving equivalent circuits [9,10], effective medium theory [11], surface impedance extraction [12,13] and modal dispersion curve [14,15] are utilized to delineate the engineered metasurface. However these, techniques are inappropriate for investigating antennas utilizing metasurface composed of few unit cells. The Theory of Characteristic Modes (TCM) established at the Moment Of Method (MOM) is actually a favorable technique for antenna plan due to the physical judgment it delivers into the radiating phenomena occurred in the antenna. The theory of characteristic modes has been opportunely used to investigate and plan various antennas [16-21]. Lin et al. [22], used the theory of characteristic modes for the modeling, analysis, and judgment of a low-profile wideband metasurface antenna which is supplied by a microstrip line throughout aperture-coupling. In addition, Characteristic Mode Analysis (CMA) is utilized to inhibit the undesirable higher-order modes of the metasurface in multiport antenna systems for bettering the radiation act [23].

The aims of this study are planning a low-profile wideband microstrip antenna utilizing metasurface and use the CMA to examine and explain the mechanism of action of the suggested antenna. The antenna is composed of a rectangular patch in sandwiched the middle of the metasurface and the ground plane. The coaxial probe supplier is adopted, where the interior conductor of the coax is linked to the patch and the exterior conductor is linked to the ground plane. Comprehensive Modal Weighting Coefficients (MWC) with consideration of electric field coupling are measured to examine the broadband procedure and the radiation features.

**Characteristic Mode (CM) Theory For Antennas With Multi-Layered Medium**

The conventional characteristic mode theory was first evolved for PEC objects in free space [24]. In contrast to the Electric Field Integral Equation (EFIE) for PEC objects in free space, the Mixed-Potential Integral Equation (MPIE) with spatial domain Green’s Functions (GFs) of multi-layered medium are evolved for the established characteristic root equation [25]. The mixed-potential integral equation with spatial domain GFs of multi-layered medium gives the ability to precisely model the surface currents on metallic conductors entombed inside the multi-layered medium. The ground plane and dielectric substratum in the mixed potential integral equation is supposed to be perpetually in the transverse path. Keeping in mind the frame condition on the PEC, that is, the tangential ingredients of the electric field on the PEC surfaces are zero, the mixed-potential integral equation that assigns the unidentified current J and incident field Ei can be written as illustrated [26-29].

(1)

Where Ga and Gq are the spatial domain, GFs for the vector as well as scalar potentials, respectively. The closed-form term of the spatial domain GFs can be gained utilizing the discrete complex image method [26-31]. By employing the typical Galerkin’s operation to the mixed-potential integral equation in (1), the matters of the sequel impedance matrix Z can be illustrated as follows:

Where fm (r) is the renowned RWG fundamental functions

known over triangle pairs on the radiating patch. Following the operation of the conventional characteristic mode theory for PEC objects, a generalized eigenvalue equation for the mixed-potential integral equation can be written as follows: (2)

Where [R] and [X] are the actual and unreal components of the Moment Method impedance matrix Z, respectively. Eigenvector Jn and eigenvalue λn can be gained by solving (3). The modal significance (MS) is illustrated as follows:

(3)

Peculiar modes form a full series of solutions, and thus the whole current can be shown as a linear superposed of these mode currents

(4)

Where α n indicate the modal weighting coefficient (MWC) and can be calculated by (5)

The expression in (5) signifies the modal excitation coefficient, and Ei indicates the external excitation. Utilizing mutuality theorem, the nominators in (6) can also be rewritten as follows: (6)

En indicates the electric field because of the modal current density Jn and Ji signifies an affected current density on a coupler. On the contrary, to a delta-gap voltage origin, if we utilize a probe as the coupler, the feed probe at the feed position can be modelled as a uniform current [33]. Employing this interpretation and replacement (7) into (6), the Modal Weighting Coefficient (MWC) with consideration to the probe feed coupling can be illustrated as follows: (7)

Where r0 indicates the feed situation and l indicates the probe length. Thus we can utilize the (8) to calculate the modal weighting coefficient modal weighting coefficient of the suggested probe-feed metasurface antenna.

**Antenna Design**

The construction of the suggested antenna is illustrated in **Figure 1**. The antenna composed of 3 metal layers, the metasurface, the driven patch, and the ground from upper to lower. The thickness of the 2 F4BM350 substrates (r=3.5 and tan δ=0.001) is 1.5 mm. To obtain a low profile and easy manufacture, 2 substrate layers stack with each other without air gap. The internal part of the 50-SMA connector is connected to the patch and the external conductor is attached to the ground plane. The adopted metasurface is a periodic construction.

With nine rectangle metal plates in a 3 3 layout. Planned for the 5-GHz Wi-Fi bands (4.9GHz-5.9 GHz), the antenna measurements are calculated using the full-wave simulator HFSS. The final achieved antenna measurements are illustrated in **Table 1**.

Lp | Wp | S | h1 | h2 | PL | PW | Lf | Lg | Wg |
---|---|---|---|---|---|---|---|---|---|

9.1 | 7 | 0.8 | 1.5 | 1.5 | 12 | 7 | 5.3 | 50 | 50 |

**Table 1.** Measurements of the antenna (mm).

**Methodology**

Characteristic mode analysis of the antenna design: Characteristic mode analysis is adopted to interpret the mechanism of action of the metasurface antenna. The coaxial probe supplier is withdrawn and all other geometric measurements of the patch and metasurface are maintained identical. The characteristic mode analysis procedure can be achieved utilizing the method of moments-based characteristic mode request in commercial simulation software FEKO, where the ground plane and dielectric layers are unlimited extension in x-and y-dimensions utilizing planar multilayer substrate make. Method of moments for infinite planar multilayer substrate can be resolved using Green’s functions in FEKO. For this distinctive mode structure, currents, remote fields, adjacent fields and characteristic modes requests are permitted. The measured Modal Significance (MS) of the 1^{st} ten modes of the composition without the supplier is illustrated in **Figure 2**.

Modal current and radiation arrangement of J1-J7 is illustrated in **Figures 3 (a-g)** and **4 (a-g)**.

The feed point is signalled by a black circle. It can be noticed that the modal E-field of J1, J7 at the feed site is approximately maximal where the field of unwanted modes is too small **Figure 5 (a-g)**. For the coaxial probe feed by electric field coupling can be noticed as a Capacitive Coupling Element (CCE), and a random mode is stimulated capacitive if a capacitive coupling element is situated at the site of its electric field peak [34,35], J1 and J7 will be maximally stimulated **Figure 6 (a-c)**. For calculating the addition of every mode current to the whole radiated power, Modal Weighting Coefficient (MWC) with consideration to electric field coupling is measured using equation (6)

(3)

It can be noticed from the gained results as illustrated in **Figure 7** that J1 (at the inferior band) and J7 (at the superior band) are well stimulated, which will assist in a broadband procedure and a linear broadside radiation arrangement. Furthermore, some unwanted modes have been inhibited because of the feed situation, which will decrease the crosspolarization levels.

The manufactured antenna is illustrated in **Figure 6**. The radiation arrangement have been simulated in full-wave simulator ANSYS HFSS 18.0 and additionally calculated in an anechoic chamber at variable frequencies. The simulated and calculated results are illustrated in **Figure 8** with good acceptance.

Additionally, it can be noticed from **Figures 7** and **8(a)** and **8(b)** that the dual-mode wideband procedure of return loss coincides to the efficient stimulation of the 2 main modes. The calculated -10 dB impedance bandwidth is around 30% (4.89-6.62 GHz), through which the calculated peak income achieves from 6.96 to 8.21 dBi and the simulated radiation efficacy is more than 90%. Normalized radiation arrangements are shown in **Figure 9(a)** and** 9(b)** for 5 GHz, **Figure 9(c)** and **9(d)** for 6.5 GHz.

Furthermore, the cross-polarization levels are lower than 18 dB across the bandwidth because of the inhibition of unwanted modes as shown in the characteristic mode analysis procedure. The correlation of the act of the suggested antenna and several other linearly polarized metasurface antennas are illustrated in **Table 2**.

Antenna structures | Size (λ_{03}) |
-10 dB |S11| BW (%) | Efficiency | Boresight gain (dBi) |
---|---|---|---|---|

Ref (5) Ref (11) Ref (14) Ref (21) Suggested antenna |
1.1 × 1.1 × 0.061 0.88 × 0.88 × 0.069 1.05 × 1.05 × 0.06 0.72 × 0.72 × 0.075 0.95 × 0.95 × 0.057 |
25 15 28 20 30 |
>76% >70% >92% >90% >90% |
>9.0% >7.5% >6.0% >7.6% >6.96% |

**Table 2.** Correlation of the act of the suggested antenna and novel dual-layer wideband patch antennas utilizing metasurface.

A broadband low-profile linearly polarized patch antenna utilizing metasurface for 5- GHz WiFi procedure has been introduced examined and analytically substantiated. The adopted coaxial probe supplier is simple to manufacture and match. CMA of the antenna construction has presented a good interpretation and description of the mechanism of action involving wideband procedure and the radiation peculiarity. The characteristic mode analysis is procedure can additionally be protracted to other patch antenna utilizing the coaxial probe feed.

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