Design of Dual Band Microstrip Antenna for Wi-Fi and WiMax Applications

In this paper, a dual band rectangular microstrip patch antenna with microstrip line is presented. The proposed antenna is designed on FR4 substrate with thickness 1.5 mm and relative permittivity 4.3. The antenna is designed to operate at 2.4/5.8 GHz bands for Wi-Fi/WiMax applications. The obtained return loss is -32.77dB at 2.4 GHz with 7.4% bandwidth and -25.955 dB at 5.8 GHz with 8.17% bandwidth. The practical and simulation result are computed. It is noted that there is a good agreement between the simulation and measured result (using vector network analyzer (VNA).


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A planar Multiband Antenna for GPS, ISM and WiMAX Applications was propsed in [10]. The antenna's entire area is 59.5x47 mm 2 and is printed on an FR-4 substrate and fed by a 50 Ohm microstrip line. Inset Feed Toppled H-Shaped Microstrip Patch Antenna for PCS/WiMAX Application was proposed in [11]. H-shaped microstrip patch antenna with grounded plane is investigated for triple band operation. Theproposed antenna of dimension 40×40 is designed on FR4 substrate with dielectric constant εr=4.4 and height h=1.60 mm.
In this paper, a rectangular dual-band microstrip antenna for WiFi/WiMax applications in 2.4/5.8 GHz bands is presented. The antenna consists of a rectangular patch that contains five rectangular and a rectangular slot in ground plane. The slot in the ground enhances the gain and bandwidth while the slots in the patch improves the return loss. The proposed antenna is simulated using CST microwave studio 2016 and the obtained radiation characteristics of the antenna are presented.

Antenna Design
The geometry of the proposed antenna is illustrated in Figure 1, it consists of a rectangular patch whose width and length are 18.2 mm and 22 mm respectively. The dielectric material selected for the design is FR-4 which has a dielectric constant 4.3 and a thickness h=1.5 mm. The antenna is fed by a 50Ω microstrip line with a width 3.7 mm for impedance matching. Five rectangular slots are etched on the patch which helps achieve dual band radiation at the desired frequencies. The patch and ground plane are made of copper with thickness 0.035 mm. A rectangular slot is introduced in ground which has dimension of 40×40 mm. Tables and Figures are   The following equations are used to calculate the dimensions of microstrip antenna [1]. The width of patch is found by: where C is the velocity of light , 0 is the resonant frequency and is the dielectric constant of substrate. The following equations gives effective dielectric constant of substrate and length extension ∆ : where h is high of substrate.
The length of the patch is found from: the length and width of the ground are given by the following equations: feeder length and feeder width for the microstrip feed line are obtained by the following equations:

Parametric Study
A parametric study is done for obtaining the best parameters for the antenna. The effect of changing the width, length of patch and width of transmition feed to the return loss are studied as shown in Figure 2, Figure 3 and Figure 4.
As seen from Figure 2, Figure 3 and Figure 4, changing width of patch effects on the 5.8 GHz frequency mostly. As the value of W increases, the 5.8 GHz frequency is shifted to the left. W=18.2 mm is chosen for having the best compromise between return loss and bandwidth. On the other hand, changing patch length affects the 2.4 GHz frequency more. As the value of L increases, the 2.4 GHz shifted to left and 5.8 GHz shifted to right. L=22 mm is chosen to obtain radiation at 2.4 GHz and 5.8 GHz. As for the effect of feeder width, its value affects the impedance matching of microstrip feed to the impedance. =3.7 mm is chosen as the best value where a good impedance marching is obtained at the two frequencies.

Results and Discussion
The return loss vs. frequency of the proposed antenna is shown in Figure 5. The return loss is found at 2.4 GHz and 5.8 GHz 32.77 dB and -25.955 dB respectively. The band width obtained at these frequencies are 7.4% in the range (2.3 GHz-2.492 GHz) and 8.17% in the range (5.586 GHz-6.06 GHz). VSWR is always real and positive value for practical applications. Small value of VSWR means that the antenna is matched with the transmission line. Antenna is ideal at VSWR value equal to be 1. When antenna and feed are not matched, some electric energy cannot transfer to the antenna (i.e. reflection occurs). The polar plots for the directivity characteristic for the two frequencies are shown in Figure 7. The Gain of the proposed antenna for the two frequencies is shown in Figure 8. The 3D-radiation pattern for the proposed antenna for the two frequencies is shown in Figure 9. Figure 10 shows the current distribution for the proposed antenna at the designed frequencies.  Figure 11 shows the simulation and the measured results. It is noted that there is a slight different between the measured and simulation result. This different is attributed to the manufacturing errors which consist of variation of with the frequency, fringing effect and due to discontinuity. Fabricated antenna of front view and back view as shown in Figure 12.  Table 2 shows a comparison among the proposed antenna and antenna in refrence in term of antenna size, resonant frequency and porpose of antenna. As we seen from this table that the proposed antenna is smaller in size and sutable for dual band.

Conclusions
In this paper, a dual band rectangular microstrip antenna at 2.4 GHz/5.8 GHz bands for Wi-Fi/WiMax applications is presented. The antenna consists of a rectangular patch with five slot in and a rectangular slot in ground. The result shows acceptable return loss, bandwidth and gain making it suitable for Wi-Fi/WiMax. The proposed antenna has two bands (2.314-2.492) GHz and (5.586-6.06) GHz in which the reflection coefficient is less than -10 dB.The proposed antenna was fabricated and simulated result (using CST) and measured result (using VNA) are obtained and compared.