Triple-band antenna with defected ground structure (DGS) for WLAN/WiMAX applications

This paper presents a triple-band rectangular patch antenna that can be operated in three different resonance frequencies of 2.40 GHz, 3.50 GHz, and 5.80 GHz for WLAN and WiMAX applications. The FR-4 substrate with dielectric constant of 4.3 is used, with the dimensions of the substrate 34×30×1.6mm3. The performance of the rectangular patch antenna has been simulated and measured and the proposed patch antenna operates at three different resonance frequencies of WLAN and WiMAX which are 2.35-2.54 GHz, 3.45-3.57 GHz and 5.74-5.83 GHz. These results correspond to a simulated bandwidth of 197 MHz, 118 MHz and 90 MHz. The radiation pattern of nearly omni-directional is obtained. Overall, the results obtained show the designed antenna have a good performances of the three operating bands


Introduction
Recently, wireless connectivity has been extensively used especially in mobile devices. The higher demand for wireless connectivity for example the Wireless Local Area Network and Worldwide Interoperability for Microwave Access known as WLAN and WiMAX among users are tremendously high and continuously growth every day. A method of wireless allocation for two or more devices within an area and also provide an access point to the internet is known as WLAN. As for WiMAX, it supports mobile users, vagrant users and fixed wireless applications. Generally, WLAN and WiMAX follows IEEE 802.11 and IEEE 802.16 standard specifications respectively. The range of resonant frequencies for WLAN are from 2400 MHz -2484 MHz, 5150 -5350 MHz and 5725 -5825 MHz bands and WiMAX are from 2400 -2690 MHz, 3400 -3690 MHz and 5250 -5850 MHz for broadband wireless access network [1].
In designing an antenna, it is essential to cover multiple bands. The performance of the antenna which include the return loss, radiation pattern, antenna gain and also efficiency of the antenna are considered to meet the requirement of the multiple bands communication system.
Abundant of multiband antenna have been designed in order to obtain the desired antenna features for wireless system. A coplanar waveguide (CPW) fed compact dual-band proposed by Y. Zhuo et al patch antenna utilizes a U-shaped slot and two mitered corners printed on polydimethylsiloxane (PDMS) substrate with dielectric constant of 2.65 to accomplish two operating bands which meet IEEE 802.11a/b/g standard for WLAN applications [2] and H. Zhai et al presented a novel compact triple-band antenna comprises of three simple circular-arc-shaped strips for WLAN and WiMAX applications [3]. Next, [4][5][6][7] proposed a novel coplanar waveguide CPW-fed antenna printed on FR-4 substrate. F. Li et al reported the design of triple-band monopole antenna by inserting S-shaped meander strip into a C-shaped strip [4], L. Zhu et al presented miniaturized slot antenna for triple-band operation [5], Y. Xu et al proposed an S-shaped strip antenna with a rectangular ring slot together with a crooked U-shaped strip and at the bottom there are three straight strips antenna having overall dimensions of 35×25×1mm 3 [6], and Q. Zhao et al proposed a wide-slot triple-band antenna includes a a square slot in the middle of the ground, a rectangular shaped feeding strip with two sets of planar  [14], and C. Byrareddy et al proposed a compact triple-band rectangular microstrip antenna comprises of a rectangular-shaped patch, two identical slots symmetrically placed on the radiating patch, and twin inset fed with a large ground plane printed on FR-4 substrate having overall dimensions of 40×48×1.6mm 3 [15]. Last of all, A. Manouare et al proposed a novel triple band patch antenna made out of three emanating components with partial ground plane etched on Rogers 4350 20×43mm 2 [16]. Basically, the proposed antenna from [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] having the return loss ,S11 smaller than -10 dB and accomplishes good performances for both WLAN and WiMAX applications. All of the designs have been presented in numerous shapes and techniques to obtain the desirable features and defeat the restrictive weaknesses of microstrip antenna in covering multiband operations.
However, there are several limitations such as complex structures, large size and certain operating application need to be solved in order to obtain the desirable specification of the antenna. Thus, this paper proposed a triple-band rectangular patch antenna with a simple structure consist of inset fed on radiating patch and introduced a DGS which consists of square-ring slot with multiple vertical slots asymmetrically that can operate in frequency bands of 2400 MHz, 3500 MHz, and 5800 MHz for various application especially WLAN and WiMAX.

a. Implementation stages of Triple-band Antenna
The implementation of this project consists of two main stages which are the software simulation and hardware fabrication. After the antenna design has been finalized, which is the rectangular patch antenna, the parameters of the antenna are determined. The rectangular patch antenna is designed and simulated using the CST Software. The design is modified until it achieves the desired results.

b. Design process for Triple-band Antenna
The  (2) Where, the patch effective length, Leff represents by c 2f r√ ε reff .

c. Simulation and fabrication process
The next process is simulation using the CST Studio Suite software and fabrication process. Basically, there are five steps in designing the antenna in CST Software. The steps can be summarized as creating a new project, modelling an antenna, inserting a waveguide port, setting the field monitor, and running the simulation. After the design process has been verified the fabrication process is done. Fig.1(a) shows the design of the rectangular patch antenna from the top view. The radiating element of the antenna has been modified to obtain the desired S11 results of antenna performance by introducing inset feed. The bottom view of the rectangular patch antenna as shown in Fig.1(b) where this bottom part has been modified by creating a square ring slot together with few other slots to form a DGS where 1mm width of the slots. All parameters involved in the design are listed in Table 1. The tripleband patch antenna prototype has been shown in Fig. 2.

Result and Discussion
The proposed triple band antenna with rectangular shaped patch antenna with additional ground square-ring slot and asymmetrical vertical slots has been designed and fabricated. The performance of the simulation rectangular patch antenna has been compared with measurement. The parameters of the triple band antenna are listed as in Table 1 has been optimized to get the desired S11 results as in Fig  3. The return loss S11 obtained is less than -10dB.  Fig.4 shows the S11 or return loss for simulation with different length by 2 mm. The simulated rectangular patch antenna is compared with three different length 32, 34 and 36 mm. The proposed antenna length of 34 mm shows a better performance with the S11 less than -10 dB and achieved the required impedance bandwidth. The fabricated triple band rectangular patch antenna is measured using the Vector Network Analyzer (VNA). The impedance bandwidth values are compared with the simulation result. Fig.5 shows the impedance bandwidth for both measured and simulated result of the proposed rectangular patch antenna. The results obtained from the measurement are tabulated in Table 2. The simulation of proposed triple band antenna, Electric-field (E-Field) radiation pattern been done. The radiation patterns of the triple band rectangular patch antenna are shown in Fig.6 (a)-(c) at desired operating frequency of 2400 MHz, 3500 MHz, and 5800 MHz. It can be seen that the radiation pattern for all frequency bands are almost omnidirectional. The gain obtained from the simulation for these three frequency bands are 2.017dBi, 2.994dBi, and -3.362dBi respectively. (c) Figure 6: The E-Field radiation pattern simulation of the proposed triple-band rectangular patch antenna at (a) 2400 MHz (b) 3500 MHz (c) 5800 MHz.

Conclusion
A triple-band rectangular microstrip patch antenna with square-ring slot and asymmetrical vertical slots has been designed and fabricated. The simulation and measurement results of the rectangular patch antenna has been analysed. The reflection coefficient, S11 of the three frequency bands of 2.4 GHz, 3.5 GHz, and 5.8 GHz achieved less than -10dB. The simulated and measured results show that