This research presents a triband compact printed antenna for WLAN and WiMAX applications. The antenna structure consists of a folded open stub, long and short L-shaped strips, and asymmetric trapezoid ground plane. Besides, it is of simple structure and operable in 2.4 GHz and 5 GHz (5.2/5.8 GHz) WLAN and 3.5/5.5 GHz WiMAX bands. The folded open stub and long and short L-shaped strips realize impedance matching at 2.4, 3.5, 5.2, and 5.8 GHz, and the asymmetric trapezoid ground plane fine-tunes impedance matching at 5.2, 5.5, and 5.8 GHz. In addition, the equivalent circuit model consolidated into lumped elements is also presented to explain its impedance matching characteristics. In this study, simulations were carried out, and a prototype antenna was fabricated and experimented. The simulation and experimental results are in good agreement. Specifically, the simulated and experimental radiation patterns are omnidirectional at 2.4, 3.5, and 5.2 GHz and near-omnidirectional at 5.5 and 5.8 GHz. Furthermore, the simulated and measured antenna gains are 1.269–3.074 dBi and 1.10–2.80 dBi, respectively. Essentially, the triband compact printed antenna covers 2.4 GHz and 5 GHz (5.2/5.8 GHz) WLAN and 3.5/5.5 GHz WiMAX frequency bands and thereby is a good candidate for WLAN/WiMAX applications.
Recent decades have witnessed increased adoption of wireless communications technologies in a wide variety of applications, including laptop computers, mobile phones, and portable devices. The phenomenon contributes to a rise in demand for compact multiband antennas.
In [
As a consequence, various techniques have been proposed to further improve antenna coverage encompassing 2.4/5.2/5.8 GHz WLAN and 3.5/5.5 WiMAX bands [
Comparison between the existing WLAN/WiMAX antennas and the proposed triband antenna.
Reference | Antenna size (mm) | WLAN (GHz) | WiMAX (GHz) |
---|---|---|---|
[ |
60 × 60 × 11.58 | 2.4 | 2.5/3.5 |
[ |
33 × 36.4 × 0.508 | 1.8/2.45/5.2 | 3.5 |
[ |
40 × 40 × 1.6 | 5.2/5.8 | 2.3/3.3/5.5 |
[ |
30 × 34 × 0.76 | 2.4/5.2 | 3.5 |
[ |
40 × 30 × 0.79 | 2.4/5.8 | 2.5/5.5 |
[ |
50 × 50 × 1.6 | 2.1 | 3.5/5.5 |
[ |
35 × 45 × 1.5 | 2.4/5.8 | 2.3/3.5/5.5 |
[ |
80 × 65 × 0.78 | 2.4 | 2.5/3.5 |
[ |
40 × 40 × 0.764 | 5.8 | 3.5 |
[ |
30 × 20 × 0.8 | 2.45/5.7 | 3.5 |
[ |
50 × 45 × 1.6 | 2.4/5.8 | 3.5 |
[ |
59 × 31 × 0.1 | 2.4 | 3.5 |
[ |
45 × 50 × 1 | 2.4 | 3.5/5.5 |
[ |
70 × 44 × 1.6 | 2.4/5.8 | 2.5/5.5 |
[ |
35 × 38 × 1 | 5.8 | 1.8/3.5 |
[ |
29.6 × 14.8 × 1.5 | 2.4 | 2.5/3.5 |
[ |
30 × 40 × 0.8 | 5.2/5.8 | 2.3/3.5/5.5 |
[ |
50 × 50 × 1.6 | 5.2/5.8 | 3.5 |
[ |
80 × 60 × 0.2 | 2.4/3.65 | 2.3/2.5/3.5 |
[ |
35 × 25 × 1 | 2.4/5.2/5.8 | 3.5/5.5 |
[ |
96 × 73 × 14 | 2.4/5.2/5.8 | 2.5/3.5 |
[ |
24 × 27 × 1.6 | 2.4/5.2/5.8 | 3.5 |
[ |
22 × 29 × 0.508 | 2.4/5.2/5.8 | 3.5 |
[ |
35 × 19 × 1.6 | 2.4/5.2/5.8 | 3.5/5.5 |
[ |
29 × 21 × 1.6 | 2.4/5.2/5.8 | 3.5/5.5 |
[ |
50 × 50 × 1 | 2.4/5.2/5.8 | 3.5/5.5 |
Proposed | 17 × 23.5 × 1.6 | 2.4/5.2/5.8 | 3.5/5.5 |
Specifically, this research proposes a WLAN/WiMAX triband compact printed antenna operable in 2.4 GHz and 5 GHz (5.2/5.8 GHz) WLAN and 3.5/5.5 GHz WiMAX bands. The antenna structure consists of a folded open stub, long and short L-shaped strips, and asymmetric trapezoid ground plane. In the study, simulations were carried out using computer simulation technology (CST) microwave studio, and experiments were undertaken using a fabricated prototype antenna. The simulation and experimental results are in good agreement, validating the suitability of the proposed triband antenna for WLAN and WiMAX applications.
The organization of this research is as follows: Section
Figures
The proposed WLAN/WiMAX triband antenna: (a) top view and (b) side view.
The asymmetric trapezoid ground plane is incorporated to fine-tune impedance matching at 5.2, 5.5, and 5.8 GHz. Table
The optimal dimensions of the WLAN/WiMAX triband antenna (unit: mm).
Parameter |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dimension | 23.5 | 17 | 1 | 0.5 | 1.1 | 6.2 | 2.1 | 1.2 | 0.4 | 0.2 | 2.3 | 3 | 0.2 | 7 | 9 | 14.82 | 7.1 | 8.2 | 13.45 | 7 |
In the antenna design evolution, simulations were carried out using CST software by varying dimensions of three radiating components, and the reflection coefficient (
Evolution of the WLAN/WiMAX triband compact printed antenna.
In the parametric study of the antenna, the dimensions of a folded open stub, long and short L-shaped strips, and asymmetric trapezoid ground plane were varied and the reflection coefficient (
The basic structure of the proposed antenna consists of a folded open stub and long and short L-shaped strips, as shown in Figures
The radiating elements: (a) a folded open stub (Antenna1), (b) a folded open stub and a long L-shaped strip (Antenna2), (c) afolded open stub and long and short L-shaped strips (Antenna3).
Simulated
In Figure
In addition, the overall length of the folded open stub (
To improve impedance matching at the upper frequency band (i.e., 5.2, 5.5, and 5.8 GHz), a triangular-shaped strip was incorporated into the existing ground plane to realize the asymmetric trapezoid ground plane (proposed antenna), as shown in Figure
Simulated
With the theoretical formulation of the input impedance characteristics, the expression for the input impedance of the CPW equivalent lossless transmission line can be expressed as [
The normalized input impedance on the Smith chart whose standing wave ratio (SWR) is 2 is equivalent to
Comparison between the simulated
In Figure
In Figure
The matching network topologies used in several antennas are equivalent circuit models [
To discuss the relation between the triband frequency operation and input impedance properties of each antenna element, the equivalent circuit model is built, as shown in Figure
Equivalent circuit model of the WLAN/WiMAX triband compact printed antenna.
The resonant frequency can be calculated using the following equation:
The initial values of
In Figure
Simulated surface current distribution of the WLAN/WiMAX triband antenna at (a) 2.4, (b) 3.5, (c) 5.2, (d) 5.5, and (e) 5.8 GHz.
At the second stage, a parallel RLC (
At the third stage, a parallel RLC resonant circuit (
In addition, at the fourth stage (asymmetric trapezoid ground plane), a coupling capacitor (
The optimal component values of an equivalent circuit model of the proposed antenna.
Lumped element | Value |
---|---|
|
32 Ω |
|
0.17 nH |
|
4.7 pF |
|
12 Ω |
|
1.5 nH |
|
2 pF |
|
49 Ω |
|
0.39 nH |
|
5.36 pF |
|
32 Ω |
|
12 pF |
|
0.23 nH |
|
5 pF |
|
28.5 Ω |
|
0.18 nH |
|
4.7 pF |
|
0.23 nH |
|
2 pF |
|
7.8 pF |
|
0.8 nH |
|
4.2 pF |
|
200 nF |
|
36 Ω |
|
2.8 nH |
|
0.25 pF |
|
49 Ω |
|
0.15 nH |
|
4.2 pF |
|
10.27 pF |
|
0.0775 nH |
In Figures
Comparison between the simulated input impedance and
Figures
In particular, at 5.2, 5.5, and 5.8 GHz, the surface current is concentrated along the edge of the trapezoid ground plane, thereby fine-tuning impedance matching of the upper frequency bands. In essence, the triband characteristic of the antenna is a collective function of the folded open stub, long and short L-shaped strips, and asymmetric trapezoid ground plane.
A prototype of the WLAN/WiMAX triband compact printed antenna was fabricated, as shown inFigure
Prototype of the WLAN/WiMAX triband antenna.
Simulated and measured
Figures
Simulated and measured radiation pattern of the WLAN/WiMAX triband antenna at (a) 2.4, (b) 3.5, (c) 5.2, (d) 5.5, and (e) 5.8 GHz.
Figures
Simulated and measured gain of the WLAN/WiMAX triband antenna at (a) 2.4, (b) 3.5, (c) 5.2, (d) 5.5, (e) and 5.8 GHz.
Simulated and measured antenna gains.
Frequency | 2.4 GHz (2.4–2.484 GHz) | 3.5 GHz (3.4–3.6 GHz) | 5.2 GHz (5.15–5.35 GHz) | 5.5 GHz (5.25–5.85 GHz) | 5.8 GHz (5.725–5.825 GHz) |
---|---|---|---|---|---|
Simulated | 2.059–2.078 dBi | 2.180–2.215 dBi | 1.270–1.980 dBi | 1.269–3.074 dBi | 2.974–3.007 dBi |
Min. | 2.059 dBi at 2.4 GHz | 2.180 dBi at 3.48 GHz | 1.270 dBi at 5.35 GHz | 1.269 dBi at 5.34 GHz | 2.974 dBi at 5.811 GHz |
Max. | 2.078 dBi at 2.484 GHz | 2.195 dBi at 3.6 GHz | 1.980 dBi at 5.15 GHz | 3.074 dBi at 5.68 GHz | 3.007 dBi at 5.725 GHz |
|
|||||
Measured | 1.75–1.85 dBi | 1.80–1.92 dBi | 1.10–1.71 dBi | 1.15–2.80 dBi | 2.18–2.18 dBi |
Min. | 1.75 dBi at 2.41 GHz | 1.80 dBi at 3.40 GHz | 1.10 dBi at 5.35 GHz | 1.15 dBi at 5.34 GHz | 2.23 dBi at 5.82 GHz |
Max. | 1.85 dBi at 2.48 GHz | 1.87 dBi at 3.60 GHz | 1.71 dBi at 5.15 GHz | 2.80 dBi at 5.59 GHz | 2.50 dBi at 5.73 GHz |
This research proposed a WLAN/WiMAX triband compact printed antenna using a folded open stub, long and short L-shaped strips, and asymmetric trapezoid ground plane. The triband antenna is of simple structure and operable in 2.4 GHz, 5 GHz (5.2/5.8 GHz) WLAN and 3.5/5.5 GHz WiMAX bands. The folded open stub achieves resonant frequencies at 2.4 and 5.8 GHz, and the long and short L-shaped strips at 3.5 GHz and 5.2 GHz, respectively. The asymmetric trapezoid ground plane is incorporated to fine-tune impedance matching at 5.2, 5.5, and 5.8 GHz. The equivalent lumped-element circuit of the proposed antenna was also studied and validated, which exhibits triband resonant characteristics. Simulations were carried out, an antenna prototype fabricated, and experiments undertaken. The simulated and experimental far-field radiation pattern of the triband antenna is omnidirectional at 2.4, 3.5, and 5.2 GHz and near-omnidirectional at 5.5 and 5.8 GHz. The simulated and measured antenna gains are 1.269–3.074 dBi and 1.10–2.80 dBi, respectively. The simulation and experimental results are in good agreement. Essentially, the proposed triband compact printed antenna covers 2.4 GHz, 5 GHz (5.2/5.8 GHz) WLAN, and (3.5/5.5 GHz) WiMAX frequency bands and therefore possesses high potential for WLAN/WiMAX applications.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
This work has been supported by the Thailand Research Fund through the TRF Senior Research Scholar Program with Grant no. RTA6080008. The authors would like to express their deep gratitude to the Faculty of Technical Education, Rajamangala University of Technology Isan Khonkaen Campus, and to the Antenna and Electromagnetic Applications Research Laboratory, King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand.