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A rectangular slot antenna with improved bandwidth
Int. J. Electron. Commun. (AEÜ) 66 (2012) 465–466
Contents lists available at SciVerse ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.de/aeue
A rectangular slot antenna with improved bandwidth Xu-bao Sun ∗ , Mao-yong Cao, Jian-jun Hao, Yin-jing Guo College of Information, Electrical Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266510, China
a r t i c l e
i n f o
Article history: Received 30 March 2011 Accepted 13 October 2011 Keywords: Antenna Microstrip line Bandwidth
a b s t r a c t A rectangular microstrip slot antenna fed by a microstrip line, which achieves a very large bandwidth on a relatively thin substrate, is presented. The performance is achieved by employing a combination of a rectangular slot in the ground plane, and the use of the microstrip line perpendicular to the rectangular slot. An additional square slot in the ground plane is used to produce the wideband characteristics of the antenna. Simulated and measured results show that a 36% fractional impedance bandwidth is achieved with respect to the centre frequency of 2.4 GHz and a relatively stable pattern with change of frequency. © 2011 Elsevier GmbH. All rights reserved.
1. Introduction Microstrip patch antennas are widely used in wireless communications due to their inherent advantages of low profile, less weight, and low cost, together with ease of integration with microstrip circuits. However, the main disadvantage of microstrip antennas is the small bandwidth. So the improvement of bandwidth becomes an important need for many applications such as high speed networks [1]. To increase the bandwidth of the microstrip patch antenna, many different techniques have been proposed, such as using a thicker substrate, using a E-shaped patch antennas [2], or employing multilayer structures with parasitic patches, which excite multiple resonant modes [3,4]. Recently, in order to improve the bandwidth and reduce the antenna size, a small circular patch antenna concentrically embedded in an annular-ring, with a cross-slotted ground plane has been reported [5], but these methods often use coaxial probes or inserts foam material between the patch and the ground plane, so leading to an increase in fabrication complexity. In this paper, a microstrip line fed single-layer rectangular slot antenna on a thin substrate (about 0.0050 ) is proposed and a 36% fractional impedance bandwidth is achieved. Its fabrication is easier than that for the conventional slot antenna on multilayer dielectric substrates, and it can operate at centre frequency 2.4 GHz for WLAN and satellite communication applications.
plane is split into two parts by the square slot and a rectangular slot cut in the centre of the ground plane. The other plane is a microstrip line to feed the slot antenna. This slot antenna is printed on a RT/duroid 5880 substrate with relative dielectric constant (εr ) 2.2 and 1.6 mm of thickness (h). There is only a single-layer substrate between the ground plane and the microstrip feed line. The very wide bandwidth of the proposed antenna is achieved because of the various resonant modes that are generated between the slotted ground plane and the microstrip feed line. The frequencies for the multiple resonant modes are merged by adjusting the parameters of the antenna. The optimised dimensions of the proposed antenna are as follows: L1 = 76.4 mm, L2 = 46 mm, D1 = 30 mm, D2 = 6 mm, W2 = 10 mm, W1 = 1 mm.
2. Antenna design The configuration of the proposed antenna is shown in Fig. 1. It is composed of a microstrip feed line and a ground plane. The ground
∗ Corresponding author. E-mail address: [email protected] (X.-b. Sun). 1434-8411/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2011.10.008
Fig. 1. Antenna configuration.
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X.-b. Sun et al. / Int. J. Electron. Commun. (AEÜ) 66 (2012) 465–466
Fig. 2. Measured and simulated return loss.
Fig. 4. Measured and simulated antenna patterns at f = 2.5 GHz.
microstrip line-fed antenna. The radiation patterns of the proposed antenna were measured over the entire impedance bandwidth, for brevity, we only gives the measured radiation patterns at 2.5 and 2.7 GHz. The normalized simulated and measured radiation patterns are shown in Fig. 3a and b for the xoz and yoz planes respectively. It is seen that this antenna has Fig. 4 nearly omnidirectional radiation characteristics with poor front-to-back ratio, which is caused by the slot in the ground plane. However, it also shows a relatively stable pattern with change of frequency, the gains at 2.5 and 2.7 GHz being 1.5 and 2 dB respectively. 4. Conclusions
Fig. 3. Measured and simulated antenna patterns at f = 2.7 GHz.
A rectangular slot antenna fed by microstrip line is proposed, which produces a very large bandwidth on a relatively thin substrate. Simulated and measured results show that there is an improved bandwidth, a relatively stable pattern and that its fabrication is easier than that for the conventional slot antenna. References
3. Simulation and measurement results The simulation results are obtained by using Matlab software based on the moment method in spectral domain [6]. Fig. 2 shows the simulated and measured results of return loss for the proposed antenna. It is noted that simulated results are in good agreement with the measured results, while the impedance bandwidth was measured using the Agilent network analyser. The impedance bandwidth for which the return loss is greater than 10 dB is 860 MHz from 2.02 to 2.88 GHz, which is about 36% fractional bandwidth with respect to the centre frequency of 2.4 GHz. This is a considerable bandwidth for a single-layer thin-substrate
[1] Yang F, Zhang X-X, Ye X, Rahmat-Samii Y. Wide-band E-shaped patch antennas for wireless communications. IEEE Trans Antennas Propag 2001;49(July (7)):1091–100. [2] Ge Y, Esselle KP, Bird TS. E-Shaped patch antennas for high-speed wireless networks. IEEE Trans Antennas Propag 2004;52(December (12)):3213–9. [3] Rafi Gh, Shafai L. Broadband microstrip patch antenna with V-slot. IEE Proc Microw Antennas Propag 2004;151(5):435–40. [4] Lu J-H. Bandwidth enhancement design of single-layer slotted circular microstrip antennas. IEEE Trans Antennas Propag 2003;51(5):1126–9. [5] Bao XL, Ammann MJ. Compact annular-ring embedded circular patch antenna with cross-slot ground plane for circular polarisation. Electron Lett 2006;42(4):192–3. [6] Balanis CA. Antennas theory analysis and design. second edition New York: John Wiley & Sons, Inc.; 1997.
Contents lists available at SciVerse ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.de/aeue
A rectangular slot antenna with improved bandwidth Xu-bao Sun ∗ , Mao-yong Cao, Jian-jun Hao, Yin-jing Guo College of Information, Electrical Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266510, China
a r t i c l e
i n f o
Article history: Received 30 March 2011 Accepted 13 October 2011 Keywords: Antenna Microstrip line Bandwidth
a b s t r a c t A rectangular microstrip slot antenna fed by a microstrip line, which achieves a very large bandwidth on a relatively thin substrate, is presented. The performance is achieved by employing a combination of a rectangular slot in the ground plane, and the use of the microstrip line perpendicular to the rectangular slot. An additional square slot in the ground plane is used to produce the wideband characteristics of the antenna. Simulated and measured results show that a 36% fractional impedance bandwidth is achieved with respect to the centre frequency of 2.4 GHz and a relatively stable pattern with change of frequency. © 2011 Elsevier GmbH. All rights reserved.
1. Introduction Microstrip patch antennas are widely used in wireless communications due to their inherent advantages of low profile, less weight, and low cost, together with ease of integration with microstrip circuits. However, the main disadvantage of microstrip antennas is the small bandwidth. So the improvement of bandwidth becomes an important need for many applications such as high speed networks [1]. To increase the bandwidth of the microstrip patch antenna, many different techniques have been proposed, such as using a thicker substrate, using a E-shaped patch antennas [2], or employing multilayer structures with parasitic patches, which excite multiple resonant modes [3,4]. Recently, in order to improve the bandwidth and reduce the antenna size, a small circular patch antenna concentrically embedded in an annular-ring, with a cross-slotted ground plane has been reported [5], but these methods often use coaxial probes or inserts foam material between the patch and the ground plane, so leading to an increase in fabrication complexity. In this paper, a microstrip line fed single-layer rectangular slot antenna on a thin substrate (about 0.0050 ) is proposed and a 36% fractional impedance bandwidth is achieved. Its fabrication is easier than that for the conventional slot antenna on multilayer dielectric substrates, and it can operate at centre frequency 2.4 GHz for WLAN and satellite communication applications.
plane is split into two parts by the square slot and a rectangular slot cut in the centre of the ground plane. The other plane is a microstrip line to feed the slot antenna. This slot antenna is printed on a RT/duroid 5880 substrate with relative dielectric constant (εr ) 2.2 and 1.6 mm of thickness (h). There is only a single-layer substrate between the ground plane and the microstrip feed line. The very wide bandwidth of the proposed antenna is achieved because of the various resonant modes that are generated between the slotted ground plane and the microstrip feed line. The frequencies for the multiple resonant modes are merged by adjusting the parameters of the antenna. The optimised dimensions of the proposed antenna are as follows: L1 = 76.4 mm, L2 = 46 mm, D1 = 30 mm, D2 = 6 mm, W2 = 10 mm, W1 = 1 mm.
2. Antenna design The configuration of the proposed antenna is shown in Fig. 1. It is composed of a microstrip feed line and a ground plane. The ground
∗ Corresponding author. E-mail address: [email protected] (X.-b. Sun). 1434-8411/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2011.10.008
Fig. 1. Antenna configuration.
466
X.-b. Sun et al. / Int. J. Electron. Commun. (AEÜ) 66 (2012) 465–466
Fig. 2. Measured and simulated return loss.
Fig. 4. Measured and simulated antenna patterns at f = 2.5 GHz.
microstrip line-fed antenna. The radiation patterns of the proposed antenna were measured over the entire impedance bandwidth, for brevity, we only gives the measured radiation patterns at 2.5 and 2.7 GHz. The normalized simulated and measured radiation patterns are shown in Fig. 3a and b for the xoz and yoz planes respectively. It is seen that this antenna has Fig. 4 nearly omnidirectional radiation characteristics with poor front-to-back ratio, which is caused by the slot in the ground plane. However, it also shows a relatively stable pattern with change of frequency, the gains at 2.5 and 2.7 GHz being 1.5 and 2 dB respectively. 4. Conclusions
Fig. 3. Measured and simulated antenna patterns at f = 2.7 GHz.
A rectangular slot antenna fed by microstrip line is proposed, which produces a very large bandwidth on a relatively thin substrate. Simulated and measured results show that there is an improved bandwidth, a relatively stable pattern and that its fabrication is easier than that for the conventional slot antenna. References
3. Simulation and measurement results The simulation results are obtained by using Matlab software based on the moment method in spectral domain [6]. Fig. 2 shows the simulated and measured results of return loss for the proposed antenna. It is noted that simulated results are in good agreement with the measured results, while the impedance bandwidth was measured using the Agilent network analyser. The impedance bandwidth for which the return loss is greater than 10 dB is 860 MHz from 2.02 to 2.88 GHz, which is about 36% fractional bandwidth with respect to the centre frequency of 2.4 GHz. This is a considerable bandwidth for a single-layer thin-substrate
[1] Yang F, Zhang X-X, Ye X, Rahmat-Samii Y. Wide-band E-shaped patch antennas for wireless communications. IEEE Trans Antennas Propag 2001;49(July (7)):1091–100. [2] Ge Y, Esselle KP, Bird TS. E-Shaped patch antennas for high-speed wireless networks. IEEE Trans Antennas Propag 2004;52(December (12)):3213–9. [3] Rafi Gh, Shafai L. Broadband microstrip patch antenna with V-slot. IEE Proc Microw Antennas Propag 2004;151(5):435–40. [4] Lu J-H. Bandwidth enhancement design of single-layer slotted circular microstrip antennas. IEEE Trans Antennas Propag 2003;51(5):1126–9. [5] Bao XL, Ammann MJ. Compact annular-ring embedded circular patch antenna with cross-slot ground plane for circular polarisation. Electron Lett 2006;42(4):192–3. [6] Balanis CA. Antennas theory analysis and design. second edition New York: John Wiley & Sons, Inc.; 1997.