|Year : 2009 | Volume
| Issue : 6 | Page : 294-298
Successful Design of Singly-fed Wideband and High Gain Micro Strip Antenna
Anil B Nandgaonkar, Shankar B Deosarkar
Department of Electronics and Telecommunication Engineering, Dr. Babasaheb Ambedkar Technological University, Lonere - 402 103, Dist. Raigad, Maharashtra, India
|Date of Web Publication||18-Jan-2010|
Anil B Nandgaonkar
Department of Electronics and Telecommunication Engineering, Dr. Babasaheb Ambedkar Technological University, Lonere - 402 103, Dist. Raigad, Maharashtra
| Abstract|| |
A major disadvantage of the micro strip-patch antenna is its inherently narrow impedance bandwidth of only a couple of per cent. Intensive research is going on to develop bandwidth-enhancement techniques by keeping its size as small as possible. In this paper, square ring MSA with two nearly square slots is designed, simulated, fabricated and tested. It is a singly-fed, wideband and high gain micro strip Antenna. The proposed antenna is left-hand circularly polarized and operates in 5-6 GHz frequency band. The impedance bandwidth with an input VSWR of two is obtained as 16.23% while the 6dB axial ratio bandwidth is measured over 4.52%.
Keywords: Bandwidth enhancement, Circular polarization, Micro strip antenna, Size reduction, Square ring, Square slot
|How to cite this article:|
Nandgaonkar AB, Deosarkar SB. Successful Design of Singly-fed Wideband and High Gain Micro Strip Antenna. IETE J Res 2009;55:294-8
| 1.Introduction|| |
Extensive research and development in micro strip antennas (MSAs) and arrays, exploiting their advantages such as low weight, low volume, low cost, conformal configuration, compatibility with integrated circuits, and so on, have led to diversified applications  .
Currently there is a boom in the development of personal communication service (PCS) devices as they are now deeply integrated into society. The PCS arena covers everything from cellular phones that incorporate digital cameras and web browsing to wireless local area networks (WLAN). Since they can all be linked together, their applications are no longer limited. In recent years, practical applications of wireless LAN systems are represented by 802.11a, 802.11n standards , . In indoor wireless LAN systems, it is expected that the stable communication performance is obtained by using a circular polarized antenna even if the polarization is rotated by the reflection at die surface of a wall and so on , .
A WLAN is a flexible data communication network used as an extension to, or an alternative for, a wired LAN in a building. They are primarily used in industrial sectors where employees are on the move, in temporary locations or where cabling may hinder the installation of wired LAN. Increasingly, more and more wireless LANs are being set up in home/home-office situations as the technology is becoming more affordable. Industry giants are already predicting that 90% of all notebooks will contain integrated WLAN by the end of year 2008 ,, .
With progress and expansion comes the need for faster technology and higher transfer rates. The ongoing wireless LAN standardization and research and development activities worldwide justify the fact that WLAN technology will play a key role in wireless data transmission. Cellular network operators have recognized this fact, and strive to exploit WLAN technology and integrate this technology into their cellular data networks ,, .
The proposed square ring MSA is a singly fed with bandwidth from 5050 MHz to 5850 MHz or 13.8% within 2:1 VSWR. Thus the antenna can clearly support the IEEE 802.11a Wireless local area network (WLAN) bands at 5.15-5.35/5.725-5.825 GHz and 5.15-5.35/5.470-5.725/5.725-5.925 GHz for HyperLAN 2 applications  .
| 2.Antenna Design and Geometry|| |
We present singly fed circularly polarized nearly square micro strip antennas (MSAs) with various configurations. To begin with, a nearly square patch is designed followed by modified patch in the form of nearly square ring and then square ring MSA with two nearly square slots. The patch length (L l ), and width (L 2 ) determines the orthogonal resonant frequencies, and are critical parameters in the design because of the inherent narrow bandwidth of the patch. In practice, considering the effect of the fringing fields, the effective dimensions of diagonally fed nearly square MSAs are different from the physical dimensions which are shown by dotted lines in [Figure 1]. For the fundamental TM 10 mode, the L 1 should be slightly less than l/2, where l is the wavelength in the dielectric medium. The fundamental TM 10 mode implies that the field varies one l/2 cycle along the length, and no variation along the width of the patch. A nearly square MSA operating at TM 10 mode can be visualized as a transmission line, because the field is uniform along the width and varies sinusoidal along the edge length , .
A nearly square MSA, as shown in [Figure 2], is designed with length, L 1 = 26 mm and a width, L 2 = 23.55 mm. Ground plane and the patch are separated by the air dielectric with thickness, 'h' equal to 3.2 mm ,, . The outer dimensions of the ring correspond to that of a nearly square MSA and a square slot is cut in the center of the patch, which increases the path length of the surface current thereby reducing the resonance frequency. The patch is fed along the diagonal which is very close to the slot. The antenna can be made compact by increasing the slot dimensions. However, it has been shown that, at no point on the ring, impedance matching is possible for 50 V coaxial fed-point  . The other possible configuration for compact circularly polarized radiation is singly-fed square ring MSA with two nearly square slots at the centre of the patch ,, . The nearly square MSA has a length, L 1 = 25 mm and a width, L 2 = 22.6 mm with slot length of 6 mm x 6 mm and the ground plane and the patch thickness, with air as dielectric, is h = 2.8 mm.
[Figure 3] shows the geometry of a square MSA with two nearly square slots. Both the slots have length of 6 mm and width of 8 mm, and placed at (x = -3, y = 4) and ( x = 3, y = -4) respectively. The square MSA has a length and a width of 22.6 mm. Ground plane and the patch are separated by the air dielectric with h equal to 3 mm. The radius of the feed conductor of co-axial probe is optimized to 0.25 mm and is located along the diagonal of the patch at (x = -2.3, Y = -4.25). The antenna is placed on λo = λo ground plane ,, .
| 3.Results and Discussion|| |
Parametric variation effects for the change in slot length, slot width and slot position are carried out and the results are tabulated in [Table 1],[Table 2],[Table 3] respectively. It is observed that the bandwidth increase with increase in slot length and width up to certain limit. Further increase in these parameters decreases the bandwidth as the effective area decreases. Decrease in aperture area results in decrease in directivity, efficiency and gain.
We first design a nearly square patch is first designed followed by a modified patch in the form of nearly square ring and then square ring MSA with two nearly square slots. The design of square ring MSA with two nearly square slots was optimized using the results obtained in [Table 1],[Table 2],[Table 3]. The simulated and experimental results of the proposed MSA are observed as below.
3.1 Nearly Square Micro Strip Antenna
In this case, the bandwidth for axial ratio (AR) ≤ 3 dB is obtained 2.2% and for AR ≤ 6 dB is 6.3% as shown in [Figure 4]. Impedance bandwidth for VSWR ≤ 2 and return loss bandwidth for R.L. ≤ -10 dB are found to be 19.34% and 16.04% respectively  . The value of L 1 / L 2 = 26/23.55 = 1.1 implies separation of 9.4% between the two resonant length.
3.2 Nearly Square Ring Micro Strip Antenna with Square Slot
Size reduction of 7.7% is obtained with this configuration as compared to the nearly square MSA without slot, however, the axial ratio bandwidths as well as the impedance bandwidth are reduced. Bandwidth for AR ≤ 3 dB is observed as 1.8% and for AR ≤ 6 dB is obtained as 5.6% which is shown in [Figure 4]. Impedance bandwidth for VSWR ≤ 2 and return loss bandwidth for R.L. ≤ -10 dB are found to be 16.93% and 14.40% respectively  .
3.3 Square Ring Micro Strip Antenna with Two Nearly Square Slots
This configuration is compact with reduction of size by 27.97% to that of the nearly square MSA without slot and found suitable for the WLAN applications. The bandwidth for AR ≤ 3 dB is observed as 1.2% and for AR # 6 dB is obtained as 5.5% as shown in [Figure 4]. Impedance bandwidth for VSWR ≤ 2 and return loss bandwidth for R.L. ≥ -10 dB are found to be 16.23 and 11.10% respectively  .
The simulated and experimental VSWR and return loss responses of all the three configurations are shown in [Figure 5] and [Figure 6] respectively.
In all the above configurations left hand circular polarization (LHCP) is obtained for the feed location as mentioned. If the feed is shifted to the other diagonal, right hand circular polarization (RHCP) is obtained. The antenna efficiency is found over 90% in all the three configurations. [Figure 7] shows the simulated LHCP and RHCP radiation patterns of the proposed MSA configuration.
The bandwidth for VSWR ≤ 2, and for AR ≤ 6 dB, maximum gain, radiation efficiency and size reduction of all these configurations are summarized in the [Table 4].
| 4.Conclusion|| |
A novel singly-fed wideband and high gain MSA has been successfully fabricated and tested. The proposed antenna is left-hand circularly polarized and operates in 5-6 GHz frequency band. The impedance bandwidth with an input VSWR of 2:1 is obtained as 16.23% while the 6 dB axial ratio bandwidth is measured over 4.5%.
| 5.Acknowledgment|| |
The authors would like to thank Dr. K. P. Ray, Head of Antenna Division, SAMEER IIT Campus, Mumbai, for making available the test facilities. We would also like to thank Mr. Loenymoon, Signet Instruments, Mumbai, for the required dielectric and help in fabrication of antenna.
| Authors|| |
Anil B. Nandgaonkar, Lonere - 402 103, Maharashtra State, INDIA did M.E. in 2000 from Dr. B.A. Marathwada University, Aurangabad and doing Ph.D.at Dr. B.A.T.U. Lonere in the area of microstrip antennas.
Presently he is working as a faculty of E& TC Department of Dr. Babasaheb Ambedkar Technological University, Lonere. He has a teaching experience of around 18 years. His research area includes antennas, microwaves and EMI/EMC. He has around 15 research papers in various international and national journals/conferences to his credit.
Mr. Nandgaonkar is Associate member of IETE and life member of ISTE, India. He is a recipient of National Merit Scholarship during his graduation.
Shankar B. Deosarkar, Lonere - 402 103, Maharashtra State, INDIA, did M.E. in 1990 and Ph.D. in 2003 from S.R.T. Marathwada University, Nanded, India. His major field of study includes microwaves and antennas.
Presently he is working as a Professor and Head of the E& TC Department of Dr. Babasaheb Ambedkar Technological University, Lonere. He has a teaching experience of over 20 years. In addition to his regular duties, he has also worked as the Controller of Examinations of the Dr. B. A. T. U. Lonere from 1990 to 2007. His research interests are in the area of antennas, microwaves, EMI/EMC and signal integrity issues in high speed circuits. He has around 25 research papers in various international and national journals/conferences to his credit.
Dr. Deosarkar is Fellow of IETE and life member of ISTE, India. At present four research scholars are doing Ph.D. under his guidance.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4]