Federal Communication Commission’s (FCC) allotment of the UWB ranging from 3.1GHz to 10.6GHz in 2002 [1], has made a great impact on commercial uses of this technology. Several antenna types have been used to implement this technology among which the microstrip patch antennas are of great importance because of their eye-catching attributes as they are light weight, low profile, inexpensive and top of all, quick and simple to fabricate [2]. Despite the progressions in designing microstrip antennas for UWB technology, the major issues are bandwidth, gain and radiation losses which limit their performance. To shorten the limitations, different design techniques have been implemented to achieve the UWB using microstrip patch antennas. Some of the noteworthy techniques include aperture coupling [3], stacking [4], slot compact planar design [5], parasitic patch [6] and thickening the substrate.
With the advancements in antenna technology for UWB applications, the interference challenges in the frequency bands were the major ones to consider. The Wireless Local Area Network (WLAN) technology has significant contribution to electromagnetic interferences with the UWB applications. Numerous techniques have been devised to
eliminate the interference in the UWB due to WLAN bands which include a rectangular tuning stub entrenched on a circular annular ring [7], a printed UWB antenna with couple slotted elements (H-shaped) for WLAN notching [4]. A few of the other approaches towards band-notching include Co-Planar Waveguide (CPW) fed C-shaped slot antenna [8], an antenna with a wide slot [9], a CPW-fed rectangular patch antenna with L-shaped slot in ground plane[10], an inverted U-slot antenna [11], a circular radiating patch with two L-shaped slots in the ground [12], a rectangular patch antenna with an E-shaped slot [13] and a CPW resonant cell as narrow stop-band filter in CPW feed-line [14].
In this paper, a CPW-fed planar monopole staircase antenna with a WLAN notch band characteristic is presented. The WLAN band notch is achieved by subtracting a U-shaped slot in the feed-line of the antenna. The stair-case structure covers the UWB range while the U-shaped slot in the feed-line prevents the interference with WLAN systems. The detailed parametric analysis in term of Voltage Standing Wave Ratio (VSWR) has been presented for the proposed antenna. Furthermore, gain, current distribution and radiation pattern plots of the proposed antenna are also presented. The proposed paper is formulated to describe the antenna geometry in section-II, modeling, analysis and comparison between results are presented in section-III while section IV concludes the paper.
II. BAND NOTCH ANTENNA GEOMETRY
The geometry of the proposed CPW fed antenna with WLAN band-notch is given in Fig. 1. The antenna is designed on a cost effective FR4 substrate with thickness 1.6mm, dielectric constant of 4.4 and with a compact size of 40x30mm
2. There are 8 ‘Area’ steps added in increasing
order from bottom to top. With the addition of each area step, increase in bandwidth is noticed which subsequently helps in achieving the ultra wideband. The U-shaped slot is added at 3.5mm from the bottom end of the transmission line with nearly square shaped CPW ground plane with dimensions 12.8x13.0mm
2 on either side. The gap width ‘g’
and the distance between the radiating patch and CPW
2013 3rd IEEE International Conference on Computer, Control & Communication (IC4), NUST-PNEC, Karachi
ground ‘d’ are kept 0.5mm and 1.2mm, respectively. The proposed antenna is simulated using 50Ω SMA (Sub-Miniature version A) connector to increase the accuracy of the simulated results. Table I shows the parametric dimensions of the antenna in detail.
(a)
(b)
Fig. 1. (a) Geometry of proposed antenna with WLAN notch (b) Prototype
TABLE I. DESIGN PARAMETERS OF THE PROPOSED ANTENNA
Parameters Size(mm) Parameters Size(mm2)
L 40.0 Area 1 1.5 x 8.4
W 30.0 Area 2 1.5 x 12.4
Lc 12.8 Area 3 1.5 x 15.4
Wc 13.0 Area 4 1.5 x 18.4
Lr 14.0 Area 5 1.5 x 21.4
Wr 3.0 Area 6 1.5 x 24.4
Ln 8.1 Area 7 1.5 x 27.0
Wn 0.6 Area 8 4.5 x 29.4
Wd 2.2
III. ANTENNA MODELING AND RESULTS
In this section, the simulated results of various parameters of the proposed planar monopole antenna are presented. The results of the VSWR, gain (dB), current distribution and radiation patterns are analyzed and discussed. The parameters of the proposed antenna are analyzed by varying one parameter while keeping the other parameters unchanged.
A. UWB Monopole Antenna without Notch-Band
The Ultra wideband is achieved by adding each ‘Area’
step to the patch of the antenna. The variation of VSWR
versus frequency of the planar monopole antenna without
notch-band technique and varying parameter ‘d’ is studied.
The simulation results in Fig. 2 shows that the impedance
bandwidth is efficiently improved by altering the parameter
‘d’. As the separation distance between the ground and the
patch increases, the impedance bandwidth reduces with a
notch from 6.542GHz to 9.356GHz which is not desirable.
With the increase in parameter ‘d’ from 1.2mm to 1.4mm,
the antenna is operating in the UWB range and covers less
bandwidth when compared with d=1.2mm. The simulated
VSWR graph of the proposed antenna is shown in Fig. 3,
where the antenna is operating from 2.688GHz to
17.506GHz with VSWR<2 which provides a wide fractional
bandwidth of more than 146%.
Fig. 2. VSWR vs. Frequency graph varying ‘d’ and keeping other variables constant
Fig. 3. VSWR vs. Frequency graph of the proposed antenna without
band notch characteristic
2013 3rd IEEE International Conference on Computer, Control & Communication (IC4), NUST-PNEC, Karachi
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B. UWB Monopole Antenna with Notch-Band Function
A U-shaped slot is subtracted from the transmission line
which ensured the rejection of the WLAN frequency band
from 5.15GHz-5.35GHz and 5.725GHz-5.825GHz. Several
dimensions of the U-shaped slot are varied to obtain the
optimum results. Fig. 4 shows the VSWR graphs of the
proposed antenna by varying the slot parameter Ln while all
other parameters fixed. For Ln=8.1mm, the desired band is
rejected while for Ln= 7.9mm, the lower band of the WLAN,
5.15GHz, is not notched. Similarly when we keep
Ln=8.3mm, the upper band of the desired range is not
rejected. Fig. 5 shows the VSWR versus frequency plot
when Wn is varied. With Wn=0.5mm and 0.7mm, the lower
band of the WLAN band is not notched so we take
Wn=0.6mm for further study.
Fig. 4. VSWR vs. Frequency graph varying Ln keeping other parameters constant
Fig. 5. VSWR vs. Frequency graph varying Wn keeping other parameters constant
The simulated and measured results of the VSWR of the proposed antenna are shown in Fig. 6. The antenna has two resonant bands 2.844GHz-5.008GHz and 5.940GHz-13.928GHz. From 5.010GHz to 5.938GHz, the VSWR>2, verifies the rejection of the unwanted WLAN band. The prototype of the proposed antenna has been tested using vector network analyzer.
Fig. 6 Simulated and measured VSWR vs. Frequency graph of the proposed antenna with WLAN Band-Notch characteristic
The values of several other parameters, before and after implementing the notch in the UWB range at 5.5 GHz, are shown in Table II.
TABLE II. PARAMETERS OF THE PROPOSED ANTENNA AT 5.5 GHZ
PARAMETER WITHOUT U-
SHAPED SLOT
WITH U-
SHAPED SLOT
MAXIMUM U (W/SR) 0.2063 0.0480
PEAK DIRECTIVITY 3.1628 3.0685
PEAK GAIN (dB) 3.694 0.603
RADIATION EFFICIENCY 1.1680 0.3713
FRONT TO BACK RATIO 4.1131 1.8531
C. Current Distribution, Antenna Gain and Radiation
Characteristics
The comparison between the gain plots of the proposed
antenna, with and without notching, is shown in Fig. 7.
Before subtracting the U-shaped slot from the transmission
line, the proposed antenna has positive gain results between
5GHz to 6GHz range but after the band-rejection, the gain
drops steeply for the WLAN frequency range.
Fig. 8 (a-d) depicts the surface current distribution of the
notching technique applied to the antenna at different
frequencies of 4GHz, 5.5GHz, 7.5GHz and 10GHz,
respectively. The current distribution is relatively normal at
4GHz, 7.5GHz and 10GHz. However, the surface current
density appears to be concentrated around the U-shape slot at
5.5GHz which verifies that antenna is not operating on that
frequency range.
Fig. 9 (a-d) shows the radiation patterns of the proposed
planar monopole antenna at 4GHz, 5.5GHz, 7GHz and
10GHz, respectively. The proposed antenna has a bi-
directional dumb-bell shape in the xz-plane throughout the
frequency range and an omni-directional pattern in the yz-
plane which remains constant throughout the antenna’s
operating range.
2013 3rd IEEE International Conference on Computer, Control & Communication (IC4), NUST-PNEC, Karachi
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Fig. 7. Gain of the proposed antenna with and without band-notch characteristic
(a) (b)
(c) (d)
Fig. 8. Simulated current distributions at (a) 4GHz (b) 5.5GHz (c) 7.5GHz (d) 10GHz
In this paper, a CPW-fed planar monopole antenna is presented which covers UWB range (i.e. 3.10GHz to 10.6GHz) and efficiently rejects the WLAN band (i.e. 5.15GHz-5.35GHz and 5.725GHz-5.825GHz) which is reported to cause interference due to operating power differences. UWB is achieved by using staircase design and the WLAN band is notched by embedding a U-shaped notch in the feed line. The proposed antenna has a fractional bandwidth of over 135%, is simple, easy to fabricate, cheap,
2013 3rd IEEE International Conference on Computer, Control & Communication (IC4), NUST-PNEC, Karachi
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compact in size and can be used in UWB wireless communication systems.
REFERENCES
[1] Federal Communications Commission, First report and order,
Revision of Part 15 of commission's rule regarding UWB
transmission system FCC 02-48,Washington, DC, 2002.
[2] H.Schantz, The Art and Science of Ultra Wideband Antennas, Artech House, 2005.
[3] S. Dan and Y. Lizhi, "A Broadband Impedance Matching Method for Proximity-Coupled Microstrip Antenna," IEEE Transactions on Antennas and Propagation, vol. 58, 2010, pp. 1392-1397.
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[5] C. Y. D. Sim, C. Wen-Tsan, and L. Ching-Her, "Compact Slot Antenna for UWB Applications," Antennas and Wireless Propagation
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[6] A. A. Eldek, "A Broadband Double Dipole Antenna with Triangle
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[7] Y. Gao, B.-L. Ooi, and A. P. Popov, "Band-notched ultra-wideband
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[8] A. Subbarao and S. Raghavan, "A band notched slot antenna for
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[9] Y. Y. Hyung Kuk, L. Yohan, L. Woosung, Y. Young Joong, H. Sang
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[10] W. Henan and L. Yingsong, "Bandwidth enhancement of a wide slot
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[11] C. Kyungho, K. Jaemoung, and C. Jaehoon, "Wideband microstrip-
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[12] H. Lee, Y. Jang, J. Kim, and J. Choi, "Wideband monopole antenna
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[13] Z. Cui, Y.-C. Jiao, L. Zhang, and F.-S. Zhang, "The band-notch function for a printed ultra-wideband monopole antenna with E-
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[14] S. W. Qu, J. L. Li, and Q. Xue, "A Band-Notched Ultrawideband
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2013 3rd IEEE International Conference on Computer, Control & Communication (IC4), NUST-PNEC, Karachi
