Analysis of L-Shaped Slot Loaded Circular Disk
Wireless Pers Commun DOI 10.1007/s11277-012-0730-3 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna for Satellite and Radio Telecommunication J. A. Ansari · Anurag Mishra · N. P. Yadav · P. Singh · B. R. Vishvakarma © Springer Science+Business Media, LLC. 2012 Abstract In the present paper a dual frequency resonance antenna is achieved by introducing L- shaped slot in circular disk patch. It is analysed by using circuit theory concept. The resonance frequency is found to be 5.087 and 8.455 GHz and the 10 dB bandwidth of the proposed antenna for lower and upper resonance frequency is found to be 4.39 and 4.66 % respectively. It is easy to adjust the higher and lower band by changing the dimensions of notch and slot introduced in the antenna. The frequency ratio is found to be 1.6621. The gain and efficiency of the proposed antenna is found to be 9.50 dB at lower resonance however it is 7.0 dB at upper resonance frequency whereas the efficiency at lower and upper resonance is found to be 94.6 and 88.2 %.The theoretical results are compared with IE3D simulation results which are in good agreement. Keywords Notch loaded patch · Slot loaded patch · Circular diskpatch · Dual band antenna 1 Introduction Microstrip patch antenna are attractive due to their advantages such as low cost, light weight, low profile planer configuration and easy to manufacture. Recently, dualband antenna is found wide applications in wireless and satellite communication. The rapid development J. A. Ansari · A. Mishra (B) · N. P. Yadav · P. Singh Department of Electronics & Communication, University of Allahabad, Allahabad 211002, India e-mail: [email protected] J. A. Ansari e-mail: [email protected] N. P. Yadav e-mail: [email protected] P. Singh e-mail: [email protected] B. R. Vishvakarma Department of Electronics Engineering, I. T. BHU, Varanasi 221005, India e-mail: [email protected] 123 J. A. Ansari et al. in WLAN technology demands the antenna having high performance, dualband and good radiation characteristics. During the recent years there has been rapid development in dualband microstrip antenna due to its wide application in many communication systems. Number of papers have been reported for dualband operation such as probe fed Circular microstrip antenna [1], slot loaded circular disk patch antenna [2], slot loaded circular microstrip patch antenna with meandered slits [3], Dualband N-shaped patch antenna [4], Compact dualband suspended semicircular microstrip antenna with half U-slot [5],Half U-slot loaded semicircular disk patch antenna [6]. One of the technique to obtain the dualband operation by the way of cutting slots parallel to the radiating edge of the patch [7,8], cutting square slot in the patch [9,10]. The loading of the slot on the radiating patch increases the current length that results in lowering fundamental resonance frequency which corresponds to reduced antenna size when compared with conventional patch antenna at the given operating frequency. In this investigation we have proposed new patch antenna configuration that shows dualband operation. The proposed antenna is L-slot loaded circular disk patch antenna that provides a significant size reduction and good impedance bandwidth. Dual frequency is tuned by changing the dimensions of the notch and slot. A parametric study has been carried out using the circuit theory concept by varying the length, width of the notch and slot. Various antenna parameters are calculated as a function of frequency for different value of notch, slot length and width. 2 Configuration and Analysis The side view and top view geometry for the proposed antenna with current distribution are shown in Fig. 1. Analysis of proposed antenna is carried out by considering the disk patch of radius ‘a’ equivalent to the square patch of side 2a [11]. The resonance frequency of circular disk patch is given as [12] fr = knm c √ 2πae εe (1) where knm is the mth zero root of the derivative of Bessel function of order n, c is the velocity of light and εe is the effective dielectric constant of the substrate [12], ae effective radius of the circular disk patch. The effective radius ae of the circular disk is calculated by equating the area of disk to the expanded rectangular patch with dimension (L e × We ), where L e and We are effective length and effective width of the rectangular patch and can be calculated by [13]. The equivalent circuit of the circular disk patch is shown in Fig. 2 in which the circuit parameters, i.e. resistance (R1 ), inductance (L1 ), and capacitance (C1 ) are calculated by [13]. εe εo L W cos−2 (π xo /L) 2h 1 L1 = 2 ω C1 Qr R1 = ωC1 C1 = (2) (3) (4) in which L = length of the rectangular patch, W = width of the rectangular patch, x 0 = feed point location along length of the patch, h = thickness of the substrate material 123 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna X Feed point slot gap between slot L-slot loaded patch Y h notch ε r Foam Ground plane Coaxial feed Top view Side view (a) (b) Fig. 1 Geometry of L-slot loaded circular disk patch antenna with its current distribution for lower and upper resonance frequency (a) fr1 = 5.12 GHz, (b) fr2 = 8.39 GHz and Qr = √ c εe fh where c = velocity of light, f = design frequency, εe = effective permittivity of the medium which is given by [12] εe = εr + 1 εr − 1 10h −1/2 + 1+ 2 2 W where, εr = relative permittivity of the substrate material Due to two symmetrical L-slot cut in the disk patch resonance behavior changes. The Analysis of the proposed antenna is classified in two parts. 123 J. A. Ansari et al. Fig. 2 Equivalent circuit of circular disk patch R1 C1 L2 C2 ΔC ΔL R1 L1 C1 L1 R2 ΔC ΔL (a) (b) Fig. 3 (a) Equivalent circuit of circular disk patch due to effect of notch. (b) Modify equivalent circuit disk patch antenna 2.1 Analysis of Notch Loaded Disk Patch Antenna When the notch is incorporated in the circular disk patch (L n × Wn ), the two currents flow in the patch, one is the normal patch current and resonates at the design frequency of the initial patch; however the other current flows around the notch resulting into second resonance frequency. Discontinuities due to notch incorporated in the patch are considered in terms of an additional series inductance (L) and series capacitance (C) that modify the equivalent circuit of circular disk patch as shown in Fig. 3, in which series inductance (L) and series capacitance (C) can be calculated as [14,15]. hμ0 π (L n /L)2 8 Ln C = .C g L L = and where μ0 = 4π × 10−7 H/m, L n = depth of the notch, C g = gap capacitance and is given by [16]. The value of resistance R2 after cutting the notch is calculated by [17]. It may be noted that the two resonant circuits, one is the initial R1, L1 and C1 of the circular disk patch as shown in Fig. 2 and another one is after cutting the notch (Fig. 3a) which are modified in Fig. 3b, are coupled through mutual inductance (L m ) and mutual capacitance (Cm ). Thus the equivalent circuit of the notch loaded disk patch antenna can be given as shown in Fig. 4a, b. 2.2 Analysis of Slot Loaded Disk Patch Antenna When the slot is embedded in the patch, having dimension (L S × W S ), it can be analysed by using the duality relationship between the dipole and slot [18]. The radiation resistance of 123 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna Znotch Zpatch Lm Lm Cm Cm Znotch Zpatch Zm (b) (a) Fig. 4 (a) Equivalent circuit of coupled notch loaded patch antenna. (b) Modified equivalent notch loaded resonant circuit slot on the half disk patch can be given as ⎡ 2 ⎤ kLS k 2 cos θ π 2 cos − cos 2 2 η0 cos α ⎢ ⎥ Rr = ⎦dθ ⎣ 2π sin θ (5) 0 which yields 1 1 Rr = 60 C + ln(k L S ) Ci (k L S ) + sin(k L S ) [Si (2k L S ) 2Si (k L S )] + cos(k L S ) 2 2 kLS × C + ln + Ci (2k L S ) 2Ci (k L S ) 2 in which C is Euler’s constant = 0.5772/ and Si and Ci are the sine and cosine integrals. Now the total input impedance of the slot can be given as [19,20]. Z slot = η02 4Z cy (6) in which η0 = 120π and LS kLS Z cy = Rr (k L S ) − j 120 ln − X r (k L S ) − 1 cot WS 2 where, Rr is the real part and equivalent to the radiation resistance of slot and Xr is the input reactance of the slot and given as [20], L s and Ws are length and width of the slot. Now the equivalent circuit of proposed antenna can be given as shown in Fig. 5. Hence the total in put impedance of proposed antenna can be calculated from Fig. 5 as, Z T = (Z ∗ ) + Z m Z patch Z patch + Z m (7) where Z∗ = Z slot Z notch Z slot + Z notch 123 J. A. Ansari et al. Znotch ZS1 Z notch ZPatch Zm ZS2 Zslot (a) Z patch Zm (b) Fig. 5 (a) Equivalent circuit of Circular disk patch antenna with L-shaped slot. (b) Modified equivalent circuit of proposed antenna where Z Patch is the input impedance of the microstrip patch antenna which is calculated from Fig. 2 as Z patch = and and in which Z slot = Z notch = L2 = C2 = and Zm = 1 1 R1 + jωC1 + 1 jωL 1 Z S1 Z S2 Z S1 + Z S2 jω R1 L 2 jωL 2 + R1 − R1 L 2 C2 ω2 L 1 + 2L C1 C 2C + C 1 1 jωL m + jωCm where Lm and Cm are the mutual inductance and mutual capacitance between two resonant circuits and given as [15]. Lm = C 2p (L 1 + L 2 ) + Cm = − (C1 + C2 ) + C 2p (L 1 + L 2 )2 + 4C 2p (1 − C 2p )L 1 L 2 2(1 − C 2p ) (C1 + C2 )2 − 4C1 C2 (1 − C −2 p ) 2 where C p = √ (8) (9) 1 Q1 Q2 and Q 1 and Q 2 are quality factors of the two resonant circuits Now using Eq. (7) one can calculate the various antenna parameters for the proposed antenna, such as reflection coefficient, VSWR and return loss. 123 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna 0 Return loss(dB) -5 Theoretical Simulated -10 -15 -20 -25 4 5 6 7 8 9 10 Frequency(GHz) Fig. 6 Variation of return loss with frequency along with theoretical and simulated results (R = 15 mm, Ln = 18 mm, Wn = 1 mm, Ls = 9 mm, Ws = 1 mm, h = 1.5 mm, εr = 1.07) 0 Return loss(dB) -5 -10 Ln=18mm Ln=19mm Ln=20mm -15 -20 -25 4 5 6 7 8 9 10 Frequency(GHz) Fig. 7 Variation of return loss with frequency for different value of notch depth ‘L n ’ 3 Radiation Pattern The radiation pattern for L-slot loaded circular disk patch antenna is calculated as [19]. E(θ ) = J n k0 RV0 e jk0 r1 [Jn+1 (k0 R sin θ ) − Jn−1 (k0 R sin θ )]. cos nφ (10) E(φ) = J n k0 RV0 e− jk0 r1 [Jn+1 (k0 R sin θ ) − Jn−1 (k0 R sin θ )]. cos θ sin nφ (11) where V0 = radiating edge voltage = h E 0 Jn (R), r1 = distance of an arbitrary far-field point, R = radius of half circular fed disk patch 123 J. A. Ansari et al. 0 Return loss(dB) -5 -10 Wn=1.0mm Wn=1.5mm Wn=2.0mm -15 -20 -25 4 5 6 7 8 9 10 Frequency(GHz) Fig. 8 Variation of return loss with frequency for different value of notch width ‘Wn ’ Table 1 Calculated bandwidth for different value of notch depth Notch depth Lower resonance frequency (Ln ) mm Bandwidth (MHz) Centre frequency ( GHz) Bandwidth (%) Bandwidth (MHz) Upper resonance frequency Centre frequency ( GHz) Bandwidth (%) 18.0 223 5.087 4.39 394 8.455 4.66 19.0 258 5.392 5.03 323 8.443 3.90 20.0 290 5.609 5.47 282 8.247 3.48 4 Design and Specifications Design specifications for L-shaped slot loaded circular disk patch antenna Substrate material Foam Relative permittivity of the substrate (εr ) Thickness of the dielectric substrate (h) Radius of the half disk patch (R) Depth of the notch (L n ) Width of the notch (Wn ) Length of the slot (L s ) Width of the slot (Ws ) Distance between L-slot (s) Feed location (x0 , y0 ) 1.07 2.5 mm 15.0 mm 18.0 mm 1.0 mm 9.0 mm 1.0 mm 2.0 mm (0.0, 3.6 mm) 123 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna Table 2 Calculated bandwidth for different value of notch width Notch width Lower resonance frequency (Wn ) mm Bandwidth (MHz) Centre frequency ( GHz) Bandwidth (%) Bandwidth (MHz) Upper resonance frequency Centre frequency ( GHz) Bandwidth (%) 1.0 223 5.087 4.39 394 8.455 4.66 1.5 196 4.989 3.93 328 8.184 4.01 2.0 192 4.897 3.90 306 7.919 3.86 0 Return loss(dB) -5 Ls=9.0mm Ls=8.5mm Ls=8.0mm -10 -15 -20 -25 4 5 6 7 8 9 10 Frequency(GHz) Fig. 9 Variation of return loss with frequency for different value of slot length ‘L s ’ 0 Return loss(dB) -5 -10 Ws=1.0mm Ws=1.5mm Ws=2.0mm -15 -20 -25 4 5 6 7 8 9 10 Frequency(GHz) Fig. 10 Variation of return loss with frequency for different value of slot width ‘Ws ’ 123 J. A. Ansari et al. Table 3 Calculated bandwidth for different value of slot length Slot length Lower resonance frequency Upper resonance frequency (LS ) mm Bandwidth (MHz) Centre frequency ( GHz) Bandwidth (%) Bandwidth (MHz) Centre frequency ( GHz) Bandwidth (%) 9.0 223 5.087 4.39 394 8.455 4.66 8.5 229 4.990 4.59 436 8.680 4.95 8.0 233 4.855 4.80 469 7.909 5.27 Table 4 Calculated bandwidth for different value of slot width Slot width Lower resonance frequency Upper resonance frequency () mm Bandwidth (MHz) Centre frequency ( GHz) Bandwidth (%) Bandwidth (MHz) Centre frequency ( GHz) Bandwidth (%) 1.0 223 5.087 4.39 394 8.455 4.66 1.5 257 5.260 4.89 434 8.815 4.92 2.0 287 5.485 5.27 460 9.220 4.99 0 Return loss(dB) -5 -10 s=2.0mm s=2.4mm s=2.8mm s=3.2mm -15 -20 -25 4 5 6 7 8 9 10 Frequency(GHz) Fig. 11 Variation of return loss with frequency for different value of gap of L-slot ‘s’ 5 Results and Discussion The variation of return loss with frequency for L-slot loaded circular disk patch antenna is shown in Fig. 6 along with simulated results using IE3D [20]. From the figure, it is observed that the antenna resonates at two frequencies fr1 = 5.087 GHz and fr2 = 8.455 GHz (simu- 123 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna 1.68 1.66 Frequency ratio 1.64 Theoretical Simulated 1.62 1.6 1.58 1.56 1.54 1.52 1.5 1.48 18 18.5 19 19.5 20 Notch depth(mm) Fig. 12 Variation of frequency ratio for different value of notch depth 1.68 1.67 Theoretical Simulated Frequency ratio 1.66 1.65 1.64 1.63 1.62 1.61 1.6 1.59 1.58 1 1.2 1.4 1.6 1.8 2 Notch width(mm) Fig. 13 Variation of frequency ratio for different value of notch width lated fr1 = 5.12 GHz, fr2 = 8.398 GHz) and 10 dB bandwidth is found to be 4.39 % for lower resonance whereas it is 4.66 % for upper resonance frequency (simulated 4.28 and 4.45 % respectively). Frequency ratio of upper to lower resonance frequency is found to be 1.6621 (simulated 1.6402). The theoretical results are in good agreement with simulated results. It is observed that both the theoretical and simulated results for bandwidth are in good agreement at lower and upper resonance frequency. Figures 7 and 8, shows the variation of return loss with frequency for the different value of notch depth (L n ) and notch width (Wn ). From Fig. 7, it is found that lower and upper resonance frequency shifts towards lower side as the notch depth increases but corresponding 123 J. A. Ansari et al. 2 1.95 Theoretical Simulated Frequency ratio 1.9 1.85 1.8 1.75 1.7 1.65 1.6 1.55 1.5 8 8.2 8.4 8.6 8.8 9 Slot length(mm) Fig. 14 Variation of frequency ratio for different value of slot length Theoretical Simulated Frequency ratio 1.7 1.68 1.66 1.64 1.62 1.6 1 1.2 1.4 1.6 1.8 2 slot width(mm) Fig. 15 Variation of frequency ratio for different value of slot width bandwidth decreases as shown in (Table 1), while increasing the notch width higher resonance frequency shifts to right side and lower resonance frequency shifts to left side. The variation of bandwidth for different notch width is shown in Table 2. The variation of return loss with frequency with slot length (L s ) and slot width (Ws ) is shown in Figs. 9 and 10. It is observed that for decreasing the value of slot length, higher resonance frequency shifts towards higher side whereas the lower resonance shifts slightly to lower side and bandwidth for both the resonances increases as shown in Table 3, while increasing slot width both the resonance frequencies shift to higher side. The calculated bandwidth for different slot width is shown in Table 4. Further increasing the value of the length and width of the slot dualband behaviour will change. 123 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna Relative radiative power(dB) 0 -2 -4 Theoretical Simulated -6 -8 -10 -12 -50 0 50 Angle(degree) Fig. 16 Radiation pattern of L-shaped slot loaded circular disk patch antenna for lower resonance frequency Relative radiative power(dB) 0 -2 -4 Theoretical Simulated -6 -8 -10 -12 -80 -60 -40 -20 0 20 40 60 80 Angle(degree) Fig. 17 Radiation pattern of L-shaped slot loaded circular disk patch antenna for upper resonance frequency Figure 11 shows the variation of return loss with frequency for different value of gap (s) of the L-slot. It is observed that for increasing the value of gap between the L-slot both the resonance frequency shift to right side. Figures 12 and 13, shows that the ratio of resonance frequencies f2 /f1 for different value of notch depth and notch width. It is found that the resonance frequency decreases with increasing the notch depth, while it is directly proportional to notch width. Figures 14 and 15 shows the ratio of resonance frequencies f2 /f1 for different value of slot length and slot width. It is observed that the ratio of frequency increases with decreasing the value of slot length, while it increases with increasing the slot width. 123 J. A. Ansari et al. 10 8 6 Gain(dB) 4 2 0 -2 Theoretical Simulated -4 -6 -8 3 4 5 6 7 8 9 10 Frequency(GHz) Fig. 18 Variation of gain with frequency for L-shaped slot loaded circular disk patch antenna 100 90 Theoretical Simulated 80 Efficiency(%) 70 60 50 40 30 20 10 0 3 4 5 6 7 8 9 10 Frequency(GHz) Fig. 19 Variation of efficiency with frequency for L-shaped slot loaded circular disk patch antenna Radiation pattern for proposed antenna is shown in Figs. 16 and 17. The theoretical results show good agreement with the simulated results for lower and upper resonance frequency however there is minute deviation in the beam widths. The gain and efficiency of the proposed antenna are shown in Figs. 18 and 19. From the figure, it is observed that the gain of the antenna at two frequencies is 9.50 and 7 dB (simulated 9.8 dB and GHz, 6.2 dB) and efficiency is 94.6 % for lower resonance whereas it is 88.2 % for upper resonance frequency (simulated 91 and 79.6 %). 123 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna 6 Conclusion From the analysis it is concluded that compact L-shaped slot loaded circular disk patch antenna can operate at two resonance frequencies 5.087/8.445 GHz and useful for dualband operation. The resonance frequency is highly dependent on the notch and slot dimensions with gap of the slot. References 1. Tiang, J. J., Islam, M. T., Misran, N., & Mandeep, J. S. (2011). 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Zeland softwere, Inc. (2008). IE3D simulation software, version 14.05. Zeland software, CA. 123 J. A. Ansari et al. Author Biographies J. A. Ansari was born in 1966 in Gahmar, Ghazipur (U.P.), India. He received the B.Sc. and B.Tech. degrees in Electronics and Telecommunications from University of Allahabad, Allahabad, India, in 1987 and 1989. The M.Tech degree in Communication Systems from the Institute of Technology, Banaras Hindu University (BHU), Varanasi, India, in 1991, and the Ph.D. degree from Mahatma Gandhi Chitrakoot Gramodaya Vishvavidyalaya, Chitrakoot (Satna), India, in 2000. He has published 92 papers in different national and international journals and conference proceedings. His current area of research is microstrip antenna, millimeter wave, and fiber optics. He is presently working as a Professor with the Department of Electronics and Communication, University of Allahabad. Anurag Mishra was born in Varanasi (U.P.), India in 1984. He received his B.Sc. and M.Sc. (physics specialization in Electronics) Degree from University of Allahabad 2004 and 2006 respectively. He is a research scholar in Department of Electronics and Communication, University of Allahabad, Allahabad (India). He published more than 44 papers in different international journals and international and national conferences. He is currently working on microstrip antenna and millimeter wave propogation with wireless and biomedical application. N. P. Yadav was born in village Gorain, Varanasi (U.P.), India in 1984. He received his B.Sc. and M.Sc. (Electronics) degree, from V. B. S. Purvanchal University in 2004 and 2006 respectively. He is a research scholar in Department of Electronics and Communication, University of Allahabad, Allahabad (India). He published more than 50 papers in different international journals, international and national conferences. He is currently working on microstrip antenna. 123 Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna P. Singh was born in village Semra, Chandauli (U.P.), India in 1984. He received his B.Sc. and M.Sc. (Electronics) degree, from V. B. S. Purvanchal University in 2004 and 2006 respectively. He is a research scholar in Department of Electronics and Communication, University of Allahabad, Allahabad (India). He published more than 45 papers in different international journals, international and national conferences. He is currently working on microstrip antenna. B. R. Vishvakarma was born in Dhananjaipur, Jaunpur (U.P.), India in 1944. He received the B.Sc. (Engg.), M.Sc. (Engg.), and Ph.D. degrees in electronics engineering from Banaras Hindu University (BHU), Varanasi, India, in 1969, 1972, and 1977, respectively. From 1973 to 1975, he was a Senior Research Fellow with the Department of Electronics Engineering, Institute of Technology (IT), BHU, where he carried out research work on microwave scattering and ferrite devices. In 1984, he rejoined the Department of Electronics Engineering, IT, BHU, as a reader, where he is presently working as a Professor of electronics engineering, His professional interests include the area of microwave and millimeter wave propagation, radar, scattering, ferrite devices, electronic scanning antennas, microstrip antennas, piezoelectric effects in bone, electromagnetic interaction (both energetic and informational) with biographical media. He has published more than 190 research papers in international reference journals and proceedings. He has also published one monograph on microwave ferrite junction circulator and a textbook Electromagnetic Fields and Applications. His two papers on microwave/millimeter wave propagation were awarded a Certificate of Merit (1993, 1994) and a paper on microstrip antenna was awarded the Institution Medal of Institution of Engineers (India) for 1996–1997. 123
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