Nowadays, microstrip patch antennas are important device in wireless communication systems. These antennas have been successfully utilized in many communication systems [1,2,3] such as satellite communication/links (vehicular GPS), cellular communication system (GSM/CDMA), wireless personal area (Bluetooth links), wireless local area network (Wi-Fi) and synthetic aperture radar (SAR). There are different techniques by which these antennas can be designed for various wireless applications such as proximity coupling , aperture coupling [5,6], loading of notches , slots [8,9,10], parasitic elements , L-strip fed [12,13], microstrip line feeding [14,15,16,17,18,19]. One of the important techniques is inset feeding by which patch antenna can be excited to achieve dual-band and multi-band frequencies for wireless communications.
The various contributions of researchers and scientists on microstrip line feeding are reported such as, analysis and design of annular patch antenna with electromagnetically coupled microstrip feed line , crescent-shaped multiband planar monopole antenna for mobile wireless applications , microstrip antenna array formed by microstrip line fed tooth-like-slot patches , printed wide-slot antenna with a modified L-shaped microstrip line for wideband applications , microstrip line-fed printed wide-slot antenna with a parasitic center patch , broadband T-shaped microstrip-fed U-slot coupled patch antenna . All the above reported papers are of microstrip line fed patch antennas which lack theoretical analysis, equivalent circuit diagram and has complicated antenna geometry.
In this view, the main objective of this paper is to present theoretical analysis, equivalent circuit diagram, total input impedance and radiating structures of microstrip line fed rectangular patch antenna with split-ring resonator (SRR)for wireless communications. Theoretical analysis of microstrip line fed rectangular patch antenna loaded with parasitic element and split-ring resonator has been presented using circuit theory concept based on modal expansion cavity model. The proposed antenna structures have been realized with the proto-type radiating structures to obtain dualband characteristics. Variation of dimensions of the proposed antenna for the gap between parasitic element, split-ring resonator, length and width of microstrip line are discussed in next section.
2 Antenna designs
A rectangular patch with SRR and parasitic patch antenna along with similar proto-type microstrip line fed patch antennas are shown in Fig. 1. The Fig. 1(a) shows the side view of antennas. Antenna 1 is shown in Fig. 1(b), conventional microsrtip line fed patch antenna of dimensions L×W is excited by the 50 Ω microstrip line. Antenna 2 is shown in Fig. 1(c), it is similar to the Antenna1 except it has parasitic element of dimension L×W and gap between the fed patch and parasitic patch is G. Figure 1(d)-(e) is the proposed radiating structure with top and bottom view. The proposed radiating structure is Antenna 3 which has SRR on ground plane and parasitic patch is placed parallel to the fed patch on same plane at a distance G. A rectangular patch of dimension L×W is fed through microstrip line fed. The feeding is given at end of microstrip line via coaxial connector of diameter 0.72 mm. Design specification of the antennas are given in Table 1.
Figure 2 shows the current distribution on radiating structure of the Antenna 3 at lower (0.9 GHz) and upper (1.8 GHz) resonance frequencies. From the figure, it has been observed that proposed radiating structure has two directions of currents flowing on the radiating patch. The first is normal to the patch and other current flows due to the coupling between the fed patch with parasitic patch and the radiating patch with SRR. These combine mechanism provide dual band operation.
3 Theortical analysis and its equivalent circuits
A simple rectangular patch is considered as a parallel combination of resistance R1, inductance L1, and capacitance C1 circuit and its input impedance is represented as Zp. The equivalent circuit of the rectangular patch is shown in Fig. 3(a), where R1, C1 and L1 can be defined as [20,21], (1) (2) (3)
L- Length of rectangular patch,
W- Width of rectangular patch,
H- Thickness of the substrate material,
X0-x coordinates of feed point, i.e.,X0 = Ls,
εe - effective permittivity of the medium.
The equivalent circuit of the parasitic patch is shown in Fig. 3(b), its input impedance is represented as Zpp, where R2, C2 and L2can be calculated as R1, C1 and L1 with same equations, here X0 is considered as 0. The equivalent circuit diagram of the gap between the fed patch and the parasitic patch Zcc is shown in Fig. 3(c), which is represented as the combination of capacitances Cg and Cp1. The expression of gap capacitance Cg and plate capacitance Cp1 of the microstrip line can be calculated as [22,23,24] (4) (5)
CL is the terminal capacitance of the open circuited conductor is given as,
where Cll is the conductor extension length, εeff is effective dielectric constant.
Z0is characteristic impedance of the patch, c is the velocity of light.
The microstrip line of the rectangular patch is considered as combination of L and C. The equivalent circuit of the microstrip line rectangular patch is shown in Fig. 3(d), where LL and CL are inductance and capacitance of strip [22, 23].
Resonance frequency of the microstrip line antenna is given as, (8)
Les = LS +ΔLS,
εre- Effective dielectric constant,
Les -Effective increase in length of strip,
εr -Dielectric constant,
Therefore, the total input impedance (Zin) of antenna can be calculated by equivalent circuit diagram Fig. 4 as (10)
where Lc and Ccis the inductance and capacitance of SRR’s can calculated as .
Now using equation (10) the total input impedance of the proposed antenna is calculated. Their various antenna parameters such as reflection coefficient, VSWR and return loss are calculated as:
Z is the input impedance of the microstrip fed (50 Ω).
and RL=20 log |r|
4 Discussion of results
The antennas 1, 2, and 3 have been simulated using software IE3D based on Method of Moments. Figure 5 presents the variations of reflection coefficients for different radiating structures. Antenna1 is resonating at 4.1 GHz below −10 dB offer a bandwidth of 139 MHz (3.94-4.12 GHz) which can be utilized for satellite communication. Antenna 2 is resonating at three distinct frequency modes 3.144 GHz, 3.252 GHz and 3.804 GHz. In theses frequency bands only 3.804 GHz frequency has efficient bandwidth of 441 MHz (3.696-3.864 GHz) that can be utilized for down link in satellite communication. Antenna 3 resonates at two distinct frequencies modes 0.9 GHz and 1.8 GHz below −10 dB and meets the requirement of mobile communication. It is observed that on incorporating parasitic elements and SRR resonating frequencies shift toward lower side. This is due to the increase radiation resistance of the proposed antenna. There is a dip at 1.5 GHz in proposed antenna, this is observed because gap between the parasitic patch and fed as well as gap between SRR arms.
Figure 6 shows the variation of reflection coefficient with frequency for the proposed antenna. The simulated, theoretical and reported experimental results of the microstrip line fed rectangular patch antenna with parasitic element and SRR are in close agreement. From figure it is observed that the antenna shows dual frequency behavior with frequency ratio 2.0 (Simulated) and 2.12 (theoretical). Theoretical results are based on circuit theory concept based on cavity model whereas simulated results are obtained using IE3D software that is based on Method of Moments. Further, analysis of the antenna 3 is shown in figures 7 to 10 which are based on circuit theory concept are described below.
From Figure 7, it is observed that on decreasing the substrate thickness (H=1.5 mm to 0.5 mm) frequency ratio decreases from 2.0 to 1.27 whereas on increasing the substrate thickness (H=1.5 mm to 2.5 mm) frequency ratio increases to 2.96. This happens because on increasing and decreasing the height of the substrate equations (1), (4) and (6) are effected which is responsible for variation in resonance frequency of the radiating patch.
Figure 8 shows the variation of reflection coefficient with frequency on decreasing (Ws=4 mm to 2 mm) and increasing (Ws =4 mm to 6 mm) the width of microstrip line, there is no change in the frequency ratio of upper to lower resonance frequency whereas slight shifting is observed on both upper and lower resonance frequencies. This is due to the capacitance CL which is directly proportion to width of microstrip line Ws, from equation (7).
From Figure 9, it is observed that on increasing the length of the microstrip line (Ls =21.6 mm to 29.6 mm), lower and higher resonance frequencies shift towards lower resonance side whereas there is no change in the frequency ratio of upper to lower resonance frequency. This affects the equation (8) as resonance frequency of the microstrip line f is inversely proportional to the length microstrip line Ls.
Figure 10 shows that on decreasing gap between the fed patch and parasitic patch (G=4 mm to 3 mm), the upper and lower resonance frequencies shift towards the lower side. Further, on increasing G=4 mm to 7 mm, upper and lower resonance frequencies shift towards higher side. This happens because the gap capacitance Cg is affected on increasing and decreasing the gap between fed patch and parasitic patch G i.e., from equation (4), Cg changes exponentially on variation of G. Thus, there is no huge variation on varying G.
From Figure 11, shows the radiation pattern at lower (0.9 GHz) and higher (1.8 GHz) resonance frequency and antenna shows circular polarization. The 3 dB beam width at lower resonance frequency for Etheta, phi=0° is 130.33° and Etheta, phi=90° is 88.92° whereas at higher resonance frequency for Etheta, phi=0 is 165.83° and Etheta, phi=0 is 83.7°.
From the above analysis it is inferred that theoretical results are in close agreement with simulated and reported experimental results for inset fed rectangular patch antenna loaded with parasitic element and split ring resonator. The frequency ratio of the proposed antenna depends on microstrip length and width, thickness of dielectric substrate and gap between parasitic patch. The proposed antenna has frequency ratio 2.0 and maximum gain 1.8 dBi. The proposed antennas can be utilized for wireless communications such as mobiles and down linking for satellite communications.
J. Bahl, S. S. Stuchly, and M. A. Stuchly, “A new microstrip radiator for medical application,” IEEE Trans. Microwave Theory Tech., vol. MTT-28, pp. 1464–1468, 1980. Google Scholar
J. C. Batchelor and R. J. Langley, “Microstrip ring antennas operating at higher order modes for mobile comunications,”Proc. Inst. Elect. Eng., pt. H, vol. 142, pp. 151–155, 1995. Google Scholar
N. Herscovivi, N. H. Nashua, and E.Dziadek, “Omni-directional antennas for wireless communication,Antennas and Propagation Society International Symposium, vol. 1, pp. 556 – 559, 1999. Google Scholar
Q. Rao, T.A. Denidni, A.R. Sebak and R.H. Johnston, “Microstrip fed single-layered substrate aperture coupled microstrip antenna,” IEE Proc.-Microw. Antennas Propag., vol. 152, pp. 89-92, 2005. CrossrefGoogle Scholar
A. Singh, J.A. Ansari, Kumari Kamakshi, Anurag Mishra and Mohammad Aneesh, “Compact notch loaded half disk patch antenna for dualband operation,” Annal Telecommunication, vol. 69, pp. 475-483, 2014. CrossrefGoogle Scholar
M. Habib, T.S Islam, and J. S Mandeep, “Printed prototype of a wideband S-shape MSA for Ku/K band applications,” ACES Journal, vol. 28, No.4, 2013. Google Scholar
M. Aneesh, J. A. Ansari, A. Singh, Kamakshi, and S. S. Sayeed, “Analysis of Microstrip Line Feed Slot Loaded Patch Antenna Using Articial Neural Network,” Progress In Electromagnetics Research B, vol. 58, 35-46, 2014. CrossrefGoogle Scholar
A. Singh, J.A. Ansari, Kamakshi, M.Aneesh and S.S Sayeed, “Analysis of Slot Loaded Compact Patch Antennas for Dualband Operation,” International Journal of Applied Electromagnetics and Mechanics10.3233/JAE-140020 Google Scholar
A. Singh, J.A. Ansari, Kamakshi, M.Aneesh and S.S Sayeed, “L-strip proximity fed gap coupled compact semi-circular disk patch antenna,” Alexandria Eng. J., vol. 53, pp. 61–67, March 2014. CrossrefGoogle Scholar
M. K. Meshram, Analysis of L-strip proximity fed rectangular microstrip antenna for mobile base station,Microwave Opt. Technol. Lett., vol. 49, pp. 1817–1821, 2007. Web of ScienceCrossrefGoogle Scholar
A. K. Singh, M. K.Meshram, and B. R. Vishvakarma, “L-Strip proximity fed shorted rectangular microstrip antenna mobile communication,” Microwave Opt. Technol. Lett., vol. 52, pp. 1567-1571, 2010. CrossrefWeb of ScienceGoogle Scholar
P. Pirinoli, G. Vecchi, and M. Orefice, “Full-wave spectral analysis and design of annular patch antenna with electromagnetically coupled microstrip feed line,” IEEE Trans. Antenna Propg., vol. 52, pp. 2415-2424, 2004. CrossrefGoogle Scholar
C. H. See, R. A. Abd-Alhameed, D. Zhou, T. H. Lee, and P. S. Excell, “A crescent-shaped multiband planar monopole antenna for mobile wireless applications,” IEEE Antennas Wireless Propag. Lett., vol. 9, pp. 152-156, 2010. Web of ScienceCrossrefGoogle Scholar
H. Wang, X. B. Huang, D. G. Fang, and G. B. Han, “A microstrip antenna array formed by microstrip line fed tooth-like-slot patches,”IEEE Trans. Antennas Propag., vol. 55, pp. 1210-1214, 2007. Web of ScienceCrossrefGoogle Scholar
Y. Sung, “A printed wide-slot antenna with a modified L-shaped microstrip line for wideband applications,” IEEE Trans Antennas Propag, vol. 59, pp. 3918-3923, 2011. Web of ScienceCrossrefGoogle Scholar
Y. Sung, “Bandwidth enhancement of a microstrip line-fed printed wide-slot antenna with a parasitic center patch,”IEEE Trans. Antennas Propag., vol. 60, pp.1712-1217, 2012. CrossrefWeb of ScienceGoogle Scholar
Y.-W. Jang, “Broadband T-shaped microstrip-fed U-slot coupled patch antenna,” Electronics Lett., vol. 38, pp. 496-498, 2002. Google Scholar
G. Kumar and K.P. Ray, Broadband Microstrip Antenna, USA, Artech House, 2003. Google Scholar
I.J. Bahal and P.Bartia, Microstrip patch antenna, Artech House,1980. Google Scholar
M. Meada, “Analysis of gap in microstrip transmission line,” IEEE Trans. Antennas propag., vol. 32, pp. 1375-1379, 1972. Google Scholar
J. D. Baena et al., “Equivalent-Circuit Models for Split-Ring Resonatorsand Complementary Split-Ring Resonators Coupled to Planar Transmission Lines,”IEEE Trans. Microwave Theory Tech., vol. 53, pp. 1451-1462, 2005. CrossrefGoogle Scholar
Zeland, IE3D simulation software, Version 14.05, ZelandInc., USA, 2008. Google Scholar
About the article
Ashish Singh received his B.Tech degree in Applied Electronics and Instrumentation from the Uttar Pradesh Technical University, India, in 2007. He completed his M.Tech. and D.Phil. degrees in Communication Technology from Department of Electronics and Communication, University of Allahabad in 2009 and 2015 respectively. He has published more than 40 research papers in different national and international journals and conference proceedings. His are of interests are Patch Antenna, Millimeter waves, Optical communication and Bio-medical Instrumentation. He worked as an Assistant Professor in Raghu Engineering College, Visakhapatnam. Presently, he is working at same designation in NMAMIT, Nitte India.
Mohamad Aneesh received his B.Tech. Degree in Electrical and Electronics Engineering from Uttar Pradesh Technical University, India in 2007 and completed his M. Tech degree in Advance Communications System form Sam Higginbottom Institute of Agriculture, Technology & Sciences Allahabad, India in 2009 and completed his D.Phil. degree from Dept. of Electronics & Communication University of Allahabad, Allahabad, India in 2015. He has published more than 40 research papers in different national and international journals and conference proceedings. His areas of interest are Patch antenna, Neural Network, and Optical communication. He worked as Assistant Professor in Dr. Rizivi College of Engineering, Kaushambi. Nowadays. he is working as Assistant Professor in Dr. Ambedkar Institute of Technology for Handicapped, Kanpur, India-208024.
Kamakshi received her B.Tech. degree in Electronics Engineering from the Institute of Engineering and Rural Technology Allahabad, U.P., India in 2007. She completed her M.Tech. and D.Phil. degrees in Communication Technology from Department of Electronics and Communication, University of Allahabad in 2009 and 2017 respectively. She has published more than 40 research papers in different national and international journals and conference proceedings. Her area of interests is Broadband antennas, and Millimeter waves. Nowadays, she is working as an Assistant Professor in IMS Engineering College, Ghaziabad, India.
J. A. Ansari
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. 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 100 research 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, Allahabad, India.
Published Online: 2017-11-10