Metamaterial Monolayer Coupled Enhanced Transmission in ...Metamaterial Monolayer Coupled Enhanced...
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Metamaterial Monolayer Coupled Enhanced Transmission in Parallel Plate Dipole Antenna Sarin V.P 1* , Rohith K. Raj 2 , Lindo A.O 3 , C.K Aanandan 3 , Mohanan P 3 and Vasudevan K 3 1 Department of Electronics, Govt. College, Chittur, Palakkad, Kerala, Email: [email protected] 2 Department of Electronics, Govt. College, Mananthavady, Kerala, Email:[email protected] 3 Centre for Research in Electromagnetics and Antennas, Cochin University of Science and Technology, Cochin-22, Kerala, India, Email: [email protected] Abstract—A metamaterial monolayer cover is implemented using split ring resonators (SRR) for enhancing transmission in a parallel plate dipole antenna operating in the S band. The proposed design is the metamaterial incorporated version of the parallel plate dipole antenna. The front to back ratio is considerably improved by enhancing the magnetic resonant strength in the close proximity of the top slit and the antenna shows F/B ratio better than 25 dB. The antenna is fabricated on a low cost substrate of dielectric constant 4.4. The experimental, simulation and computational studies of the antenna with the metamaterial cover is discussed in this paper. 1. INTRODUCTION Enhanced transmission phenomenon has fascinated the research community after the theoretical work proposed by Bethe on the theory of diffraction through subwavelength holes [1]. Bethe proposed that transmission can be modeled using a magnetic dipole parallel to the slot and electric dipole excitation perpendicular to the metal screen. D.R Jackson and Oliner explained the extra ordinary transmission phenomenon by using the leaky wave theory [2]. They came into a conclusion that the corrugations on the metal plates are responsible for the excitation of an infinite number of spatial harmonics and special case excites fast waves and provides leaky radiation. Periodic corrugations on the entrance and exit faces of the slit tremendously enhance the transmission power. The invention of Metamaterials has boosted the research on the enhanced transmission for a variety of applications. The theoretical/experimental works relating the transmission enhancement through subwavelength hole using metamaterials was proposed from the Pennsylvanian group [3-5]. The theoretical formulations suggest that the excitation of material polariton on the entrance and exit faces is responsible for the transmission enhancement. In this paper we are proposing the practical realization of transmission enhancement in a parallel plate dipole antenna configuration using an array of split ring resonators. The antenna design we have selected is the parallel plate dipole antenna proposed recently for getting directional radiation characteristics without utilizing ground planes [6]. The front to back ratio of the antenna was found to be 16 dB. Directional radiation pattern for the antenna was obtained by merging the electric and magnetic resonances of the parallel plate dipole. In this paper, we have stacked an SRR layer over the stacked dipole antenna and the design gives a higher front to back ratio. Transmission enhancement is achieved by enhancing the magnetic resonant strength in close proximity of the top slit. The experimental studies of the antenna were carried out using HP 8510C network analyser and the simulation was done using Ansoft HFSS. The resonant mechanisms are verified computationally using the Matlab based FDTD codes. 2. GEOMETRY OF THE ANTENNA The layout of the stacked plate antenna with the metamaterial slab layer is shown in fig.1. The stacked metal slab pair serves as the basic building block of the antenna. The lower dipole antenna is fed using a microstrip to slot line transition. The design of the balun transition is available in [7]. Parallel plate dipole antenna is obtained by stacking the initial dipole element with the same dipole at a stacking height of h 2 . Each layers of the antenna are fabricated using an FR4 substrate of dielectric constant 4.4 and height 1.6mm. The final antenna is obtained by stacking a split ring resonator layer over the top of the stacked dipoles. The stacking height is denoted by h 3 . The split ring resonator element is resonating at around 3 GHz which is same as that around the stacked dipole antenna. The design of the spilt ring resonator is adopted from the standard design procedures [8]. The SRR dimensions are r=5.2mm, s=1mm, w=1mm and d=1mm. The other dimensions of the antenna are L d =20mm, W d =8mm, L g =W g =14mm, W s =0.35mm, L 0 =0mm, D=4mm, W m =3mm, h 1 =1.6mm, h 2 =3.2mm and h 3 =1.6mm. 978-1-4673-5225-3/14/$31.00 ©2014 IEEE
Transcript of Metamaterial Monolayer Coupled Enhanced Transmission in ...Metamaterial Monolayer Coupled Enhanced...
Metamaterial Monolayer Coupled Enhanced Transmission in Parallel Plate Dipole Antenna
Sarin V.P1*, Rohith K. Raj2, Lindo A.O3, C.K Aanandan3, Mohanan P3 and Vasudevan K3
1Department of Electronics, Govt. College, Chittur, Palakkad, Kerala, Email: [email protected]
2Department of Electronics, Govt. College, Mananthavady, Kerala, Email:[email protected]
3Centre for Research in Electromagnetics and Antennas, Cochin University of Science and Technology, Cochin-22,
Kerala, India, Email: [email protected] Abstract—A metamaterial monolayer cover is implemented using split ring resonators (SRR) for enhancing transmission in a parallel plate dipole antenna operating in the S band. The proposed design is the metamaterial incorporated version of the parallel plate dipole antenna. The front to back ratio is considerably improved by enhancing the magnetic resonant strength in the close proximity of the top slit and the antenna shows F/B ratio better than 25 dB. The antenna is fabricated on a low cost substrate of dielectric constant 4.4. The experimental, simulation and computational studies of the antenna with the metamaterial cover is discussed in this paper.
1. INTRODUCTION
Enhanced transmission phenomenon has fascinated the research community after the theoretical work proposed by Bethe on the theory of diffraction through subwavelength holes [1]. Bethe proposed that transmission can be modeled using a magnetic dipole parallel to the slot and electric dipole excitation perpendicular to the metal screen. D.R Jackson and Oliner explained the extra ordinary transmission phenomenon by using the leaky wave theory [2]. They came into a conclusion that the corrugations on the metal plates are responsible for the excitation of an infinite number of spatial harmonics and special case excites fast waves and provides leaky radiation. Periodic corrugations on the entrance and exit faces of the slit tremendously enhance the transmission power. The invention of Metamaterials has boosted the research on the enhanced transmission for a variety of applications. The theoretical/experimental works relating the transmission enhancement through subwavelength hole using metamaterials was proposed from the Pennsylvanian group [3-5]. The theoretical formulations suggest that the excitation of material polariton on the entrance and exit faces is responsible for the transmission enhancement.
In this paper we are proposing the practical realization of transmission enhancement in a parallel plate dipole antenna
configuration using an array of split ring resonators. The antenna design we have selected is the parallel plate dipole antenna proposed recently for getting directional radiation characteristics without utilizing ground planes [6]. The front to back ratio of the antenna was found to be 16 dB. Directional radiation pattern for the antenna was obtained by merging the electric and magnetic resonances of the parallel plate dipole. In this paper, we have stacked an SRR layer over the stacked dipole antenna and the design gives a higher front to back ratio. Transmission enhancement is achieved by enhancing the magnetic resonant strength in close proximity of the top slit. The experimental studies of the antenna were carried out using HP 8510C network analyser and the simulation was done using Ansoft HFSS. The resonant mechanisms are verified computationally using the Matlab based FDTD codes.
2. GEOMETRY OF THE ANTENNA The layout of the stacked plate antenna with the metamaterial slab layer is shown in fig.1. The stacked metal slab pair serves as the basic building block of the antenna. The lower dipole antenna is fed using a microstrip to slot line transition. The design of the balun transition is available in [7]. Parallel plate dipole antenna is obtained by stacking the initial dipole element with the same dipole at a stacking height of h2. Each layers of the antenna are fabricated using an FR4 substrate of dielectric constant 4.4 and height 1.6mm. The final antenna is obtained by stacking a split ring resonator layer over the top of the stacked dipoles. The stacking height is denoted by h3. The split ring resonator element is resonating at around 3 GHz which is same as that around the stacked dipole antenna. The design of the spilt ring resonator is adopted from the standard design procedures [8]. The SRR dimensions are r=5.2mm, s=1mm, w=1mm and d=1mm. The other dimensions of the antenna are Ld=20mm, Wd=8mm, Lg=Wg=14mm, Ws=0.35mm, L0=0mm, D=4mm, Wm=3mm, h1=1.6mm, h2=3.2mm and h3=1.6mm.
978-1-4673-5225-3/14/$31.00 ©2014 IEEE
Fig. 1 Geometry of the proposed antenna
3. RESULTS AND DISCUSSIONS The resonant characteristics of the antenna with and without the metamaterial slabs are shown in fig. 2. The initial antenna is resonating at 3.08 GHz. The 2:1 VSWR bandwidth is found to be 11.2% around the resonance. The detailed parametric analysis of the parallel plate dipole antenna is available in [6].The parallel plate dipole antenna combines the electric and magnetic resonances of the stacked plates to get directional radiation coverage. The stacked structure can be viewed as a parallel plate resonator in which the resonant frequency is strictly determined the plate parameters and on the stacking height. The stacking height determines the phase velocity of propagation in between the plates. For lower stacking heights, the wave will be more bound between the plates and the radiation efficiency will be low. Increase in stacking height enhances the phase velocity and it in turn increases the radiation efficiency of the antenna. The final design shows a 2:1 VSWR bandwidth of 13% from 2.77GHz to 3.17GHz around 2.96GHz. In the experiment the resonances are found to be merged. The lower resonance is the magnetic resonance of the split ring resonator and the final resonance is the parallel plate dipole resonance. The 3D radiation patterns of the antennas are shown in fig.3. The design with the metamaterial slab shows superior radiation performance as compared to the initial design. The radiated power in the two back lobes is reduced considerably in the design as compared to the initial one. It shows a broadside beam pattern and it resembles like that of a microstrip patch antenna. Fig. 2 Reflection characteristics In conventional dipole designs, we require a large ground plane plates placed quarter wavelength below the dipole plates to ensure directional well matched resonance and hence it affects compactness of the antenna. The 2D radiation patterns of the antenna were measured and are shown in fig.6. The radiation patterns of the stacked dipole antenna without the metamaterial cover are also shown along with it for comparison. It is observed that the final antenna shows a F/B ratio of 25dB at resonance.
Fig. 3 Radiation characteristics a) 3D pattern with SRR, b) 3D pattern without SRR, c) Measured ECO and d)
Measured HCO We have computed the resonant mechanism of the antenna using the FDTD based Matlab codes and is shown in fig. 4.
It is observed that the resonance is contributed by the anti parallel current distributions on the stacked slab pair. This confirms the presence of the magnetic resonant mode. The electric and magnetic field distributions of the antenna also conforms the presence of the magnetic resonant mode. It is observed that the magnetic field distributions shows symmetric cosine distributions in between the stacked plates and the electric field distributions shows slight phase alterations within the plates giving a slow wave mode. It is observed that the stacking height of the SRR layer affects the F/B ratio of the antenna. We have also performed variations in stacking height on the radiation characteristics of the antenna. It is observed that for a stacking height of h3=0.8mm, the outer rings of the two SRR are illuminated well and it corresponds to the magnetic resonance offered by the outer ring. Increase in stacking height enhances the coupling between the inner and outer rings and hence it reduces the resonant frequency of the SRR. This conditions gives a very good front to back ratio. It is made into notice that electric dipole excitations are possible for higher stacking heights and it reduces the front to back ratio considerably.
Fig. 4 Resonant mechanism
4. CONCLUSION We have implemented enhanced transmission phenomenon using metamaterials on a stacked dipole plate antenna. Transmission enhancement is achieved by enhancing the magnetic resonant strength in close proximity of the slit. The technique increases the front to back ratio up to 25 dB and the design is devoid of large reflecting ground planes as compared to conventional ground plane backed dipole and microstrip antennas. The resonant mechanisms of the antenna are well studied and this technique surely paves ways for getting super directive antennas in the microwave and terahertz regime.
5. ACKNOWLEDGEMENTS The authors acknowledge University Grants Commission and Department of Science and Technology, Govt. of India for financial support
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