In this paper, the design of frequency reconfigurable low profile antenna using metasurface (FRAMS) is presented for wireless applications. The designed structure incorporates two substrate layers: rectangular patch with feeding line is printed on the upper face and ground plane on the lower face of first substrate whereas, a metasurface (MS) on the upper face of the second substrate. A periodically positioned double split ring-shaped resonator (DSRSR) structure along the x- and y-axis forms the metasurface. The desired frequency reconfigurability is achieved by rotating the meta surface layer. The High Frequency Structure Simulator V15 has been utilized for the designing and analysis of the proposed antenna. The suggested frequency reconfigurable antenna effectively tunes from 4.97 to 6.09 GHz, thus providing a 20.2% fractional tuning range with 1.12 GHz bandwidth.
Due to the enormous development, profound research, and rapid proliferation of communication
technology, wireless devices are continuously supporting several applications at the same time. It is
completely unrealistic to support multiple antennas for multiple applications in one system [
A metasurface (MS) provides an optimum choice to deal with this kind of problem. A
metasurface is generally a type of two-dimensional surface version of metamaterials. This material
can produce unique electromagnetic properties by adjusting the shape, size, and arrangement of unit
cell structures. Thus, introducing MS into reconfigurable antennas can help us to achieve multiple
reconfigurations [
This paper aims to discuss the design of a metasurface based frequency reconfigurable antenna possessing wide bandwidth and tuning range. The designing methodology for the suggested antenna is elaborated in Section 2. Section 3 elucidates the results and discussion part. In the end, the conclusion is presented in Section 4.
The geometrical pattern of double layered structure of the FRAMS is depicted in Figure 1. Rogers RO4350B substrate material with a thickness of 1.524 mm is used to design the antenna. The dielectric loss tangent (tan δ) and relative permittivity (εr) of the substrate are 0.0037 and 3.48, respectively. Due to the prominent features such as excellent dimensional stability and low loss, Rogers RO4350B substrate material is used in the design. A rectangular patch with side dimensions (Pl, Pw) and a circular ground plane with a diameter (D) is implemented on the upper and lower face of the first substrate layer as shown in Figure 1 (a). To achieve excellent impedance matching, the suggested antenna is excited by a 50 Ω microstrip feed line. The periodically arranged DSRSR unit cells constituting the MS are mounted on the upper face of the second substrate layer as shown in Figure 1 (b). The enlarged structure of the unit cell and a side view showing two substrate layers is elucidated in Figure 1(c) and Figure 1(d), respectively. The desired frequency reconfigurability is obtained by rotating this metasurface layer. The direction of rotation angle (θr) possesses equal symmetry along horizontal and vertical directions. Thus, θr = - θr, and the maximum rotation angle considered is 900.
The reliable and commercially available Ansoft’s three-dimensional, finite element method (FEM) based HFSS solver is used for performing the electromagnetic simulations and obtaining the resonance characteristics in SRR structures [17]. The unit cell is placed inside a simulation model for characterizing the metamaterial properties. Each simulation model consists of a dual-port waveguide mode with perfect electric (PE) and perfect magnetic (PM) conductor boundaries assigned along appropriate wall pairs. A dielectric slab is placed at the center of the waveguide set up [18]. Waveports are applied along both sides from –x to +x. The values of transmission (S21) and reflection (S11) coefficient are obtained from this arrangement. From Figure 2, it is revealed that a strong reflection of -32.26 dB is observed at 7.97 GHz. This frequency corresponds to the resonance of the left-handed metamaterial (LHM) structure. Resonance occurs at a frequency that is similar to the frequency where the logarithmic transmission has the lowest value. The minimum value of the first transmission of the proposed structure is -54.50 dB at 8.93 GHz [19]. The magnitude and phase of S11 and S21 are illustrated in Figure 3. The metamaterial behavior is determined from the phase reversal behavior of S11 and S21 at a particular frequency. Figure 4 shows the real and imaginary values of both coefficients that are further used to evaluate the negative characteristics of permeability and permittivity. where, V1 and V2 are the combined terms describing the sum and difference of S11 and S21, respectively. k0 symbolizes the free space wave number, d represents the substrate thickness, µr and εr signify the relative permeability and permittivity, respectively.
The MATLAB script is then generated using the expressions given in mathematical formulations to derive the complex permittivity and permeability curves. Figure 5 (a) and Figure (b) show the real and imaginary values of extracted permeability and permittivity, respectively. From these figures, it is revealed that these parameters are simultaneously negative in 7.94 to 8.5 GHz which is the required frequency region of interest.
(a) (b)
The reflection coefficient is an important performance parameter that judges the frequency reconfigurability operation of an antenna. It has been clearly illustrated from Figure 6 that as θr changes from 00 towards 300, 600, and 900, the resonant frequency shifts its value from 4.97 to 6.09 GHz with 20.2% fractional tuning range and 1.12 GHz bandwidth. The best matching condition is observed at a 5.92 GHz value that corresponds to 600 angle. As θr further increases, the resonant frequency decays. The frequency range chosen for the operation is 4.5 GHz to 6.5 GHz.
Parametric analysis is done to evaluate the effect of important geometrical parameters such as ‘a’, ‘b’, and ‘g’ on the performance of an antenna. These parameters play a vital role in designing the antenna and are varied with a step size of 1mm. The effect of parameter ‘a’ on the performance of an antenna is elucidated in Figure 7. As the value of parameter ‘a’ decreases from 10 to 9 mm, the resonant frequency moves along the upper side whereas, as the value increases from 10 to 11 mm, the resonant frequency moves along the lower side. The effect of parameter ‘b’ on the resonant frequency is illustrated in Figure 8. When the value of ‘b’ is changed from 4 to 3 mm, a slight shift towards the left side is observed and on increasing the value of ‘b’ from 4 to 5 mm, the resonant frequency shifts slightly towards the right side of the original curve. Figure 9 depicts the effect of parameter ‘g’ on the antenna performance. The resonant frequency shifts towards the left side on decreasing the value of ‘g’ to 1.4 mm and the right side on increasing the value to 3.4 mm. From the abovementioned parametric analysis, the optimal values of parameters ‘a’, ‘b’, and ‘g’ are 10 mm, 4 mm, and 2.4 mm, respectively.
Voltage standing wave ratio (VSWR) is an important performance parameter since it is linked to the reflection coefficient that in turn leads to the impedance matching. There will be poor impedance matching if a larger mismatch is observed between VSWR and the reflection coefficient. As a result, VSWR for antenna should be ≤ 2 to achieve acceptable impedance matching [22]. The VSWR at different rotation angles is illustrated in Figure 10. From this Figure, it is noticed that observed VSWR is 1.0546, 1.1396, 1.0200, and 1.8169 corresponding to 00, 300, 600, and 900 rotation angles. The minimum value of VSWR at 600 indicates the best matching of impedance.
The radiation pattern of FRAMS at θr = 00, 300, 600, and 900 in correspondence to 4.97 GHz, 5.33 GHz, 5.92 GHz, and 6.09 GHz, respectively are elucidated in Figure 11. It is clearly shown that the observed radiation patterns are quite similar in all of the four states. The x-z plane shows a bidirectional radiation pattern and the y-z plane shows an omnidirectional radiation pattern. This clearly shows that metasurface helps in achieving the desired frequency reconfigurability without affecting the polarization. These plots also indicate that co-polarization is more as compared to crosspolarization resulting in high polarization purity of the designed antenna. The gain of the antenna changes from 5.84 to 6.93 dB in the frequency range of operation. (c) (d) Figure 11: Radiation pattern (a) x-z and y-z plane for θr = 00 at 4.97 GHz (b) x-z and y-z plane for θr = 300 at 5.33 GHz (c) x-z and y-z plane at θr = 600 for 5.92 GHz (d) x-z and y-z plane for θr = 900
Ref. No.
The comparison of the proposed antenna with the other reported antennas is shown in Table 2. It is well understood from the table that the suggested antenna provides higher bandwidth, wider tuning range, and acceptable gain at all resonating frequencies.
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