диафрагмированные волноводные фильтры / a2056ee5-2962-4466-99f3-990534db7931

Abstract— A compact coplanar waveguide (CPW) fed dual band antenna is designed by metamaterial inspired Split ring resonator. The radiating element Hexagonal Closed Ring Resonator (Hex-CRR) and a Non Bianisotropic split-ring resonator (NB-SRR) are connected together. The overall antenna dimension is 31.7 × 25 × 1.6 mm3. The prototype antenna covers bandwidth of 36 MHz (2.677−2.713 GHz) and 2057 MHz (5.513−7.57 GHz) with center frequency of 2.7 GHz and 6 GHz, respectively. In order to improve the impedance matching of the antenna, CPW-fed line with tapered impedance transformer line and sunk in the ground plane are introduced. Hex-CRR is used to create a lower frequency band and NB-SRR offers higher frequency band. To miniaturize the size of the antenna, inner NB-SRR dimensions are taken as smaller than the resonant wavelength. The prototype antenna has consistent Omnidirectional (H-Plane) radiation pattern, and dipole (E- Plane) radiation pattern of both resonant frequencies.

Keywords— Dual band antenna, Hexagonal closed ring resonator, Non Bianisotropic Split Ring Resonator (NB-SRR), Sunk ground.

I. INTRODUCTION

Now a day with advancement in wireless communication systems and its applications, there are developments in the field of compact printed CPW-fed antennas having a multi frequency band. These antennas help in cost reductions and improve space usage. The other advantages of these types of antennas are light weight, low profile and easy integration with surface mount device [1, 2]. Recently, several designs for dual band antennas are reported in literature. In some of these antennas dual band is designed by making different types of slots in radiating element. The antennas designed by these designs have a narrow impedance bandwidth of the two operating frequencies [3]. Some other designs for dual band are having broad impedance bandwidth, but achieved gain is less. A split ring resonator is the metamaterial element having two concentric metallic rings which has split in both rings. The split is a key factor to achieve antenna miniaturization [5]-[9]. NBSRR is a basic structure of metamaterial tends to improve the antenna radiation characteristics such as impedance bandwidth, gain [10], and reduce cross polarization [11]. NB-SRR based metamaterial can be used to design filters and achieve miniaturization [12].

In this paper, a compact coplanar waveguide (CPW) fed dual band antenna is proposed by Hex-CRR and NB-SRR. Non bianisotropic split ring resonator is one of a type of SRR in which both rings are connected together through metal strip,

which is used to improve the bandwidth of higher frequency range.

II. ANTENNA DESIGN

The A schematic diagram of the proposed antenna is shown in Fig. 1. It has both Hex-CRR and NB-SRR, and designed on 31.7 × 25 × 1.6 mm3 FR-4 substrate. The radiating element Hex-CRR and NB-SRR joined together to improve the antenna performances, such as gain and impedance bandwidth. The radius of the ring resonators are represented by r1, r2 and r3 from a common center (o) and width (w) of all three rings are equal. The split (s) in both rings of non bianisotropic split ring resonator (NB-SRR) provides bandwidth improvement.

Fig. 1. Schematic representation of proposed antenna.

Initially, the conventional ground plane is designed, then later it is replaced by sinking ground plane [13] for better impedance matching along with a CPW-fed line with tapered impedance transformer line. The trace width of the CPW-fed line is fixed to maintain simplicity. The width of the symmetrical ground plane g1=14.85 mm, height of the ground plane g2=11 mm, length of the feed line g3=8 mm and spacing between the ground plane and feed line are u=0.3 mm. The dimensions of the antenna are shown in Table I. The width of the tapered transmission line at junction of feeding is represented tf and width of other tapered transmission lines is given by

The characteristic impedance [13] is 59.07 Ω. Here, α=0.93.

The width of the tapered transmission lines is 1.4 mm and 1.12 mm using the value of n= 1, 2 in equation 1.

The formula for the calculating resonant frequency of HexCRR is given by [14]

Where C is the speed of light and S is the length of the sides of the hexagon. The resonant frequency of NB-SRR is same as SRR and it is given by [4]

III. RESULTS AND DISCUSSION

High Frequency Structure Simulator (HFSS) electromagnetic simulator software is used to conduct the simulation. The return loss characteristics of the proposed antenna is shown in Fig. 2. It exhibits less than -10 dB impedance bandwidth of 36 MHz (2.677−2.713 GHz) and 2057 MHz (5.513−7.57 GHz) with center frequency of 2.7 GHz and 6 GHz, respectively. NB-SRR creates a higher frequency band and the small metal strip between the rings are used to improve the bandwidth of the higher frequency band. Outer Hex-CRR is responsible for generating lower frequency band to cover WLAN application.

(a)

(b)

Fig. 3. Simulated current distribution (a) at 2.7 GHz, (b) 5.9 GHz

(a)

(b)

Fig. 5. Radiation patterns of proposed antenna (a) 2.7 GHz, (b) 6 GHz.

The surface current distribution of the proposed antenna at 2.7 GHz and 5.9 GHz are depicted in Fig. 3(a)-3(b). It clearly shows that, at 2.7 GHz the current is along the NB-SRR and at 5.9 GHz the current is along the Hex-CRR. The gain of the antenna is plotted as a function of frequency, which is shown in Fig. 4. It shows that, the maximum gain of 2.54 dB is observed at 6 GHz resonant frequency. Fig. 5 illustrates, the far field radiation pattern of the antenna. The consistent dipole radiation pattern is obtained in E-plane ( =0°) and omnidirectional pattern is obtained in H-plane ( =90°) for both dual band characteristics.

IV. PARAMETERS EXTRACTION OF NONBIANISOTROPIC SPLIT RING RESONATOR

The band characteristics of Non-Bianisotropic Split Ring Resonator is examined by the classical waveguide theory method [15]. The reflection coefficient (S11) and transmission coefficient (S21) are found, and from this S-parameters, permeability characteristics are extracted. The S-parameters (S11 & S21) are plotted against as a function of frequency as depicted in Fig. 6. It shows the stop band behaviour at 5.6 GHz and pass band behaviour at 6 GHz. Thus, the pass band is responsible for obtaining higher resonance frequency of 6

Fig. 6. Band characteristics of NB-SRR.

Fig. 7. Negative Permeability characteristics of NB-SRR at 5.6 GHz.

V. CONCLUSION

A composite Hex-CRR and NB-SRR metamaterialinspired antenna is designed for dual band operation. By introducing a tapered impedance transformer line and sunk into the ground plane, the better impedance matching is achieved. NB-SRR created a higher frequency band and enhances the bandwidth of the higher frequency band. NBSRR band characteristics as well as negative permeability are discussed in detail. The proposed antenna has a small size,