диафрагмированные волноводные фильтры / 5bd2ffad-930a-43db-906a-948918fad6b3

Abstract—Design of novel cross slot fed hexagonal dielectric resonator antenna (DRA) of dimension 20 × 20 × 10 mm3 having substrate of material FR-4 is presented in this paper. The proposed antenna has a frequency range of 6.60–7.14 GHz in C-band, which includes the INSAT transmission frequency (6.725–7.025 GHz). The design frequency here is taken as 6.855 GHz which is fit for the application of STM link 1 and also applicable for the advanced microwave scanning radiometer channels (AMSR-E) of the earth monitoring system aqua satellite. The concepts and design parameters of the proposed antenna is theoretically analyzed and experimentally verified. The hybrid mode HEM111 is achieved by using a symmetric cross slot. The simulated impedance bandwidth and the radiation efficiency are found to be 7.88% and 93.7% respectively.

Index Terms—Circular polarization, dielectric resonator antenna, cross-slot feed

I. INTRODUCTION

Now-a-days the dielectric resonator antenna designs have received much more considerable attention for their various advantages such as light weight, compact size, fabrication simplicity, high power handling capability [1], [2]. Due to the use of dielectric materials, there arises absence of surface waves and negligible conductor losses and hence DRAs are preferred to the other conventional antennas. DRAs maintain high radiation efficiencies and also low loss characteristics. At two nearby frequencies more than one resonant mode can be supported by DRAs, which makes these useful for various applications with the single device.

Several methods have been proposed by researchers to enhance the radiation efficiency and impedance bandwidth. Mohamad I. Sulaiman et al. [3] investigated circularly polarized (CP) rectangular DRA using open half loop consisting three metallic strips to obtain impedance bandwidth 7% ranging from 2.95–3.62 GHz. G. Almpanis et al. [4] proposed an off-set cross-slot coupled CP-Cylindrical DRA in which impedance bandwidth of 4.7% was attained. Yong Ding et al. [5] analyzed a hybrid DRA using zonal-slot (cross-slot with L-probe) to obtain dual band ranging from 2.7–2.87 GHz and 4.45–5.36 GHz. Additional CP modes can be achieved by means of stair-shaped [6], trapezoidal [7], or inclined slot fed rectangular [8] structures. Raghuraman Selvaraju et al. [9] realized a rectangular DRA for WLAN (2.4 GHz) and C-band (3.8–4.4 GHz) applications. Meng Zou et al. [10] investigated stacked rectangular DRA which is circularly polarized to

obtain wide dual band of 1.77–2.00 GHz and 2.38–2.96 GHz. Xiaosheng Fang et al. [11] represented a slot-fed circularly polarized DRA for dual band operation taking into account the quasi TE111 and TE113 modes excitation. They found axial ratio bandwidth as 6.30% and 3.68% for lower and upper bands respectively. Kai Xu Wang et al. [12] investigated a rotated stair-shaped CP DRA with a wide bandwidth for 5G Wi-Fi and ISM band (5.8 GHz) applications. Amjad A. Omar et al. [13] proposed the co-planar waveguide (CPW) fed slot coupled linearly polarized dual rectangular DRA and found that the DRAs dimensions only affect the resonant frequencies. They have also concluded that the slots have no impact on it. Imran Khan et al. [14] investigated an array of rectangular conformal patch fed rectangular DRA and found the gains of 7.852 dB, 9.083 dB, 10.55 dB and 9.568 dB at 4.2 GHz, 5.2 GHz, 6.2 GHz, and 7 GHz respectively. Yongfeng Wang et al. [15] analyzed a slot-fed stacked cylindrical DRA to achieve 11 dB gain and a wide band 1.6 GHz, with 26% frequency range.

As per the observances in literatures, we have anticipated a new shape of DRA i.e. cross-slot coupled hexagonal shaped DRA (CS-HDRA), to achieve more radiation efficiency along with enhanced gain for high frequency range applications, which is hardly found in the literatures. In our proposed CS-HDRA, the HEM111 mode is excited. The CS-HDRA is positioned on the ground plane and HEM111 mode with lowest resonant frequency is excited by means of a microstrip line feeding mechanism. Using Ansoft HFSS of version 2015.1, the return loss, radiation patterns and antenna gain of CSHDRA are studied.

Apart from the introduction in Section I, the geometrical model of our proposed CS-HDRA is discussed in Section II. The top and front views along with the simulated structure using HFSS are shown in Fig. 1 and Fig. 2 respectively. In Section III, we have discussed the found results which include S-parameter and bandwidth, VSWR and gain, radiation patterns along with mode analysis. A comparison is carried out among the other antennas and is represented in Table II. The paper has been concluded in Section IV. We found a return loss of −28.235 dB, a gain of 5.392 dB, %BW of 7.88, VSWR of 1.08, radiation efficiency of 93.7% for the CS-HDRA. The smaller size with higher efficiency (93.7%) makes the CSHDRA more advantageous.

(b) Front view of the CS-HDRA Fig. 1.

Fig. 2. Trimetric view of the CS-HDRA in HFSS.

II. ANTENNA STRUCTURE

Fig. 1 shows the structural views of our CS-HDRA. The top view and front view are shown in Fig. 1(a) and Fig. 1(b) respectively. The DRA is designed using ceramic material Al2O3 with relative permittivity of 9.8. The substrate used is Flame Retardant 4 (FR-4 epoxy) material having a dielectric constant of 4.4 with dimensions as 80 × 80 × 1.6 mm3. The dimension of hexagonal DRA is 20×20×10 mm3. A 50 ohm micro strip feed line is coupled to a symmetric cross slot for the excitation of the CS-HDRA. The micro strip line has a length of lm = 48 mm and width of wm = 3 mm. A lumped

Fig. 3. Return loss plot of the CS-HDRA.

port is assigned at the feed for the excitation of designed antenna. 50 ohm is given as the line impedance of the antenna. Two rectangular slots in a cross-coupled manner is imprinted on the ground plane having length ls = 15 mm and width ws = 3 mm. Considering the above optimized parameters the proposed hexagonal DR antenna has been designed using HFSS software and are listed in the Table I.

The trimetric view of designed CS-HDRA in HFSS is represented in Fig. 2.

Making use of the symmetrical cross-slot coupling method enables a good CP operation in the CS - HDRA.

III.RESULTS AND DISCUSSION

A.S-Parameter and bandwidth:

Return loss vs. frequency curve (S11) of the proposed CSHDRA is shown in Fig. 3. The return loss here obtained is −28.235 dB at resonant frequency of 6.855 GHz. From the S parameter curve the bandwidth obtained is 0.54 GHz (7.88%).

B. VSWR and gain:

For practical implementation, VSWR of any antenna must be within 1–2. In our proposed DRA the VSWR obtained at design frequency 6.855 GHz is 1.08 which is low enough and advantageous. Fig. 4 represents the VSWR plot of the proposed CS-HDRA.

Fig. 5 shows 3D-polar plot of the gain at design frequency 6.855 GHz. 2D-plot of gain vs. frequency in the broadside direction within the operating range, i.e. 6.60–7.14 GHz is shown in Fig. 6.

The gain at resonant frequency 6.855 GHz of the proposed CS-HDRA is found to be 5.392 dB.

Fig. 4. VSWR vs. Frequency plot of the CS-HDRA.

Fig. 5. 3D-polar plot of gain of the CS-HDRA.

Fig. 6. 2Dplot of gain vs. angle of the proposed CS-HDRA.

C. Radiation patterns:

As cross-slot coupling mechanism is used in our proposed CS-HDRA, it is set to follow circular polarization. Fig. 7 shows the E-Plane (XZ) radiation pattern which includes the

Fig. 7. Radiation pattern of the CS-HDRA in E-Plane.

Fig. 8. Radiation pattern of the CS-HDRA in H-Plane.

Left hand circular polarized (LHCP) and Right hand circular polarized (RHCP) gain traces. Same as Fig. 7, Fig. 8 represents H-Plane (YZ) radiation pattern. Here solid line and symbolized line are used for distinguishing LHCP and RHCP gains.

Fig. 9 and Fig. 10 show E-plane and H-plane co-polarization and cross-polarization plots respectively. Co-polarized and cross-polarized radiation patterns in the E-Plane at resonant frequency 6.855 GHz are shown in, Fig. 11. Fig. 12 shows the same patterns for the H-plane. The solid line represents the copolarization which is desired polarization whereas symbolized line represents cross-polarization which is undesired one.

D. Radiation efficiency:

Our proposed CS-HDRA yields a radiation efficiency of 93.7% at design frequency i.e. 6.855 GHz, shown in Fig. 13.

E. Mode in proposed CS-HDRA:

Fig. 14 represents the electric field distribution in front view and cross-sectional view of the proposed CS-HDRA which demonstrates the hybrid electromagnetic mode i.e. HEM111. HEM111 mode radiates like short horizontal magnetic dipole.

Fig. 9. E-Plane co-polarization & cross-polarization plots of CS-HDRA.

Fig. 12. Co-polarized and cross-polarized radiation patterns in the H-Plane of CS-HDRA.

Fig. 10. H-Plane co-polarization & cross-polarization plots of CS-HDRA.

Fig. 13. Radiation efficiency plot of the proposed CS-HDRA.

Fig. 11. Co-polarized and cross-polarized radiation patterns in the E-Plane of CS-HDRA.

The electric field distribution is shown in Fig. 14. The top view is shown in Fig. 14(a). Fig. 14(b) shows its side view. The figure ensures that the CS-HDRA is excited in HEM111 mode.

The modal fields inside the antenna induce surface charges and surface currents. In other words, we can say that the modal fields are supported by the surface charges and surface currents along the feed line to the antenna. The surface current distribution along the microstrip feed line of the CS-HDRA is shown in Fig. 15. Here high current values are caused by the electric conduction current concentrations.

A comparison is carried out among the other antennas, found in literatures which are designed in the nearby operating frequency range of our proposed CS-HDRA and it is represented in Table II. In this comparison, it is shown that, the return loss of −28.235 dB, a gain of 5.392 dB, %BW of 7.88%, VSWR of 1.08 and a radiation efficiency of 93.7% are found in the case of our CS-HDRA which in most of the literatures as shown in the table are not available. The 4th row shows that, Yongfeng Wang et al. got an 11 dB gain and % BW 26, since bandwidth is ranging from 5.4 to 7.0 GHz. But considering the operating range as 6.60–7.14 GHz, we can easily construct an outline that the proposed CS-HDRA is relatively more effective and efficient than the other designed

(a) Top view of electric field distribution operating at HEM111 mode

(b) Side view of electric field distribution operating at HEM111 mode

Fig. 14.

ones. Moreover, further modification may easily make our proposed one, more efficient and effective in the future.

IV. CONCLUSION

A cross-slot coupled microstrip line fed hexagonal DRA has been demonstrated. The DRA has single point microstrip line feed having cross slot coupling mechanism. Field distributions of the HEM111 mode of hexagonal DRA have been studied. The resultant radiation efficiency and impedance bandwidth are 93.7% & 7.88% respectively. By considering the outcomes at design frequency 6.855 GHz, it has been verified that microstrip patch antenna for the wireless application of STM

Fig. 15. Surface current distribution along the microstrip feed line of the CS-HDRA.

link1, having an operating frequency range 6.749–6.851 GHz with resonant frequency 6.8 GHz can be effectively replaced by our proposed CS-HDRA. Again rectangular microstrip patch antenna with c-slots having resonant frequency 6.8 GHz with 82% efficiency and band pass filter for RFID application having center frequency 6.85 GHz of dimension 28 mm × 15.25 mm can also be replaced by the CS-HDRA. The radiation patterns and gains as well as the cross polarization and co-polarization plots are investigated. Making the use of symmetrical cross-slot, realization of a dual-band/multiband CP operation is quite difficult. So, the further modification in this proposed DRA i.e. stacking, two or more layers of hexagonal DRAs with symmetric/asymmetric slot may be worked out to achieve the multiband/dual-band operations for the enhancement of the % bandwidth and characteristics. The effect of identical shaped slot coupling in the proposed DRA may also be carried out as one of the future work.

Acknowledgements: The valuable comments of the reviewers are gratefully appreciated.

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