DUAL BAND DIELECTRIC RESONATOR ANTENNA FOR HIGH-SPEED APPLICATIONS

The antennas for wireless communication devices have undergone a tremendous expansion from the external monoband resonant antenna to the internal non-resonant multi-band antenna. In this paper, a dual-band dielectric resonator antenna for high-speed applications is proposed. Due to the complex edge-shaped boundary between the dielectric and air in a rectangular dielectric resonator antenna, a complex closed form of expression is difficult to achieve. To address this problem a half-cut cylinder is placed over the rectangular dielectric to achieve excellent radiation characteristics. This proposed antenna provides a wide dual-band response with fractional impedance bandwidth of 21.92% and 19.09%while operating from7.32 GHz to 9.12 GHz and 10.71 GHz to 12.95 GHz. It provides an average gain of 3dBi with high gain stability in the entire operating frequency band. The radiation efficiency is found to be 96% due to low ohmic and dielectric losses. The cross-polarization is around 20 dB lesser than the co-polarization. Its gain and directivity can further be enhanced by implementing serial and parallel array structures. This design uses HFSS 14.0 commercial electromagnetic simulation tools.


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DBDRA FOR HIGH-SPEED APPLICATION achieve high channel capacity. The field correlation can be extracted from the impedance matching and s-parameter measurement. It is a challenge to upscale microstrip patch antenna as the radiator into microwave and mm-wave band, Garg, Bhartia, Bahl, and Ittipiboon [3]. While comparing patch antenna with DRA, it has been reported that in patch antenna capacitive effect dominates, which results in a non-spectral wave or ghost wave. It is highly affected by a surface wave and fringing field, whereas DRA is free from it. The patch antenna is affected by mode coupling due to which there will be creations of degenerative modes, whereas DRA is powered by Hybrid LSE and LSM mode. The patch antenna is operated by conduction current whereas, DRA is operated by displacement current, which never leads to ohmic losses. Therefore DRA technology is emerging as a new and viable alternative to conventional low gain and low profile radiating elements. It has huge potential to become the next generation of antenna technology. A DRA is a resonant antenna, fabricated from low-loss microwave dielectric material, the resonant frequency of which is predominantly a function of size, shape, and material permittivity, Petosa, Ittipiboon, Antar, Roscoe and Cuhahi [4]. The impedance bandwidth is a function of the material's permittivity and aspect ratio. The emphasis will be on the compact design of RDRA as a front-end radiating and sensing device to address the needs of portable wireless applications such as PDAs, PCS, WSNs, etc. The aim is to enhance the bandwidth performance to meet the requirements for emerging broadband or ultra-wideband system for high-speed communication. To design a high sensitive and high gain device for commercial sensors, defense, and medical electronics.
In this paper, a modified filleted dual-band dielectric resonator antenna for high-speed applications is proposed, Tripathi, Sahu, Kumari, Parkash, Singh and Kumar [5]. The filleted structure is obtained by placing a half-cut cylindrical dielectric of radius 5 mm made up of low Resonance is said to be a condition in which the field exists without having any excitation. The resonant frequency is never a real number if the radiator is radiating. This multifunctional dual-band antenna resonates within 7.32 GHz to 9.12 GHz and 10.71 GHz to 12.9 GHz with -10 dB impedance fractional bandwidth of 21.92% and 19.09% respectively. The realized radiation efficiency is 96% having a cross-polarization of -20 dB.
The structure of the antenna is presented in Section II. The operating mechanism is described in Section III. The output and input characteristics of the proposed antenna is described in Section IV. Finally, conclusions are made.

STRUCTURE OF THE ANTENNA
where, λ g 1 and λ g 2 are the longest and shortest guided wavelength. The length of the quarter wave transformer (L) is: The dimension of the transmission line, along with the quarter-wave stub, is 2.5×28×0.35 mm 3 .
The bottom portion of the substrate is covered with a perfect electrical conductor (PEC) as an infinite ground plane. According to the boundary value problem, the field in a region of space is determined from the knowledge of the field over the boundary of the region. The ground plane is a perfectly conducting plane. The boundary condition at PEC has a vanishing tangential component of E (Element source = Image element source) over the plane. It is similar to the solution for a current element adjacent to a plane conductor. When the width of the substrate is narrow, it results in high input impedance, much higher than 50Ω, whereas when the width of the substrate is wide, it results in low input impedance of the DRA. So by controlling the width of the substrate, impedance matching can be accomplished.
The lower permittivity of the substrate results in increasing the coupling of energy into the DRA.
It has been reported that higher bandwidth can be achieved by increasing the substrate thickness or by increasing the size of the radiator. An air gap is introduced at the top of the substrate by placing a thin foam spacer having = 1 of dimension 50×50×1 mm 3 . The air gap is responsible to enhance the resonant frequency and to reduce the radiation Q-factor [6]. Therefore, there is enhancement in the impedance bandwidth and there will be modification of the matching 4401 DBDRA FOR HIGH-SPEED APPLICATION profile. A rectangular dielectric resonator antenna made up of Teflon having =2.1, tan = 0.001 of dimension 20×10×3.5 mm 3 is placed over the foam spacer. The shape of the dielectric resonator antenna, its resonant frequency and radiation Q-factor are calculated based on the dielectric wave guide model, Petosa [7]. A half cylindrical structure made up of Alumina 2 3 having = 9.8, tan = 0.002) of dimension 20×10 mm 2 cut along XY plane having radius 5 mm is placed over the rectangular structure. The half-cut cylindrical structure is used to increase the effective electrical area of the radiator. The calculation of the resonant frequency of this stacked configuration requires certain adjustments as there is a significant shift in the desired resonant frequency. Therefore, some experimental optimization may be required to maximize the coupling. This top cylindrical structure may be useful in providing high mechanical strength when the antenna will be operated in free space.
The mode within the guide is made up of plane waves reflecting at an angle from the boundaries between dielectric, interfering within the slab to produce different field patterns. The differences are in phases of reflections at the boundaries and in the evanescent field in the dielectric region.
If the angle of reflection 1 is greater than the critical angle , where,θ c = sin −1 (

PRINCIPLE OF OPERATIONS
The fundamental approach to achieving a wide-band design is to activate different field patterns or modes to initiate different field configurations. Basically, there are three methods to improve can alter the dimensionality of the boundary value problem and introduce a higher-order mode through the creation of a fringing field. As the slot will operate close to the resonance, bandwidth increases, but it constitutes an increase in back radiation level, which reduces the front-to-back ratio. The front to back ratio is the difference between maximum gains, usually in 0° to that of 180°. The bandwidth can be improved by adding one or more resonant element having a resonating frequency close to one another to achieve multiple resonances. All these points are taken into consideration while placing a half-cut cylinder over the rectangular dielectric. It is supported by a thicker stacked dielectric with a slot. The major attractive feature of this design is to increase the surface area. This structure is somehow similar to the array configuration. The proximity of the stacked structure ensures high coupling.
The bottom dielectric radiator has a rectangular geometry. It is because, in rectangular DRA length, width and depth constitute two degrees of freedom (length/width and depth/width), which provides several aspect ratios and radiation Q-factor for a fixed resonant frequency. Design equations determine the resonant frequency and radiation Q-factor for the fundamental structures. At the boundary between the two structure mode conversion takes place and the dominant mode becomes hybrid 11 . The overall field pattern within the device is the contribution of the ground plane, microstrip transmission line, quarter-wave stub, air gap, aperture, a stacked combination of lower rectangular and upper filleted dielectric resonator. These factors, when combined with an isolated DRA structure will load the antenna and shift the calculated resonant frequency, radiation Q-factor and radiation characteristics mainly cross-polarization levels.
Detail knowledge of the internal field structure and the coupling coefficient is mandatory to characterize the antenna. So the overall performance of a DRA depends upon generated modes, amount of coupling, and frequency response of the impedance. These quantities are difficult to determine without using any numerical techniques, Garg [10].
The radiation field pattern of 11 mode is similar to a short horizontal magnetic dipole. Due to system complexities there are no concrete solutions of the field patterns of a cylindrical dielectric resonator antenna. Magnetic wall boundary condition is suitable for the approximate calculation of the field at different points in space.
The point of excitation is said to be a sensitive point. The power will be real above the cutoff and imaginary below the cutoff. So we need to nullify the imaginary part by placing the source at the point of (i) maximum electric field (at λ/4) (ii) polarization matching (iii) 50Ω impedance matching (iv) minimum mode coupling & mode degeneracy. In the presence of the source, DRA can be characterized by Helmholtz's equation. Helmholtz's equation is the sun in electromagnetic from which electric and magnetic fields can be calculated from the electric and magnetic current density by taking the route of potential functions. The potential function can be calculated through scalar manipulations so that we can avoid complicated vector manipulation.
Electric and magnetic vector potentials are man-made quantities, Huang and Boyle [11]. From this output characteristic graph, it is found that radiation is basically concentrated in the broadside direction with = 0°. Though high conductivity infinite ground is placed at the bottom of the antenna but still it is found that there is considerable back radiation with front to back ratio of around -30 dB. It means power is mainly concentrated in the main lobe and low power is being wasted in the back lobe of the radiator, Mohanty and Mohapatra [13]. Further the radiation pattern is found to be symmetric along the z-axis.   [14]. This parameter plays a significant role in near field ultra-wideband communication where transmission range is relatively poor due to low transmitted power. DRA technology is still in its early stages of development, and more research is required to overcome some of the challenges associated with fabricating a large number of DRA elements and assembling them into an array. A wide variety of dielectric material is available based on its mechanical, electrical, and thermal properties. In the millimeter and microwave frequency, the operation tolerance control of the dielectric material is the most tedious, which leads to the difficulty to achieve high design accuracy. DRA uses an insufficient and un-matured numerical technique for its performance analysis (especially Rectangular DRA). It is required to improve RDRA's mathematical modeling to analyze its design characteristics. Hybrid DRA with active switching elements can be useful for beamforming and beam splitting techniques, Ali, Jamaluddin, Gaya and Rahim [15].

5.CONCLUSION
Wireless near field ultra-wideband communication has been undergoing tremendous growth in respectively. Though due to a double infinite ground plane this structure is somehow bulky but its electrical characteristics are found to be very robust. This antenna is suitable for modern high-speed ultra wideband internet of things and enhanced mobile broadband applications.

CONFLICT OF INTERESTS
The author(s) declare that there is no conflict of interests.