DESIGN AND SIMULATION OF DIELECTRIC RESONATOR ANTENNA (DRA) WITH CO-AXIAL PROBE FOR WIRELESS APPLICATION AND SIMULATION OF DIELECTRIC RESONATOR ANTENNA (DRA) WITH CO-AXIAL PROBE FOR WIRELESS APPLICATION.”

: In this paper a Dielectric resonator antenna (DRA) consists of a rectangular geometry and a printed rectangular patch on top of it in order to achieve better performance and operation without significant increase in antenna size. DRA structure is proposed at a height of 2 mm from the ground plane and patch incorporated at the height of 3.638 mm. This work is mainly focused on increasing the potential parameters of DRA and analyze high frequency band. The proposed antenna is designed to resonate at 25 GHz and by varying the DRA size ‘a, then the simulated results shows variation in Return Loss. The impedance bandwidth of the DRA (23.417 GHz-26.961 GHz) and return loss is 26.543951dB.The proposed DRA is analyzed and design using CST-MSW (2010). The simulated result shows the Far field, smith chart. We have estimated the wavelength, frequency, bandwidth, Return loss and directivity .


Introduction
Dielectric resonators have established great interest in current years for their latent applications in microwave and millimeter wave communication systems. They have been extensively used as a tuning component in shielded microwave circuits such as filters, oscillators, and cavity resonators. With an suitable feed arrangement, they can also be used as antennas, and they offer efficient radiation [1]. Also micro strip antenna at higher microwave band applications such as satellite communication and radar application usually offers high metallic losses. So, the DRA can be a good alternative for these requirements as it overcomes the problem of high losses due to minimum surface wave losses. DRA generally made up of temperature stable dielectric materials of high dielectric constants (10-100) for microwave applications. Resonant frequency of DRA can be easily varied by suitably choosing the dielectric constant of the resonator material and its dimensions [2]. DRAs of different shapes such as disc, hemispherical, rectangular, and ring have been presented in the literature [3], [2], [4], [5]. The rectangular dielectric resonators are preferred because they are easy to fabricate and offer more degree of freedom to control the resonant frequency and quality factor. Many investigations have been conducted to enhance bandwidth and gain of DRA [6], [4], [7], [8] but front to back ratio (FBR) of DRA has not been presented so far. Micro strip fed DRA act as a magnetic dipole and suffers with problem of back lobe. So in this paper reflector plane is used to improve the FBR.

Dra Structure With Co-Axial Probe
When a dielectric resonator is not entirely enclosed by a conductive boundary, it can radiate, and so it becomes an antenna. Figure 1.1 shows the geometry of the proposed rectangular DRA (ε r 1=11.9) with size of a*a*h. A printed patch antenna with size of b*b on a substrate (ε r 2= 2.2) is placed on the top of the dielectric resonator. The DRA is fed using a coaxial probe, with a distance x 0 from the center of the DRA. The height of the feed probe above the ground plane is l. By optimizing the structure parameters, the DRA and the patch antenna can resonate at two different frequencies. The rectangular dielectric resonator provides the first resonance frequency f1 while the patch antenna resonates at the second frequency f2. In addition, this way of attaching the DRA presented the advantage of allowing a convenient reuse of the same feeding circuit with various dielectric resonators.
Where "a" is the length and breadth of the DRA, "a"= 2.5mm Where "h" is the height of DRA, h=2.0mm and "b" is the length and breadth of the patch, b= 2.0mm.
The feed position is x 0 distance away from the centre of x-axis. The probe is inserted up to "l" distance in DRA. Top-view of proposed DRA is shown in Figure 1

Design Parameters of DRA Structure
We have estimated the Bandwidth, Return loss, Frequency, Directivity, Wavelength and Radiation efficiency.

1) Directivity -:
The directivity is defined based on the total power radiated by the antenna of interest. 2) Bandwidth-: Bandwidth of an antenna is the range of frequency within which its performance of certain characteristics conforms to a specified criterion. Such antenna characteristics may be input impedance, radiation pattern, beam width, polarization, side lobe level, gain, beam direction, and so on. The bandwidth is usually expressed as the ratio between the upper and lower frequencies with acceptable performance. The frequency slot is shown in Figure 1 It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency 5) Far-field-: In the reactive near-field region, at close proximity to the antenna, reactive field predominates. In the far-field (Fraunhofer) region, roughly at r > 2d 2 / λ with d the scale size of antenna, angular field distribution is essentially independent of the distance from the antenna. The far-field is shown in Figure 6. In the far-field region, the dominant electric field components usually lie in a plane passing through the antenna. The far-field thus includes radio waves and microwaves several wavelengths from most types of antennas, as well as all the shorter-wave EM radiation in the electromagnetic spectrum (infrared, light, UV, X-rays, etc.).

Varying Dra Sizes
The DRA is investigated first by varying DRA length and breadth and its simulated result is shown in respective figure. Simulated results are based on Return Loss at different frequencies.
By varying size of DRA i.e., "a", we calculated improved Return Losses which covers frequency. We have estimated different Return Loss at different value of "a. The simulated waveform is shown in Figure 1.8 we have take a =1.9mm the Return loss is -31.059 at Frequency 33.31 GHz. The simulated waveform is shown in Figure 1.9 we have take a=2.0mm the Return loss is -33.4916 at Frequency 31.75 GHz.   The simulated waveform is shown in Figure 1.11 we have take a=2.2mm the Return loss is -28.718102 at Frequency 28.81 GHz. The simulated waveform is shown in Figure 1.12 we have take a=2.3mm the Return loss is -27.823662 at Frequency 27.43 GHz.  The simulated waveform is shown in Figure 1.14 we have plotted the graph at different values of "a" and the combined Return Loss graph is shown in Figure 1.14.

Conclusion
In DRA which is composed of a probe-fed rectangular dielectric resonator and a rectangular patch antenna on top of it. We have experimentally investigated the device performance and parameters such as Return Loss, Bandwidth, Wavelength, Directivity and Radiation Efficiency. Such a hybrid antenna with compact size can provide sufficient impedance band-width and improved Return Loss and much improved Bandwidth across the desired frequency bands, which are very attractive for WLAN applications. In addition, this way of attaching the DR presented the advantage of allowing a expedient reuse of the same feeding circuit with various dielectric resonators. In comparison with micros trip radiating elements, DRA radiators have better radiation efficiency and operate over wider bandwidths. An outstanding property of DRA is their intrinsically low loss. At microwave frequencies, the losses due to the skin effect on micro strip antennas may become significant. In distinguish, there are no conductors present on DRA, and the dielectric losses are much smaller than conductor losses.