An Array of Four Cylindrical Dielectric Resonator Antenna for Wideband Monopole Like Radiation

An Array of Four Cylindrical Dielectric Resonator Antenna for Wideband Monopole Like Radiation

Vinay Kumar Prajapati 1, Amit Kumar2, Anamika3

GALGOTIAS UNIVERSITY

1(M. Tech-Communication Engineering, Galgotias University, INDIA) 2(Assistant Professor, SEECE, Galgotias University, INDIA)

3(M. Tech-Communication Engineering, Galgotias University, INDIA)

Abstract – The main aim to present this paper is to increase the bandwidth of the dielectric resonator antenna (DRA). A four element cylindrical dielectric resonator antenna (CDRA) array above the ground plane is introduced here. CDRA is very easy to design and excited with HE11 mode excited in each CDRA by centrally placed dielectric resonator in which TM01 mode excited. In this paper the effect of design parameters such as permittivity of materials, height of probe, radius of cylinders and the arrangement of dielectric layers investigated and the excited modes are also been confirmed by simulations. The simulation is performed on CST Microwave studio. The introduced cylindrical dielectric resonator antenna (CDRA) can offer an impedance bandwidth of ~23.08% for return loss below -10dB where frequency range is from 3.57 to 4.50 and resonance frequency is 3.98GHz with monopole like radiation pattern and it is stable in the passband with a gain of 1.560dB.

KEYWORDS- Dielectric Resonator (DR) ,Dielectric resonator antenna (DRA), Impedance Band Width (IBW), Cylindrical Dielectric Resonator Antenna (CDRA), Reflection Co-efficient (S11).

excited in each DRA element and the composite field patterns result in a uniform monopole-like radiation pattern over a wide bandwidth [15]. Some previous studies [16],

1. also used four element probe-fed cylindrical DRA (CDRA) but their array elements were arranged in a conventional way and their aim was to study the broadside linearly polarized radiation with shaped directional patterns using HEM11 mode.

   1. INTRODUCTION

      Dielectric resonator antennas (DRAs) have been proposed during the last two decades and significant advances are being made in developing them for many applications. One major aspect of the research with DRA is how to enhance the element bandwidth as evident from survey of open literature, e.g., [1][3]. For DRAs with broadside radiation, different shapes [4][6] and composite structures [1], [7],

      [8] have been investigated. For monopole type radiation pattern, only a few handful investigations with DRAs are available in open literature. The TM01 mode in coaxial feeding dielectric ring resonator was used to generate monopole-like radiation in [9]. The narrow impedance bandwidth of the structure in [9] was improved by introducing an air gap between the DRA and the ground plane in [10], [11]. Two broadband variants of dielectric ring resonator have recently been proposed in the form of coax-fed disc-ring [12] and rod-ring [13] combinations, respectively. An electric monopole-fed dielectric ring has been reported as an ultra wideband antenna in [14]. In this paper, we present a new approach with a four element cylindrical dielectric array where the HEM11 mode is

      Fig. 1. Four-element cylindrical DRA fed by a central coaxial probe.(a) Top view, (b) cross-sectional view at AA plane.

      From a practical point of view, it is easy to design the CDRA array excited with the dominant HEM11 mode than a ring resonator with mode as the latter one suffers from the inherent narrow bandwidth. The antenna geometry is shown in Fig. 1 and is described in Section II. Though this consists of more numbers of dielectric blocks compared to the previous designs, it shows some added advantages like

      simple design without much optimization of parameters, easy excitation of HEM11 mode in each CDRA element and planar geometry with compact size. The design parameters were determined using analytical formula and then optimizing through simulation studies as described in Section III. The excited resonant modes responsible for monopole-like radiation over a wide operating frequency are critically examined and discussed in Section III.

   2. THEORY

      The resonant frequency is one of the important parameters needed to design this dielectric resonator antenna. The approximate calculation of resonant frequency for the TM01 mode and HE11 mode for conventional cylindrical DRA can be done by following expressions.

      For TM01

      The resonant frequency calculated by-

      when low dielectric constant materials are used which is clear from equation (2) and (4), and it also depends upon the (a/h) ratio. In this paper we maintain (a/h) as 1 so that fractional impedance bandwidth is mainly function of dielectric constant. Here multilayer concept of dielectric is introduced in dielectric resonator antenna to enhance the fractional bandwidth. From relations (1) to (5), it is clear that if the dielectric constant of the material gets higher, both the resonant frequency and bandwidth will decrease and if dielectric constant gets lower, both the resonant frequency and bandwidth increases. So for multilayer DRA, lower dielectric constant section improves the bandwidth and higher dielectric constant section helps to lower the resonant frequency and vice-versa. Arrangement of different permittivity in a DR is decided based on simulation results. For exciting the TM01 mode in central DR probe coupling is used. The amount of coupling can be optimized by adjusting the probe height as well as optimal dielectric constant used for central dielectric resonator.

      PARAMETERS-

      Fr

      2a

      c

      ( r 2)

      3.282 a

      2h

      (1)

      h- height of probe, p=height of cdra,

      p= height of cylinders

      r1 = dielectric constant of cylinder 1,

      And radiated Q factor is calculated by-

      rad r

      Q 0.008721 0.888413e0.0397447

      (2)

      r 2 = dielectric constant of cylinder 2,

      r 3 = dielectric constant of cylinder3, dielectric constant of cylinder 4,

      r 4 =

      0.3 0.2 a 38 r

      = dielectric constant of cdra

      1

      h

      28

      cdra

      a

      a 4.32226 3.5 a

   3. THE ANTENNA CONFIGURATION

      9.498186

      2058.33

      e

      h

      h

      h

      A four-element cylindrical DRA (CDRA) is schematically shown in Fig. 1. Each candidate of the composite structure

      Where a, h, and r are radius, height and dielectric constant respectively of dielectric resonator.

      For HE11

      The resonant frequency calculated by-

      is of height p , radius a and different relative permittivity

      r1 , r 2 , r 3 and r 4 and they are packed together in a compact way on a metallic ground plane (GP). The array is centrally excited by a coaxial probe of height h and radius r0 which itself is surrounded by a small dielectric rod

      of radius r, height p and relative permittivity rcd . It

      6.324

      a

      a 2

      (3)

      actually touches the surfaces of all four CDRAs. Since with,

      Fr

      a

      2 0.27 0.36 2h 0.02 2h

      the small dielectric rod acts as a modified probe touching

      r

      each CDR and helps in launching fields from probe to

      Q-factor given by-

      a 1 a 2

      CDRAs. From simple calculation it can be shown that the radius of the central dielectric rod r=(2-1)a is a limiting

      205

      1.3 a

      2h 80 h

      (4)

      value when all four CDRAs come closest to each otherand

      Qrad 0.01007 r 1 100e

      h

      The radiation Q-factor can be used to estimate the fractional impedance bandwidth of a DRA-

      maintain physical contacts amongst themselves as shown in Fig.1. This is the design value for the proposed antenna. A probe touching a CDRA surface is suitable for exciting the dominant HEM11 mode [18], and thus the feed arrangement in our proposed antenna can easily excite each

      Bandwith (BW )

      VSWR 1

      (5)

      CDRA element with the dominant HEM11 mode. The

      Qrad

      VSWR

      resulting electric field in individual CDRA is linearly polarized as described in [19]. When four CDRAs, as in Fig. 1, are simultaneously excited, the composite electric field

      In order to achieve large fractional impedance bandwidth

      the Q-factor should be less and this can be possible only

      patterns look like that shown in Fig. 9(a), obtained from simulation data. It is apparent that the electric field

      components lying on XY-plane face their counter vectors and thus cause null radiation along the broadside of the antenna. Rather, the resultant electric fields are polarized along Z-axis and thus lead to a vertically polarized radiation surrounding the radiating structure like a quarter wave electric monopole. Since both the monopole and the composite CDRA structure effectively produce identical radiation fields, uniform monopole-type pattern can be achieved over the full matching bandwidth.

   4. DESIGN AND RESULTS

Fig 2. Simulated return loss of four elements CDRA. [a = 2

For studying the characteristics of the proposed antenna our

mm, p 10mm, p 12mm

and h 8mm , r = .828

initial considerations for each CDRA were,

r1 =9.4, r 2 =9.9, r 3 =8.6, r 4 =10 and , rcd =15, a=2mm and p=12mm HEM11,and and the mode resonant

mm,

rcd

15 , ro

0.1mm and hp= 8 mm]

frequency in an individual element was calculated as 3.91

GHz using the design formula [20]

TABLE.I IMPEDANCE BANDWIDTH AT DIFFERENT DIELECTRIC CONSTANT

OF CYLINDERS AND CDRA ARRANGEMENT

C a a 2

F r

2a

1.71 0.1578

h h

(6)

and h 8mm,

r1

1

r=.828 mm, h

3mm

15 , r

0.1mm

Where C is the velocity of light in free space. The value of

rcd was chosen on the basis of commercially available high dielectric constant material and the resulting optimum input impedance matching was studied using Ansofts microwave studio cst . For simulating the structure we have used the wave port mode of excitation for the coaxial feed and the radiation boundary was fixed at a distance of, being the free space wavelength corresponding to the lowest component of the frequency sweep. Fast sweep mode has been employed to generate the results and a few samples were verified using the results obtained from discrete sweep mode. Good agreement was revealed in each case. Maximum S

1. (S-parameter) value of 0.01 was chosen for terminating the adaptive solution and this gives accurate simulation results. Some representative results for different antenna parameters are shown through Figs. 35. The height if the central dielectric close to that of each CDRA shows good impedance matching and as such has been chosen for the present studies. The effect of the relative permittivity of the central dielectric rod is shown in Fig. 3.

2. In the table-1 we showed the possible impedance bandwidth at different dielectric constant of four cylinders and central dielectric resonator antenna

   c rcd o

   Cylind er1 ( r1 )	Cylinde r2 ( r 2 )	Cylinde r3 ( r 3 )	Cylinder 4 ( r 4 )	CDRA ( cdra )	Impedanc e Bandwidt h (%)
   9.4	9.9	8.6	10	15	23.08

   Fig. 2(b). Simulated return loss of four element CDRA for different dielectric constant of the central DRA [a = 2 mm, p 10mm, p 12mm and h 8mm , r = .828 mm,

   (CDRA).

3. And in the table -2 we have shown the possible bandwidth and impedance bandwidth at different dielectric constant of central dielectric resonator antenna (CDRA).

   , rcd

   15 , ro 0.1mm ]

   TABLE II. BANDWIDTH AND IMPIDANCE BANDWIDTH AT DIFFERENT DIELECTRIC CONSTANT OF CDRA

   [a = 2 mm, p 10, mm, p 12mm and h 8mm, r =

   10dB) with monopole like radiation pattern which is stable in the pass band with the gain 1.56 dB at 3.98 GHz. The proposed antenna is suitable for C-band application like in WiMAX.

   Dielectric Constant( cdra )	Bandwidth(GHz)	Impedance F F Bandwidth H L % FC
   cdra = 12	0.91	21.66
   cdra = 13	0.92	22.21
   cdra = 14	0.91	20.9
   cdra = 15	.93	23.08

   .828 mm, hc 3mm rcd

   15 , ro 0.1mm]

   REFERENCES

   1. A. Petosa, A. Ittipiboon, and Y. Antar, Broadband dielectric resonator antennas, in Dielectric Resonator Antennas, K.M. Luk, K. W. Leung, and R. S. Press, Eds. Hertfordshire, U.K.: Research Studies Press Ltd., 2003.

   2. A. A. Kishk, Experimental study of broadband embedded dielectric resonator antennas excited by a narrow slot, IEEE Antennas Wireless Propag. Lett., vol. 4, pp. 7981, 2005.

   3. R. Chair, A. A. Kishk, and K. F. Lee, Wideband simple cylindrical dielectric resonator antennas, IEEE Microw. Wireless Compon. Lett., vol. 15, no. 4, pp. 72417243, Apr. 2005.

   4. Amit Kumar, Utkarsh Besaria, Rajeev Gupta Galgotias University, S R Group of Institution, MNNIT Allahabad IOSR Journal of Electronics and Communication Engineering (IOSR- JECE) e-ISSN: 2278- 2834,p- ISSN: 2278-8735. Volume 6, Issue 4 (May. – Jun. 2013)

   5. J. A. Evans, M. J. Ammann, and Z. Wu, A novel hybrid inverted-L antenna with wide bandwidth, presented at the Inst. Elect. Eng. Int. Conf. Antennas and Propagation, Mar. 2003.

      The optimal design parameters are for the four element CDRA is a = 2 mm, p 10, mm, p 12mm and h 8mm, r = .828 mm, cdra 15 , ro 0.1mm The return loss below 10dB where frequency range is from 3.57 GHz to 4.50 GHz and resonance frequency is

      4.04 GHz shown in Fig. 3, corresponding to that the percentage impedance bandwidth of ~23.08% has been obtained.

      The Far field radiation pattern at f =3.98 GHz can be shown in Fig4 which shows a maximum gain of 1.507 dBi.

      Fig.3. 3-D view simulated gain of the four element cylindrical dielectric [a=2mm, mm p 10mm, p 12mm and h 8mm , r =

      .828 mm, cdra 15 , ro 0.1mm ]

4. CONCLUSION

The wide four element cylindrical dielectric resonator antenna (CDRA) is proposed with coaxial probe excitation. It is simply excited by central DR which is located in the center of three element arrangement where TM01 mode is excited in central DR and HE11 mode is excited in each CDRA element. The mode patterns have been confirmed by H-field distribution in central DR and each CDRA. The return loss curve shows 36% impedance bandwidth (S11 <

1. A. A. Kishk, Y. Yin, and A. W. Glisson, Conical dielectric resonator antennas for wideband applications, IEEE Trans. Antennas Propag., vol. 50, no. 4, pp. 469474, Apr. 2002.

2. K. W. Leung, K. M. Luk, K. Y. Chow, and E. K. N. Yung, Bandwidth enhancement of dielectric resonator antenna by loading a low profile dielectric disk of very high permittivity, Elect.Lett., vol. 33, no. 9, pp. 725726, Apr. 24, 1997.

3. A. A. Kishk, X. Zhang, A. W. Glisson, and D. Kajfez, Numerical analysis of stacked dielectric resonator antennas excited by a coaxial probe for wideband applications, IEEE Trans. Antennas Propag., vol. 51, no. 8, pp. 19962006, Aug. 2003.

4. R. K. Mongia, A. Ittipiboon, P. Bhartia, and M. Cuhaci, Electric monopole antenna using a dielectric ring resonator, Elect. Lett., vol. 29, no. 17, pp. 15301531, Aug. 19, 1993.

5. S. M. Shum and K. M. Luk, Characteristics of dielectric ring resonator antenna with an air gap, Elect. Lett., vol. 30, no. 4, pp. 277278, Feb.17, 1994.

6. G. P. Junker, A. A. Kishk, A. W. Glisson, and D. Kajfez, Effect ofair- gap on cylindrical dielectric resonator antenna operating in TM mode, Elect. Lett., vol. 30, no. 2, pp. 9798, Jan. 20, 1994.

7. S. W. Ong, A. A. Kishk, and A. W. Glisson, Wideband disc-ring dielectric resonator antenna, Microw. Opt. Technol. Lett., vol. 35, no. 6, pp. 425428, Dec. 2002.

8. S. H. Ong, A. A. Kishk, and A. W. Glisson, Rod-ring dielectric resonator antenna: research articles, Int. J. RF and Microwave Computer-Aided Engineering, vol. 14, no. 6, pp. 441446, Nov. 2004.

9. M. Lapierre, Y. M. M. Antar, A. Ittipiboon, and A. Petosa, Ultra wideband monopole/dielectric resonator antenna, IEEE Microw. Wireless Compon. Lett., vol. 15, no. 1, pp. 79, Jan. 2005.

10. D. Guha and Y. M. M. Antar, Four-element cylindrical dielectric resonator array: broadband low profile antenna for mobile communications, presented at the Proc. XXVIIIth General Assembly of the URSI, New Delhi, India, 2005.

11. G. Drossos, Z. Wu, and L. E. Davis, Four-element planar arrays employing probe-fed cylindrical dielectric resonator antennas, Microw. Opt. Technol. Lett., vol. 18, no. 5, pp. 315319, 1998.

12. G. Drossos, Z. Wu, and L. E. Davis, Linear array consisting of four probe-fed cylindrical dielectric resonator antennas, Microw. Opt.Technol. Lett., vol. 18, no. 6, pp. 367370, 1998.

13. G. P. Junker, A. A. Kishk, and A. W. Glisson, Input impedance of dielectric resonator antennas excited by a coaxial probe, IEEE Trans. Antennas Propagat., vol. 42, no. 7, pp. 960966, Jul. 1994.

14. D. Kajfez, A. W. Glisson, and J. James, Computed modal field distributions for isolated dielectric resonators, IEEE Trans. Antennas Propag., vol. 32, no. 12, pp. 16091616, Dec. 1984.

15. A. A. Kishk, A. Ittipiboon, Y. M. M. Antar, and M. Cuhaci, Slot excitationof the dielectric disk resonator, IEEE Trans. Antennas Propag., vol. 43, no. 2, pp. 198201, Feb. 1995

16. Raghvendra Kumar Chaudhary1, Kumar Vaibhav Srivastava2, Animesh Biswas3Department of Electrical Engineering Indian Institute of Technology Kanpur, INDIA 208016 Asia-Pacific Conference on Applied Electromagnetics (APACE 2010)

17. A. A. Kishk, Wide-band truncated tetrahedron dielectric resonator antenna excited by a coaxial probe, IEEE Trans. Antennas Propag., vol. 51, no. 10, pp. 29132917, Oct. 2003.

18. Debatosh Guha, Senior Member, IEEE, and Yahia M. M. Antar, Fellow, IEEE IEEE Transaction on Antennas and Propagation,

    Vol. 54, No. 9, September 2006

19. Raghvendra Kumar Chaudhary1, Kumar VaibhavSrivastava2,AnimeshBiswas3Department of Electrical Engineering Indian Institute of Technology Kanpur, INDIA 208016 Asia-Pacific Conference on Applied Electromagnetics (APACE 2010)