Achieving high gain and large bandwidth using hybrid DR antennas to feed short horns Nasimuddin1 and Karu Esselle2 1Institute for Infocomm Research, Singapore 2Centre for Electromagnetic and Antenna Engineering Department of Electronic Engineering, Macquarie University Sydney, NSW 2109, Australia Email: nasimuddin@i2r.a-star.edu.sg, karu@ieee.org

Outline Introduction Gain-Enhancement using Surface Mounted Short Horns (SMSH) DRAs with SMSHs, designed for high gain Hybrid dilectric resonator on patch (DRoP) antennas with SMSHs, designed for high gain over wide bandwidth Conclusion

Introduction DRA has the advantages of low cost, compactness, high efficiency and a low profile. Traditional microstrip antennas and dielectric resonator antennas have gains around 6 dBi to 8 dBi.

To enhance the gain of DRAs, several methods have been employed: offset dual-disk dielectric resonators (DR) stacking parasitic DR with an air gap between radiating and parasitic DRs Use of composite layered high permittivity DR dielectric resonator loaded waveguide antenna with parasitic dielectric directors. In most cases the gain enhancement is limited or the structure is complex. We propose to integrate DRAs and hybrid antennas with surface mount short horns to enhance gain significantly.

Typical Structure of DRA integrated to a surface mounted short horn (SMSH) Role of DRA: Radiating Element Feed to SMSH   The SMSH is excited by the DRA. q Total Radiation is a combination of the radiation from DRA and the aperture of the SMSH. Supporting Material of SMSH also effect the radiation properties.

Design of SMSH for Maximum Gain A SMSH, with an aperture coupled DRA, has been designed to give maximum gain at 6.0 GHz. The distance (D) in the bottom of the SMSH from edge is less than or equal to o/4. Select the shortest height of SMSH to achieve high gain, for a given taper angle of SMSH. For this height, we investigate the gain variation with the taper angle of SMSH, to achieve highest gain.

Gain vs frequency for various SMSH heights

Gain variation with horn height around 6 GHz The gain increases with increasing height up to 0.15 o and then starts to decrease. Smallest possible horn height with optimum gain is 0.15o at 6 GHz. Maximum Gain for around 8.50 mm horn height

Gain vs frequency for different taper angles of SMSH

Fabricated DRA with SMSH   SMSH aperture is 48.1 mm  43.1 mm, ground plane is 60 mm  60 mm. The rectangular DRA is located symmetrically over a rectangular aperture-coupled slot in the ground, which excited by a 50- microstrip line feed. The rectangular DRA dimensions are: length = 12.8 mm; width = 7.3 mm; height = 6.35 mm; dielectric constant = 9.8; and loss tangent = 0.002. Aperture coupled feeding structure dimensions are: aperture length = 6.4 mm; aperture width = 1.24 mm; stub length (s) = 1.8 mm; microstrip width = 1.16 mm; substrate dielectric constant = 3.38; loss tangent = 0.0022 and thickness = 0.508 mm. Other horn dimensions are: area at lower (substrate) level = 27 mm  32 mm; taper angle = 45o: and height (H) = 8.1 mm (0.15o). The total height of structure is only 0.172 o i.e. 8.61 mm at 6.0 GHz. SMSH fabricated using solid Copper block

Return loss of DRA with SMSH Measured return loss (RL) at 5.95 GHz is -13.5 dB and -10 dB RL bandwidth is 3.2 %.

Measured gain of DRA alone is 3.7 dBi Gain Enhancement Gain at 5.95 GHz: Theoretical gain : 8.8 dBi Measured gain : 8.5 dBi Measured gain of DRA alone is 3.7 dBi For SMSH fabricated from copper block Gain enhancement due to SMSH is 4.8 dB

E-Plane Radiation Pattern at 5.95 GHz

H-Plane radiation pattern at 5.95 GHz

E-Plane radiation pattern at 6 GHz

H-Plane radiation pattern at 6 GHz

Another Prototype with DRA To verify the effect of supporting material we fabricated another SMSH with foam as supporting material. It gives a further gain enhancement of around 1.5 dB. Gain of aperture coupled DRA with different horns (metal support and foam support) Gain at 5.95 GHz: Measured Metal gain is 8.50 dBi Air gain is 9.84 dBi Theoretical Metal gain is 8.80 dBi Air gain is 9.4 dBi

Rectangular Dielectric Resonator on Patch with SMSH To increase the bandwidth, we replaced the DRA with a hybrid Dielectric Resonator on patch (DRoP) antenna Rectangular Dielectric Resonator on Patch with SMSH Feed Microstrip Line : W = 1.16 mm, stub length = 2.6 mm h = 0.508 mm, r = 3.38, tan = 0.0022 Lower coupling aperture: 8.4 mm  0.9 mm Upper coupling aperture: 6.8 mm  0.7 mm   Patch substrate: 12 mm  16 mm h = 0.762 mm, r = 2.45, tan = 0.001 Patch : 9.05 mm  8.1 mm DRA : 7.02 mm  12.0 mm h = 6.35 mm, r = 9.8, tan = 0.002 q

Fabricated DRoP with SMSH

Theoretical and Experimental results of the rectangular DRoP antenna with SMSH Measured Impedance bandwidth is 24.4% Theoretical and measured Gain

E & H-plane radiation patterns of the DRoP antenna with SMSH at 6 E & H-plane radiation patterns of the DRoP antenna with SMSH at 6.5 GHz E-Plane H-Plane

A Cross-Shaped Dielectric Resonator on Patch with SMSH

Comparison of rectangular and Cross-DR on patch: VSWR The measured 2:1VSWR impedance bandwidth of the rectangular DR on patch is 6.04 to 8.0 GHz (27.9%) and cross DR on patch is 23% (6.06GHz to 7.64GHz).

Comparison of rectangular and Cross-DR on patch: Gain The measured gain of both antennas is more than 9dBi within the 2:1 VSWR impedance bandwidth.

CONCLUSIONS A theoretical and experimental study has been conducted on achieving high gain with wideband performance. Various DRAs and hybrid (DRoP) antennas coupled to SMSHs have been considered. The DRoP antennas integrated to SMSHs have high gain, wide bandwidth and low profile. We achieved 28% 2:1 VSWR bandwidth, and gain over 9 dBi within this bandwidth, using a rectangular DRoP and SMSH. We demonstrated a 4.9 dB gain improvement at 5.95GHz with a SMSH fabricated from a copper block. The total height of the structure is only 8.6 mm, i.e. 0.172 o. The SMSH supporting material affects both the gain and radiation patterns. The measured results in general show good agreement with results obtained using CST Microwave Studio.