Design of a Small Size Dielectric Loaded Helical Antenna for ...

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Fig. 2. Computed and measured return loss for 3-turn BBHA Fig. 3. Computed and measured normalized radiation pattern for 3-turn BBHA at 2.4 GHz Fig. 4. Computed and measured AR for 3-turn BBHA Fig. 5. Computed and measured normalized gain for 3-turn BBHA B. 3-turn BBHA loaded with Teflon A Teflon rod (�r = 2.1) is introduced inside the helix, which reduces the antenna size by 50% in volume. The size of the copper strips is optimized using HFSS to 20 mm × 10 mm. The diameter of the antenna is reduced to 26 mm while the spacing between each turn reduces to 20 mm. The pitch angle is 13.76°. Fig. 6 shows that the antenna still exhibits a return loss of at least 10 dB from 2.2 GHz onwards. It exhibits good directivity with an HPBW of 70° and a wide gain bandwidth of about 800 MHz, as shown in Figs. 7 and 8 respectively. 49 The gain at 2.4 GHz is 3.27 dBic. The highest gain is 3.98 dBic at 2.6 GHz. The computed gain bandwidth of an unloaded antenna of the same size shifts to the higher frequencies as compared to the antenna loaded with the dielectric. The AR bandwidth is about 400 MHz, as shown in Fig. 9. The computed AR bandwidth of an unloaded antenna of the same size shifts to higher frequencies. Fig. 6. Computed and measured return loss for 3-turn BBHA loaded with Teflon Fig. 7. Computed and measured normalized radiation pattern for 3-Turn BBHA loaded with Teflon at 2.4 GHz Fig. 8. Computed and measured normalized gain for 3-turn BBHA loaded with Teflon Fig. 9. Computed and measured AR for 3-turn BBHA loaded with Teflon Authorized licensed use limited to: National University of Singapore. Downloaded on May 03,2010 at 14:47:24 UTC from IEEE Xplore. Restrictions apply.
C. 3-turn BBHA loaded with Macor The dielectric Macor has a permittivity of 5.8 at 2.4 GHz. With its introduction, the dimensions of the antenna change to a diameter of 20 mm and a spacing between each turn of 20 mm. The size of the copper strips is optimized to 20 mm × 5 mm. The pitch angle is 17.7°. The antenna volume is only 30 % of the original antenna. The antenna has a return loss of at least 10 dB from 2.2 GHz onwards, as shown in Fig. 10. While the antenna retains its directivity, the back lobe has increased substantially. The HPBW of the antenna is 80° (as shown in Fig. 11) which is 10° wider than the antenna loaded with Teflon. The gain bandwidth is reduced with the introduction of the higher permittivity dielectric load. The measured gain at 2.4 GHz is 2.6 dBic. The highest gain is 3.7 dBic at 2.6 GHz. This gain is lower than the gain of the antenna loaded with Teflon, as shown in Fig 12. The gain bandwidth shifts to higher frequencies for the antenna of the same size without the dielectric. The AR bandwidth is about 400 MHz and it shifts to higher frequencies when the antenna is not loaded with the dielectric, as shown in Fig. 13. Fig. 10. Computed and measured return loss for 3-turn BBHA loaded with Macor Fig. 11. Computed and measured normalized radiation pattern for 3-turn BBHA loaded with Macor at 2.4 GHz Fig. 12. Computed and measured normalized gain for 3-turn BBHA loaded with Macor 50 Fig. 13. Computed and measured AR for 3-turn BBHA loaded with Macor D. Performance Comparison The dimensions and performance of the three antennas are compared in Table I, Figs. 14 and 15. It is found that there is no change in the gain bandwidth when the antenna size is reduced and loaded with Teflon. However, the gain bandwidth becomes narrower when the antenna is loaded with Macor, while the antenna size is reduced further. The AR bandwidth becomes smaller as the permittivity increases while the antenna size reduces. The gain at 2.4 GHz reduces when the permittivity increases. TABLE I DIMENSIONS OF EACHBBHA LOADED WITH DIFFERENT DIELECTRIC Dielectric �r Diameter Spacing between each turn Size compared to unloaded BBHA Air 1 32 mm 25 mm 100 % Teflon 2.1 26 mm 20 mm 50 % Macor 5.67 – 6.03 20 mm 20 mm 30 % Fig. 14. Measured AR for 3-turn BBHA loaded with dielectric of different permittivity Fig. 15. Measured gain for 3-turn BBHA loaded with dielectric of different permittivity Authorized licensed use limited to: National University of Singapore. Downloaded on May 03,2010 at 14:47:24 UTC from IEEE Xplore. Restrictions apply.
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Design of a Small Size Dielectric Loaded Helical Antenna for ...

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