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

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
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