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

III. A REDUCED SIZED TWO-ELEMENT BBHA ARRAY
For satellite communications, usually high-gain antennas
are required. To this end, we have designed a two-element
array using the Macor-loaded BBHA, which is different from
the conventional dielectric loaded helical antenna array [7].
This is because the inter element spacing between the
BBHAs of 0.2� at the operating frequency of 2.4 GHz is
much smaller and there is no need for a ground plane. Hence,
the overall size of the Macor-loaded BBHA array is smaller
compared to the conventional dielectric loaded helical
antenna array. Fig. 16 shows the coordinate system employed
here for the two element BBHA.
�
y�
2�
1�
Fig. 16. Coordinate system of a two element BBHA.
The computed normalized radiation pattern of this array is
shown in Figs. 17 and 18 in different � planes. It is found
that when the two elements are placed very close together
with port excitations 180º out-of-phase with each other, the
gain increases significantly.
Fig. 17. Computed normalized radiation patterns for 1-element
BBHA and 2-element BBHA at � = 0º.
Fig. 18. Computed normalized radiation patterns for 1-element
BBHA and 2-element BBHA at � = 90º.
��
x
51
IV. CONCLUSION
This paper considers methods for the size reduction of the
helical antenna. There is little freedom to vary the pitch angle
and diameter of a helical antenna to reduce the size without
affecting the antenna performance. In addition, the ground
plane of a conventional helical antenna needs to be large
enough for good antenna performance.
The bifilar helical antenna (BBHA) is a suitable candidate
for size reduction, since it does not require a ground plane.
Introducing a suitable dielectric rod can further reduce the
size. It is found that the antenna size can be reduced by a
dielectric rod with higher permittivity, but at the expense of
the gain and the bandwidth.
In this paper size reductions in volume are achieved of a
BBHA with a Teflon dielectric and a Macor dielectric of 50%
and 70% respectively.
ACKNOWLEDGEMENT
This work was partly supported by the departmental vote of
the Department of Electrical and Computer Engineering,
National University of Singapore.
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