SAMPE Journal - July/August 2017 - 31
Article
Radiation Properties Measurements
To characterize the antenna
performance of the textile antenna,
the return loss and radiation pattern,
as the most important parameters
were required to be measured. The
return loss of an antenna could be
expressed as:
RL=-20log|G|
Figure 1. The schematic of the proposed broadband microstrip antenna.
determined by using combination
of transmission line theory and
electromagnetic simulation software
HFSS. The length (L) and width (W)
of the antenna radiation patch was
initially obtained from the following
equations11:
[1]
[2]
where c is the speed of light; f is the
resonant frequency of the antenna;
er is the dielectric constant of the
substrate; ee is the effective dielectric
constant; DL is the equivalent
radiation gap length. Moreover,
ee and DL were calculated by the
following formulas:
[3]
[4]
where h is the thickness of the
substrate. The accurate dimensions of
the radiation patch were determined
utilized HFSS and the patch
dimensions are listed in Table 1.
Experimental
Fabrication of the Antenna
In this study, two broadband
antennas with copper pasted and
screen printed radiation patch were
fabricated. Nine layers of E-glass
plain-weave fabrics were adopted
to fabricate the substrate of the
antenna; the fabric weight was 160g/
m2 and the warp and weft density
was 12 end/cm. The ground planes
of the antennas were made up of
copper foil with thickness of 0.05mm
and the radiation patches were
fabricated with copper foil and silver
ink respectively for comparison. The
copper foils were directly adhered on
the top and bottom glass fabrics before
resin infiltrate as radiation patch and
ground plane. The printed radiation
patch was cured in a 150°C vacuum
oven for 50 minutes after screen
printing process. Then, the radiation
patch, ground plane and the nine
layers of glass fabric were integrated
together as composite antennas
using vacuum assistant resin transfer
molding (VARTM). Epoxy resin was
used in the composite antennas. The
photographs of the copper pasted
broadband antenna (CPBA) and
silver ink printed broadband antenna
(SPBA) are illustrated in Figure 2.
where RL is the return loss in
operating frequency and G is the
reflection coefficient. In this study, the
return loss was measured by 8722ES
Microwave Network Analyzer. The
radiation pattern of an antenna is a
plot of the gain characterizing the
far-field radiation performance at
a specific frequency. The radiation
pattern was measured in anechoic
chamber using HP 8510C Antenna
Test System. The antenna was fixed
with a termination of the section port,
and then the signal of the vertical
polarization was transmitted to the
antenna. The radiation pattern was
obtained from the signal received by
the 360° rotating antenna.
Mechanical Properties Measurements
The tensile tests and bending test
of yarns were performed per Chinese
National Standard Testing Method
GB/T 1040.4-2006 and GB/T 14492005 respectively. Tensile tests for
composites were performed on a
QJ-212C universal testing machine
(Shanghai Qingji Instrumentation
Technology Co., Ltd., Shanghai,
China) with a crosshead speed of 2
mm/min, a gauge length of 50 mm
and a distance between the grips of
150 mm. The tensile strength (sT)
is calculated with the following
equation:
Table 1. Dimensions of the proposed broadband microstrip antenna. (Unit: mm).
SAMPE Journal, Volume 53, No. 4, July/August 2017
31
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