Digital Signal Processing Reference
In-Depth Information
Figure 4.70
Practical layout of a patch antenna for 915 MHz on a printed circuit board made
of epoxy resin (reproduced by permission of Trolleyscan, South Africa)
where
w
p
>
3
λ/
2:
120
λ
w
p
R
r
=
+
(ε
r
−
1
)
4
+
·
(
4
.
95
)
48
·
h
p
w
p
ε
r
+
1
2
If the patch antenna is operated at its resonant frequency the phase difference
between the patch edges
a
and
b
is precisely 180
◦
. Figure 4.69 shows the path of
the electrical field lines. At the entry and exit edges of the patch the field lines run
in phase. The patch edges
a
and
b
thus behave like two in-phase fed slot antennas.
The polarisation of the antenna is linear and parallel to the longitudinal edge
L
p
.See
Figure 4.71.
Due to the type of power supply, patch antennas can also be used with
circular
polarisation
. To generate circular polarisation, an emitter element must be supplied
with signals with a phase angle of 90
◦
at only two edges that are geometrically offset
by 90
◦
.
It is a relatively simple matter to amalgamate patch antennas to form
group anten-
nas
(Figure 4.72). As a result, the gain increases in relation to that of an individual
element. The layout shown in the figure comprises in-phase fed emitter elements. The
approximately
λ/
2 long patch elements are fed via almost non-radiative line sections
of around
λ/
2 in length connected in series, so that the transverse edges
a
-
a
or
b
-
b
of the patch element lie precisely wavelength
λ
apart. Thus the in-phase feed to the
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