Digital Signal Processing Reference
In-Depth Information
Due to the popularity of the Yagi - Uda antenna both as an antenna for radio and
television reception and also in commercial radio technology, there is a huge amount
of literature on the operation and construction of this antenna design. Therefore, we
will not deal with this antenna in more detail at this point.
4.2.5.8 Patchormicrostripantenna
Patch antennas
(also known as
microstrip
or
planar antennas
) can be found in many
modern communication devices. For example, they are used in the latest generations
of GPS receivers and mobile telephones, which are becoming smaller all the time.
Thanks to their special construction format, patch antennas also offer some advantages
for RFID systems.
In its simplest form, a patch antenna comprises a printed circuit board (e.g. Teflon
or PTFE for higher frequencies) coated (i.e. metallised) on both sides, the underside of
which forms a continuous ground (Kraus, 2000). On the top there is a small rectangle,
which is supplied via a microstrip feed on one side, feeders through the base plate
(see Figure 4.71) or capacitive coupling via an intermediate layer (aperture coupled
patch antenna; see Kossel (n.d.), Fries and Kossel (n.d.)). Planar antennas can therefore
be manufactured cheaply and with high levels of reproducibility using PCB etching
technology (see Figures 4.69 and 4.70).
The length
L
p
of the patch determines the resonant frequency of the antenna. Under
the condition
h
D
≤
λ
:
λ
2
−
h
D
L
P
=
(
4
.
93
)
Normally the substrate thickness
h
D
is 1 - 2% of the wavelength.
The width
w
p
influences the resonant frequency of the antenna only slightly, but
determines the
radiation resistance R
r
of the antenna (Krug, 1985). Where
w
p
<λ/
2:
λ
w
p
2
90
R
r
=
+
(ε
r
−
1
)
4
+
·
(
4
.
94
)
ε
r
+
1
2
48
·
h
p
w
p
a
b
L
p
a
b
W
p
E
h
D
L
p
Ground
Figure 4.69
Fundamental layout of a patch antenna. The ratio of
L
p
to
h
D
is not shown to
scale
Search WWH ::
Custom Search