Ground Plane Size, Resonant Frequency and Soldering Notes for GPS Patch Antennas
1307038
1307038
Application Note
Ground Plane Size , Resonant Frequency and Soldering
Notes for GPS Patch Antennas
Patch Environment
The size of the ground plane the patch antenna is mounted on, and
the protective enclosure that it is placed in, greatly effect the
performance of the antenna. The size of the ground plane changes
antenna gain and impedance. Antenna impedance is effected by
the type of plastic used, its thickness, and the air gap spacing
between the patch and the housing. Table 1 shows the optimized
air gap and plastic thickness for various ground plane sizes. This
chart is based on general purpose ABS housing, and will vary for
different materials.
Table 1 Plastic Thickness for Various Size Antenna
Ground Planes
Ground Plane Size
1.375
2.0
3.0
4.0
Air Gap Spacing
.045
.045
.045
.045
Plastic Thickness
.070
.080
.085
.090
Out of Band Rejection
The ANPC-129 and ANPC-13X series of GPS antennas provide
filtering for unwanted signals outside of the GPS pass-band. The
ANPC-13X series has been designed with a 2 pole ceramic filter.
The ANPC-129 series has no filter component, but provides
significant out of band rejection because of its inherent band-pass
impedance qualities.
Antenna
ANPC-129 series
ANPC-130 (1)
ANPC-134 (5)
+/- 50 MHz
> -6 dB
>-25 dB
>-27 dB
500<F<1400 MHz
>-20 dB
>-42 dB
> -52 dB
Table 2 Out of Band Rejection Specification
Soldering Directions for ANPC-129
The ANPC-129 is shipped with a direct solder pen designed for
PC board connections. Coaxial cable can be soldered to the back
of the patch if proper care is taken to prepare the cable and make
the solder connection (see Diagram). We recommend RG-316
coaxial cable because of its Teflon core. It is critical to the
impedance match that the .04鈥?dielectric gap (see Diagram) be
maintained. If using a lower grade coaxial cable, use even more
care in soldering to prevent the core from expanding under the
heat of the soldering iron; thermal expansion of the core beyond
.04鈥?will cause a degradation in input impedance.
.400
.040
.150
Outer Jacket
Note: unit of measure in inches
Patch Resonant Frequency
M/A-COM has carefully designed the patch antenna to resonate 4
MHz higher than the GPS frequency of 1575.42 MHz. We did this
knowing that GPS OEMs would always enclose the patch antenna
in some type of plastic housing. Plastic enclosures typically cause
a downward shift in resonant frequency of the antenna. The
amount of frequency shift is related to the dielectric constant of
the housing material and its thickness. (See Table 1 above for the
recommended housing parameters.)
Environmental Capability
The ANPC-129 and ANPC-13X series of antennas have been
qualified to a number of General Motors Engineering Standards
and passed the Electronic Module Validation Test.
Center Conductor
Braid
Testing
Our comprehensive testing includes thermal shock, moisture sus-
ceptibility, random vibration, salt fog, mechanical shock, drop test,
power temperature cycling, low temperature endurance, biased
humidity, electrostatic discharge, and immunity to radiated elec-
tromagnetic fields. For specific test information, see our applica-
tion note entitled:
GPS Antenna Considerations for Automotive
Applications.
Pin Output
V2.00
M/A-COM Division of AMP Incorporated
s
North America: Tel. (800) 366-2266, Fax (800) 618-8883
s
Asia/Pacific: Tel.+85 2 2111 8088, Fax +85 2 2111 8087
s
Europe: Tel. +44 (1344) 869 595, Fax+44 (1344) 300 020
www.macom.com
AMP and Connecting at a Higher Level are trademarks.
Specifications subject to change without notice.
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