mirror of
git://projects.qi-hardware.com/ben-wpan.git
synced 2024-11-30 02:35:20 +02:00
36 lines
1.4 KiB
Plaintext
36 lines
1.4 KiB
Plaintext
|
Revised via spacing
|
||
|
|
|
||
|
|
|
||
|
|
Tests of PCB antenna performance revealed a sharp drop in received power
|
||
|
|
at 2440 MHz, roughly the middle of the antenna's frequency range.
|
||
|
|
|
||
|
|
This drop can be seen in the red (ant-120A0) and blue (ant-120B2) curve
|
||
|
|
of [1].
|
||
|
|
|
||
|
|
The test setup consisted of an atusb board with discrete balun and an
|
||
|
|
antenna with only a single ground plane as the sender, and a set of
|
||
|
|
antennas (see directory ../ants/) connected to an USRP2+XCVR2450 as the
|
||
|
|
receiver. The receiving antennas had two ground planes, connected with
|
||
|
|
vias spaced roughly 5 mm apart. (See ECN0004.)
|
||
|
|
|
||
|
|
According to figure 1 of [2], the vias connecting the ground planes at
|
||
|
|
the edge of the antenna should be spaced at around 50 mil, four times
|
||
|
|
closer than 5 mm.
|
||
|
|
|
||
|
|
After adding more vias to one of the receiving antennas, sensitivity
|
||
|
|
improved drastically, as shown in the purple (ant-120C0) curve of [1].
|
||
|
|
The same improvement could be observed in a set of ten antennas that
|
||
|
|
all had shown the drop before the addition of more vias.
|
||
|
|
|
||
|
|
The remaining drop of about 10 dB in the middle of the spectrum is
|
||
|
|
probably caused by the sending antenna. A commercially produced 2.54
|
||
|
|
GHz antenna at the receiver showed a similar drop when used with the
|
||
|
|
same sender.
|
||
|
|
|
||
|
|
[1] http://downloads.qi-hardware.com/people/werner/wpan/three-ants.png
|
||
|
|
[2] http://www.ember.com/pdf/120-5052-000_Designing_with_a_PCB_Antenna.pdf
|
||
|
|
|
||
|
|
|
||
|
|
Conclusion: place vias at the edge of the ground plane facing the
|
||
|
|
antenna with a spacing no larger than 50 mil.
|