Root/ecn/ecn0007.txt

Source at commit f87bdce41f2b24efa3de561ecaa1ff2fcbe78906 created 8 years 9 months ago.
By Werner Almesberger, atusb/fw/Makefile: added auxiliary Flash programming target (for development)
1Revised via spacing
2
3
4Tests of PCB antenna performance revealed a sharp drop in received power
5at 2440 MHz, roughly the middle of the antenna's frequency range.
6
7This drop can be seen in the red (ant-120A0) and blue (ant-120B2) curve
8of [1].
9
10The test setup consisted of an atusb board with discrete balun and an
11antenna with only a single ground plane as the sender, and a set of
12antennas (see directory ../ants/) connected to an USRP2+XCVR2450 as the
13receiver. The receiving antennas had two ground planes, connected with
14vias spaced roughly 5 mm apart. (See ECN0004.)
15
16According to figure 1 of [2], the vias connecting the ground planes at
17the edge of the antenna should be spaced at around 50 mil, four times
18closer than 5 mm.
19
20After adding more vias to one of the receiving antennas, sensitivity
21improved drastically, as shown in the purple (ant-120C0) curve of [1].
22The same improvement could be observed in a set of ten antennas that
23all had shown the drop before the addition of more vias.
24
25The remaining drop of about 10 dB in the middle of the spectrum is
26probably caused by the sending antenna. A commercially produced 2.54
27GHz antenna at the receiver showed a similar drop when used with the
28same sender.
29
30[1] http://downloads.qi-hardware.com/people/werner/wpan/three-ants.png
31[2] http://www.ember.com/pdf/120-5052-000_Designing_with_a_PCB_Antenna.pdf
32
33
34Conclusion: place vias at the edge of the ground plane facing the
35antenna with a spacing no larger than 50 mil.
36

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