IEEE 802.15.4 subsystem
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IEEE 802.15.4 subsystem Git Source Tree
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Source at commit 873f80cb4dac00800826958f9869ec55dbd9e91c created 10 years 7 months ago. By Werner Almesberger, tools/atrf-txrx/atrf-txrx.c: option -q becomes "quick" and uses aggressive polling | |
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1 | Revised via spacing |
2 | |
3 | |
4 | Tests of PCB antenna performance revealed a sharp drop in received power |
5 | at 2440 MHz, roughly the middle of the antenna's frequency range. |
6 | |
7 | This drop can be seen in the red (ant-120A0) and blue (ant-120B2) curve |
8 | of [1]. |
9 | |
10 | The test setup consisted of an atusb board with discrete balun and an |
11 | antenna with only a single ground plane as the sender, and a set of |
12 | antennas (see directory ../ants/) connected to an USRP2+XCVR2450 as the |
13 | receiver. The receiving antennas had two ground planes, connected with |
14 | vias spaced roughly 5 mm apart. (See ECN0004.) |
15 | |
16 | According to figure 1 of [2], the vias connecting the ground planes at |
17 | the edge of the antenna should be spaced at around 50 mil, four times |
18 | closer than 5 mm. |
19 | |
20 | After adding more vias to one of the receiving antennas, sensitivity |
21 | improved drastically, as shown in the purple (ant-120C0) curve of [1]. |
22 | The same improvement could be observed in a set of ten antennas that |
23 | all had shown the drop before the addition of more vias. |
24 | |
25 | The remaining drop of about 10 dB in the middle of the spectrum is |
26 | probably caused by the sending antenna. A commercially produced 2.54 |
27 | GHz antenna at the receiver showed a similar drop when used with the |
28 | same 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 | |
34 | Conclusion: place vias at the edge of the ground plane facing the |
35 | antenna with a spacing no larger than 50 mil. |
36 |