IEEE 802.15.4 subsystem
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IEEE 802.15.4 subsystem Git Source Tree
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| Source at commit 805db6ebf5d80692158acadf88e239da9d3e67af created 6 years 3 months ago. By Stefan Schmidt, fw/atusb: add extra steps needed for HULUSB in README | |
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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 | |
