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