Ground plane for quater wave planar antenna + questions
时间：04-05
整理：3721RD
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Hi all - new to RF, although I have electronics background. I occasionally make singled sided hobby pcbs at home. I am trying to add a wireless link to a device using a Linx TRM-900-NT + ANT-916-SP transceiver/antenna combo. I'm aiming for ~5m range
So I read and read and search forums to learn. I would appreciate some help to check my understanding is correct, and answer some question.
1) 1/4 wavelength for 916Mhz is 82mm - which refers to electrical length not physical length. On a PCB ground counterpoise this would be more like 82*.66 = 54.12mm ?
2) The earlier revision of the Splatch datasheet shows a max of 1/4" microstrip to fed it. Ok, but all literature says to keep the counterpoise not less than 1/4 wavelength. So a good 5cm exclusion zone.
a) Clearly the transmitter chip is in this zone - and will interfere
b) In the shown PCB layout (earlier datasheet) the rest of the electronics is only about 1" away (based on chip size). This would mean a counterpoise of around 1/16 wavelength.
3) Keyfobs operate at lower frequencies and hence require even large ground plane. Clearly a keyfob functions yet doesn't have a ground plane anywhere near 1/4 wavelength
4) If a 1/2wave dipole is two identical sides and is standalone (meaning no ground plane required) why are the 1/4pole ground planes so large? As in the Splatch is tiny, yet I'm required to allocate a ground space much larger than it. Is this all for minor gain benefit?
5) Does making the counterpoise less than 1/4 wavelength really worry you? I've read that 1/10 is the degradation point
Onto my circuit
5) Can I feed this antenna (the Splatch) from CPW?. So I can keep everything on a single layer.
6) What length ground plane can I get away with. 20mm?
7) With the newer revision of the Splatch datasheet it doesn't specify maximum length. So can I just give myself 20-40mm exclusion zone and run the CPW that distance?
8) In terms of microstrip vs cable vs CPW it is not so important as long as you match the impedance?
Bit of a brain-dump...thanks for reading :)
So I read and read and search forums to learn. I would appreciate some help to check my understanding is correct, and answer some question.
1) 1/4 wavelength for 916Mhz is 82mm - which refers to electrical length not physical length. On a PCB ground counterpoise this would be more like 82*.66 = 54.12mm ?
2) The earlier revision of the Splatch datasheet shows a max of 1/4" microstrip to fed it. Ok, but all literature says to keep the counterpoise not less than 1/4 wavelength. So a good 5cm exclusion zone.
a) Clearly the transmitter chip is in this zone - and will interfere
b) In the shown PCB layout (earlier datasheet) the rest of the electronics is only about 1" away (based on chip size). This would mean a counterpoise of around 1/16 wavelength.
3) Keyfobs operate at lower frequencies and hence require even large ground plane. Clearly a keyfob functions yet doesn't have a ground plane anywhere near 1/4 wavelength
4) If a 1/2wave dipole is two identical sides and is standalone (meaning no ground plane required) why are the 1/4pole ground planes so large? As in the Splatch is tiny, yet I'm required to allocate a ground space much larger than it. Is this all for minor gain benefit?
5) Does making the counterpoise less than 1/4 wavelength really worry you? I've read that 1/10 is the degradation point
Onto my circuit
5) Can I feed this antenna (the Splatch) from CPW?. So I can keep everything on a single layer.
6) What length ground plane can I get away with. 20mm?
7) With the newer revision of the Splatch datasheet it doesn't specify maximum length. So can I just give myself 20-40mm exclusion zone and run the CPW that distance?
8) In terms of microstrip vs cable vs CPW it is not so important as long as you match the impedance?
Bit of a brain-dump...thanks for reading :)
The "ground-plane" antenna is a compromise concept to replace the real ground plane with a quarter-wave monopole by a smaller structure.
You can find a number of books on various designs, mostly for radio-amateur use.
All designs attempt to get a good match to the feed line at a particular frequency, and a reasonable radiation pattern. More important at longer short waves that one can use a small antenna without taking a lot of volume.
At UHF, you can experiment with many other designs. Dimensions are small and I do not see any gain by using a GPA, against a patch, Yagi or a parabolic reflector.