RFA020 Questions

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SteveT

Senior Member
My lovely brother gave me a URF/ERF pair for christmas. I love my brother :)

Questions

1: The datasheet says "The optimum chip antenna orientation is when laid flat, so best results are generally obtained
when the URF PCB is laid flat (parallel with the floor)."

Whilst I don't doubt RevEd's vast technical knowledge, I just can't get my head round this. In my mind (addled as it is) this would not give an omnidirectional radiation pattern but would, in fact, have two great null areas on the axis of the chip antenna. Surely to get an omni pattern the module should be mounted vertical ?

As I eventually intend to use these to control a robot, null areas are a no-no. Or am I barmy?????

2: The said robot will be used to wind up, impress, plague, etc my grandkids who range from 10 years old to 1 years old.
What sort of material could I use to protect the ERF module that is transparent to RF.

I had a quick google but got flumoxed quickly when they started talking about grp radomes being made with one layer of grp to match the frequency of the radio wave passing through it (narrow band) and then going on to mention multi-layer lay ups which may include a metal mesh layer (wide band).

Isn't there some common household object such as an aerosol cap for instance that could be pressed into service?

I'm asking here because I know there are several hams on this forum. I do intend to breadboard the ERF module and try a range test eventually.
 
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Goeytex

Senior Member
Whilst I don't doubt RevEd's vast technical knowledge, I just can't get my head round this. In my mind (addled as it is) this would not give an omnidirectional radiation pattern but would, in fact, have two great null areas on the axis of the chip antenna. Surely to get an omni pattern the module should be mounted vertical ?
Click to expand...
Surely not ....

A chip antenna radiates differently from a straight piece of wire. In a proper design, the chip antenna combined with the actual PCB forms (in effect) 1/2 wave dipole. The recommended orientation is determined by how the chip is placed on the board (Among other things). Without looking at the layout of the ERF modules, I highly doubt that Rev_Ed would publish errant data on antenna orientation. My bet is that the orientation recommendation comes from the actual designer/manufacturer of the modules and is correct.

For more information on chip antennas, Johansontechnology.com has some good technical notes that cover radiation patterns & orientation.
 
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SteveT

Senior Member
Goeytex said:
For more information on chip antennas, Johansontechnology.com has some good technical notes that cover radiation patterns & orientation.
Click to expand...
Yep, this is one of the pages I looked at. Here is a pdf of the page http://www.johansontechnology.com/images/stories/tech-notes/ip/Johanson%20Technology%20Antenna%20Mounting%20Techniques.pdf
It's only when you get to 'layout tips #4' that you get an omnidirectional radiation pattern, but that is with two chip antennas.

As I said before, I don't doubt RevEd's technical knowledge, I just can't get my head round it.
 
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AllyCat

Senior Member
Hi Steve,

It looks to me as if you may be theoretically correct. See this link which finishes with the statement "The polarization is parallel to the long axis of the chip, so maximum radiation is perpendicular to the long axis. There is a deep null (nearly 40 dB!) looking at each end of the chip. This would be a big problem if an omnidirectional pattern is required from a horizontal circuit board. When the board is vertical, the pattern is omnidirectional."

However, in practice I doubt if there is a major problem unless you want to work near the maximum range of the devices. With a claimed range of 500 metres, even in a -40dB null could give a range of about 5 metres, but in practice (except perhaps in a genuine "open field") signals will probably bounce off objects in other directions and still be received.

Similarly, many radio devices are enclosed within plastics enclosures with little apparent effect. Certainly many plastics are very "lossy" dielectrics, so make poor (RF) cables, but interestingly polythene is an excellent dielectric so that might be my choice (e.g. a milk bottle?).

Cheers, Alan.
 
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Goeytex

Senior Member
If the goal is to get a true omnidirectional pattern that also gives maximum range, then the chip antenna is probably not a good choice. However for a toy robot project the ERF modules with the chip antenna should be more than adequate.

I can tell you from my experience in testing quite a few 2.4Ghz RF modules with chip antennas that the range is reduced when the boards are oriented vertically. Best range is achieved when the modules are oriented horizontally and the chip antennas on the respective modules are parallel to each other.
 
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westaust55

Moderator
SteveT said:
What sort of material could I use to protect the ERF module that is transparent to RF.
Click to expand...
Try some polycarbonate sheeting. Sold under names such as Lexan. It is far more impact resistance than perspex.

ABS, polycarbonate and even polystyrene supposedly have less than 8% attenuation at frequencies associated with wireless LAN ( 2.4 GHZ etc).
Nothing found relative to thickness but seemingly based on a report I came across say of the order of 3 to 5 mm.
 
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SteveT

Senior Member
Cheers guys for your input.

Goeytex: "Best range is achieved when the modules are oriented horizontally and the chip antennas on the respective modules are parallel to each other." Magic word that, 'parallel'. Now that makes perfect sense. I can't guarantee parallel with my application though.

AllyCat: Alan, the thought of reflected signals never even occurred to me, cheers for that.

westaust55: Thanks for the link, very interesting reading. That's another thing that never occurred to me, to look at these materials like (as Alan pointed out) dielectrics.

At this moment in time, I think I'll probably go for a vertical orientation to assure an omnidirectional radiation pattern. I more than likely won't need maximum range or anywhere near it.

Lexan looks like the material of choice for protection.

Thanks again lads for all the help. Happy new year.

Steve
 
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AllyCat

Senior Member
Hi Steve,

Yes, the data implies that the package should be considered as a monopole antenna (i.e. has a circular radiation pattern but reducing to nulls along the long axis) so "parallel" orientations would certainly seem best.

But the link also says that the dimensions of the Earth Plane are very important, so presumably radiation effectively occurs also from it. However, the earth plane is NOT at right angles to the monopole (and thus is not symmetrical and notionally infinite, as is normally the case) which may explain the disagreement about which is the best plane to use for "omnidirectional" reception.

Cheers, Alan.
 
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