# Helical antennas and orientation

A batch of questions here really (if it helps I'm operating at 433.92MHz):

1. How should I orient a helical antenna with respect to my board (i.e. my "ground plane") to get the best range performance?

2. What should the dimensions of my ground plane have to be in order to get good performance / how much does this matter compared to orientation?

3. I'm also wondering what effect (if any) the relative orientation of these types of antennas between the transmitter and receiver has on link quality (due to polarization?).

4. Is the antenna pattern directional for these types of antennas (related to 3), and if so how narrowly?

Sorry if this question is a little bit all over the place - I've got an EE background, but RF can be kind of mysterious (if you know what I mean)...

Regards, Vic

 3-d visuals would be really helpful in helping me get my head around this as well [/Edit]

[Edit2] 5. Going to attempt some ASCII art here - what's the best way to mount my antennas? slashes (/) are the helix orientation, underbars (_) are the ground plane, and vertical bar (is the feed point):

    Transmitter                             Receiver
**A**
/                                     /
/                                     /
/                                     /
/                                     /
____|____                             ____|____

**B**
////////                              ////////
_|_________                           _|_________

**C**
////////                              ////////
_|_________                           ________|__

**D**
/
/
/
/                                  ////////
____|____                             _|_________

**E**
/
/
/
/                                  ////////
____|____                             ________|__


[/Edit2]

• Do you have a part number for that antenna? – Kevin Vermeer Oct 28 '10 at 15:53
• – vicatcu Oct 28 '10 at 16:29
• They say that "HE Series antenna patterns have not been fully characterized as of this time. The patterns below illustrate typical patterns for antennas of this type.", and then give patterns and layouts. What are you looking for beyond this information? – Kevin Vermeer Oct 28 '10 at 16:33
• @reemre see Edit2 above – vicatcu Oct 28 '10 at 16:45
• @vicatu - Nice artwork. If you can control the orientation that precisely, why are you using helical antennas? A directional antenna would give you better signal strength if you have that much control, the helical antenna will radiate it in all directions. – Kevin Vermeer Oct 28 '10 at 16:52

First, a caveat - I'm primarily a CE, so this is just my understanding of the matter:

1. Generally, the worst reception is when the antenna is upside-down, or nearly so, and the best is when it is vertical. However, horizontal orientations are nearly as good as vertical; the radiation pattern is usually something like this, with "up" in the picture corresponding to the positive Z axis (defects overemphasized):

2. Again, your antenna manufacturer will likely have a reference design for this. Sarantel publishes sample gerbers for many of its antennas. If the antenna is not directly coupled with a ground plane, near-field radiation will still be helpful.

3. No idea. I doubt that it would matter as long as both antennas had decent signal strength. Back-to-back might not be ideal, but everywhere else should work fine.

4. No, it's hardly directional at all.The reason you use a helical antenna is because you want near-omnidirectional performance. If orientation is controllable, use a different antenna.

• can you add some explanation of how to "read" your drawing? as I look at the page, the coil axis would be facing me with the signal feed point being "on the page", right? Signal strength in a direction is related to the distance from the origin to the curve in that direction? – vicatcu Oct 28 '10 at 16:33
• Is the pattern symmetric if you were to visualize it in 3d? – vicatcu Oct 28 '10 at 16:34
• @vicatu - I edited my picture to clarify what was going on. The green line is the PCB, the thing with slashes is the antenna. Ignoring the effects of the ground plane, the effect would (in theory) be the same if the PCB was rotated 90 degrees. – Kevin Vermeer Oct 28 '10 at 16:50
• @vicatu - Did that really answer your question? You approved it pretty fast. I'd wait a while for someone with a better understanding to come in. – Kevin Vermeer Oct 28 '10 at 18:29