I know that a linear array of microstrip patches can be either horizontal or vertical depending on its orientation.
Does the feed (input port of the array) determine the direction of polarization?
Electrical – How to tell the polarization (horizontal or vertical) of a microstrip linear array antenna just by inspection
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Related Solutions
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.
A monopole antenna is one half of a proper dipole antenna. If you rotated the proper dipole through 90 degrees then the polarization direction follows the rotation. Because a monopole needs a ground plane to operate correctly, rotating it thru 90 degrees creates a bit of a mess mathematically and it becomes a bit unclear how the polarization changes precisely.
This is how a (ground referenced) monopole is "derived" from a free-space dipole (position c in the diagram below): -
This derivation is based on the fact that all lines of electric field along the horizontal centre-line of the dipole are effectively 0V and therefore can be replaced with a central ground-plane (without affecting dipole performance). The implication of this is that the lower half of the centre-ground-planed dipole can be discarded leaving a single monopole on a ground-plane.
The words that accompany this diagram in wiki are: -
Showing the monopole antenna has the same radiation pattern over perfect ground as a dipole in free space with twice the voltage
In other words I believe the basic premise of the question is slightly flawed.
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Best Answer
The short answer is yes, the position of the feed of a single patch determines the horizontal vs. vertical polarization of that patch.
Since all the patches in the linear array are fed in the same way, this determines also the polarization of the array.
See this article, which covers the working of single-patch antennas:
Some excerpts:
[...]
The relevant section for your question is the following:
[...]
The previous image, which in the article is used to illustrate how to obtain a circular polarization, explains why the feed position determines the polarization: feed1 and feed2 excite different linearly polarized modes (TM10 and TM01), which combine to give circular polarization. From that it is clear (read the text in the article) that if only one feed is present, it excites just one linearly polarized mode.