Can I improve the directivity of an X-band radar module with integrated plane-patch antenna?
The Patch-Plane Antenna

The antenna in question is is called a patch-plane (or plane-patch) antenna -- a patch antenna with a reference plane behind it. You can see it here (the four lighter green squares near the corners).



According to the datasheet, the directivity looks like this:



From behind its detection capability is about 63 times weaker assuming you are on the same level with it. If you are not on the same level, it is more than 250 times weaker.

So... perhaps you mount it up high and angle it downward. This will also help you to control detection range.

You should also be aware of and try to avoid reflections. RF is just EM (like light) and it bounces off stuff too! ...especially metals and liquid electrolytic solutions (like salt water). 

The Reflector

A wave-guide won't help. What you need here is a reflector. I'm sure you've seen a satellite dish before. That's it's purpose: to refocus the back lobe into the forward direction and reduce the side lobes (e.g. improve directivity).



Designing one is beyond the scope of what I will answer here. If you choose to proceed with a reflector approach, ask again with your more specific questions, @reference me, and I'll respond in more detail.

Initial Search Volume Approach

Actually, I invented a RADAR architecture specifically designed to deal with this type of scenario called Angle-of-Arrival-Assisted Relative Interferometry (ARI) and wrote a few academic papers on the topic ([A], [B], [C], etc). A complete implementation is probably beyond you (and overkill for your application), but here's the basic idea:



You can partially overlap multiple modules and correlate their detections to reject out-of-area-of-interest targets. You can create a nice focused detection zone in this way. In ARI, that intersection region is called the Initial Search Volume (ISV). 

In Conclusion...

Good luck! Neat project.

Quick note (thanks @AndrejaKo!):


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