What's wrong with the 77GHz antenna design?

[tony_lth]

Hi, Gurus,
I designed a conventional 1X6 patch antenna for 77GHz, and got the max gain 14.2dB.
I want to increase the gain more than 1dB but with limited length, so I designed an antenna with the following pattern.
The problem is that this pattern also have the max gain 14dB., even I made is 1X8 patch.
So what's wrong with my design?
Best,
Tony Liu

 

[vfone]

Try using straight lines between antennas:

https://www.mdpi.com/remotesensing/remotesensing-14-03597/article_deploy/html/images/remotesensing-14-03597-g001.png

 

[tony_lth]

Hi, @vfone,
yes, I know it works with straight lines. But I have limited length, so I have to fold the line.
Any comment.
Best,
Tony Liu

 

[volker@muehlhaus]

But I have limited length, so I have to fold the line.

Decreasing the distance between elements too much reduces the gain.

 

[vfone]

I think you get radiation loss from folded lines discontinuities, which straight lines don't have.
Try using inset feeding, which somehow compensate the small length of the lines, which also give less mutual coupling between patch elements, resulting in higher array gain.

 

[volker@muehlhaus]

I think you get radiation loss from folded lines discontinuities, which straight lines don't have.

The main issue is "stacking distance"

I created a patch array in my EM tool with 6 or 8 identical patches (all same size, not stepped as shown by tony).
I used probe feed so that we have no issue from meandered lines.

With 6 patches spaced at lambda/2, directivity is 14.1 dBi
With 8 patches spaced at lambda/2, directivity is 14.7 dBi, so the benefit of 2 extra elements is not that much

If we squeeze the 8 elements as shown here, with reduced spacing 0.57 * lambda/2, directivity drops to 14.4 dBi
So indeed, it doesn't make much difference for gain if we go from 6 elements at regular spacing to 8 elements with much reduced spacing.