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Cable length influences gain or just bad design

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Andre.Lubbock

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I have been looking at data for a 4G cellular microstrip antenna similar to below
cable length.pngantenna.jpg.

The peak gain and efficiency vary wildly depending on 1000mm or 125mm cable length – cutdown figures
cable length.png

The manufacturer explanation “It's a bit difficult to keep the same performance of both the 1000mm cable length and 125mm cable length version due to ground is really important for 4G/LTE antenna and cable's braid is one of ground for this antenna as there is no more space to be ground, therefore the performance of 1000mm cable length is better than 125mm cable length”

Does this make sense or is it just a poor antenna ?
 

The explanation sounds make sense. Have you tried to simulate different cable bent pattern? For example, straight, 90 degrees bent,...
 

Yes, the cable shield is part of the radiating structure for this design. It is not just "ground"

Ground in such PCB antennas is a difficult topic, I just published a paper on this a few days ago:
https://muehlhaus.com/support/antenna/pcb-em
 
volker@muehlhaus said:
Yes, the cable shield is part of the radiating structure for this design. It is not just "ground"

Ground in such PCB antennas is a difficult topic, I just published a paper on this a few days ago:
https://muehlhaus.com/support/antenna/pcb-em
Click to expand...

Nice article! I am not an expert of antenna, this article is very useful for me. Is there some kinds of PCB antenna less sensitive to ground/ambient change? For example, I would not like the mobile phone signal getting much worse just because I use my left hand to hold the phone instead of the right hand.
 
Last edited:

cariban said:
Is there some kinds of PCB antenna less sensitive to ground/ambient change?
Click to expand...

My design work is for other devices (not mobile phones), but I am afraid there is no magic "plug & play" solution to solve this.

Regarding your structure above, an antenna designer could make the antenna less sensitive to cable effects, by blocking common mode. But it requires a different antenna design then.
 

If the difference is more than the dB/meter loss of
the bulk cable, then it's not just about the cable.
You could get the specs and do the arithmetic, to
say.
 

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