antenna-theory.com

[mordhwajpatel]

Hi,
I am a into Smat phone design and look at RF design and antenna design,
There is a interesting scenario I am facing now.
We have a smart phone design which support LTE Band B12,B14,B5, B2,B4.
(B12,B14,B5 covers 700MHz to 900mhz, and B2,B4 covers 1700MHz-2100MHz)
The antenna is at the bottom end of device which is a Inverted F type on the device body.(we use LDS type antenna ).

The issue is as below(Observed in Low Band only:
*The device TIS is good at Low Tx power coming from device.
* TIS drops by 20-25dB when Tx is transmitted at higher power.

Debug:
* There is a small PCB which includes USB connector and Antenna switches etc just below the antenna.
* The presence of this PCB is causing Rx band noise to increase when device is transmitting at higher power.
*I tested this with external antenna also, presence of the same PCB in the antenna vicinity causes increase in Rx band noise for Low bands.

There is no noise generated from the device itself, but the presence of this small PCB is causing it.

Now, If I cut the PCB from middle(There are several traces going along), the noise goes significantly down.

Now, My question is, How can the presense of a PCB(metal structure, copper traces) is , sort of, picking up Tx power and increasing noise in Rx band?