CE certification test with narrow band Printed IFA for GSM

[Danidogg]

Hi guys,

I designed a printed IFA antenna on FR4 PCB for GSM900 and DCS1800 bands. The return loss at the 900MHz band (880-960) is below -5dB, but for the 1800MHz (it's -3.8dB at 1710MHz and -2.1dB at 1880MHz). The impedance mach is very good, the average gain is well above 0dB for both bands and the radiation pattern is fairly omnidirectional.

But I'm worried about the bandwidth, I'm not sure if it is sufficient to pass EN5502 and EN5504 tests I'm planning to get for my design.

This is my first time with the test and I need your advise, please help.

Thanks in advance

 

[WimRFP]

EN 55022 and EN 55024 are related to unwanted emissions and immunity for EM fields. They are not related to GSM performance testing.

The gain and return loss will affect the performance of your GSM communication (coverage).

When RL = 3 dB in the TX band, you have a bad match. This will likely result in less radiated power as the PA of the GSM module can't delive all its power to the antenna.

Please check the GSM module documentation on antenna VSWR (or Return Loss). It would be good if you could have VSWR< 2 (RL > 9.5 dB), but I know that frequently you need to accept higher VSWR because of space limitations.

 

[Danidogg]

Thanks a lot WimRFP,

Good thing to know the test doesn't measure the GSM performance or coverage.

Speaking of the performance of the antenna, I will be using the system only to periodically upload data to a remote server via GPRS using FTP. So how about I shift the band to the uplink channels (because I can have RL as low as -25db and VSWR as good as 1.02 even if the band is very narrow)?

 

[WimRFP]

I don't know the link budget, but is good to have the lowest VSWR (or best RL) in the transmitt band of the module (may depend on where you live).

Regarding EMC testing. Try to get the standards and/or at least a good book on practical EMC (such as EMC for product Engineers, Williams), otherwise your device will likely not pass the tests.

The GSM module may be fine, but when you put it on a PCB with a microcontroller, a switching regulator and some other hardware, EMC limits are easily exceeded. You need good PCB layout and when long wires can be connected to the device in real world, immunity testing can be problematic also.

When you go to a test house for a (preliminary) test, make sure you attend the test. You know how to operate the device, and you can learn from it to change teh design to get better EMC.