Impedance matching (VSWR mismatch)

Wireless and IoT RF and Wireless
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1

Hi,

How do I perform impedance matching for RF antenna and front-end connections with impedance of 50 ohms on both?

The VSWRs are different.

Regards,
John Bagshaw

2

This is beyond my direct level of experience but you are going to need the proper test equipment to measure and match the impedances such as a VNA as described in the Rohde Schwarz video Understanding VSWR and Return Loss

3

Hi John,

If you observe power reflection, then there is something that is not 50 ohm.
Three things come into mind:

  1. There is non-50 ohm media between the antenna and the front end.
  2. Either antenna or the front-end is not 50 ohm at the frequency in question.
  3. Something is loading the antenna (e.g. grounded metal in near-field).

First should probably check that the cable from the antenna to the front-end is 50ohm and of good quality.

Cheers,
Heke, AsamaLab.

4

Hi @heke, thanks for the reply. The antenna has two channel ports (RHCP and LHCP) and we’ve been connecting one to the front-end as we wanted to test one channel. Would this be an issue? And I checked the cable is a 50 Ohm cable. Please what are your suggestions to resolve the three points you outlined earlier. Thank you.

5

Hi John,

It largely depends on the antenna whether the channels interact or not. One thing you could try is to terminate the unused port to 50 ohm.

How do you measure the VSWR in your setup?

Cheers,
heke