Battling Standing Wave

[robismyname]

I'm new to RF so please be sensitive to this when you read my post.

I have an application where I am transmitting 2.4 Ghz in a Faraday Cage. The antenna is 2.2dbi vertically polarized. Some waves are absorbed by the cage wall but many are being reflected and are adding together to create standing waves. Standing waves are a bad thing but I dont fully understand why at the moment. Prior test results demonstrated that the reflected energy is being homogenized (mixed/added) together. The result of this is that the receiver appears to be picking up the transmitting signal at a constant power level regardles of the location of the receive antenna, contributed by the standing waves. In this particular application this is not a good thing.

Is there a way that I can get reduce the standing waves without changing frequency?

Will changing polarization of the TX and RX antenna limit the amount of standing waves that are present.

 

[Just_Me]

If you are transmitting and receiving inside the same Faraday Cage, I would think the direct wave would be significant stronger than any reflected wave.

To give you any better answer I would need to better understand exactly what you are trying to accomplish.

It sounds like your experiment should be conducted in a RF anechoic chamber rather the a traditional Faraday Cage. An open antenna test range may be a suitable compromise.

Is this a work project or a school project? Either way, I think you may be in over your head.

 

[robismyname]

This is a school project.......my school was assigned to do some work for a local company. I am transmitting inside the cage to a receiver that is also inside the cage. The receiver antenna is conected to a dispaly unit outside of the faraday cage via a penetrator that goes through a portion of the cage wall. Anechoic chamber is irrelevant because the application being tested will be used in a faraday cage as I described it. We are trying to get data out (TX) of the cage to the outher side of the wall via the Receiver. Understand that the Transmitter is in the cage, the receiver antenna is in the cage but the receiver is outside the cage. Does this help any?

 

[key2_altfire]

We'll need more information to help solve your problem.

When you say "standing waves," do you mean this in the same sense as standing wave ratio ("SWR") within the RF radiator system? High SWR in the radiator means the RF power reflects back down your transmitter's cable and goes into the output final stage. This can blow the transistors, but the main concern to hobbyists is the reduction in dB of gain that a high SWR causes. Some amplifiers these days can transmit into an open or short circuit with no ill effects (infinite SWR).

Depending how close your antenna is to the cage there could be RF coupling where the faraday cage is now your antenna. Lower frequencies will have less of a tendency to couple, but 2.4 GHz can be a rascally critter, especially considering a lot of consumer-level equipment is barely within tune at this frequency and can have significant harmonics (aka intermodulation distortion or IMD).

 

[Just_Me]

This is a school project.......my school was assigned to do some work for a local company. I am transmitting inside the cage to a receiver that is also inside the cage. The receiver antenna is conected to a dispaly unit outside of the faraday cage via a penetrator that goes through a portion of the cage wall. Anechoic chamber is irrelevant because the application being tested will be used in a faraday cage as I described it. We are trying to get data out (TX) of the cage to the outher side of the wall via the Receiver. Understand that the Transmitter is in the cage, the receiver antenna is in the cage but the receiver is outside the cage. Does this help any?

So the 2.4 is just a data link?

If so, are you saying you can not get a stables signal?

 

[Just_Me]

We'll need more information to help solve your problem.

When you say "standing waves," do you mean this in the same sense as standing wave ratio ("SWR") within the RF radiator system? High SWR in the radiator means the RF power reflects back down your transmitter's cable and goes into the output final stage. This can blow the transistors, but the main concern to hobbyists is the reduction in dB of gain that a high SWR causes. Some amplifiers these days can transmit into an open or short circuit with no ill effects (infinite SWR).

Depending how close your antenna is to the cage there could be RF coupling where the faraday cage is now your antenna. Lower frequencies will have less of a tendency to couple, but 2.4 GHz can be a rascally critter, especially considering a lot of consumer-level equipment is barely within tune at this frequency and can have significant harmonics (aka intermodulation distortion or IMD).

I think he actually means multi-path, but that seems irrelevant to his requirements unless I missed something.