How to understand how much current an active antenna draws

[huytergan]

Assuming that I have a GHz antenna with integrated LNA. I can use power supply to feed the LNA integrated to the antenna. How I can measure how much current the whole system draw?

 

[albbg]

Simply insert a amperometer in series between power supply and antenna.

 

[huytergan]

Simply insert a amperometer in series between power supply and antenna.

Using a resistor between them and make measurement on that with a multimeter couldn't be efficient since it's high freq and the resistor might not be suitable?

 

[betwixt]

The LNA is the 'active' part and will draw a small DC current, you could do it with a series resistor but you would have to break the line anyway so it would be simpler to just use an meter and measure the current directly. The current will not vary with the signal amplitude or frequency so whatever you measure will be the same if the meter is taken out of line again.

Brian.

 

[albbg]

No, the (low level) RF signal will not affect the DC measurement. However the insertion of the measurement system, if not properly RF decoupled will affect the RF performances of the antenna.
If you want just measure once the current consumption you can use the multimeter that has to be removed during the normal operation of the antenna.

 

[huytergan]

No, the (low level) RF signal will not affect the DC measurement. However the insertion of the measurement system, if not properly RF decoupled will affect the RF performances of the antenna.
If you want just measure once the current consumption you can use the multimeter that has to be removed during the normal operation of the antenna.

So I can use just multimeter between power supply and antenna. Please verify I m just making sure that I understood correctly

 

[albbg]

Correct. Remove then the multimeter when you want operare normally the antenna

 

[D.A.(Tony)Stewart]

Multimeter wires may interefere with reception due to inductance added to the wires or ground plane but should not affect DC currents. Since current meters simply use the full scale at the the best resolution with a voltage drop resistor drop , to measure in situ.

1. estimate your current and desired Vrange to choose a ground current. e.g. 100 mV/ 1 mA= 100 ohms
2. Insert R on the power or ground path (whichever is easy) with the smallest physical part you can. To improve RF performance adding 100 pF in parallel with R or less rated for your RF band. (Physically small) then the V(R)/R is your current.

 

[huytergan]

Correct. Remove then the multimeter when you want operare normally the antenna

I wanna ask one more Question. I did measure the current. After some voltage level, the current remained same even tho I increased the voltage( between the supply volt. limits of LNA). Does that mean it is okay

 

[betwixt]

It doesn't mean anything useful. The LNA will have a rated voltage and that is what you should apply when measuring the current. The actual relationship between applied voltage and current is decided by the manufacturer or the LNA and the devices within it, for practical purposes all you need to know is what the current is at the voltage you are using. If you are unsure, with the LNA connected, measure the voltage from its host device and use that to measure the current.

Brian.

 

[albbg]

Probably there is a LDO (low drop out voltage regulator) insider the antenna, then the lna is always supplied with the same voltage, thus the current consumption doesn't change on the whole input voltage range

 

[D.A.(Tony)Stewart]

I wanna ask one more Question. I did measure the current. After some voltage level, the current remained same even tho I increased the voltage( between the supply volt. limits of LNA). Does that mean it is okay

What function can you imagine is included in the device to do this? It must also provide a constant impedance for input and output matching.

I conclude you have not found/read any device specs. Is that OK?.