Confused! how much power transferred from antenna to receiver(on conjugate matching)

:roll:
Re-read the conjugate matching concept, Conjugate matching between source impedance and load impedance means the maximum power should be transferred from source to load, the efficiency is 50%.

but confused by it today! When antenna impedance and receiver impedance are well matched for conjugate matching,if the antenna obtains -100dBm Rx power for instance at some frequency,how much power will be delivered to the receiver assuming no loss on the transmission line?

-100dBm, or -103dBm? thanks.

Re-read the conjugate matching concept, Conjugate matching between source impedance and load impedance means the maximum power should be transferred from source to load, the efficiency is 50%.

Click to expand...

No, if correct ideal matching is transmission loss 0%.

if the antenna obtains -100dBm Rx power for instance at some frequency,how much power will be delivered to the receiver

Click to expand...

If there is no loss in transmission line, what is delivered to the antenna is also delivered to the receiver, if antenna efficiency is 100%.
A 100 % effective antenna does not consume any power, it is a loss-less transformer between your circuit and surrounding space.

if you are already measuring on antenna, you have factored the antenna gain and loss, if comparing to reference antenna, then add antenna gain (dBi) and insertion loss.

rf1008 said:

:roll:
Re-read the conjugate matching concept, Conjugate matching between source impedance and load impedance means the maximum power should be transferred from source to load, the efficiency is 50%.

but confused by it today! When antenna impedance and receiver impedance are well matched for conjugate matching,if the antenna obtains -100dBm Rx power for instance at some frequency,how much power will be delivered to the receiver assuming no loss on the transmission line?

-100dBm, or -103dBm? thanks.

Click to expand...

Bear in mind rf1008, that the 'impedance' is the complex E/I relationship for all circuit elements involved, and power 'loss' can only be achieved by conversion of RF energy to thermal energy, usually due to Ohmic (resistive) losses but also by dielectric losses to (again) thermal energy.

If you had 3 dB (50%) 'loss' in a conjugate match, you would have to explain via physics where the conversion of 50% of the electrical energy went into becoming thermal energy. One should then be able to perform an experiment with a 1,000 Watt transmitter and quite literally see some circuit element 'glowing red' due to a 50% power loss ... again in practice this does not occur since a complex E/I relationship is being expressed as the 'surge impedance' ('surge' is an old descriptive term not used today but could be used to represent a "dt" (delta time) term) and not a literal 'resistance'.


RF_Jim

The said 50% power loss will be observed if you model a RF source by an ideal voltage or current source and a resistor. In case of an lossless antenna, the real impedance is representing the (possibly transformed) free space impedance, not a physical resistor.

In case of a transmitter PA, it depends. A class-A output stage will in fact involve a real output impedance with losses and less than 50% overall efficiency. In a class C/D/F whatsover switching PA, there's no physical resistor representing the real output impedance.

thanks to all.It's a simple problem on foundation concept.

I believe the maximun power will be delivered to receiver,the whole power received by antenna will be ransferred to receiver if conjugate matched,100% delivered.
I think the conjugate matching theorem is based on ideal voltage/current source with no impedance. The transfer efficiency is 50% when use one impedance to present the internal impedance of source to match with external load.

I think the conjugate matching theorem is based on ideal voltage/current source with no impedance.

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Impedance matching has no solution for ideal voltage sources.