Does a receiving antenna radiate the power received?

Question

Let's consider the case of linear dipole antenna or Hertz dipole.

I know that the antenna acts as a transducer and it radiates the E-M waves due to the acceleration and decelaration of the electrons or charges in the wire. While receiving the signal, it is said that the E-M waves induce a voltage at the input end of the antenna. (Let's call this open circuit voltage Voc ).

My doubt:

1. If the incoming E-M wave can induce a voltage won't it accelerate or decelerate the electrons in the wire and doesn't this acceleration cause further radiation (lets call it secondary radiation) of E-M waves?
2. Won't this secondary radiation lead to loss in the effectively received power?

It would be really helpful if I get a clarification on this.

Answer 1

If the incoming E-M wave can induce a voltage won't it accelerate or decelerate the electrons in the wire and doesn't this acceleration cause further radiation (lets call it secondary radiation) of E-M waves?

Yes, an antenna can re-radiate power that it receives, provided that the impedance at the antenna does not match the (complex conjugate of the) impedance of the cable and device that it is feeding.

Sometimes antenna elements are designed to re-radiate. They are usually just passive antenna elements that are short circuited at what would be their feedpoint. Old television receiver antennas, (Yagi antennas) had such elements, known as directors and reflectors. The purpose of these re-radiating elements is to provide directional gain for the overall antenna. This works by the incoming waves from the station having constructive interference with the re-radiated waves from the passive elements.

Won't this secondary radiation lead to loss in the effectively received power?

Yes, if the impedance of the antenna does not match (the complex conjugate of) the impedance of the feedline and the receiver, the re-radiated energy will be an effective loss to the receiver. Thus, an important aspect of Radio Frequency (RF) design is matching impedances.

Answer 2

If you have a power supply with V volts, connected to a resistor with V volts, is the resistor a power supply?

A receiving antenna can be considered to be a negative power supply, just like a resistor, and 'radiates' that negative power, if you take that frame of reference. The 'negative power' that it 'radiates' has an effect on the EM field: the EM field is different because an antenna is there.

If you do the math, the 'negative power' that is 'radiated' is the power that is received: it all works out regardless of where you start.