How Much Power Must We Extract From a Receiver Antenna to Effect Communications?

Abstract

Subject to the laws of classical physics - the science that governs the design of today's wireless communication systems - there is no need to extract power from a receiver antenna in order to effect communications. If we dispense with a transmission line and, instead, make the front-end electronics colocated with the antenna, then a high input-impedance preamplifier can measure the open-circuit voltage directly on the antenna port without drawing either current or power. Neither Friis' concept of noise figure, nor Shannon information theory, nor electronics technology dictates that we must extract power from an antenna.

Figures (14)

• Figure 1: Receiver loop antenna a) and Thevenin-equivalent circuit b): the open-circuit voltage is proportional to the time-derivative of the magnetic flux passing through the loop, and the series impedance is equal to the self-impedance of the antenna.
• Figure 2: Receiver antenna is connected to a preamplifier having input impedance, $Z_{\mathrm{in}}$.
• Figure 3: Common cathode triode vacuum tube amplifier functions as a voltage-controlled current source: C-battery creates negative grid-to-cathode bias resulting in high input impedance; output power is provided entirely by B-battery which creates a positive plate-to-cathode potential.
• Figure 4: Common-source JFET amplifier is the solid-state counterpart of the triode vacuum tube amplifier of Fig. \ref{['triode']}.
• Figure 5: Unity-gain buffer amplifier: op amp circuit provides high input impedance and precise voltage-gain of one.