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Antenna Fundamentals part. 1

Antenna Fundamentals part. 1

Antenna,EMCAbstract: A proper understanding of antennas requires familiarity with electromagnetics, circuit theory, electronics, and signal processing.

How does an antenna pick up a signal and convert it to something useful to a receiving circuit? What is the current path for the signals received or transmitted from an antenna? Why are there different types of antennas, and why do they have different shapes? What are the standard engineering terms associated with antenna technology? How are signals from antennas amplified?

The subject of antennas may seem beyond reach for many engineers, but a working knowledge of the operation and functional characteristics of antennas is an essential component of the EMC knowledge base. It is the starting point for understanding many EMC requirements and test procedures and for resolving compliance issues. The basics of antennas can be deduced from fundamental principles of electromagnetics and electric circuits. Even a rudimentary understanding can prove to be invaluable in solving EMC problems.


Antennas have two complementary functions: converting electromagnetic waves into voltage and current used by a circuit, and converting voltage and current into electromagnetic waves which are transmitted into space. Signals are transmitted through space by electromagnetic waves consisting of electric fields measured in Volts per meter and magnetic fields measured in Amps per meter. Depending on the type of field being detected, the antenna takes on a particular construction. Antennas designed to pick up electric fields, like the antenna of Figure 1a, are made with rods and plates while antennas made to pick up magnetic fields, as in Figure 1b, are made from loops of wire. Sometimes parts of electric circuits may have characteristics that unintentionally make them antennas. EMC is concerned with reducing the probability of these unintentional antennas injecting signals into their circuits or influencing other circuits.

Consider the antenna of a car radio. As the electric field V/m hits the antenna it impresses a voltage along its length m*V/m = V relative to ground. The receiver detects the voltage between the antenna and ground. Another way to think of this type of antenna is as one lead of a voltmeter measuring the potential in space. The other lead of the voltmeter is the ground of the circuit.

Figure 1. a Electric field antenna and b magnetic field antenna.


Some antennas are made of loops of wire. These antennas detect the magnetic field rather than the electric field. Just as a magnetic field through a coil of wire is produced by the current in that coil, so too a current is induced in a coil of wire when a magnetic field goes through that coil. The ends of the loop antenna are attached to a receiving circuit through which this induced current flows as the loop antenna detects the magnetic field. Magnetic fields are generally directed pe

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