Antennas for radiation emission measurement are treated separately from antennas for radiated susceptibility testing to show the importance of different antenna parameters in the two cases. With antennas for emission measurements the key parameters are bandwidth, sensitivity, dynamic range and absence of cross or intermodulation products in the case of active antennas with built in amplifiers. Important parameters for antennas used in susceptibility measurements include bandwidth, gain/power requirement, beamwidth/spot size, power dissipation, size and mass. Such topics are discussed in the following chapter. This one looks in detail at the types of receiving antennas that are widely used for radiated emission testing. They are discussed in sequence, beginning with the passive monopole which has the least complicated construction.

6.1 Passive Monopoles

6.1.1 Construction

These are amongst the simplest receiving antennas used for EMC measurements. They consist of a conducting rod of defined length connected to an impedance matching circuit which usually feeds a 50 ohm cable to a matched 50 ohm input of an EMI receiver. The impedance-matching circuit consists essentially of a base loading coil with sufficient inductance to resonate with the capacitive reactance of the monopole element at frequencies of interest, see Figure 6.1. A more sophisticated matching circuit may use

transformer coupling or a tapped loading inductor as shown in Figure 6.2.

Figure 6.1: Simple monopole antenna and base loading coil

Figure 6.2: Simple impedance matching circuits for monopole antennas

The design of an EMC antenna is perhaps more complicated than that of a communications antenna by...