The shielded Loop Antenna HFRA 5164 was designed to generate magnetic fields for immunity tests from a few kHz up to 120 MHz. A typical application is the immunity testing for medical equipment acc. to IEC 61000-4-39 from 150 kHz to 26 MHz, where the transmit loop antenna is located 50 mm apart from the EuT surface. For this purpose, a special fixture (HFRASpacer50) is supplied with the HFRA 5164, which clamps the 16 mm shaft of the loop antenna and provides the necessary spacing to the EuT surface (see Fig. 1). The transmit loop is designed to be connected directly to the 50 Ω output of a class-A power amplifier. For the monitoring of the generated fields, we recommend using the shielded monitoring loop FESP 5134-1, which can also interface directly to 50 Ω measuring equipment. Together with the optional Loopholder 5164-39, the small sensing loop can be simply clamped on the transmit loop at a distance of 50 mm, without any need for tools (see Fig. 2). This allows for simultaneous monitoring of the generated field-strength while performing immunity tests (and eventually required level control).

The electrostatic shield provides both, outstanding symmetry and strong rejection of unwanted parasitic E-fields, which makes the use of sheath current suppressors obsolete.

For the economic generation of magnetic fields in the RFID frequency band at 13.56 MHz, a compensation network NFCN 1356 is available, which is specially tailored to the HFRA 5164. This network achieves an optimum impedance matching at the dedicated RFID-Band, resulting in significant power savings in the respective frequency range. For short time (1 min.) a typical magnetic field-strength level of 26 A/m with 50 W power can be achieved at a distance of 50 mm at 13.56 MHz.