Schwarzbeck 420 NJ Elements For SBA 9113 Balun

The Schwarzbeck 420NJ elements for the SBA 9113 were designed because of the drastical increase of mobile phones and handheld transmitters within the last years. Various disturbances generated a need for new, more efficient immunity test methods with good reproducability. Existing radiated immunity tests with test distances typically between 1 m to 3 m require expensive power amplifiers. Several investigations in the very close surrounding of mobile phones and handheld transmitters have shown, that such devices can generate very high fieldstrengths in the order of some 100 V/m with only a few Watt power. With existing immunity test methods the effort is extremely high to generate fieldstrength level as described before.

Thanks to the special shape of the 420NJ elements both can be achieved simultaneously, an enormous bandwidth and a very close distance to the EuT surface, typically 5 mm. This is an economic way to generate very high fieldstrengths with moderate power of e.g. 10 to 20 Watt. The large bandwidth of the radiating elements allows fast wideband testing without any need for antenna changes, therefore even country specific frequency bands can be tested without extra effort.

Application

The typical application of the SBA 9113 with 420NJ-elements is immunity testing of components in the automotive industry, medical, scientific or aerospace environment, where immunity against handheld transmitters is an important topic. Usually the surface of an EuT is divided into a grid with a meshwidth of e.g. 10 cm. Each gridpoint is tested for two orthogonal polarisations with the desired fieldstrength while observing the EuT condition. Typical Antenna to EuT spacings are 5 mm or 50 mm, which are provided by respective spacers of the antenna elements.

The 420NJ-elements are mounted with M4 screws at the element fixture nuts of the Balun. When mounting the flat elements care should be taken in order to avoid overtightening the threads. It is absolutely sufficient to tighten the element screws with moderate torque. Various experiments have shown that the contact at the feedpoint is always sufficient.

420NJ Elements for SBA 9113 Balun

The functional check of the SBA 9113 can be made measuring the VSWR at the N-connector of the antenna rod. The radiating antenna elements must be connected to the balun.

The VSWR depends on environmental reflections, therefore a minimum spacing of 30 cm to any reflective obstacle should be maintained. The voltage standing wave ratio is defined as the sum of the forward and reflected voltage divided through the difference of forward and reflected voltage. The VSWR can also be expressed as reflection coefficient or return loss (RL, |S11|). The reflection coefficient r is the ratio of reflected and forward voltage. The following tabular provides correspondences for the most common values, missing values can be calculated by the given equations.

[split]