Optimisation of Flexible Printed Cable with Broad Side and Edge Coupling and Alternating Arrangement of Signal and Reference Conductors

Ultra-wideband (UWB) pulse interference causes radio electronic devices (RED) to malfunction. To protect against such interference, modal filtering technology is proposed. Modal filters can be implemented at different structural levels (in the form of cables, as separate protective devices and in printed circuit boards). This allows the amplitude of UWB interference to be minimised. In addition, they can be implemented in flexible printed cables (FPCs), which have been widely used in various REDs in recent years. In this paper, we have optimised a flexible printed cable with broad side and edge coupling and alternating arrangement of signal and reference conductors. The investigation was carried out with real parameters of single-sided polyimide with a total thickness of 80 µm. We performed optimisation according to three criteria: minimisation of pulse amplitudes, maximisation of the per-unit-length mode delay difference and matching with a 50 Ω path. We have shown how the thickness of the radio-absorbing material, the distance between the conductors and their width affect the amplitude of the decomposition pulses and the difference of the per-unit-length mode delays. Thus, the optimisation allowed to achieve 17 times (Umax=0.054 V) attenuation of the UWB interference with respect to half e.m.f. This investigation shows that it is possible to attenuate dangerous electromagnetic interference in FPC with front and side connections and alternate arrangement of signal and support conductors without using additional protection devices.