A Cable is an assembly of one or more conductors normally insulated by dielectric materials and used for the transmission of electric power or signals. Different types of cables are used for transmission and communication lines such as coaxial, shielded and unshielded twisted pair, fibre optic, space wire cables.
Propagation analysis of cables is used to reveal how an electromagnetic wave propagates and couple between the conductors. The propagation properties can be defined from the cable cross-section, material properties and length. Depending on the requirements, certain approximations can be made. The usual approximation is that the cable has a uniform cross-section and the electromagnetic fields propagate as transverse electromagnetic waves. The propagation characteristics can then be defined in terms of per unit length; capacitance, mutual capacitance, inductance, mutual inductance, transfer impedance and resistance. Transfer impedance defines the mechanism by which coupling occurs through a conducting shield. External fields can also excite propagation along cables which is important to quantify.
SACAMOS (State-of-the-Art CAble MOdels for Spice) is developed by University of Nottingham (UoN) and Netherlands Aerospace Centre for European Space Agency (ESA) for modelling the cables propagation and external field coupling with all cable properties and frequency dependent values that effect performance of cables. The software generates spice sub circuits models that can be used in Ngspice, LTspice, PSpice. SACAMOS modeller is composed of three parts: Cable Builder, Cable Bundle Builder and Spice Model Builder.
The cable model building process concerns the development of individual cable models from specifications (cable datasheet). In this the cable cross-section and material properties (including frequency dependence) is fully defined. For this the per unit length properties of the cable are calculated for use in the model. The cable model GUI is shown in the figure below.
Cable Bundle Builder:
The cable bundle model building process concerns the development of cable bundle models from individual cable models and additional ground and over-shield specifications. The characterisation of the external propagation domain which involves the outside of the shields, unshielded conductors and ground plane and also the domain within over-shields. The cable builder GUI is shown below.
Spice Model Builder
Development of a SPICE cable model for a particular bundle includes the specification of the length of the bundle, any incident field excitation and the specification of the coupling between cables via the transfer impedance of imperfect shields. The generated SPICE models and their associated symbols (for Ngspice and LTspice) may be incorporated into the simulation of complete circuits. Figure below shows the incorporation of the model into a SPICE circuit model with a typical output.