Filter cable design with defected conductor transmission structures

Abstract

Electrical cables, as the industry's blood vessels and nervous system, require evolving distributed filtering for complex electromagnetic environment adaptability. This article introduces a filter cable design featuring an insulated cylinder coated with a defected conductor transmission structure (DCTS). The DCTS, with a well-designed etched pattern, functions as a boundary condition for transmitting specific frequency electromagnetic waves, similar to a lumped filter circuit. To validate this method, a low-pass filter cable is proposed with six-slot-ring defected structures, utilizing polytetrafluoroethylene as the inner dielectric, encased within a flexible printed circuit board (FPCB)-manufactured DCTS. The proposed cable, with precise dimensions (2.4 mm diameter, 340 mm length), demonstrates minimal insertion loss ( < 0.38 dB below 6 GHz) in the passband and rejection exceeding 23 dB at 7.7-25 GHz in the stopband. Further enhancements achieve attenuation exceeding 50 dB in the stopband (7.1 GHz to 20 GHz). Compared to traditional cables, this filter cable addresses electromagnetic compatibility (EMC) by cutting off the interference coupling path.

Fig. 1. The fundamental decomposition of the EMC coupling problems is addressed by filter cables.

CE conducted emissions, CS conducted susceptibility, RE radiated emissions, RS radiated susceptibility.

Fig. 2. The design of the suggested low-pass filter cable involves a defected conductor transmission structure (DCTS) which comprises of 40 square rings with varying lengths cascaded together, along with six gaps.

a The arrangement of the characteristic filter cable, illustrating the sequence of layers from the outermost to the innermost: shielding layer, transmission dielectric, DCTS, and inner cylinder dielectric. b 3D representation of the DCTS in the proposed filter cable, illustrating 40 cascaded six-slot-ring structures. c DCTS with 40 cascaded structures consisting of six-slot-ring. d Parameter diagram depicting two individual six-slot-ring structures within the DCTS.

Fig. 3

The schematic diagram of a non-uniform waveguide structure with intricate boundary conditions.

Fig. 4. The current distribution within the passband of the proposed resonator and its corresponding equivalent circuits.

a Current distribution in a single six-slot-ring defected structure. b Equivalent circuit representation of the gap. c Equivalent circuit representation of the right-angle bend. d Equivalent circuit representation of the T-junction. e The equivalent circuit diagram of a single resonant unit of the proposed filter cable. (This data has been published in ref. )

Fig. 5. The S₂₁ parameter of the low-pass filter cable with a single structural parameter.

a For different values of L_U. b For different values of W_U. c For different values of G₁. d For different values of G₂. e For different values of L₁. f For different values of S₁. g For different values of M. h For different values of N.

Fig. 6. Photograph of the fabricated low-pass filter cable.

a Inner cylinder dielectric. b Top view of the defected conductor transmission structure (DCTS) featuring 40 defected six-slot-ring structures. c Bottom view of the DCTS featuring 40 defected six-slot-ring structures. d DCTS is wrapped around the inner cylinder dielectric. e Transmission dielectric. f The completed filter cable with 40 defected six-slot-ring structures.

Fig. 7. The comparison between simulated and measured results.

a S-parameters of the proposed low-pass filter cable with 40 six-slot-ring defected structures on the defected conductor transmission structure (DCTS) without turning (This data has been published in Reference 19). b S-parameters of the proposed low-pass filter cable with 40 six-slot-ring defected structures on the DCTS with a turning radius of 0.5 m. c Group delay of the proposed low-pass filter cable with 40 six-slot-ring defected structures on the DCTS (This data has been published in Reference 19). d S-parameters of the low-pass filter cable with 3 groups for 40 cascaded six-slot-ring defected structure units.