Leaky coaxial cable, also known as a leaky cable, has a structure essentially the same as a regular coaxial cable, consisting of an inner conductor, an insulating medium, and an outer conductor with periodically spaced slots. It functions as a signal transmission line, a transmitting antenna, and a receiving antenna.
Its working principle is that electromagnetic waves propagate longitudinally within the cable while simultaneously radiating outwards through the slots in the outer conductor. At the same time, external electromagnetic fields can be induced into the cable through the slots and transmitted to the receiving end.
Based on the slot structure and working principle, leaky cables are mainly classified into two categories: radial (RMC) and coupled (CMC).
In radial (RMC) leaky cables, the slot spacing on the outer conductor is approximately equal to the operating wavelength (or half a wavelength). This structure causes signals to overlap in phase at the slots, resulting in direct outward radiation. Radial leaky cables are designed with optimization for specific frequency bands, exhibiting specific frequency characteristics within the relevant band, providing uniform signal coverage, a longer radial range, lower coupling loss, and a smaller fluctuation range.
Coupling-type (CMC) leaky cables have elongated slots or a series of small holes spaced much smaller than the operating wavelength on their outer conductors. The electromagnetic wave energy transmitted by the cable couples into the external space through these holes. The electromagnetic waves are densely distributed around the cable in the form of "surface electromagnetic waves" and attenuate rapidly with increasing distance.
