Due to the fact that Radiating Mode Cables are based on a slot design with evenly spaced, repeating slots, it is a physical rule that this will lead to Resonances.
On Eupen’s EUCARAY® Radiating Cables, it results in clearly identified Resonant Frequencies. In most cases, the Resonant Frequencies occur in non-used Bands of the Radio Spectrum, and the even multiples are actually suppressed once the Cable has been installed. In addition, their magnitude generally decreases the higher the order.
It is good practice to verify that the Resonant Frequencies of a chosen EUCARAY® Radiating Cable do not appear in the required and used RF-Band. However, should a Resonant Frequency be found in the RF-Band to be used, it does not necessarily result in a Radiating Cable being unsuitable. On Eupen EUCARAY® Radiating Cable, Resonant Frequencies occupy only about 1 MHz of bandwidth, so that the transmission at frequencies located before and after a particular Resonant Frequency is not impacted. Further, the result at the said Resonant Frequency will typically be a slight increase in the Longitudinal Loss on the Downlink and a slightly raised VSWR in the Uplink. In both cases, the impact on the working of an RF System should be quite marginal. To compare, one should also bear in mind that a well-matched Antenna will have a typical VSWR of 1.5:1.
Resonant Frequencies versus Stop Bands
Resonant Frequencies on Eupen EUCARAY® Radiating Cables should not be compared to Stop Bands of other Manufacturers Cables. Such Stop Bands, or unauthorised Frequencies, usually occupy a much wider bandwidth, and the high level of reflected signal – with VSWR typically >> 10:1 – makes it impossible to use those Cables within the given frequency band.
The illustrations 1 & 2 below show the actual impact the Resonant Frequencies have on the VSWR and the Attenuation of one Eupen RMC-type Radiating Cable.(*)
The illustrations 3 & 4 show, at same scale, the impact of a Stop Band on a competitor cable.(*)
(*) Example with 1-5/8” size, broadband radiating cables.