The transmission loss of integrated cables is closely related to frequency. This relationship is primarily determined by the frequency dependence of conductor loss, dielectric loss, and radiation loss, and the dominance of each loss mechanism shifts with frequency.
Conductor loss is a significant source of transmission loss in integrated cables, with the skin effect being its core mechanism. As signal frequency increases, the current distribution in the conductor gradually concentrates on the surface region, leading to a decrease in the effective conductive cross-sectional area and an increase in the equivalent resistance. This effect causes conductor loss to increase significantly with increasing frequency, becoming a major factor in loss growth, especially at high frequencies. For example, in the millimeter-wave band, the skin effect drastically reduces the effective utilization of the conductor, causing heat loss to multiply for the same current. Furthermore, surface roughness of the conductor also exacerbates high-frequency losses. Rough surfaces disrupt the uniform distribution of current, creating areas of excessively high local current density, further increasing energy dissipation.
The frequency dependence of dielectric loss is closely related to the polarization characteristics of the dielectric material. Electric dipoles in the dielectric material undergo periodic orientation adjustments under the influence of an alternating electric field; this process consumes energy and is converted into heat. As frequency increases, the electric field changes more rapidly, and the orientation adjustment of the electric dipoles gradually fails to keep up with the changes in the electric field, leading to a sharp increase in energy loss. This loss mechanism is particularly pronounced in microwave and radio frequency bands. For example, common substrate materials such as FR4 experience significantly increased dielectric loss at high frequencies, limiting signal transmission quality. The frequency response characteristics of dielectric loss are also directly related to the material's dissipation factor; materials with higher dissipation factors exhibit more severe energy loss at high frequencies.
The frequency correlation of radiation loss is mainly reflected in changes in electromagnetic wave radiation efficiency. As signal frequency increases, wavelength shortens, and the geometry of integrated cables may approach or exceed the signal wavelength, causing electromagnetic energy to leak out in the form of radiation. This effect is particularly prominent in open or semi-open transmission lines; for example, microstrip lines experience significant signal attenuation at high frequencies due to increased radiation loss. The intensity of radiation loss depends not only on frequency but also on the geometry of the transmission line, dielectric parameters, and the surrounding environment; high-frequency signals are more prone to energy loss through radiation.
In the low-frequency band, conductor loss typically dominates, and the effects of dielectric loss and radiation loss are relatively small. As the frequency increases to the mid-frequency range, dielectric loss begins to increase significantly, gradually becoming the main source of loss. When the frequency enters the high-frequency range, radiation loss may increase rapidly due to wavelength shortening, forming a major component of loss along with dielectric loss. This shift in loss mechanism causes integrated cables to exhibit drastically different transmission characteristics at different frequency bands. For example, in the low-frequency range, conductor loss may be dominant, while in the high-frequency range, the combined effects of dielectric loss and radiation loss must be considered.
The correlation between transmission loss and frequency in integrated cables is also reflected in signal integrity degradation. High-frequency signals experience amplitude attenuation and phase distortion during transmission due to loss, an effect particularly pronounced in long-distance transmission or high-frequency applications. For instance, in high-speed digital signal transmission, the rapid attenuation of high-frequency components limits the signal rise time, leading to eye diagram closure and increased bit error rate. Furthermore, the frequency dependence of loss can induce signal dispersion, and differences in transmission speeds of different frequency components further degrade signal quality. A complex nonlinear relationship exists between transmission loss and frequency in integrated cables, determined by the frequency characteristics of conductor loss, dielectric loss, and radiation loss.
