How high is the maximum frequency of the coaxial cable?

Jun 15, 2019

Coaxial cable is the most commonly used transmission line for RF and microwave applications because it provides reliable transmission with wide bandwidth, low loss and high isolation. The main manufacturers of launch equipment, namely radio and television, radar, GPS, emergency management systems, air and offshore processes, use coaxial cable. The use of coaxial cable is suitable for any system that must minimize signal loss and attenuation. Unlike a waveguide, a coaxial cable does not have a low cutoff frequency, but what is its frequency?

Like other parts of the electromagnetic spectrum, radio frequency (RF) is identified by its frequency in Hertz (Hz) or wavelength (meters). There is an inverse relationship between these two concepts, so that as the frequency increases, the wavelength decreases, and vice versa. The intensity of the RF signal is measured in watts. A frequency band refers to a designated portion of the RF spectrum, for example, AM and FM frequency bands used in radio broadcasting, and within this frequency band, a portion of the frequency spectrum is referred to as a bandwidth. The frequency is identified as the number of inversions or cycles of alternating current (AC) per second. For example, a broadcast station operates at a frequency of thousands of cycles per second, the frequency of which is called kilohertz (kHz); the higher frequency is millions of cycles per second, called megahertz (MHz). Radio frequency is a frequency band used primarily for the transmission of radio and television signals, ranging from 3 MHz to 3 GHz. Microwave frequencies range from ultra high frequency (UHF) 0.3 - 3 GHz, ultra high frequency (SHF) 3 - 30 GHz to very high frequency (EHF) 30 - 300 GHz.

With some exceptions, most coaxial cables do not have an actual cutoff for the specific stopband frequency, but instead use the term cutoff to indicate the highest frequency tested by the manufacturer, or when the frequency reaches the point of the coaxial cable, except for the transverse electromagnetic mode (TEM). In addition, the cable becomes a waveguide and other modes. Therefore, the coaxial cable cut-off frequency can be either within the specification of the coaxial cable or within a reasonable range to avoid transverse magnetic (TM) or lateral-to-electric (TE) propagation modes. Although the coaxial cable can still carry signals with a frequency higher than the TEM mode cutoff frequency, the TM or TE transmission mode is much less efficient, which is not ideal for most applications.