Guided wave radar liquid level gauges must be designed as a split-body type when measuring liquid levels in harsh environments, and the key factor limiting its split-body distance is the attenuation of the RF cable that connecting the front-end measurement component to the back-end transmitter when transmitting high-frequency signals. This paper analyzes the factors affecting signal attenuation of the RF cable, derives an attenuation equation applicable to different split distances, combines the non-halogen and radiation-resistant properties of materials, and based on the combustion equation, it provides methods for improving cable flame retardancy, developing low-attenuation RF cables. It then optimizes algorithms by extending the period and aligning the number of cycles to reduce the hardware dependency for high-frequency signals, and uses envelope curve algorithms to filter out interference. The life assessment of the liquid level gauge is conducted using methods such as thermal gravimetric analysis to determine the activation energy, which significantly reduces the test time and cost. The research results can fill the gap in guided wave radar liquid level gauges with medium to long split distances in harsh environments.