There are many methods to measure level of liquid in tank on ship.
One of methods is using frequency modulated continuous wave (FMCW) radar.
In this paper, a X-band frequency-modulated continuous wave radar, using a single antenna for both transmitting and receiving electromagnetic energy, is designed and implemented for a radar level gauge. Main component blocks of the radar are voltage controlled oscillator, mixer, circulator, power divider, and signal processing circuit. The pyramidal horn antenna that has about 16dBi gain is used.
The transmitting frequency sweep from 10GHz to 11GHz with 40ms sweep time. The distance between antenna and target is obtained from a beat frequency of FMCW radar. Beat frequency means a frequency difference between transmitting and receiving signal and depends on the distance to target.
Due to the mismatching of antenna impedance, the reflected signal from the antenna may be dominant over the small target echo signal, which could be overcomed by using a high pass filter to eliminate the reflected signal of the low frequency in the demodulation unit.
The minimum detectable signal of the fabricated radar is about -90dBm. The received signal is processed by fast fourier transform to find the distance to target. A small target which has radar cross section of 0.8m2 is set at 1m from antenna and moved to 4m gradually. According to distance of the target the measured beat frequency is changed from 0.7KHz to 1.8KHz.