A Two-Frequency CW Radar System for Short-Range Distances Measurements

A highly accurate system for measuring distances between two objects using two-frequency CW (continuous waveforms) has been developed and evaluated. The concept of our new range meter is based on the K-band Doppler effects phenomenon to obtain a distance between stationary or moving objects more precisely and is able to measure short-range of distances from micro-millimeter to 100-meter. The system has significant features in view of the hardware’s design because of its light weight, small size, very low power consumption and is also appropriate for numerous applications. The system model is based on the relationship between Doppler beat frequency and the distance to a stationary object and this relationship is given by d = Cφ/{4π(f1 + f2) } ................................................. (1) where φ is phase angle, C =3*10 mm/s is the wave’s velocity, the two-frequency f1 =24.1498GHz and f2 =24.1490GHz are utilized by Doppler sensors A and B, respectively, and D is the distance of a stationary or a moving object, as shown in Fig.1. The developed system which is shown in Fig.1 has two K-band Doppler CW radar which transmit two periodical and sinusoidal signals with different frequencies, simultaneously. The reflected wave signals which are received at Doppler modules are manipulated to obtain Doppler beat frequencies f1-f2 and f2-f1. The phase differenceφbetween these beat frequencies is measured. Furthermore, the distance to the object is also easily calculated using the above relation (1). The system has been theoretically and experimentally conducted and Fig.2 shows the relation between phase differences versus distances’ measurements in both theoretical and experimental computations. The Figure also shows the comparison between observation results (solid line) and theoretical results (dashed line). The first thing has been considered in our experiment was to place an object one meter distance from the Doppler modules and then it was gradually moved to 12mm by every 0.5mm step. For each step, the system detects and measures two beat frequencies. These beat frequencies are identical to those have been theortically calculated with 0.8MHz and wavelength is 375000mm. Theoretically, the beat frequency is 0.8MHz and wavelength is 375000mm while the combinition of f1 and f2 frequencies in Eq. (1) is 48.2988GHz (wavelength =6.2mm), considering that the actual distance is 2 d which is a round trip between the two modules and the object. Hence the phase difference φ is calculted for each step, which is almost identical to the phase differences with those have been measured by our observation method. If we consider the beat frequency is 0.8MHz and the phase differenceφ is 1 degree then we can able to measure the distance to 10μm precisely. Our system stands for the highest degree of measurments accuracy at notably small distances. The observed results show that our new development exhibits a phenomenal performance with very low cost design, light weight and it’s capable to employ in numerous purposes such as emerging ITS infrastructure.