Distance measurements and limitations based on guided wave 24 GHz dual tone Six-port radar

Abstract

In the following, a continuous wave radar system based on the Six-port principle will be shown for measurement tasks at enclosed systems needing micrometer accuracy as well as high update rates like tank level monitoring or hydraulic cylinder piston control. To exceed the ambiguity limit of such an interferometric system, a dual tone approach is used. The system will be presented with measurement results at 24 GHz within a WR42 waveguide to prove the feasibility of the proposed concept. Furthermore, considerations on timing will show the potential as a low-latency system, capable of high measurement data update rates, and different influences on the system performance and limitations of such a system will be discussed in comparison to alternative setups.

AMCW Radar of Micrometer Accuracy Distance Measurement and Monitoring

“…In comparison with Interferometer radar [6], AMCW radar has considerably larger ambiguity-free detection window. Dual tone Interferometer or 2-FSK radar can be used for enlarge ambiguity-free window [7], however, tones are transmitted at different time slots therefore limits the refresh rate.…”

“…Interferometric radar [7] is using only one continues-wave (CW) signal, however, its ranging window equivalents to only one wavelength. In this paper, a millimeter wave amplitude modulated continuous-wave (AMCW) radar is proposed, which occupies little bandwidth, yet can measure distance to target with micrometer accuracy with a ranging window of 15 cm.…”

Six-Port Based Interferometry for Precise Radar and Sensing Applications

“…It is obvious from the periodicity of the beat signal that the unambiguous range is extended from about 6 mm for the single tone evaluation of $f_1$ or $f_2$ up to 60 mm. This range extension depends on the selected frequency spacing and is limited to a few meters, which is discussed in [68]. …”

Micrometer Sensing With Microwaves: Precise Radar Systems for Innovative Measurement Applications

“…However, this also means a varying transmit frequency, thus a poor phase noise and a large standard deviation of the range measurement. For unmodulated CW radars, this effect was described analytically by [26], [27]. Moreover, it was shown that a close target leads to a strong correlation of sent and received phase noise due to the short propagation time, causing a smaller root mean square (RMS) distance error.…”

“…Examples are the measurement of levels of fluids and solids in storage tanks [2]- [4], where a radar sensor is preferred over conventional systems to avoid direct contact to the sample. Especially if oil or gas at a high pressure is used, for example to displace pistons or hydraulic cylinders, radar systems are an attractive alternative [5]- [7].…”