Six-Port Based Interferometry for Precise Radar and Sensing Applications

Abstract

Microwave technology plays a more important role in modern industrial sensing applications. Pushed by the significant progress in monolithic microwave integrated circuit technology over the past decades, complex sensing systems operating in the microwave and even millimeter-wave range are available for reasonable costs combined with exquisite performance. In the context of industrial sensing, this stimulates new approaches for metrology based on microwave technology. An old measurement principle nearly forgotten over the years has recently gained more and more attention in both academia and industry: the six-port interferometer. This paper reviews the basic concept, investigates promising applications in remote, as well as contact-based sensing and compares the system with state-of-the-art metrology. The significant advantages will be discussed just as the limitations of the six-port architecture. Particular attention will be paid to impairment effects and non-ideal behavior, as well as compensation and linearization concepts. It will be shown that in application fields, like remote distance sensing, precise alignment measurements, as well as interferometrically-evaluated mechanical strain analysis, the six-port architecture delivers extraordinary measurement results combined with high measurement data update rates for reasonable system costs. This makes the six-port architecture a promising candidate for industrial metrology.

A dataset of radar-recorded heart sounds and vital signs including synchronised reference sensor signals

“…A detailed description of the radar system is given in 17 . The Six-Port is a completely passive structure which basically consists of three quadrature hybrid couplers and one Wilkinson divider 29 . As indicated by its name, the Six-Port has two input and four output signals.…”

Six-port reflectometer in WR15 metallic waveguide for free-space sensing applications

“…More information about the model construction is given in [9]. The calibration coefficients ‫ݕ‬ and ‫ݕ‬ ᇱ are determined by fitting the measured powers to the models (7) and (8). For comparison purposes, the calibration constants are determined for the 1 st (y 3 = y 4 and y 5 = y 6 = y 7 = 0), the 2 nd (y 6 = y 7 = 0) and the 3 rd orders.…”

“…The six-port technique has been introduced in the 1970s as a simple technique for measuring power and reflection coefficient in the microwave regime [1]. Since then, a variety of six-port systems have been exemplary demonstrated in metallic guide, substrate integrated waveguide (SIW), planar and monolithic forms [2]- [8]. Each technology presents own advantages and drawbacks in terms of circuit size, power consumption, immunity to temperature/hygrometry variations, fabrication facility, system integration, measurement performance and cost [8].…”

“…Since then, a variety of six-port systems have been exemplary demonstrated in metallic guide, substrate integrated waveguide (SIW), planar and monolithic forms [2]- [8]. Each technology presents own advantages and drawbacks in terms of circuit size, power consumption, immunity to temperature/hygrometry variations, fabrication facility, system integration, measurement performance and cost [8]. Therefore, the choice of the technology is mainly driven by the requirements of the targeted application.…”

A 24 GHz Waveguide based Radar System using an Advanced Algorithm for I/Q Offset Cancelation

“…This technology was developed in the 1970s by Engen and Hoer for power measurements (Engen and Hoer, 1972), and was converted to an alternative microwave receiver setup in recent years (Li et al, 1994;Koelpin et al, 2016). Within the Six-Port junction two input signals are superimposed with a static phase shift of π/2 among each other.…”