Sarah Linz

Six-Port Based Interferometry for Precise Radar and Sensing Applications.

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 compact, versatile six-port radar module for industrial and medical applications

The Six-port receiver has been intensively investigated in the last decade to be implemented as an alternative radar architecture. Plenty of current scientific publications demonstrate the effectiveness and versatility of the Six-port radar for special industrial, automotive, and medical applications, ranging from accurate contactless vibration analysis, through automotive radar calibration, to remote breath and heartbeat monitoring. Its highlights, such as excellent phase discrimination, trivial signal processing, low circuit complexity, and cost, have lately drawn the attention of companies working with radar technology. A joint project involving the University of Erlangen-Nuremberg and InnoSenT GmbH (Innovative Sensor Technology) led to the development of a highly accurate, compact, and versatile Six-port radarmodule aiming at a reliable high-integration of all subcomponents such as antenna, Six-port front-end, baseband circuitry, and digital signal processing in one single package. Innovative aspects in the RF front-end design as well as in the integration strategy are hereby presented, together with a system overview and measurement results.

A microwave interferometer based contactless quasi-TEM waveguide position encoder with micrometer accuracy

Position measurement plays an important role in industrial process technology. Hereby, a waveguide based position sensor system for industrial applications is described. The proposed system features a Phase Locked Loop controlled 24 GHz signal source, an interferometric Six-Port receiver structure, a radar coupler, and a terminated quasi-TEM parallel plate waveguide structure. Furthermore, the system concept comprises a target, which can be applied both touching and contactless in the waveguides fringing field, reflecting a part of the transmitted wave. To obtain the targets position information, the reflected wave is compared to a reference signal with respect to the relative phase difference. Hence, this phase shift is directly related to the position information.

A multiband 2-port VNA for biomedical applications based on two six-port-junctions

This paper presents a triple band two port vector network analyzer (VNA) consisting of two six-port-junctions for biomedical concentration measurements. The microwave sensing system is designed to operate with a 10% bandwidth around 6.6 GHz, 19.7 GHz and 32.4 GHz. An embedded coplanar permittivity sensor will be applied for measurements of aqueous glucose solutions. The entire microwave sensing system is designed, fabricated and characterized with different glucose concentrations in binary solutions.

Precise and fast frequency determination of resonant SAW sensors by a low-cost Six-Port interferometer

Surface acoustic wave (SAW) resonators are used for a broad range of wireless sensing applications, some of them having high demands on the resolution as well as the measurement update rate. This paper presents a new interrogation method for precise and fast frequency determination of passive SAW resonators based on instantaneous frequency measurement (IFM) by a low-cost Six-Port interferometer. By using a delay line, the frequency measurement is reduced to a phase measurement that can be instantaneously evaluated by the Six-Port network. No complex signal processing is necessary providing high update rates and low hardware costs. A demonstrator in the 2.4 GHz frequency band shows the feasibility and the precision of the concept with measurement times of only a few microseconds.

Ultra-short-range, precise displacement measurement setup with a near field slot-line antenna and a dedicated spiral calibration

This work introduces a precise measurement setup for displacement analysis in the near field of a tapered slot-line antenna from 0mm up to 20mm distance. Enhanced accuracy is achieved by a dedicated spiral reconstruction algorithm accounting for the near field effects. Moreover, the precision of the system in the micrometer range is guaranteed by four synchronous 24 bit analog-to-digital converters and a decimation factor of 10, leading to an overall update rate of 1 kHz.

61 GHz Six-Port radar frontend for high accuracy range detection applications

Range detection is an challenging task, especially if high accuracy has to be reached. The hereby proposed 61 GHz continuous wave radar system is based on a phase detector using Six-Port technique. For accuracy enhancement an improved isolation radar coupler has been introduced for broadband frequency modulated continuous wave radar as well as narrow band radar techniques. Furthermore, a Six-Port network based on four hybrid couplers is presented. Finally, the most important system sub-components have been validated by measurements.

Improved calibration procedure for six-port based precise displacement measurements

In this paper an improved calibration procedure for six-port based displacement measurement radar is proposed. The entire system characterization is done only using several measurements of the target at known positions and no additional calibration standards are required. The proposed calibration has been experimentally verified for a six-port based displacement measurement radar operating at 24 GHz. The performed measurements within the target position range 0 - 18.75 mm prove a significant improvement of the accuracy with respect to the other reported algorithms.

ADC depending limitations for Six-Port based distance measurement systems

This publication will show some considerations for selecting an appropriate analog-digital-converter (ADC) in Six-Port based radar systems for distance measurements. It will be discussed how the ADC resolution is limiting the overall system range resolution. Furthermore, configurations with non-synchronous sampling of the four baseband signals and their influences on the system performance will be investigated.

High-Speed Resonant Surface Acoustic Wave Instrumentation Based on Instantaneous Frequency Measurement

Surface acoustic wave (SAW) resonators are used for a broad range of wireless sensing applications, some of them having high demands on the resolution as well as the measurement update rate. This paper presents a new interrogation method for precise and fast frequency determination of passive SAW resonators based on instantaneous frequency measurement by a low-cost six-port interferometer. Using a delay line, the frequency measurement is reduced to a phase measurement that can be instantaneously evaluated by the six-port network. No complex signal processing is necessary providing high update rates and low hardware costs. An in-depth analysis of the system concept and its building blocks is presented, and the advantages as well as the limitations are discussed and compared with the current state of the art. Finally, a demonstrator in the 2.4-GHz frequency band shows the feasibility and the precision of the concept with measurement times of only a few microseconds.