Christoph Dahl

A millimeter-wave based measuring method for the differentiation of atherosclerotic plaques

In this contribution, a novel measuring method for the differentiation of intra vascular plaque types is presented. The proposed method operates contact free because of the mm-wave based approach. Fundamentals concerning material properties of blood and plaque, and electromagnetic barrier reflections are discussed. Furthermore, a test setup consisting of a miniaturized sensor setup is introduced that clarifies the measuring concept. Additionally, results of 3D electromagnetic field simulations as well as first measurements ex situ performed on non-human genetic materials are shown and discussed in detail.

A two-dimensional radar simulator for level measurement of bulk material in silos

In this contribution, a two-dimensional radar simulator, which is used to determine the specifications and to predict the accuracy of a scanning radar system for filling volume measurement of bulk solids in silos, is presented. The simulator is based on a simple scattering model using polar coordinates in order to achieve an efficient implementation. Additionally, a detection algorithm based on a speckle filter has been tested for an exemplarily bulk solid scenario, and the influence of the penetration depth of the bulk solid, the antenna beam width, and the filling level on the measurement error has been analyzed.With a minimum signal to noise ratio of 10 dB, a measurement error smaller 2 m has been obtained for the given scenario.

Conceptual design of a dielectric hemispherical lens antenna with a congruent radiation pattern for beam steering applications

In this contribution a dielectric hemispherical antenna allowing wide range beam steering for 24 GHz radar applications is presented. A feeding concept for a hemispherical lens is developed using the geometrical-optical lens approach, therewith a high gain of 24 dBi is achieved with a lens radius of 90 mm. The lens is fed by a corrugated horn antenna to provide a low side lobe level up to a steering angle of 50°. 3D-electromagnetic field simulations and measurements confirm the antenna performance in the chosen scenario.

Multi-spectral echo signal processing for improved detection and classification of radar targets

A major challenge in radar based remote sensing and imaging is to identify and to detect radar targets, and also to accurately determine their locations and sizes. This especially applies in the case of multiple, spatially distributed radar targets, as for example in radar imaging, automotive radars, and others. Previously, we have proposed a concept for multi-spectral analysis and processing of echo signals for radar level measurement of bulk solids in silos using a spatially fixed antenna beam. This approach has now also been utilized for scanning radar applications. The basic technique is to filter the radar echo signals in multiple frequency sub-bands and to incoherently combine the filtered signals. Furthermore, the variance of envelope signals is analyzed in order to allow for a differentiation between echoes from distributed, randomly arranged scatterers and from spatially isolated single scatterers. The mean over the standard deviation of the envelope signals obtained from the different sub-bands is suggested to be used as an amplitude-invariant parameter for the classification of radar targets. Results of an experimental evaluation of the concept using a mechanically scanning 75 to 80 GHz Frequency Modulated Continuous Wave (FMCW) radar system are presented. It will be shown that the proposed technique enables to largely suppress the echo signal fluctuations, which are given in scenarios of spatially distributed radar targets, and also to distinguish between different kinds of radar targets.

A Newly Developed mm-Wave Sensor for Detecting Plaques of Arterial Vessels

Background Microcalcifications within the fibrous cap of the arteriosclerotic plaques lead to the accrual of plaque‐destabilizing mechanical stress. New techniques for plaque screening with small detectors and the ability to differentiate between the smooth and hard elements of plaque formation are necessary. Method Vascular plaque formations are characterized as calcium phosphate containing structures organized as hydroxylapatite resembling the mineral whitlockite. In transmission and reflexion studies with a simple millimeter wave (mm‐wave)‐demonstrator, we found that there is a narrow window for plaque detection in arterial vessels because of the tissue water content, the differentiation to fatty tissue, and the dielectric property of air or water, respectively. Result The new sensor is based on a sensing oscillator working around 27 GHz. The open‐stub capacitance determines the operating frequency of the sensor oscillator. The capacitance depends on the dielectric properties of the surrounding material. The sensor components were completely built up in surface mount technique. Conclusion Completed with a catheter, the sensor based on microwave technology appears as a robust tool ready for further clinical use.

Fractal antenna arrays for MIMO radar applications

In this contribution, fractal antenna arrays are analyzed for their applicability in multiple-input multiple-output (MIMO) radars. Array geometries based on the Fudgeflake fractal and the Gosper island fractal are investigated. In addition, a concept for the combination of both fractals is shown in order to increase the flexibility concerning the number of transmitting and receiving antennas. The presented fractal MIMO concepts can be utilized in order to improve the angular resolution and to reduce the sidelobe level for a given number of transmitting and receiving antennas. It is shown that a fractal MIMO concept with 21 transmitting antennas and 21 receiving antennas improves the angular resolution to 4.6 degrees and reduces side lobe level by 3.1 dB compared to a MIMO configuration based on two linear arrays with the same number of antenna elements. In addition, the results are experimentally validated by broadband radar measurements.

An electronically reconfigurable reflectarray element based on binary phase shifters for K-band applications

A reflectarray concept which allows electronic beam-steering by using a binary phase approximation is presented. The proposed antenna element works at 24 GHz and is comprised of an aperture-coupled patch antenna with an open-ended microstrip line on the backside to obtain the proper phase distribution on the reflectarray aperture. Electronic beam-steering is achieved by applying PIN diodes on the individual reflectarray elements. To simplify the control process of the antenna, the elements function as one-bit phase shifters either reflecting with a 0° or 180° phase shift. The reflectarray element is verified by measurements obtained with a prototype in a waveguide simulator setup.