B. Will

High Precision Radar Distance Measurements in Overmoded Circular Waveguides

Distance measurements in overmoded waveguides are an important application for industrial radar systems. The accuracy of the measurements is deteriorated by the appearance of higher order modes in the metal tube, although the frequency-modulated continuous-wave method is used with a large bandwidth. This paper describes the problems caused by dispersion and multimode propagation and presents a solution in the form of mode-matched antennas for feeding the overmoded waveguide. It is shown that different modes, e.g., the H11 and H01 modes, are equally well suited for precision distance measurements, as is demonstrated both by simulations and measurements.

Radar Distance Measurements in Over-sized Circular Waveguides

One of the main tasks of industrial radar systems is the determination of distances to a reflecting object. An important application is the measurement in metal tubes e.g. by means of the FMCW method. A comparison of measurements in metal tubes and in free-space shows that several problems arise due to the non-perfect coupling between the feeding antenna and the metal tube. This contribution describes the problems caused by dispersions and multi-mode propagations, and presents approaches for their solution

Comparative study of moisture measurements by time domain transmissometry

Time domain transmissometry (TDT) is an emerging technology in the field of moisture measurements. While time domain reflectometry (TDR) is a well-known method for moisture measurements since the 1980s, TDT measurements were not applied until the last decade. The key benefit of TDT measurements is the robustness against multiple reflections along the sensor resulting in higher measurement accuracy and lower requirements concerning the electronics. However, transmission measurements in soil, grain, or other bulky goods yield some difficulties. Especially the realization of a second measuring port at the end of the sensor is challenging. This contribution gives an overview on TDT systems for moisture measurements. Beside the theoretical background, existing sensors and measurement systems are compared and illustrated in detail.

A planar orthomode transducer for broadband applications at 25 GHz using a stepped waveguide technique

In this contribution, a novel planar orthomode transducer is presented. It is based on a stepped waveguide technique that makes the transducer small and easy to handle. Several electromagnetic simulations were performed in order to optimize the transducers structure and to investigate possible production tolerances, respectively. The developed orthomode transducer was built up and measured in a back to back assembly. The broadband measurement results as well as its planar structure allow different kind of feeding which make the presented orthomode transducer suitable for numerous applications.

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 monostatic antenna-reflector system for ultra-short-range radar applications

In this contribution, a novel antenna-reflector system is introduced, which consists of a planar waveguide orthomode transducer, a lens-horn antenna and a transpolarizing reflector. The proposed antenna system eliminates short-range clutter effects like root point reflections and antenna ringing effectively. The setup enables ultra-short-range radar measurements as they are used e.g. for material characterization measurements. Results of 3D-electromagnetic field simulations as well as measurements, that prove the effectiveness of the antenna setup are shown and discussed in detail.

A multi directional dielectric lens approach for antennas used in industrial RADAR applications

A multi directional dielectric lens approach for beam steering on the basis of an ellipsoidal antenna is presented in this paper. Good antenna characteristics allow a modification of the feeding device used for the desired beam steering in industrial RADAR applications at 24 GHz. Based on a geometrical-optical lens approach and 3D-electromagnetic field simulations the antenna is investigated and the resulting effects of the modification are discussed. The antenna beam is steerable in a wide range, only limited by the antenna dimensions. Using a movable waveguide or multiple feeding elements in one antenna within the same plane, an adjustable beam direction as well as a multistatic beam steering can be realized. Measurements of a prototype confirm the expected behaviour and demonstrate the applicability of the dielectric ellipsoidal lens antenna for beam steering in industrial RADAR applications.

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.

A new approach on broadband calibration methods for free space applications

The application of free space measurements depends on the practicability of the respective calibration procedure. Due to necessary changes of the distance between used antennas or a precise positioning of calibration standards, the suitability of free space setups is limited. This contribution deals with a calibration technique for free space applications, which uses the change of the electrical length by means of small frequency variations. Thus, this technique enables free space calibrations without the necessity of antenna displacements. Furthermore, the bandwidth of this procedure is not limited due to ambiguities of mechanical displacements during the calibration procedure. Additionally, the presented calibration technique is based on the Thru-Line-Network (TLN) method. Hence, symmetrical and reciprocal measurement objects can be characterized within the calibration procedure.

Time domain transmission sensors for soil moisture measurements

Delay time measurements, e.g. time domain reflectometry (TDR), are a well-established method for the measurement of permittivity in various materials, especially in soils. However, the accuracy offered by common TDR measurements is limited due to multiple reflections caused by the material under test. This contribution deals with new sensor designs for the characterization of soil moisture using time domain transmission (TDT) measurements. The basis of the advanced TDT technique is a new waveguide concept, which offers the possibility to perform transmission measurements in soils. Thus multiple reflections along the waveguide do not influence the measurement accuracy. By using a so-called “concentric reversion coupler” TDT measurements can be performed without a measuring port at the end of the sensor.