Christian M. Schmid

A 77-GHz Cooperative Radar System Based on Multi-Channel FMCW Stations for Local Positioning Applications

In this paper, a radar system for local positioning applications is presented. The system consists of frequency modulated continuous-wave (FMCW) stations operating in W-band that are loosely coupled using time-delayed ramp start signals. A centralized signal processing approach allows to relax the required synchronization accuracy between the stations and further leads to a cancellation of phase noise and phase distortions caused by imperfect FMCW ramps. All stations are equipped with an antenna array and multiple receivers. Thus, a signal processing approach is developed in this work that combines the positive effects from the centralized processing with the information from the antenna array in a digital-beamforming based approach to improve the multipath robustness of the overall system. The developed theory is confirmed in measurements carried out with a prototype system consisting of two stations. Various measurements in multipath environments confirm the improved robustness leading to a worst-case root-mean-square position error of 15 mm under strong multipath conditions which were simulated inside an anechoic chamber.

On the Effects of Calibration Errors and Mutual Coupling on the Beam Pattern of an Antenna Array

The beam pattern of an antenna array is one of the most important characteristics of classical phased arrays and of more modern smart antenna, digital beamforming and multiple-input multiple-output array systems. Most approaches to designing such systems are based on an ideal mathematical model, which leads to an ideal beam pattern. However calibration errors and mutual coupling are real-world effects that often deteriorate the beam pattern and thus the array performance. In this paper we present worst-case boundaries and a statistical analysis of the beam pattern deviation for linear, angle-independent calibration error and mutual coupling models. We provide general results as well as specialized results for calibration errors and coupling between adjacent channels of linear arrays. The results provide an understanding of the influence of different array design parameters. They are also meant as tools for specifying tolerance and channel coupling requirements as well as for the analysis of the probabilities to achieve a beam pattern within certain boundaries.

BLASTDAR—A Large Radar Sensor Array System for Blast Furnace Burden Surface Imaging

In this paper, we present a radar sensor system for real-time blast furnace burden surface imaging inside a fully operative blast furnace, called BLASTDAR, the blast furnace radar. The designed frequency-modulated continuous-wave (FMCW) radar sensor array operates in the frequency band around 77 GHz and consists of several nonuniformly spaced receive and transmit antennas, making it a multiple-input multiple-output radar system with large aperture. Mechanical steering is replaced by digital array processing techniques. Off-the-shelf automotive-qualified multichannel monolithic microwave integrated circuits are used. By means of this configuration, a virtual antenna array with 256 elements was developed that guarantees the desired angular resolution of better than 3°, and a range resolution of about 15 cm. Based on the single-channel FMCW signal model, this paper will derive a multichannel signal model in combination with a digital beamforming approach and further advanced signal processing algorithms. The implementation of a simulation tool covering the whole design process is shown. Based on these simulation results, a system configuration is chosen and the obtained setup is defined and presented. A description of the manufactured cost-efficient radio frequency and baseband boards together with the housing design shows the practical implementation of the sensor. For the system calibration, two different methods are listed and compared regarding their performance. Verification measurements confirm the predicted performance of the developed sensor. Several measurements inside a fully operational blast furnace demonstrate the proper long-term functionality of the system, to the best of our knowledge, for the first time worldwide. It is in continuous operation since about two years in blast furnace #5 of voestalpine Stahl GmbH, Linz.

An IQ-modulator based heterodyne 77-GHz FMCW colocated MIMO radar system

In this work the realization of a 77-GHz frequency-division multiple-access-based frequency-modulated continuous-wave multiple-input multiple-output radar with four transceiver channels in conjunction with a non-uniform linear antenna array is presented. The radar system, consisting of an RF-frontend utilizes transceiver chips with integrated inphase/quadrature-modulators to generate the frequency shifted transmit signals and a field programmable gate array-based baseband board, is used for test measurements to verify the system performance and to demonstrate the beamforming capability as well as the accuracy of the digital-beamforming method.

Design of a linear non-uniform antenna array for a 77-GHz MIMO FMCW radar

In this paper the design and the implementation of a linear, non-uniform antenna array for a 77-GHz MIMO FMCW system that allows for the estimation of both the distance and the angular position of a target are presented. The goal is to achieve a good trade-off between the main beam width and the side lobe level. The non-uniform spacing in addition with the MIMO principle offers a superior performance compared to a classical uniform half-wavelength antenna array with an equal number of elements. However the design becomes more complicated and can not be tackled using analytical methods. Starting with elementary array factor considerations the design is approached using brute force, stepwise brute force, and particle swarm optimization. The particle swarm optimized array was also implemented. Simulation results and measurements are presented and discussed.

A 77-GHz FMCW radar transceiver MMIC/waveguide integration approach

System integration is an important aspect in todays mm-wave systems. Monolithic microwave integrated circuits (MMICs) operating at mm-wave frequencies have become inexpensive and are now available even for lower volume applications. Most systems, however, rely on radio frequency (RF) substrates, bare-die chips and wire bonding, which makes them hard to handle and expensive. In this paper we present one possible solution: the integration of a 77-GHz frequency-modulated continuous-wave (FMCW) radar transceiver MMIC with an antenna in package that directly feeds a WR12 waveguide. The proposed system does not require RF substrate, is based on a packaged transceiver MMIC with a ball grid array, and has a WR12 interface that allows for a flexible combination with other WR12 components. We present simulation results of the MMIC to WR12 transition as well as measurement results of the integrated module.

Millimeter-wave phase-modulated backscatter transponder for FMCW radar applications

A millimeter-wave phase-modulated backscatter transponder in the E-band for readout with a frequency-modulated continuous-wave (FMCW) system is presented in this paper. Backscatter transponders have the advantage that, while no complete radio-frequency front end hardware, including signal generation, is required, they offer the capability to establish a one-way communication between the transponder and an interrogator. As we used an FMCW radar system as an interrogator, it is possible to extract range information as well as the modulated information from the transponder. In this paper we present the system basics as well as a fabricated prototype from which we obtained measurement results.

Mutual Coupling and Compensation in FMCW MIMO Radar Systems

Abstract This paper deals with mutual coupling, its effects and the compensation thereof in frequency-modulated continuous-wave (FMCW) multiple-input multiple-output (MIMO) array radar systems. Starting with a signal model we introduce mutual coupling and its primary sources in FMCW MIMO systems. We also give a worst-case boundary of the effects that mutual coupling can have on the side lobe level of an array. A method of dealing with and compensating for these effects is covered in this paper and verified by measurements from a 77-GHz FMCW radar system.

Measurement-based delay-and-sum signal processing for linear antenna arrays

In this paper we presented a method for designing a delay-and-sum beamformer based on measured data. A big advantage over other methods is that no sophisticated external measurement equipment is needed. Only a single radar target is required. Furthermore it is robust against out of center rotation. There is no need to rotate the array about any well-defined (phase) center. The proposed method is very capable especially as both the computational requirements and the requirements on the measurement scenario are low. We also presented simulation results which support the method proposed. Preliminary measurement results have also confirmed the proposed concept.

A 77-GHz cooperative secondary radar system for local positioning applications

In this paper a cooperative radar system for local positioning applications operating at 77 GHz is presented. The proposed system is based on multiple frequency-modulated continuous-wave based stations which transmit their measured signals to a common processing unit. The required station synchronization accuracy is relaxed due to the centralized processing. Furthermore phase noise and sweep non-linearity effects can be mitigated in the signal processing. Measurements carried out using a realized prototype with two stations show a performance improvement of approx. 6 dB compared to conventional methods that are based on the exchange of preprocessed data.