Reinhard Feger

A 77-GHz FMCW MIMO Radar Based on an SiGe Single-Chip Transceiver

This paper describes a novel frequency-modulated continuous-wave radar concept, where methods like nonuniform sparse antenna arrays and multiple-input multiple-output techniques are used to improve the angular resolution of the proposed system. To demonstrate the practical feasibility using standard production techniques, a prototype sensor using a novel four-channel single-chip radar transceiver in combination with differential patch antenna arrays was realized on off-the-shelf RF substrate. Furthermore, to demonstrate its practical applicability, the assembled system was tested in real world measurement scenarios in conjunction with the presented efficient signal processing algorithms.

A Fully-Integrated 77-GHz UWB Pseudo-Random Noise Radar Transceiver With a Programmable Sequence Generator in SiGe Technology

This paper describes a fully-integrated 77-GHz ultra-wideband pseudo-random noise (PRN) radar transceiver in a Silicon-Germanium technology. The transceiver is equipped with a programmable pseudo-random binary sequence (PRBS) generator, which is realized in a current-mode logic topology and can be operated with a clock rate of up to 4.25 GHz to enable a range resolution of 3.5 cm. The signal generation unit is simplified by including a frequency multiplier to create a 76.5-GHz carrier signal from a single 4.25-GHz input, that is also used as a clock for the PRBS generator. The transceiver achieves a phase noise of -105.3 dBc/Hz at 1-MHz offset frequency, a transmit output power of 6.2 dBm, a receive gain of 24 dB and an input-referred 1-dB compression point of -14 dBm. Track&hold circuits included in the receive path allow the use of a sub-sampling technique to reduce the IF data rate down to 1 MHz. Radar measurements with two PRN transceivers with different primitive polynomials were done concurrently to show a fundamental function of the programmable PRBS generator. Radar measurements with the PRN and the frequency-modulated continuous-wave (FMCW) principles show comparable results and the PRN radar proves to be a real alternative to the FMCW radar.

A DLL-Supported, Low Phase Noise Fractional-N PLL With a Wideband VCO and a Highly Linear Frequency Ramp Generator for FMCW Radars

This paper describes a frequency synthesizer for frequency-modulated continuous wave (FMCW) radars, operating in combination with a frequency multiplier, at 77 GHz. The fractional-N phase-locked loop (PLL)-based synthesizer is equipped with a wideband voltage-controlled oscillator, which is realized with CMOS transistors in a current-reuse technique, and a delay-locked loop (DLL). Utilized as a frequency multiplier for the reference signal, the DLL improves both the phase noise performance of the PLL and the linearity of the frequency sweep generated by the PLL. Two types of voltage-controlled delay lines used in the DLL are also introduced and compared in this paper. Both show a good performance in terms of phase noise and can be easily realized in a standard CMOS technology. The false-lock issue of the DLL is also discussed and a solution is proposed. Furthermore, a frequency multiplier is used to multiply the output frequency of the PLL by a multiplication factor of 18. This architecture enables an increase in the target resolution and an improvement in the accuracy of the measurements of FMCW radars.

A Four-Channel 94-GHz SiGe-Based Digital Beamforming FMCW Radar

This paper presents a multi-channel frequency-modulated continuous-wave (FMCW) radar sensor operating in the frequency range from 91 to 97 GHz. The millimeter-wave radar sensor utilizes an SiGe chipset comprising a single signal-generation chip and multiple monostatic transceiver (TRX) chips, which are based on a 200-GHz fT HBT technology. The front end is built on an RF soft substrate in chip-on-board technology and employs a nonuniformly distributed antenna array to improve the angular resolution. The synthesis of ten virtual antennas achieved by a multiple-input multiple-output technique allows the virtual array aperture to be maximized. The fundamental-wave voltage-controlled oscillator achieves a single-sideband phase noise of -88 dBc/Hz at 1-MHz offset frequency. The TX provides a saturated output power of 6.5 dBm, and the mixer within the TRX achieves a gain and a double sideband noise figure of 11.5 and 12 dB, respectively. Possible applications include radar sensing for range and angle detection, material characterization, and imaging.

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.

Sparse antenna array design and combined range and angle estimation for FMCW radar sensors

In this paper the design of sparse antenna arrays and signal processing algorithms for non-parametric high resolution range and angle estimation algorithms for FMCW radar sensor arrays are presented. Since the performance of such systems strongly depends both on the antenna placement as well as the adequate algorithms, the close relation between antenna hardware and signal processing is exploited in the development of the whole system. The theory is verified by measurements utilizing a system operating at 24 GHz and using a four element array with interelement spacings larger than half a wavelength for each array element. The simulations and measurements show promising results which makes the system attractive for applications where only few channels are available and high gain and therefore large array elements are necessary, which would prohibit the use of classical half-wavelength spaced arrays.

FMCW MIMO Radar System for Frequency-Division Multiple TX-Beamforming

In this paper, a prototype automotive radar sensor is presented that is capable of generating simultaneously multiple transmit (TX) beams. The system is based on a four-channel 77-GHz frequency-modulated continuous-wave (FMCW) radar system. The number of beams, their radiated power, steering angle, and beam pattern can be changed adaptively. This is achieved by the utilization of orthogonal waveforms applied to different beams in combination with digital beamforming on the receive side. Key components are vector modulators in the TX path controlled by digital-to-analog converters. The performance of the system is shown in measurements focused on beam pattern, signal-to-noise ratio, and susceptibility in case of interfering targets at cross-range. Measurement results are discussed and compared to theory and simulations. Furthermore, crest factor minimization of the vector modulators control signals is introduced and used to increase the achievable TX power, which will be also shown in measurements.

A versatile FMCW Radar System Simulator for Millimeter-Wave Applications

For the successful design of low-cost and high-performance radar systems accurate and efficient system simulation is a key requirement. In this paper we present a new versatile simulation environment for frequency-modulated continuous-wave radar systems. Besides common hardware simulation it covers integrated system simulation and concept analysis from signal synthesis to baseband. It includes a flexible scenario generator, accurate noise modeling, and efficiently delivers simulation data for development and testing of signal processing algorithms. A comparison of simulations and measurement results for an integrated 77-GHz radar prototype shows the capabilities of the simulator on two different scenarios.

A 77-GHz FMCW front-end with FPGA and DSP support

Recent advances in the development of semiconductors allow the realization of low cost 77-GHz radar front-ends suitable for automotive applications. The requirements on the angular resolution often force designers to implement antenna arrays. In the last decade the trend moves towards digital array processing instead of analog beamforming because of the availability of cheap digital signal processors (DSP). In the case of an n-element receive array, the system must be capable of processing n receive channels in parallel resulting in a big amount of data. Field programmable gate arrays (FPGA) deliver the processing power and flexibility to handle the collected data and allow, in conjunction with a DSP, the implementation of sophisticated signal processing algorithms. This paper deals with the implementation of a 77-GHz frequency modulated continuous wave (FMCW) prototype radar system. The system is designed for use in array processing applications, with a maximum of eight parallel receive channels. The functionality of the prototype system is demonstrated in an imaging application. With the help of a portal axis the radar is moved along a synthetic aperture in order to reconstruct the reflectivity map of the imaging area.