Martin Hitzler

A reference measurement setup for the deployment and test of multiple-input-multiple-output (MIMO) arrays is essential when a new array is optimized according to specific application requirements. For such a reason, in this article, a testbed for the performance assessment of 1-D and 2-D MIMO arrays at 300 GHz for radar applications is proposed. The system is based on monolithic microwave integrated circuit (MMIC) to dielectric waveguide (DWG) transitions, which makes the array element positions independent of the positions of the MMICs on the hardware back-end. The antenna arrays to be tested are fed through DWGs, which are extremely mechanically flexible and easy to reconnect to different antenna arrays. The effectiveness of the proposed testbed is demonstrated by the test of three different antenna arrays made of three transmitters and two receivers. One 1-D MIMO array and two 2-D MIMO arrays are designed for this purpose. The antenna positions are optimized through a genetic algorithm based on the analysis of the ambiguity function associated with the array. This optimization shows that even with a reduced number of array elements, it is possible to perform direction of arrival (DoA) estimation on both azimuth and elevation angles at 300 GHz. The optimized antenna arrays are then tested through the proposed system. An analysis of the measured ambiguity functions associated with the arrays shows a strong agreement with the simulated ones and demonstrates the functionality of the system.

The packaging technology for transitions to dielectric waveguides in the frequency range above 100 GHz is complex and must be highly precise, and the waveguides are usually permanently connected. This letter presents a transition from a monolithic microwave integrated circuit (MMIC) to a flexible dielectric waveguide at G-Band (140-220 GHz), which is self-aligning and, thus, reduces the requirements for packaging accuracy. Furthermore, the transition is mechanically decoupled to avoid mechanical stress to the MMIC and to reconnect it arbitrarily often. A patch radiator on a quartz-glass carrier is excited by a coupler on the MMIC. It feeds the HE ₁₁ mode into a rigid, high-permittivity dielectric dome, which increases the coupling efficiency. The flexible dielectric waveguide is placed above the dome and fixed with Rohacell half shells. The minimum insertion loss measured with a back-end-of-line (BEOL) MMIC is 3.0 dB at 168 GHz.

A high-resolution frequency-modulated continuous wave imaging radar for short-range applications is presented. A range resolution of about 1 cm is achieved with a bandwidth of up to 16 GHz around 160 GHz. In order to overcome losses and large tolerances on a printed circuit board (PCB), eight coherently coupled monolithic microwave integrated circuits (MMICs) are used, each with one transmit and receive antenna on-chip and each representing a single-channel radar system. The signals on the PCB are below 12 GHz, which facilitates fabrication and enables a design with low-cost substrates. The MMIC comprises a phase noise (PN)-optimized architecture with a fully integrated on-chip frequency synthesizer. Due to partly uncorrelated PN between the frequency synthesizer components, the noise level is increased in bistatic radar measurements between two different MMICs, which is explained by a thorough PN analysis. Time-division multiplexing is used to realize a multiple-input multiple-output system with a virtual array of 64 elements and an angular resolution better than 1.5° for the designed array. The positioning tolerances of the MMICs are included into the design resulting in a robust array design. The high-resolution radar performance is proven by imaging radar measurements of two exemplary scenarios.

A number of millimeter-wave (mm-wave) integrated radar sensors above 100 GHz were proposed in the past five years. The comparability between these radar systems is limited due to different semiconductor processes, synthesizer topologies, and external periphery. Especially, the issue of using a monostatic or bistatic radar monolithic microwave integrated circuit (MMIC) for single-chip sensors is not discussed in detail. This paper provides a comparison between the different properties of bistatic and monostatic MMICs based on two realized almost identical silicon germanium (SiGe)-MMICs at 154 GHz. In the monostatic case, the influence of the transmit-receive coupler on the performance of the system is explained. In the bistatic case, the illumination of a focusing lens and the leakage from transmitter to receiver are investigated. All properties are verified by measurements. The system performance of the monostatic and bistatic MMIC are compared by the calculated link and noise budget. The detection performance and the signal-to-noise ratio performance are evaluated in two radar measurements. Limitations and suggestions for improvement are given for monostatic and bistatic mm-wave frequency-modulated continuous-wave radar MMICs.

On-chip antennas are frequently used as radiating elements for MMICs operating above 100 GHz. Their radiation pattern is wide since the radiator extension is typically about half a wavelength. In a package the wide radiation pattern is easily disturbed by interference from parasitic radiation of the package. In this paper an approach to minimize and adjust the interference of the package is proposed and applied to a QFN housing. A structured metal sheet positioned between chip and exposed pad is used to generate enough degrees of freedom for the optimization of the 3D-radiation pattern in open-cavity and molded QFN packages. For the open-cavity QFN package a U-shaped slot is introduced, which reduces the propagation of surface waves to the sides and creates a uniform radiation pattern. For the molded QFN package with opening around the on-chip antenna a corrugated metal sheet is introduced. This leads to a robust packaged radar MMIC with on-chip antenna at 160 GHz, which provides a directed radiation pattern to boresight. Both optimized radiation patterns are well-suited for the illumination of dielectric lenses, which results in a higher lens gain and a lower side lobe level of the lens pattern compared to the standard QFN packaging. The proposed concepts are verified by measurements for the open-cavity and molded QFN package at 160 GHz.

The dynamic range of frequency modulated continuous wave (FMCW) radar sensors is often limited by the phase noise of the ramp signal. Especially at millimeter wave (mm-wave) frequencies, a low phase noise signal is very difficult to obtain. In this paper, a new system architecture, which is implemented in a low-cost, ultracompact FMCW radar monolithic microwave integrated circuit (MMIC) at 160 GHz, is proposed to address this topic. The approach is based on a frequency offset synthesizer, whose upconverting mixer is driven by a stabilized low phase noise local oscillator (LO) signal. This LO is generated by a fixed-frequency phase locked loop with a 2^N divider. The upconversion of the ramp signal with the stabilized LO signal leads to an excellent mm-wave phase noise of -89 dBc/Hz at a frequency offset of 1 MHz. By integrating the antennas on the MMIC, interconnects at mm-wave frequencies to package or printed circuit board are avoided and a simple assembly and interconnection technology is feasible. The ultracompact MMIC is realized on an area of only 2 mm², including the integrated antennas. A precision below 5 μm for range measurements is demonstrated with the radar sensor. Additionally, the radar performance is evaluated with two different voltage-controlled oscillators for the generation of the ramp signal.