Joerg Schoebel

Short-Range Ultra-Broadband Terahertz Communications: Concepts and Perspectives

We propose the concept of ultra-broadband terahertz communication, based on directed non-line-of-sight (NLOS) transmissions. Potential applications of such a system supporting multi-gigabit data rates are given, and put into the context of currently emerging WLANs/WPANs. The technology and propagation constraints serve as boundary conditions for the determination of the required antenna gain to support ultra-broadband communication. Resulting high-gain antenna requirements will necessitate highly directed transmissions. We propose the use of omni-directional dielectric mirrors to support directed NLOS paths. Their performance is investigated with ray-tracing simulations of a terahertz propagation channel in a dynamic office environment, which is calibrated with measured building-material and mirror parameters. We demonstrate that a directed NLOS path scheme will make a terahertz communication system robust to shadowing. Furthermore, we show that dielectric mirrors covering only parts of the walls will significantly enhance the signal coverage in a typical indoor scenario.

Performance Analysis of Future Multigigabit Wireless Communication Systems at THz Frequencies With Highly Directive Antennas in Realistic Indoor Environments

In this paper, a simulation environment encompassing realistic propagation conditions and system parameters is employed in order to analyze the performance of future multigigabit indoor communication systems at tetrahertz frequencies. The influence of high-gain antennas on transmission aspects is investigated. Transmitter position for optimal signal coverage is also analyzed. Furthermore, signal coverage maps and achievable data rates are calculated for generic indoor scenarios with and without furniture for a variety of possible propagation conditions.

Design considerations and technology assessment of phased-array antenna systems with RF MEMS for automotive radar applications

Planar array antennas are attractive for use in future automotive radar systems due to their flexibility in design and control of radar beams. The complexity and cost of a radar front-end phased array can be decreased by applying a beam-steering/switching concept, which reduces the number of parallel RF and baseband signal paths. RF-microelectromechanical systems (MEMS) subsystems are employed because of their excellent RF properties and potential low-cost manufacturability. We present design considerations for prototypical automotive applications of RF-MEMS-based automotive radar front-ends using phased-array antennas based on phase shifters or a Rotman lens. The single RF-MEMS switch is optimized with respect to its RF and thermomechanical behavior taking into account automotive requirements. The respective RF-MEMS subsystems, i.e., phase shifters and single-pole-multiple-throw switching networks are presented in conjunction with packaging and mounting approaches. We evaluate two different wafer-level packaging technologies using glass-frit sealing or polymer sealing. Finally, functional packaged devices are demonstrated: a glass-frit-sealed and flip-chip-mounted RF-MEMS switch and a benzocyclobutene-packaged single-pole-quadruple-throw switch network.

Time of Arrival Prediction for WLAN Systems Using Prony Algorithm

One of the important parameters for indoor localization systems based on wireless local area networks (WLANs) is estimation of time of arrival (TOA). This paper presents a technique that utilizes the channel transfer function to estimate TOA. The technique is based on the Prony algorithm, which has been used for the prediction of multipath parameters. Computer simulations for noisy and noiseless data have been performed to validate the technique. Moreover, measurements at WLAN frequencies are performed for further confirmation of the suggested technique.

Spatial Correlation and MIMO Capacity of Uniform Rectangular Dipole Arrays

In this letter, we derive an analytical expression for the spatial correlation (SC) of uniform rectangular dipole arrays for a two-dimensional (2-D) spatial power spectrum, considering both Elevation spread (ES) and Azimuth spread (AS). We show that the dipole arrays have more spatial correlation than isotropic arrays, if the ES is larger than AS. The spatial correlation considering the mutual coupling is also evaluated using ldquoEmbedded element radiation patternrdquo concept. The SC with coupling almost oscillates around SC without coupling. Using Kronecker channel model, the capacity is evaluated for the Uniform Rectangular Array (URA) involving isotropic and dipole antennas. It has been found that the capacity of the array of dipole antennas is greater than that of the omnidirectional antenna array if coupling is considered and vice versa.

Planar Antenna Technology for mm-Wave Automotive Radar, Sensing, and Communications

Planar antennas are common components in sensing applications due to their low cost, low profile and simple integration with systems. They can be used commonly at frequencies as high as 77 GHz and above, for example in automotive sensing. Also, new ultra-wideband communication systems operating around 60 GHz will heavily rely on planar antennas due to their unique properties. One special advantage of planar elements is that they can easily form array structures combining very simple elements, like microstrip patches. Also phased and conformal arrays can be built. Due to all these characteristics, planar antennas are very good candidates for building front ends for mm-wave applications in radar, sensing or communications. For some applications, which are either established today or which will become commercial in a few years, general requirements can be given. In addition to automotive radar, this mainly applies to 60 GHz ultra-broadband wireless indoor communications. Microwave imaging at 94 GHz and above is still much under research, as well as other sensing applications in the millimeter-wave region above 100 GHz. Prominent frequency bands are in the 122 and 140 GHz range1. Typical antenna requirements are multi-beam or scanning capability, high gain up to 30..36 dBi and moderate to low sidelobes. In monopulse radar systems, the sidelobes may be included in the angle determination scheme, then the sidelobe level requirements are rather relaxed. Loss is generally an important issue. Comparing a planar approach to a commercially available dielectric lens, the planar antenna exhibits significantly higher losses, especially if the beamforming device is included. The antenna efficiency of 77 GHz planar array columns is roughly 50%. These losses are caused by dielectric losses and conductor losses. To attain reliable predictions of the losses in full-wave simulations, care has to be taken in the

Integration of 0/1-Level Packaged RF-MEMS Devices on MCM-D at Millimeter-Wave Frequencies

This paper reports on the development and optimization of 0/1-level packaged coplanar waveguide (CPW) lines and radio-frequency microelectromechanical systems (RF-MEMS) switches up to millimeter-wave frequencies. The 0-level package consists of an on-chip cavity obtained by flip-chip mounting a capping chip over the RF-MEMS device using BenzoCyclobutene (BCB) as the bonding and sealing material. The 0-level coplanar RF feedthroughs are implemented using BCB as the dielectric; gold stud-bumps and thermocompression are used for realizing the 1-level package. The 0-level packaged switches have been flip-chip mounted on a multilayer thin-film interconnect substrate using a high-resistivity Si carrier with embedded passives and substrate cavities. The insertion loss of a single 0/1-level transition is below -0.15 dB at 50 GHz. The measured return loss of a 0/1-level packaged 50-Omega CPW line remains better than -19 dB up to 71 GHz and better than -15 dB up to 90 GHz. It is shown that the leak rate of BCB sealed cavities depends on the BCB width, and leak rates as low as 10-11 mbar.l/s are measured for large BCB widths (> 800 mum), dropping to 10-8 mbar.l/s for BCB widths of around 100 mum. Depending on the bonding conditions, shear strengths as high as 150 MPa are achieved.

Planar Antenna Array at D-Band Fed By Rectangular Waveguide for Future Automotive Radar Systems

Planar antennas are being used in frequencies up to 77 GHz for automotive radar because of their low profile and low-cost manufacturing. Also because of their flexibility when building phased and conformal arrays. In this paper a planar antenna around 140 GHz for the possible next generation of automotive radar is developed. This high frequency can provide narrower beams and better angular resolutions than the current sensor antennas. The structure is designed using a 3D electromagnetic simulator and is fabricated on a commercially available substrate. The fabrication consist of a common photolitography process which yields a very low-cost concept. In addition, this antenna can help to characterize the channel with planar systems, so the capabilities and limits of this technological approach can be tested. Experimental measurements were performed showing a gain of about 11 dBi and a return loss better than -10 dB over a band of 2 GHz.

An Integrated Simulation Environment for the Investigation of Future THz Communication Systems: Extended Version

The first stages of developing indoor communication systems operating at frequencies beyond 300 GHz are currently undeway. In this paper, an integrated simulation environment is introduced, where the system parameters of future THz communication systems can be estimated under realistic hardware and propagation conditions. It is shown how this simulation environment can be used to determine the most critical parameters in the whole system and may be used to derive requirements for the development of hardware components. Exemplary simulation results, taking into account various factors of influence (different modulation schemes, antenna gains and wall materials), are presented.

Performance evaluation of 60 GHz WLAN antennas under realistic propagation conditions with human shadowing

In this paper, the evaluation of different 60 GHz WLAN antenna designs is presented. Based on ray tracing and human blockage the radio propagation in a living room scenario is modeled. Then simulated 3D antenna patterns of conventional and smart antennas are linked to the radio channel data. The performance of the antennas is compared in terms of the coverage probability within the living room.