Ongoing and past research
The Microwave group started in 1992, where the research is presently supported by EU, SSF, Vinnova and VR. The microwave goup is also an active partner in the Vinnova VinnExcellence center Uppsala Center on Wireless Sensor Networks WISENET and in the Charmant (Strategic Research Center on Microwave Antenna Systems).
The research in the Microwave Group can be said to be in the areas of microwave components, circuits and systems design where the applications, developed together with national and foreign industry partners, are ranging from sensors to telecommunication.
The research in radio-front end technology in the microwave group originates from the beginning of the nineties when a strong collaboration with industry was initiated. Within this collaboration the Microwave group developed one of the first test beds for adaptive antenna base-station systems (DCS-1800) together with Ericsson Radio Access.
One of the main objectives for the sensor work has been to find cost-effective and high efficiency solutions for desing versatile communication modules for sensor applications. Thus, early in the 90'ties the Microwave group decided to put the effort into microwave circuit design using silicon based technology and later added polymer technology and now combinations of silicon and polymer. Together with Daimler Chrysler Research Center in Ulm, Germany we developed the world first frequency doubler for millimeterwave radio-link applications (55 GHz) using the then newly invented SiGe HBT technology. The work on the doubler was initiated in order to evaluate non-linear models for SiGe HBT-devices.
The modelling work was also the base for investigating the low frequency noise properties in the SiGe HBT. The research was aimed at developing non-linear physics-based millimeterwave models and low frequency (1/f-) noise models for new Si-based high frequency bipolar devices. Research was also done on measurement techniques for deriving the low-frequency noise of Si-based devices.
However these early designs where based on distributed transmission line technology which is not appropriate for miniaturisation and modern RF IC design necessary for sensor applications. Thus, together with Atmel in Germany and partners in the EU project ARTEMIS, we have developed communication modules for sensors using modern RF IC design. The frequency of operation for the modules was chosen to be in the 24 GHz ISM-band since at these frequencies full wavelength loop antennas offers good integration possibilities and can be placed at the perimeter of the chip, while leaving the area in the centre of the chip available for integration of the circuits. Thus, the monolithic integration of antennas with a commercial SiGe process, creates a self-contained sensor front-end, with no need for external RF interconnects. SiGe was selected since it is a viable low cost alterative to traditional III-V processes for fabricating fully integrated RF front-ends at microwave frequencies. The monolithic sensors contains a antenna integrated 24-GHz receiver and transmitter consisting of an LNA or PA, a voltage-controlled LO with an output buffer and a quadrature down-/up-conversion mixer. Polymers, such as polyimide and BCB, for spin coating of low resistivity silicon in combination with localized micromachining has been used for improving the gain and the radiation pattern of the antennas.
New measurement technique has been developed due to the very small dimension of the antenna integrated 24 GHz RF front-end's. The gain and radiation characterisation has to be done by mounting the antenna under test (AUT) on a foam dielectric to allow full 360 degrees characterization of the pattern. The RF connection to the antenna is provided by a wafer probe. The probe positioning equipment blocks part of the relatively omnidirectional radiation pattern and thus had to be covered with absorbers to minimize unwanted reflections. At lower frequencies, active antenna integrated arrays for telecommunication applications (repeater and small base stations) has been implemented. Antennas suitable for integration with a low-ohmic commercial SiGe process that has been investigated are meander, slot-loop, wire loop and PIFA antennas. Both low and high ohmic silicon processes has been used. By using a high resistivity wafer for the implemented receiver IC the efficiency of the on-chip antenna is improved. The clean-room facilities at the Angstrom Laboratory has also been used for fabrication of antennas using SiN membrane instead of BCB.
The inclusion of RF Microelectromechanical systems (MEMS) in combination with solid-state circuits is becoming more important at higher frequencies due to the possibility to reduce losses and improve the integration factor which can create intelligent RF front-ends. This integration demonstrates a new class of highly integrated RF components that through self-assessment and optimization can adapt to rapid and unforeseeable changes in the environment or with respect to operational demands. Thus, it is anticipated that such components can be enabled by integration of MEMS technologies with MMIC or RFIC processes. Reconfigurable RF front-end amplifiers (LNA and PA) can, for example, be used in order to adapt to parameter deviations that may occur due to process variations, temperature drift, aging or even changing operational requirements. The aim in the EU project RF-Platform is therefore to implement a 24 GHz reconfigurable LNA based on using RF MEMS and SiGe HBT technologies in combination with a reconfigurable antenna, i.e. using the technologies that are available within the project.
In the EU project e-CUBES solid-state circuits is integrated with sensors for (i) health and fitness application (in collaboration with Philips, Holland) and (ii) automotive applications (in collaboration with Infineon, Germany).
The poster below, presented at the EURIPIDES forum 2008 in Berlin dispays the research in the microwave group.
© 2011. UPPSALA UNIVERSITY, Department of Engineering Sciences,
Microwave Engineering, Box 534, SE-751 21 Uppsala
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Last updated 2011-05-30