Metamaterials and -surfaces / Gap waveguides
The Antenna group has for two decades carried out original research on changing the boundary conditions of a metal conductor by loading its surface by periodic elements. The surface can thus acquire artificial magnetic properties. This work has been published under the terms soft and hard surfaces, using an analogy with acoustics. The soft surfaces are used in, for example, hat-fed reflector antennas for Ericsson’s MINI-LINK product. The hat-fed reflectors have been a product for more than 10 years in the spin-off company Comhat AB which now is part of Arkivator AB.
As a result of this general research we have proposed a new waveguide for millimeter and submillimeter waves, referred to as “Gap waveguide” (patent pending). This technology offers lower losses and lower manufacturing cost than microstrip lines and normal waveguides at high frequency, thus meeting the demand for commercial development of frequencies above 30 GHz. The gap waveguide technology find also advantages as an efficient technology for packaging of microstrip circuits as well as active microwave, mm- and submm-wave circuits and MMICs.
The research is done in collaboration with four other European universities – Siena, Zagreb, Valencia and Carlos III – as well as research groups at Department of microelectronics and nanoscience at Chalmers.
Figure 1. Examples of gap waveguide components: Filter & two couplers.
Financiers: VR, VINNOVA (Chase)
Researchers: Prof. Per-Simon Kildal, Assist. Prof. Rob Maaskant, Dr. Eva Rajo-Iglesias (Aff. prof. from Carlos III Univ., Madrid), Dr. Esperanza Alfonso
OTA Characterization of MIMO antennas and LTE devices
Within the research centre Chase, we are doing research on a new measurement technique, aiming to characterize small antennas and complete mobile terminals with multi-port antennas for use in environments with Rayleigh fading. The system characterizations are done Over-The-Air (OTA) in contrast to previously making use of cables between the terminal and the measurement instrument, and include the system effects of the signal-processing algorithms used for antenna diversity, MIMO multiplexing and OFDM. The latter corresponds to diversity in frequency domain. The research is being performed in collaboration with Sony Ericsson, Ericsson and the spin-off company
Bluetest AB, which commercializes reverberation chambers for OTA measurements. The research has also resulted in new simple theoretical system formulas. The research has presently been extended to involve collaboration with the communications systems group.
Together with SP technical research institute of Sweden, we have developed a multiport antenna evaluator for designing terminals with multiport antennas in an efficient way. This includes numerical tools to investigate the effect of the environment on the performance of the mobile terminal. In particular, we work to take the statistics of the user into account, i.e. his/her arbitrary orientation and location. The research has been performed within reseach centres Charmant and Chase.
Figure 2. OTA measurements at spin-off company Bluetest AB
Financier: VINNOVA (Chase)
Researchers: Prof. Per-Simon Kildal, Adj. Prof. Jan Carlsson
Ultra Wide Band Antennas for Radio Astronomy
We are currently developing a new decade bandwidth antenna with constant directivity and phase center over a decade bandwidth. This unique technology generates a performance previously unheard of. The main application is future radio telescopes such as VLBI2010 and SKA (Square Kilometer Array), but the technique can also be applied to satcom terminals, radio links and medical imaging.
The latest work includes the development of a compact 1.2-13 GHz model for SKA and the analysis of its performance in reflector antenna systems. Methods have been carried out to model and test system noise temperature with integrated Low Noise Amplifiers (LNAs), when both feed and LNAs are mounted inside a cryostat (cooling machine) with a radio frequency window and cooled down to a few Kelvin.
Furthermore, we develop numerical methods to predict the imaging performance of such wideband antennas when operating at radio telescopes.
The project is a collaboration between three departments at Chalmers: Signals and Systems (antenna), Onsala Space Observatory (cryostat) and Microtechnology and Nanoscience (LNAs).
Figure 3. Illustration of reflector for SKA radio telescope fed by decade bandwidth so-called eleven feed developed at Chalmers.
Financiers: VR, VINNOVA, SEDA, others
Researchers: Assoc. Prof. Jian Yang, Assoc. Prof. Marianna Ivashina, Prof. Per-Simon Kildal
Smart Array Antennas
The continued advances of high-speed digital technology and fast-data processing are enabling totally new approaches for designing the radio frequency communication and sensing systems. This involves in particular
antennas with many elements, so-called multiport antennas, and the signals received from or transmitted at these ports are processed digitally to provide beam-forming of other smart adaptations to the statistical effects of the opposite side of the communication link, or the remote distant radio source, including the ionospherical and atmospheric effects (in radio astronomy and space sending systems) or the multipath effects of the environment (mobile communications). Such array antennas can be referred to as “smart array antennas”. MIMO antennas on mobile terminals as described previously are also smart array antennas. Smart array antennas are of interest also for the base station antennas with even smartermore advanced signal-processing capabilities than at the terminals.
Smart array antennas are used in new generation radio telescopes with station being built in Sweden, such as the LOw Frequency ARray (LOFAR) (10 MHz – 250 MHz), and in planned future international Square Kilometer Array (SKA) radio telescopes.
The current focus of our activities is on the development of electromagnetic methods and simulation tools for the analysis and optimization of active array antenna systems, including their calibration methods and signal processing algorithms.
Figure 5. Employing the antenna array technology to a radio telescope can greatly increases its sensitivity for observing multiple areas on the sky, simultaneously. Thanks to this, weak signals emitted by very distant or faint celestial objects can be studied in relatively short periods of time. With conventional single-antenna technologies, the same types of the observations will not be possible.
Figure 6. Illustration of reflector for future radio telescope SKA with smart array feed being studied at Chalmers.
Financiers: VINNOVA (VINNMER, Chase), VR, others
Researchers: Assoc. Prof. Marianna Ivashina, Assist. Prof. Rob Maaskant.
Project duration: 2010-20122015
Model-based reconstruction and classification based on near-field microwave measurements
Researchers: Prof. Mats Viberg, Assoc. Prof. Jian Yang, Assoc. Prof. Tomas Rylander, Assoc. Prof. Andreas Fhager
Research projects
The Antenna group has for two decades carried out original research on changing the boundary conditions of a metal conductor by loading its surface by periodic elements. The surface can thus acquire artificial magnetic properties. This work has been published under the terms soft and hard surfaces, using an analogy with acoustics...
Within the research centre Chase, we are doing research on a new measurement technique, aiming to characterize small antennas and complete mobile terminals with multi-port antennas for use in environments with Rayleigh fading...
We are currently developing a new decade bandwidth antenna with constant directivity and phase center over a decade bandwidth. This unique technology generates a performance previously unheard of. The main application is future radio telescopes such as VLBI2010 and SKA (Square Kilometer Array)...
The continued advances of high-speed digital technology and fast-data processing are enabling totally new approaches for designing the radio frequency communication and sensing systems. This involves in particular antennas with many elements, so-called multiport antennas...
To be completed.