Research

Antennas for mobile devices

Antenna is one of the key components affecting the communication speed and battery life of a mobile device. Department of Radio Science and Engineering studies antennas for mobile devices with a particular focus on MIMO (multiple-input multiple-output), frequency reconfigurability, carrier aggregation (CA), user effects and newly introduced designs with high metal content in the device.

As an example, the figure below illustrates a simulation model of a multiband frequency-reconfigurable handset antenna with the MIMO (multiple-input multiple-output) capability. The two identical MIMO antenna elements are shown in red and blue, and the mobile phone chassis is shown in brown. MEMS (microelectromechanical)-based digitally tunable capacitors are used in the matching circuits of the antennas to achieve frequency reconfigurability.

An example of a simulation model of a multi-band frequency-reconfigurable handset antnna with MIMO.

Pattern-reconfigurable millimetre-wave antennas

Department of Radio Science and Engineering develops antennas for next generations’ mobile communications networks. Particular focus is on centimeter and millimeter-wave pattern-reconfigurable high-gain antennas. The figures below show a simulation model and a photograph of a beam steerable 4 by 4 horn antenna array operating at 71-86 GHz.

Simulation model and a photograph of a 4 by 4 beam-steerable horn antenna array operating at 71-86 GHz.

RF-powered ubiquitous sensing and computing

An ever-decreasing energy needed to perform a binary operation has resulted from shrinking transistors in integrated circuits, and has led to increased computation speeds. Consequently, computers that were once centralized have become increasingly ubiquitous and can now be found in nearly every gadget powered by electricity. With the advancement of this development, the energy needed for computation soon becomes so low that some devices can power themselves by harvesting ambient energy from their surroundings.

Radio frequency (RF) is one of the most promising ambient energy source because wireless devices are already equipped with an antenna that can be used as an energy harvester, and because the development of wireless devices ensured that RF energy is available almost everywhere. The figure below shows a scenario where RF-powered ubiquitous devices harvest the energy needed for their operation from the waves transmitted by ambient sources. The devices also use the ambient waves to communicate with each other and in the powered net. The Department of Radio Science and Engineering develops ubiquitous RF-powered devices enabling the Internet of Things (IoT).

Antenna measurement techniques

The advancement of integrated circuit technologies has made wireless communication and other applications feasible at higher and higher frequencies. As a consequence of this development, antennas, whose size is often proportional to the wavelength, are shrinking physically. Once bulky antennas can now be integrated even on an IC chip possibly measuring only a few mm. Traditional antenna measurement techniques, however, are not well suited for characterizing integrated antennas.

The figure below illustrates one new antenna measurement technique developed in the Department of Radio Science and Engineering. The near-field of the antenna under test (AUT) on a probe station is loaded with a reflective surface. The reflection coefficient from the antenna feed port is measured multiple times using different reflective surfaces in front of the antenna during each measurement. The radiation properties of the AUT are finally solved with an inversion algorithm by fitting the measured results to a model.

Antenna is measured by recording its reflection coefficients with different loads in its near field.