K. Kelander

Bio: K. Kelander is an academic researcher from Helsinki University of Technology. The author has contributed to research in topics: Microstrip antenna & Q factor. The author has an hindex of 1, co-authored 1 publications receiving 495 citations.

Resonator-based analysis of the combination of mobile handset antenna and chassis

Abstract: The performance of the mobile phone handset antenna-chassis combination is analyzed based on an approximate decomposition of the waves on the structure into two resonant wavemodes: the antenna-element wavemode and the chassis wavemode. A double resonator equivalent circuit model is presented and used to estimate the impedance bandwidth and the respective distributions of radiation losses with typical parameter values at 900 and 1800 MHz. It is noticed that at 900 MHz, the radiation losses of the antenna element wavemode represent typically less than 10% of the total power. Thus, the antenna element works mainly as a matching element, which couples to the low-Q resonant wavemode of the chassis. At 1800 MHz, the contribution of the antenna element wavemode is larger. By enhancing the coupling and by tuning the chassis resonance, it is possible to obtain an impedance bandwidth of over 50% (6 dB return loss) at both at 900 and 1800 MHz. The results given by the equivalent circuit study are fully supported by those of three-dimensional phone-model simulations, including calculation of the SAR and efficiency values. In prototyping, the 6 dB bandwidth of 5.5% was obtained at 980 MHz with a nonradiating coupling element with a volume of 1.6 cm/sup 3/ on a 120 mm long chassis.

Methods and Apparatuses for Adaptively Controlling Antenna Parameters to Enhance Efficiency and Maintain Antenna Size Compactness

Abstract: An antenna for a communications device having configurable elements controlled to modify an antenna impedance and/or an antenna resonant frequency to improve performance of the communications device The antenna impedance is controlled to substantially match to an output impedance of a power amplifier that supplies the antenna with a signal for transmission The antenna resonant frequency is controlled to overcome the effects of various operating conditions that can detune the antenna or in response to an operable frequency band

The Theory of Characteristic Modes Revisited: A Contribution to the Design of Antennas for Modern Applications

Abstract: The objective of this paper is to summarize the work that has been developed by the authors for the last several years, in order to demonstrate that the Theory of Characteristic Modes can be used to perform a systematic design of different types of antennas. Characteristic modes are real current modes that can be computed numerically for conducting bodies of arbitrary shape. Since characteristic modes form a set of orthogonal functions, they can be used to expand the total current on the surface of the body. However, this paper shows that what makes characteristic modes really attractive for antenna design is the physical insight they bring into the radiating phenomena taking place in the antenna. The resonance frequency of modes, as well as their radiating behavior, can be determined from the information provided by the eigenvalues associated with the characteristic modes. Moreover, by studying the current distribution of modes, an optimum feeding arrangement can be found in order to obtain the desired radiating behavior.

Detecting Vital Signs with Wearable Wireless Sensors

Abstract: The emergence of wireless technologies and advancements in on-body sensor design can enable change in the conventional health-care system, replacing it with wearable health-care systems, centred on the individual. Wearable monitoring systems can provide continuous physiological data, as well as better information regarding the general health of individuals. Thus, such vital-sign monitoring systems will reduce health-care costs by disease prevention and enhance the quality of life with disease management. In this paper, recent progress in non-invasive monitoring technologies for chronic disease management is reviewed. In particular, devices and techniques for monitoring blood pressure, blood glucose levels, cardiac activity and respiratory activity are discussed; in addition, on-body propagation issues for multiple sensors are presented.

Printed Monopole Slot Antenna for Internal Multiband Mobile Phone Antenna

Abstract: A new internal multiband mobile phone antenna formed by two printed monopole slots of different lengths cut at the edge of the system ground plane of the mobile phone is presented. The antenna can generate two wide bands centered at about 900 and 2100 MHz to cover the GSM850/GSM900/DCS/PCS/UMTS bands and the 2.4-GHz WLAN band. Further, the antenna has a simple planar structure and occupies a small area of only. It is also promising to bend the antenna into an L shape to reduce its volume occupied inside the mobile phone. Good radiation characteristics are obtained over the two wide operating bands.

Multiband Handset Antenna Combining a PIFA, Slots, and Ground Plane Modes

Abstract: A multiband handset antenna combining a PIFA and multiple slots on a ground plane is presented. It is shown by means of simulations that the slots on the ground plane have a double function: to tune the ground plane resonance at low frequencies (f ? 900 MHz) and to act as parasitic radiators at high frequencies (f ? 1800 MHz). A prototype is designed and built featuring a behavior suitable for low frequencies (GSM850 and GSM900) and for high frequencies spanning from DCS1800 to Bluetooth, and including, for instance, PCS1900, UMTS2000, and other possible systems. Reflection coefficient, efficiency, and radiation patterns are measured and compared with a design without slots to prove the advantages of the slotted ground plane. The component effect is investigated to determine critical areas where the placement is not recommended. Besides, the effect of the slot of the ground plane on SAR is investigated, by discussing the effect of the ground plane and slot modes for two phone positions. The total antenna volume of the proposed design is 40 × 15 × 6 mm3.