Markus Berg

A Frequency Tuning Method for a Planar Inverted-F Antenna

A novel method is presented for electrically tuning the frequency of a planar inverted-F antenna (PIFA). A tuning circuit, comprising an RF switch and discrete passive components, has been completely integrated into the antenna element, which is thus free of dc wires. The proposed tuning method has been demonstrated with a dual-band PIFA capable of operating in four frequency bands. The antenna covers the GSM850, GSM900, GSM1800, PCS1900 and UMTS frequency ranges with over 40% total efficiency. The impact of the tuning circuit on the antennas efficiency and radiation pattern have been experimentally studied through comparison with the performance of a reference antenna not incorporating the tuning circuit. The proposed frequency tuning concept can be extended to more complex PIFA structures as well as other types of antennas to give enhanced electrical performance.

CAPACITIVE RECOGNITION OF THE USER'S HAND GRIP POSITION IN MOBILE HANDSETS

A capacitive method for measuring hand grip position on a mobile phone equipped with a dual-band planar inverted-F antenna (PIFA) and a monopole antenna was studied using difierent electrode arrangements. A capacitive sensor with a dual-electrode conflguration and an antenna-integrated capacitive sensor for hand grip recognition were developed. The sensitivities of the sensors were measured along the front, side and back of the phone. The dual-electrode sensor conflguration exhibited its best sensitivity of 29fF at the bottom end of the phone. The PIFA antenna-integrated sensor proved to have sensitivity of 420fF and the monopole antenna-integrated sensor had sensitivity of 115fF, making them both reasonable solutions for hand grip sensors in mobile applications.

Frequency-tunable DVB-H antenna for mobile terminals

In this paper a frequency-tunable inverted F-antenna (IFA) for DVB-H reception is presented. The antenna is suitable for small mobile devices (40 mm times 90 mm times 10 mm). The operating frequency of the antenna is tuned with a varactor component. The varactor loads the IFA element and thus enables it to resonate at different frequencies. This kind of tunable narrowband antenna is suitable for DVB-H reception, since one channel in a bandwidth of 8 MHz is received at a time. The antenna presented in this paper can be compared with a frequency- tunable IFA of Ying (2005), presented in a recently published patent. This proves the potential of this kind of DVB-H antenna solution in commercial applications. A special advantage of the proposed antenna is that, since it can be located in a vertical position on the long side of the ground plane, as opposed to the work of Ying (2005), GSM antennas can be located in their optimal position at the upper part of the device.

Impedance Dependency on Planar Broadband Dipole Dimensions: An Examination with Antenna Equivalent Circuits

The present paper considers the connection between complex input impedance and the physical dimensions for planar ultra wideband (UWB) antennas. The flrst time the efiect of both the actual radiator width and length for impedance behaviour is comprehensively presented. Also the efiect of feed point dimensions on complex impedance is studied. The investigations involve both UWB single-resonant dipoles to cover bandwidth ‚ 500MHz and a multi-resonant dipole for the entire Federal Communications Commissions (FCC) frequency band of 3.1{10.6GHz. Lumped-element equivalent circuits are used identically with 3D antenna simulations in order to observe the corresponding impedance behaviour with the studied antennas. The used equivalent circuits consisting of series- and parallel-resonant stages are widely accepted in the open literature. The series-resonant circuit of equivalent is observed to have the analogue to the antenna feeding area. The physical dipole dimensions in terms of a length and width are connected to parallel-resonant part, which mainly determines the antenna input impedance. The resistance of a parallel-resonant stage behaves as the maximum value of real part of dipole impedance with an in∞uence on bandwidth together with the ratio of parallel capacitance C and inductance L. The increase of the antenna physical width has an efiect on bandwidth, because of the wider the antenna, the higher the capacitance in the antenna feed. Since the traditional dipoles are used for these studies, the results can be extended in several ways for other antenna types or, for instance, to verify the efiect of body tissue, close to a wearable antenna.

Reactive near-field region radiation of planar UWB antennas close to a dispersive tissue model

This paper focuses on the radiation properties of planar Ultra Wideband (UWB) antennas in the vicinity of a dispersive layered tissue model through the range of 0-30 mm above the body model surface. Radiation properties are investigated in terms of the realized maximum gain, total antenna efficiency and radiation patterns (the plots of realized gain) at different antenna-body distances. Two planar UWB antennas are simulated in free space in this study and at multiple distances to the tissue model. Results are analyzed and discussed based on the antenna theory. When the operation distance over the boundary of antennas reactive field can be used, the performance close to free space can be achieved.

Impedance behaviour of planar UWB antennas in the vicinity of a dispersive tissue model

In Ultra Wideband (UWB) Wireless Body Area Network (WBAN) systems, the propagation environment is comprising free space and lossy medium (human body tissues), which have a very strong effect on the antenna operation. This paper investigates the UWB antenna-body tissues interaction in terms of the reflection coefficient and input impedance behavior through the range of 0-30 mm away from the body surface. Planar UWB antennas are exploited in the investigations. A layered tissue model based on the Debyes dispersion model for UWB frequencies is used in simulations. Observations are considered in relation to the antenna near-field regions and the size, i.e., the boundary distance of antennas reactive near-field is noticed to be the important factor in the evaluation of the shortest antenna-body operating distance.

Frequency-reconfigurable dual-band monopole antenna for mobile handsets

The main purpose of this paper is to present a method for electrically reconfiguring the operating frequency of a planar monopole antenna. In this method a tuning circuit composed of a RF PIN diode switch and two discrete passive components is built inside the antenna structure. This allows a DC control voltage to be brought to the diode switch along with the RF signal. Thus, this method of tuning does not require separate DC wiring, unlike commonly used structures proposed by Zachou et al. The method presented is demonstrated with a dual-band monopole antenna applicable in a mobile handset. The antenna has the capability of switching the lower band between the GSM850 and GSM900 frequency ranges with only a minor impact on the upper band. The upper band covers the frequency ranges of the GSM1800 and DCS 1900 telecommunication standards. Along with the antenna structure, the measured return loss and far-field gain are presented and discussed.

Experimental Verification of a Plane-Wave Field Synthesis Technique for MIMO OTA Antenna Testing

This paper evaluates the feasibility of a plane-wave field synthesis (PWS) technique for multiple-input multiple-output (MIMO) over-the-air (OTA) test facility, where a reference channel model is implemented. The test facility is based on a fading emulator and an anechoic chamber, equipped with multiple field emulating probes. The test facility emulates a radio channel condition using the PWS technique, based on the spherical wave theory. A simulation tool implementing the MIMO OTA field synthesis based on the PWS technique, named WIN-OTA, is established, where the WINNER II is chosen as the reference channel model. The simulation results show that the PWS technique reproduces the reference channels accurately in terms of envelope distribution, spatial and temporal correlation, and channel capacity. The WIN-OTA implementation was verified by comparing the emulated fields and the throughput from the simulations with the measurements for a practical MIMO OTA test facility. The results support the feasibility and accuracy of the field synthesis technique and the WIN-OTA implementation in MIMO OTA antenna testing.

Analysis of the Impedance Behaviour for Broadband Dipoles in Proximity of a Body Tissue: Approach by Using Antenna Equivalent Circuits

Ultra wideband (UWB) antenna operation close to tissue is examined by using lumped- element equivalent circuits in the present paper. The impact of tissue within the reactive near-fleld of the antenna is introduced in terms of e-ciency, impedance and matching to 50›. The parasitic components for the series- and parallel-resonant stages of the equivalent models are proposed for taking the impact of tissue into account on the antenna design. The flrst time the antenna impedance behaviour is presented in terms of capacitance, inductance and resistance as a function of the radiator distance on the tissue surface for UWB antennas. The capacitance was observed to increase with the distance on the tissue surface by achieving the maximum value close to the reactive near-fleld boundary. The inductance has the maximum on contact the tissue, decreasing strongly with the flrst millimetres and remaining constant with the higher distance. The maximum value of input resistance was seen to clearly increase with the distance, having the maximum value in the flrst third of the studied range, descending close to the value in free space at the boundary at the end. The results are achieved by realising electromagnetic simulations for the antennas and comparing the performance with the operation of the equivalent models.

On the evaluation of biological effects of wearable antennas on contact with dispersive medium in terms of SAR and bio-heat by using FIT technique

Considerations of biological effects, executed as the bio-heat and bio-thermal simulations, in terms of a specific absorption rate (SAR) and temperature rise in human body tissues for ultra wideband (UWB) wireless body area network (WBAN) applications are studied in this paper. 3D-electromagnetic (EM) simulation software, utilizing finite integration technique (FIT), is used in order to obtain temperatures and power losses by thermal stationary and transient solvers (TSS, TTS) in the vicinity of the modelled dispersive medium. Two different UWB antennas having excellent radiation properties are experimented on contact with tissues. The effect of the antenna input power on the temperature and maximum SARs over 1 g and 10 g averaging masses are evaluated. Obtained results are compared with the restrictions set by the institute of Electrical and Electronics Engineers (IEEE) and International Commission on Non-Ionizing Radiation Protection (I CNIRP). This paper investigates generally how much power should be fed to the UWB antenna in order to cross the maximum SAR limits in WBANs or in order the antenna start to heat the tissues significantly, both in the stationary conditions and further as the transient solutions.