Dirk Heberling

Integrated planar multiband antennas for personal communication handsets

The advent of new, multistandard mobile phone devices is an important challenge for antenna designers, as they have to implement integrated antennas with multiband operation within a volume that is rapidly shrinking. In the paper, research results concerning the input return loss, radiation characteristics and efficiency of novel internal, planar, multiband patch antennas are presented.

An improved method for measuring the radiation efficiency of mobile devices

In this paper, an improved method for measuring the radiation efficiency of small devices is introduced. The method is based on Wheelers principle of measuring the antenna impedance within two controlled environments: free space and a closed metallic box. In addition to Wheelers network model, an extended equivalent circuit is introduced, that gives an exact description of the behavior of the small device within the metallic box. This model is the basis for the determination of the radiation efficiency, independent of the size of the box and the location of the device within the box. Several measurements show that using the new method, the radiation efficiency of mobile devices can be determined very quickly and very accurately.

MR compatibility aspects of a silicon photomultiplier-based PET/RF insert with integrated digitisation

The combination of Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) into a single device is being considered a promising tool for molecular imaging as it combines the high sensitivity of PET with the functional and anatomical images of MRI. For highest performance, a scalable, MR compatible detector architecture with a small form factor is needed, targeting at excellent PET signal-to-noise ratios and time-of-flight information. Therefore it is desirable to use silicon photo multipliers and to digitize their signals directly in the detector modules inside the MRI bore. A preclinical PET/RF insert for clinical MRI scanner was built to demonstrate a new architecture and to study the interactions between the two modalities.The disturbance of the MRIs static magnetic field stays below 2 ppm peak-to-peak within a diameter of 56 mm (90 mm using standard automatic volume shimming). MRI SNR is decreased by 14%, RF artefacts (dotted lines) are only visible in sequences with very low SNR. Ghosting artefacts are visible to the eye in about 26% of the EPI images, severe ghosting only in 7.6%. Eddy-current related heating effects during long EPI sequences are noticeable but with low influence of 2% on the coincidences count rate. The time resolution of 2.5 ns, the energy resolution of 29.7% and the volumetric spatial resolution of 1.8 mm(3) in the PET isocentre stay unaffected during MRI operation. Phantom studies show no signs of other artefacts or distortion in both modalities. A living rat was simultaneously imaged after the injection with (18)F-Fluorodeoxyglucose (FDG) proving the in vivo capabilities of the system.

New method for a continuous determination of the spin tune in storage rings and implications for precision experiments

A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune-defined as the number of spin precessions per turn-is given by ν(s)=γG (γ is the Lorentz factor, G the gyromagnetic anomaly). At 970  MeV/c, the deuteron spins coherently precess at a frequency of ≈120  kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order 10^{-8}, and to 1×10^{-10} for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.

Circularly Polarized Antenna With Steerable Dipole-Like Radiation Pattern

An omnidirectional circularly polarized antenna with a rotatable dipole-shaped radiation pattern is proposed. The antenna is realized using a back-to-back coupled microstrip patch arrangement. The pattern is rotated by means of a phase shift, enabling reception (or transmission) of signals from all angles around a sphere. The method enables continuous pattern steering without the need for semiconductor or MEMS components integrated into the antenna. It also allows the use of more than one radiation pattern simultaneously, potentially providing coverage for any spherical angle. The theory is supported by simulation and measurement of four typical antenna configurations. The maximum gains are between 1.9 and 4 dBic and average axial-ratio varies between 2.5 and 3.65 dB at 2.47 GHz. The impedance bandwidth is from 2.4 to 2.51 GHz and the reconfigurable circular polarization is achieved from 2.464 to 2.484 GHz.

Multiport antennas for MIMO-systems

A very promising method to enlarge the radio channels capacity is the use of MIMO (Multiple Input Multiple Output) systems. The need to deploy more than one antenna leads to the problem of the restricted available space reserved for the antennas, especially on the terminals. Another fundamental problem is the evaluation of the MIMO performance in a realistic propagation environment. Only a global view will bring up a realistic picture about the improvements using multiple antenna technologies. First basics on MIMO-technology will be given. The second part will show in a very fundamental way the realization of a compact 4-port antenna, which provides a sufficient decoupling between the ports. In detail this had been presented already in [1]. Finally the system performance of this antenna is investigated. Based on the analysis of the diagram correlation coefficient and the mutual coupling of the elements a basic idea of the antenna performance is evaluated. Simulated correlation coefficients of typical channel matrixes taking the antenna into account will give finally an idea of the real MIMO performance.

Discrimination of scattering mechanisms via polarimetric rcs imaging [measurements corner]

Radar cross section (RCS) images describe position and scattering brightness of scattering centers of a radar target, but lack information about the underlying scattering mechanisms. This information can be valuable help for the design of radar targets, as soon as it becomes available. The proposed method uses a polarimetric approach to detect and discriminate three different scattering mechanisms, independently of the orientation of the scatterers. These mechanisms can be separately visualized for easy interpretation of the physical processes occurring at the radar target. Measurement results recorded in a compact range demonstrated the practical applicability of this approach.

Switchless Reconfigurable Antenna With 360° Steering

A novel reconfigurable antenna capable of rotating a bidirectional pattern by 360° in azimuth is proposed. The antenna has two ports, no aperture switching components, and offers a more compact solution than an array. It provides a reconfigurable pattern in the band 2.525-2.595 GHz and a fixed omnidirectional pattern from 2.235 to 2.725 GHz. The measured gains for four investigated configurations are between 2.1 and 3.1 dBi with total efficiencies between 80% and 89%. The antenna is intended to operate with software defined radio [digital beamforming or multiple-input-multiple-output (MIMO)], where the potential of pattern generation using the dual-port antenna can be fully exploited. It offers multiuser pattern reconfiguration at low cost within a limited volume.

Volume considerations in the design of dual-band handset antennas

Todays mobile phones are becoming smaller and smaller. Integrated antennas have thus a promising future when dealing with dual-band mobile handsets, since size and price requirements favor the use of planar antennas, such as the planar inverted-F antenna (PIFA). Some investigations on the reduction of the volume occupied by dual-band, planar integrated antennas for personal communications handsets are presented.

Spin tune mapping as a novel tool to probe the spin dynamics in storage rings

Precision experiments, such as the search for electric dipole moments of charged particles using storage rings, demand for an understanding of the spin dynamics with unprecedented accuracy. The ult ...