Volume 65, Issue 7-8

In the classical indirect holographic setup, a wave emitted by the measurement object is superimposed with a reference wave at the aperture of the imaging system. The resulting interference pattern can be recorded with a simple intensity detection. However, the complex object field can be obtained from the plane wave spectrum (PWS) of the interference pattern. Dedicated methods can be used to calculate the field distribution at the object position, which is equivalent to the object properties and to an image of the object, respectively. This paper shows that the resolution of the created image is constricted due to the fact that the bandwidth of the extracted field is limited by the extraction process. A relation between the maximum possible bandwidth and the geometrical dimensions of the imager setup is deduced. Furthermore, a formula for the minimum achievable resolution is derived. Experimental results are presented to illustrate the issue.

In this paper a method to realize a heterodyne frequency-modulated continuous-wave (FMCW) radar is presented. The proposed principle relies on the use of an inphase/quadrature (IQ)-modulator as single-sideband-mixer to shift the frequency of the FMCW-output away from dc. Since in any IQ-modulator phase and amplitude imbalances occur, the effect of these imbalances will be investigated by deriving the corresponding signal model. Based on this analysis, a method to compensate the imbalances by a predistortion of the modulation signal will be derived. The presented method does not require special test signals or additional hardware, but relies on a standard FMCW measurement onto a calibration target. A prototype radar system was built and used in test measurements to verify the proposed principle. The measurement results show that a suppression of unwanted signal components caused by IQ-imbalances better than 45 dB is achievable.

A multilayer K-band patch antenna element featuring polarization multiplexing is presented. It relies on a previously published design providing high polarization purity. The layer stack and, in essence, the geometry are preserved. Left- and right-handed circular polarization (LHCP/RHCP) are realized without hybrid coupler, the two feeds still sharing the same layer. The arrangement is thus very compact. For interpretation, the simulation results are cast into an equivalent circuit model. Measurements performed on a multilayer antenna with vertical transitions confirm the concept.

In this paper, a near-field probe with integrated illuminating waveguide for frequencies around 77 GHz is introduced. For such high frequencies, alignment of transmitter and receiver probes in the near-field measurement setup are difficult. So the purpose of this work is to integrate both devices into one setup for an easy and reproducible measurement procedure. The measurement probe is used to characterize individual patches on the surface of reflectarray antennas, placing the device a few millimeters above the antenna surface. This requires a high spatial resolution and a insignificant influence of the probe on the examined structure. The ability of the developed probe has been investigated in simulations and verified in near-field measurements at reflectarray structures for 77 GHz. In this extended paper version, the setup is used to investigate a test-array with polarization twisting elementary cells and the lower reflector of a folded antenna, whose characteristics are based on a bifocal design process.

The presented time-domain EMI measurement system allows for full-compliance measurements according to CISPR 16-1-1 in the frequency range from 9 kHz to 26 GHz. With the combination of ultra-fast analog-to-digital-conversion and real-time digital signal processing on a field-programmable-gate-array (FPGA) with ultra-broadband multi-stage down-conversion, time-domain methods are employed for measurements into K-band. This allows for a reduction in scan times by several orders of magnitude. A scan from 9 kHz to 26 GHz with a 9 kHz IF-filter bandwidth is completed in under 200 s, while over 5 · 10 6 frequency points are calculated. The use of low-loss components and integrated preamplifiers yields an ultra-low system noise floor power spectral density of typically below –150 dBm/Hz. The system IF dynamic range of over 60 dB allows for the measurement of high-dynamic range signals like radar pulses. Measurements of the radiated emissions of a personal computer and the nonstationary emissions of a microwave oven are presented.

In this paper the potential and limitations of using a high-voltage GaN-HEMT RF-power technology with supply modulation for increased back-off efficiency is investigated. Based on extensive on-wafer class-AB load-pull characterization at various supply voltages and input power levels followed by advanced post-processing of the measured data, the possible efficiency improvement with supply modulation is explored and the technology and device limitations are discussed. The analysis is conducted for operation at three different maximum modulation voltages 15 V, 28 V, and 48 V. Post-processing of the measurement data shows a voltage dependent possible static efficiency enhancement of 25 to 40 percentage points in the 10 dB back-off region for a WCDMA signal. For the high voltages it is shown that the efficiency increase using supply modulation for high PAPR signals is greatly reduced. This is mainly a function of the narrower load-impedance matching range at higher supply voltages.

A passive wireless temperature sensor with identification capabilities based on a phase modulation scheme is discussed in this paper. The approach presented utilizes a pulse backscatter technique based on slow wave (metamaterial) transmission lines. The focus of the work are the material engineering for the temperature-sensitive element and the integration of this element into a passive phase modulation circuit and the entire sensor tag. The approach makes use of temperature-sensitive bariumstrontium-titanate thick film capacitances. The discussed principle has been experimentally verified with a prototype.

We report here the wireless extraction of an open ended micro coil inductance L , parasitic capacitance C and resistance R using an inductively coupled passive system which consists of an electrically small magnetic loop antenna as a sensor coil and an open ended test micro coil. Wireless analytical model is developed which includes the gimmick effects generated due to parasitic coupling capacitances. The micro coil parameters i.e. inductance, inter winding capacitance and resistance are extracted from the wirelessly measured impedance signal and then compared with the analytical model. Further the inductively coupled system is simulated using COMSOL multiphyscics in ACDC module.

This paper presents an application of a Composite Right/Left-Handed (CRLH) Transmission Line resonator for a compact mass flow detector which is able to detect inhomogeneous flows. In this concept, series capacitors and shunt inductors are used to synthesize a medium with simultaneously negative permeability and permittivity – the so called metamaterial. The helix shape of the cylindrical CRLH-TL sensor offers the possibility to detect flow inhomogeneities within the pipeline which can be used to correct the detected massflow rate. A combination of two CRLH-TL structures within the same cross-section of the pipeline can improve the angular sensitivity of the sensor. A prototype was realized and tested in a dedicated measurement setup to prove the concept.

Eigenproblems of periodic structures with complicated material distribution are solved efficiently by solving corresponding excitation problems. A unit cell with periodic boundary conditions is discretised and handled by a doubly periodic hybrid finite element boundary integral technique, which even considers complex propagation constants. Instead of solving algebraic eigenproblems, the analogy to resonance problems is exploited which gives improved physical insight into the problem. Moreover, open problem types can be handled. Numerical results for composite right/left-handed waveguides in one and three dimensions confirm the presented approach.