Karel Hoffmann

A simple method for extreme impedances measurement - experimental testing

This paper directly follows and extends, where a novel method for measurement of extreme impedances is described theoretically. In this paper experiments proving that the method can significantly improve stability of a measurement system are described. Using Agilent PNA E8364A vector network analyzer (VNA) the method is able to measure reflection coefficient with stability improved 36-times in magnitude and 354-times in phase compared to the classical method of reflection coefficient measurement. Further, validity of the error model and related equations stated in are verified by real measurement of SMD resistors (size 0603) in microwave test fixture. Values of the measured SMD resistors range from 12 kOmega up to 330 kOmega. A novel calibration technique using three different resistors as calibration standards is used. The measured values of impedances reasonably agree with assumed values.

A novel vector network analyzer

A calibration procedure for perturbation two-port vector network analyzer is presented. It consists of a variable perturbation two-port placed between a device under test and a scalar network analyzer. A measured vector reflection coefficient is determined on the basis of amplitude only readings. A full correction of systematic errors is possible. The new principle was experimentally confirmed in the frequency band up to 14 GHz.

A Method for Direct Impedance Measurement in Microwave and Millimeter-Wave Bands

A novel method for direct impedance measurement using a common vector network analyzer (VNA) is introduced and experimentally verified. In commonly used methods, the input impedance or admittance of a device-under-test (DUT) is derived from the measured value of its reflection coefficient causing serious inaccuracy problems for very high and very low impedances. The proposed method makes it possible to measure a quantity that is, in the ideal case, directly proportional to the value of input impedance or admittance of the DUT, enabling accurate and stable measurement of impedances that are extremely different from the common 50-Ω reference impedance. The method can significantly reduce errors caused by the VNA.

Hidden problems in precise calibration on microstrip

A study of calibration problems on microstrip with respect to interaction of electromagnetic fields around SMA to microstrip launcher and microstrip short was carried out in frequency band up to 26 GHz. Omni Spectra SMA to microstrip launcher, 50 Omega microstrip line on Arlon CuClad 223 0.508 mm thick substrate and microstrip shorts with reflective wall above the upper side of substrate as a calibration elements were used for simulations in CST Microwave Studio. Strong influence of dimensions of shorts and distance between the shorts and the launcher on simulated calibration data was observed. Reasonable dimensions of the short and the distance between the short and the launcher making possible correct precise calibration were determined.

Generalized Approach for Phase Interferometric Measurements of Electromagnetic Field

A new generalized approach for microwave phase interferometric measurement of electromagnetic fleld using an antenna matrix (AM) was developed. The approach allows correction of most signiflcant measurement errors caused by mutual couplings of closely spaced antenna elements. It is based on vector measurements of the AM designed for the frequency 2.60GHz and Matlab simulations.

Precise Measurement Using Coaxial-to-Microstrip Transition Through Radiation Suppression

This paper presents a study about the radiation problem of coaxial-to-microstrip launchers and suggests their improvement with a novel design. The proposed solution is based on a coaxial-to-microstrip transition enclosed in a parallel-plate transmission line that has its cutoff frequency above the working frequency band of interest. Any radiated field is quickly attenuated because it is propagating inside a subcritical parallel-plate transmission line. The proposed method is extensively analyzed in the CST Microwave Studio, and simulation results are verified on fabricated test-fixture by multiple measurements. The proposed solution improves the accuracy and reduces the uncertainty during measurements on a microstrip.

Hidden problems in precise calibration on microstrip II explanation and solution

A study of calibration problems on microstrip with respect to interaction of electromagnetic fields around coaxial to microstrip launch, microstrip line and microstrip calibration standards was carried out in frequency band up to 26 GHz. Omni Spectra SMA to microstrip launch, 50 Ω microstrip line on Arlon CuClad 233 0.508 mm thick substrate and microstrip short, open and load as calibration standards were used for simulations in CST Microwave Studio. Multimode propagation in the whole structure making impossible application of standard calibration methods was discovered. A hardware solution enforcing only one mode propagation was designed and tested using a simulation testing method similar to standard calibration/verification procedure. Radical suppression of measurement uncertainties was achieved.

A novel method for direct impedance measurement in microwave and mm-wave bands

A novel method for direct impedance measurement using a common vector network analyzer (VNA) is introduced. In commonly used methods impedance or admitance of a device under test (DUT) is derived from measured value of its reflection coefficient causing serious accuracy problems for very high or very low impedances. The proposed method makes possible to measure quantity directly proportional to the value of the impedance or admittance of the DUT. This enables us to accurately measure even impedances that are extremely different from value of the 50Ω reference impedance. The method can also significantly reduce effect of uncertainties of the VNA. A suitable calibration technique is suggested and fully mathematically described. The concept of the new method was verified by software simulation.

Study of calibration standards for extreme impedances measurement

The paper describes first results of pioneering research in the field of calibration standards for the measurement of extreme impedances. It is a necessary step for the measurement of extreme impedances since the method has been developed. The proposed calibration standards are based on coaxial microwave connector APC-7 and were extensively analyzed in CST Microwave Studio at the frequency range from 0.1 GHz to 18 GHz. Some of the analyzed structures seem to be promising for measurements of tiny very high impedance structures like carbon nanotubes or atto-farad varactors.

Six-Port Spatial Electromagnetic Wave Measurement

A new method for measuring free-space electromagnetic waves, based on a scalar interferometric measurement principle similar to the six-port concept, is presented. A proof of concept was performed at frequency band 6-12 GHz. The corresponding measurement system contains both a reference channel featuring a transmitting antenna directly irradiating receiving antenna, and, a test channel which has a transmitting antenna irradiating a test object. A wave reflected or scattered by the test object, and the reference wave phase shifted in several steps, both coherent, interfere in the receiving antenna. Redundancy is exploited via a multistate regime of measurement which enables to reduce uncertainty of measurement. A geometrical representation of the approach in the complex plane makes it possible to estimate measurement uncertainties. Precise computing of uncertainties based on the Monte Carlo Method is also performed.