A Semi-Automatic Method for the Precision Measurement of Microwave Impedance

A system is described for the measurement of the magnitude and phase of the reflection coefficient over wide frequency bands. The method consists of recording the voltage at several points along the standing-wave pattern in a coaxial line. A fixed probe is used and the distance between the probe and the load is altered by successively inserting several lengths of precision coaxial line. Knowing these lengths and the frequency of the signal, a curve representing the standing-wave pattern is fitted to the experimental points by means of a computer program performing a least-squares minimization. To cover a given frequency band, the frequency is changed in discrete steps and the corresponding probe voltage recorded automatically. The measured impedance is referred directly to the characteristic impedance of air-dielectric coaxial lines.     

A Technique for Measurement of Impedance through a Lossless Transition

This paper presents a method for measurement of impedance through a transition from the slotted section transmission line to the load transmission line. The technique uses a lossless tuner as part of the transition and a precision transmission-line section. An example of a practical application of the method is given.     

Noise and sensitivity analysis for miniature E-field probes

A complete noise analysis of a miniature field probe connected to an amplification system is presented. The analysis predicts a theoretical minimum detectable E-field of 2.8 V/m for the field probe. Frequency-domain noise measurements using a spectrum analyzer, on the other hand, give a minimum detectable E-field of 16.2 V/m. In addition, time-domain noise measurements, using a slotted line and a microwave, give a minimum detectable E-field of about 13 V/m. Considering the number of approximations made in the treatment and the amount of external noise present in the laboratory, the correlation of the theory to the measurement is considered adequate. The sensitivity of the probe output voltage with respect to the various parameters is analyzed     

Analysis and Development of Ka- and Q-Band Waveguide Impedance Standards

This paper reports the salient design features and performance analysis of a precision waveguide, standard mismatches of voltage standing wave ratios (VSWRs) 1.10, 1.20 and 1.30 at Ka-band frequencies. Also standard waveguide sections and flush shorts are developed at Ka-band and Q-band and these are analyzed based on their physical dimensions, respectively. The performances of precision waveguide and standard mismatches are observed based on their dimensions and compared with measured values using slotted line technique at Ka-band. The calibration results of mismatch set are found with good agreement for their designated VSWRs with expanded uncertainties <0.03 and their traceability is established through the precision waveguide. These standards will serve as transfer standards of impedance at Ka-band and Q-band ranges and to assign the accuracy of impedance measuring instruments.     

Swept frequency reflectometer design for in-situ permittivitymeasurements

A prototype, broadband vector reflectometer for in-situ field measurements of permittivity is presented. The system was designed primarily to measure permittivity of sea ice in the 2-18-GHz frequency range but works equally well on other materials. The reflectometer design is based on FM-CW radar concepts. A linear frequency-modulated waveform is generated, and a portion of it is coupled off and passed through a delay line to serve as the local oscillator for the incident and reflected channels which receive most of the generated waveform. The reflectometer measures the complex reflection coefficient of a short monopole antenna probe. Permittivity is obtained by constructing a normalized input impedance of the probe. The impedance measured in a standard medium is based to construct a fourth-order rational function for the normalized input impedance, which is used with the measured impedance in the medium under test to obtain the permittivity. Measured permittivity data for air, 1-Butanol, and Teflon are presented     

扫频反射系数调试的一种实现方法

现阶段的驻波扫频测量调试大多采用网络分析仪,但是对器件进行驻波扫频调试时,特别是调试时间较长的情况下,可以用扫频反射计,所用设备为一台高方向性定向耦合器、一台精密衰减器和一个标准失配负载或全反射短路负载;在信号源的输出定标很准确的情况下,可以不用精密衰减器调节衰减量,改为直接调节信号源的输出电平,设定出所需反射系数进行器件的反射系数调试,此时所用设备少,在实验室内很容易实现.笔者对此时装置的不确定度进行了分析,结果表明,采用短路负载来设定反射系数效果会好得多.     

Measurement of Reflection Coefficient by Means of Slotted Line and Homodyne Detection System

A new method for measuring the complex reflection coefficient in a measurement system with a slotted line and homodyne detector is presented. The measurement involves the investigation of the change of phase angle of wave voltage along the waveguide terminated with the element under test. The principle of measurement and X-band measurement system consisting of waveguide elements are described. The signal fed to the homodyne detector is subject to the rectangular phase modulation which facilitates the construction of the modulator and increases the accuracy of phase determination. The phase shifter used in the system includes a slotted line. The reduction of the influence of residual reflections on the phase shift determination is described. Even with standard waveguide elements the measuring accuracy of amplitude reflection coefficient is found to be approximately 10-3.     

Automated Precision Polarimeter for the HF-VHF Range

An automated system for Stokes parameter-polarization analysis over the HF-VHF range is described. Axial ratio, orientation angle, polarization fraction, and polarization sense are determined by amplitude measurements using a conventional fieldintensity receiver. Six amplitude measurements from four crossed nonresonant dipoles, including quadrature sum and difference, eliminate the requirement for phase measurement. The antenna does not use active components and is adaptable for mobile or stationary operation. VSWR measurements on the antenna output cables show less than 1.2:1 (50 ohms) over the 2-70 MHz range. The antenna aperture increases from 1 × 10-5 square meters at 2.0 MHz to 0.019 square meters at 70 MHz. A solid-state sequencer processes each amplitude measurement separately through the receiver and digital conversion circuits (providing BCD output) to an incremental tape recorder. The Stokes parameter analysis is performed by an off-line digital computer using the magnetic tape data. This analysis permits computation of total received power from either set of orthogonal element measurements. When combined with the measured antenna aperture, power density (or field strength) also can be derived. Polarization fraction measurements for locally controlled signals show a mean of 1.02 as compared to a theoretical value of 1.00 (standard deviation of 0.1) over the 2-70 MHz range and polarization results consistent with propagation predictions.     

Amplification and calibration for miniature E-field probes

The amplification and signal-conditioning system for a miniature nonperturbing RF E-field probe is described. A simple calibration procedure using an X-band slotted waveguide is presented. It requires less power and space than conventional techniques requiring antenna measurements in an anechoic chamber. Measurement results demonstrate relatively small field perturbation due to the probe; and a region in the waveguide where the field is relatively uniform and suitable for calibration. Calibration accuracy is further established by comparing results with those obtained from antenna measurements in an anechoic chamber. To establish the calibration technique, the probe-amplification system is analyzed, leading to a gain equation relating the output voltage and measured field intensity, which is experimentally verified     

Progress Report of the IEEE Instrumentation and Measurement Group Technical Subcommittee on Precision Coaxial Connectors

The accuracy of RF and microwave measurements made in coaxial systems is often limited at higher frequencies by the mismatch errors from the connectors. The need for higher accuracies in coaxial impedance measurements and for improved coaxial transfer standards of attenuation and power has led to several independent designs of coaxial precision connectors within the United States and abroad. The Committee is in the process of establishing "recommended practices" to standardize definitions, testing procedures, and mechanical and electrical characteristics for precision connectors. The Recommended Practicesfor Precision Coaxial Connectors is divided into four parts. Part I describes "General Requirements and Definitions" for Laboratory Precision Connectors (LPC), General Precision Connectors (GPC), and mechanical and electrical properties. Part II describes "Parameters to be Specified" for environmental conditions and mechanical and electrical characteristics. Parts I and II were completed and approved by the Subcommittee and the Parent Committee in 1963. A draft of Part III concerning "Parameter Limits" for coaxial line sizes, axial and angular forces, critical dimensions and tolerances for mating surfaces, VSWR limits, insertion loss, leakage, contact resistance, and other characterstics has been completed. Part IV concerning "Test Procedures" is now being processed. In March, 1964, Parts III and IV will be presented to the Subcommittee for approval. When all four parts of the Recommended Practices for Precision Coaxial Connectors are approved, this document will then be submitted to the American Standards Association for consideration as a standard.     

A Portable Microwave Phase and Amplitude Test Set

Phase alignment at microwave frequencies may be made to 0.1° or less, and amplitude balance to 0.1 dB may be made simultaneously with this fully solid-state test set which is designed to be comparable in size and weight to a Tektronix oscilloscope. Provisions are incorporated for testing with either pulsed or CW signals. Present means of measuring phase and amplitude differences at microwave frequencies require either rack size equipments or a group of various pieces of test equipment such as RF generators, standing wave indicators, and slotted lines. Standard procedures are to utilize slotted lines with VSWR sampling points using a short-circuited line or line-swapping arrangement. While these methods are versatile, all have limitations in resolution and accuracy while requiring long setup times and a high degree of skill by the operator. Operating at a single-crystal-controlled microwave frequency, this test set provides a means of continuously comparing two signals, one a reference or standard; the other a signal to be adjusted. The phase and amplitude difference between these two signals may be reduced to a null by adjusting the module under test while observing two zero-center balance meters. The signals may be read to ±3 dB and ±3.0° or ±90° full scale. Accuracy is better than 5 per cent for all scales, and the null resolution is ±0.05 dB and ±0.05°. A self-contained solid-state reference signal generator produces up to 3-watts power output from a balanced varactor double stage at 1296 Mc.     

Application of Precision Connectors to High-Frequency Measurements

The availability of precision coaxial connectors which meet the specifications of the IEEE Subcommittee on Precision Coaxial Connectors has removed an important obstacle to the development of higher accuracy measurements systems over the frequency range from audio to 18 GHz. Some of the advances in techniques and standards which have resulted or are presently possible for measurements of impedance, VSWR, attenuation, phase, power, and dielectric properties of materials are reviewed. Problems relating to the connection of unknowns and standards to the terminals of an instrument are discussed with respect to measurements at audio frequencies, radio frequencies, and microwave frequencies.     

Broad-band dielectric spectroscopy of low-permittivity fluids usingone measurement cell

Dielectric spectroscopy is a relevant method for quality characterization of petrochemical products, provided that the permittivity spectra are measured with high precision over a broad frequency range. This paper describes how the permittivity of low-loss liquids such as crude oils can be measured with high precision using a single measurement cell in the broad frequency range 1 kHz to 6 GHz. The use of a single cell ensures that the whole dielectric spectrum is measured under the same conditions, which is an advantage for both on-line and laboratory applications. The permittivity spectrum is obtained by combining impedance and S-parameter measurements of a coaxial transmission/reflection cell with suitable permittivity calculation methods. The high sensitivity of the system is confirmed by measurements on crude oils and known low-loss liquids     

Finite-difference time-domain model for the feeding gap of coaxial probe driven antennas

In the finite-difference time-domain (FDTD) method, a simple and realistic feed model for coaxial probe driven antennas is proposed here. The feed zone of the antenna may be considered as an equivalent source in view of the antenna theory and a load port in view of the transmission line theory. The proposed feed model is constructed by combining the infinitesimal-gap source condition of the antenna and the equivalent load condition of the feed line. It leads to perform no additional FDTD cell modelling of the line. The transient reflected voltage and the input impedance of cylindrical monopole antennas fed by coaxial lines are calculated numerically and then compared with the accurate measurement and a full fine-grid. The FDTD results of the proposed model have a good agreement with the measured data and the fine-grid results.     

A Wide-Range CW Power Measurement Technique

An accurate power measurement technique is described, which makes possible the determination of the net power delivered to a load of arbitrary impedance over a wide power range. A standard power meter is employed to fix a reference power level. Subsequent measurements consist of dimensionless ratios that can be obtained from precision attenuators. The method is applicable to a very wide range of frequencies and was demonstrated at a frequency of 30 MHz with power measurements extending from 10-2 to 10-14 watt. Maximum uncertainties ranged from ~0.5 to 1.5 percent. This technique is applicable in the measurement of the sensitivity of very-low-level detectors, receivers, radiometers, etc.     

Matching radio frequency identification tag compact dipole antennas to an arbitrary chip impedance

A method for matching dipole antennas to capacitive or inductive arbitrary complex impedances is proposed for ultra high frequency radio frequency identification (RFID) tag antenna designs. It can be applied to straight, capacitive-loaded, meander or any small high-Q dipole topology. For this purpose, design stages are provided with the corresponding formulas. The reflection coefficient simulations and measurements of four implemented prototypes show the expected output when the RFID frequency band, bandwidth, chip impedance and maximum tag size are required as inputs for the method. The eventual S11 < 10 dB bandwidth depends on the chip impedance Q factor and the antenna size. How this bandwidth is manifested in terms of the read range is also discussed. A length ratio of up to 31.1% regarding the standard Λ/2 dipole at resonance is obtained.     

Theoretical and Experimental Investigation of the Tunable Y-Type Waveguide Standard Mismatch

Results of theoretical and first experimental investigations of a new device for the realization of variable standard values of the voltage standing-wave ratio (VSWR) are presented. The results show that the device, which consists of a Y-type waveguide power divider, an adjustable sliding short-circuit, and a matched load, can be used as a standard mismatch generating arbitrary values of the VSWR from 2 to 10 with small uncertainties.     

Design of Relaxation Oscillator Based Ultra-wideband SFQ Amplifier for Chip to Chip Interconnection

In Rapid Signal Flux Quantum (RSFQ) logic circuits, on-chip interconnects and multichip module implementations for nearby distances have already been established. However, the flexible interconnection of two distant chips is still not achieved reliably due to impedance mismatching and attenuation. In this work, we propose a circuit that allows the usage of Passive Transmission Lines (PTLs) to transfer single-flux-quantum (SFQ) pulses between two distant chips which are separated by a distance greater than 10 cm by using 50 ?? transmission lines. For this purpose, we design an SFQ amplifier circuit to deal with impedance mismatch and attenuation problems. The circuit consists of two main parts: a relaxation oscillator (RO) circuit and an impedance transformer. The RO circuit utilizes relaxation oscillations occur in the underdamped Josephson junctions. The impedance matching circuit is an 8-section Chebyshev quarter-wave transformer and it eliminates impedance mismatching problem between the amplifier circuit and PTL. We performed circuit simulations and obtained voltage amplitude of about 600 ??V at the output of the circuit. The transformer has a broadband impedance matching with a fractional bandwidth (ratio of the bandwidth of a device to its central frequency) of 1.4 and a maximum Voltage Standing Wave Ratio (VSWR, the maximum voltage divided by minimum voltage on the transmission line) of 1.5.     

ANA Calibration Method for Measurements of Dielectric Properties

Routine network analyzer calibration procedures in measurements of the dielectric properties of materials using an open-ended coaxial line probe are frequently inadequate and limit the accuracy of measurements. A calibration method, which makes use of liquids whose properties are well known, is proposed to alleviate this limitation. It is shown that even one liquid used as a standard in place of a matched load greatly improves the accuracy of measurements. Theoretical relationships and experimental results as well as some practical suggestions related to the application of this method are given.     

Effect of Power Line Interference on Microphone Calibration Measurements Made at or Near Harmonics of the Power Line Frequency

The electrical measurements required during the primary calibrations of laboratory standard microphones by the reciprocity method can be influenced by power line interference. Because of this influence, the protocols of international inter-laboratory key comparisons of microphone calibrations usually have not included measurements at power line frequencies. Such interference has been observed in microphone output voltage measurements made with a microphone pressure reciprocity calibration system under development at NIST. This system was configured for a particular type of standard microphone in such a way that measurements of relatively small signal levels, which are more susceptible to the effect of power line interference, were required. This effect was investigated by acquiring microphone output voltage measurement data with the power line frequency adjusted to move the frequency of the interference relative to the center frequency of the measurement system passband. These data showed that the effect of power line interference for this system configuration can be more than one percent at test frequencies harmonically related to the power line frequency. These data also showed that adjusting the power line frequency to separate the interference and test frequencies by as little as 1.0 Hz can reduce the effect of the interference by at least an order of magnitude. Adjustment of the power line frequency could enable accurate measurements at test frequencies that otherwise might be avoided.