Pulsed RF Signals Research Articles

Temperature-Dependent Characterization of Power Amplifiers Using an Efficient Electrothermal Analysis Technique

In this paper, we propose an efficient methodology for the electrothermal characterization of power amplifier (PA) integrated circuits. The proposed electrothermal analysis method predicts the effect of temperature variations on the key performances of PAs, such as gain and linearity, under realistic dynamic operating conditions. A comprehensive technique for identifying an equivalent compact thermal model, using data from 3-D finite element method thermal simulation and nonlinear curve fitting algorithms, is described. Two efficient methods for electrothermal analysis applying the developed compact thermal model are reported. The validity of the methods is evaluated using commercially available electrothermal computer-aided design (CAD) tools and through extensive pulsed RF signal measurements of a PA device under test. The measurement results confirm the validity of the proposed electrothermal analysis methods. The proposed methods show significantly faster simulation speed comparing to available CAD tools for electrothermal analysis. Moreover, the results reveal the importance of electrothermal characterization in the prediction of the temperature-aware PA dynamic operation.

Obtaining of carbon nanoparticles in pulsed modulated RF discharge plasma

Carbon nanoparticles were synthesized using a 13.56 MHz RF discharge plasma in pulsed mode to control the size of the nanoparticles. An Ar/CH4 gas mixture was injected into the chamber to create capacitive coupled plasma medium, the main part of which is an electrode connected to the RF generator and a grounded electrode arranged in parallel. The synthesis experiments were carried out at room temperature and under the following conditions: pressure in the working chamber 0.99 Torr; concentration of Ar(96%)+CH4(4%) gas mixture; synthesis time 5 seconds; at discharge power 10 W. The frequency of the RF discharge plasma pulse during modulation was varied from 10 Hz to 10 kHz, also the duty-cycle was 50% for each performed experiment. Experimental observations have revealed that the size of carbon nanoparticles increases with the frequency of the pulse signal. It has also been determined that by using a frequency of the modulated pulsed RF signal it is possible to control the size of carbon nanoparticles in the range of 40-70 nm. The synthesized nanoparticles were collected directly on a copper mesh for TEM microscopy, which was placed on the surface of the bottom electrode. TEM image analysis showed two types of nanoparticles, some of which are an agglomerate of nanoparticles with an amorphous structure, while the others are nanometer-sized with crystalline structures.

Waveform Optimization Using RF Pulse Signal on Voltage-Doubler Broadband Rectenna

In this article, the DC-output improvement of a broadband rectenna has been demonstrated using pulse signal. The pulse waveform is optimized by varying its duty cycle as well as its modulation frequency. The rectenna operating from 1.6 to 2.8 GHz is characterized experimentally with low/medium RF power and different loads. The optimized waveform has a duty cycle that varies between 1 and 20 % for a modulation frequency between 1 and 6 MHz. The results show that the DC voltage and the efficiency are improved over the frequency band of interest, particularly for frequencies below 1.8 GHz and those above 2.6 GHz. The DC-output improvement, compared to the 1-tone signal, is characterized by the calculation of voltage/efficiency gain. High gain values are experimentally obtained: close to 14 dB at 1.675 GHz and -20 dBm RF power. The voltage gain is greater than 0 dB for low (3 kΩ) and high (100 kΩ) loads. At 2.4 GHz and for a low load of 3 kΩ, 4-dB gain is measured at -30 dBm. For a load of 100 kΩ, the efficiency goes from 8.3 % for the 1-tone to about 74.7 % for the optimized waveform, at -15 dBm RF power level.

Precisely Synchronized NVNA Setup for Digitally Modulated Signal Generation and Measurement at 5G-Oriented Millimeter-Wave Test Bands

In this article, we present a novel nonlinear vector network analyzer (NVNA) setup for generating and measuring digitally modulated signals at millimeter-wave test bands. The first difference between this setup and commercial NVNAs is the use of a user-defined multisine signal as the phase reference, in order to enable more precise synchronization and denser spectral grid. To achieve this, a single 12.5-GHz microwave source is used for generating both the digitally modulated test signal and the phase reference, which not only offers the clock to the arbitrary waveform generator for user-defined intermediate frequency (IF) waveform generation but also provides the local oscillator drive after frequency multiplication. The second novelty of this work is the use of pulsed-radio frequency (RF) signals for NVNA phase calibration. By replacing the digitally modulated IF waveform with pulsed-RF signals, tone-by-tone phase calibration on dense spectral grids can be easily achieved under the same synchronization scheme. The validity of the proposed NVNA setup (as well as its simplified modification) and the phase calibration method is verified at the fifth-generation (5G)-oriented millimeter-wave bands of 28, 39, 43, and 70 GHz in this work, where the EVM measurements of 64-QAM test signals with a wide range of symbol rates from 0.1 to 1.5625 GSymbol/s are demonstrated reachable in practice.

Using Pulsed-RF Signals as Phase Standards for Millimeter-Wave Modulated Measurement and Calibration in Frequency Domain

This article presents the evaluation of using pulsed-radio frequency (RF) signals as multitone phase standards for modulated measurements at millimeter-wave (mm-Wave) bands, offering an alternative phase calibration choice for nonlinear vector network analyzers (NVNAs). Based on the NVNA measurements of two pulsed-RF signals generated by square-wave-driven mixers, a high correlation between magnitude and phase errors of unideal pulsed-RF signals is discovered, and an empirical method is developed to accurately estimate the phase errors according to magnitude-only measurements. To confirm its robustness and key preconditions for wide-range applications, theoretical support and explanation to the empirical method is revealed, in which the dominant waveform distortion of an applicable pulsed-RF signal can be decomposed into modulated perturbations with Sinc-like envelopes. The validity of the proposed empirical method, as well as its application for mm-Wave NVNA phase calibration, is verified by both experimental measurements and simulation results, where an estimation error (or phase calibration error) less than ±2° is demonstrated that is reachable in practice.

An Efficient Plasma Lighting System with a 300W GaN Power Amplifier Using Band-Limited Pulsed RF Signal

An Efficient Plasma Lighting System with a 300W GaN Power Amplifier Using Band-Limited Pulsed RF Signal

Characterization for Multiharmonic Intermodulation Nonlinearity of RF Power Amplifiers Using a Calibrated Nonlinear Vector Network Analyzer

This paper presents a novel realization of nonlinear vector network analyzer (NVNA) test-bed with a new phase calibration technique, in order to characterize the multiharmonic intermodulation nonlinearity of a radio frequency (RF) power amplifier (PA) under a large-signal modulated input. The NVNA test-bed uses a step recovery diode comb generator as the phase reference, which is driven by a pulsed-RF signal with a high duty cycle of over 99%. Hence all the multiharmonic intermodulation tones of interest can be measured at once. A multisine phase standard provided by a vector signal analyzer is used to calibrate the intermodulation tones at each harmonic on a dense spectral grid. Two harmonic phase standards with different fundamental frequencies are used to synchronize the phase calibration results at different harmonics. The validity of this paper is verified by comparing NVNA measurements with oscilloscope measurements of the same PA under test. This paper can be used to inspect the nonlinearity of RF amplifiers under large-signal modulated excitations in both the frequency and time domains.

Cost-Effective Brillouin Optical Time-Domain Analysis Sensor Using a Single Optical Source and Passive Optical Filtering

We present a simplified configuration for distributed Brillouin optical time-domain analysis sensors that aims to reduce the cost of the sensor by reducing the number of components required for the generation of the two optical waves involved in the sensing process. The technique is based on obtaining the pump and probe waves by passive optical filtering of the spectral components generated in a single optical source that is driven by a pulsed RF signal. The optical source is a compact laser with integrated electroabsorption modulator and the optical filters are based on fiber Bragg gratings. Proof-of-concept experiments demonstrate 1 m spatial resolution over a 20 km sensing fiber with a 0.9 MHz precision in the measurement of the Brillouin frequency shift, a performance similar to that of much more complex setups. Furthermore, we discuss the factors limiting the sensor performance, which are basically related to residual spectral components in the filtering process.

A W-Band 4-GHz Bandwidth Phase-Modulated Pulse Compression Radar Transmitter in 65-nm CMOS

This paper presents a fully integrated W-band 4-GHz bandwidth (BW) pseudo-noise (PN)-coded pulse compression radar transmitter (TX) in a CMOS technology. The PN-coded pulse compression scheme is adopted to obtain high spectral density and to lower the TX leakage using a 63-bit PN code generator based on linear feedback shift registers. We propose a sub-harmonic pumped pulse former and a pulsed power amplifier for high TX efficiency with the suppression of local oscillator (LO)/2LO leakage. A frequency synthesizer including a frequency divider chain generates a sub-harmonic LO signal, as well as a 5-GHz digital clock. Digital blocks with the PN-code generator are synchronized with the clock signal, which makes all pulses start with the same phase. The proposed TX achieves 14.5-dBm maximum output power with the tuning range of 75–81.5 GHz, and the phase noise is ${-}{\hbox{95.2}}$ dBc/Hz at a 1-MHz offset in the range of LO frequencies. In pulse mode, it generates a 4-GHz BW RF pulse signal, which corresponds to a range resolution of 7.5 cm, and the average dc power dissipation is 160 mW.

A Compact Test System for Simulating Multipath Interference

Fading and inter-symbol interference (ISI) arising from multipath effects are a common source of both latency and packet errors in wireless communications. Test methods often require large environments to produce long delays that are enough to affect the communications between a transmitter and receiver. This paper presents a simple, compact test method to produce and isolate effects from multipath interference simulating these effects produced by discrete distances. Signals with controlled delays can be created and combined using multiple antennas in two isolated small (2 foot/60 cm) cubes constructed with microwave absorber. We demonstrated this with a pulsed RF signal and a signal from an 802.11 n access point with an internal antenna. This method can be further extended to provide a compact test-bed for almost any wireless interference or coexistence test.

Effect of spectrum analyzer's impulse bandwidth on the measurement of EM waves emitted from partial discharges in multipath‐rich environment

AbstractSuperheterodyne spectrum analyzer (SA) has been widely used for receiving EM waves emitted from partial discharge (PD) because of its high sensitivity. Generally, resolution bandwidth is shown as a measurement parameter because the pulse response depends on the receiver's bandwidth. In this paper, we measure the impulse bandwidth of SA and describe the effect of the impulse bandwidth of SA on the measurement of EM waves emitted from PD in multipath‐rich environment. The results showed that the field strength of the EM waves emitted from PD is proportional to the impulse bandwidth higher than about 200 kHz and signal‐to‐noise ratio (SNR) increases with the impulse bandwidth as in the measurement of pulsed RF signals. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

디지털 고주파 메모리 구현에 관한 연구

Digital Radio Frequency Memory, ( as DRFM ), is a device with the ability to restore output to the input RF signal in the required time after storing the incoming RF signals. Therefore DRFM is widely used in Jammer, EW Simulator, Target Echo Generator, and so on. This paper proposes its hardware implementation composed with the high frequency part and the digital processing part consisting of RF input/output module and local oscillator module. It is also proposed the replicated signal generation method which is consisted of the Analog-Digital conversion in the form of pulsed RF signal quantization, and FPGA to save and produce the playback signal, and RF signals to produce a Digital-Analog Conversion in the digital processing unit. This proposed scheme applied to test board and confirmed the validity of the proposed scheme through the test results obtained by the simulated input signals.

Microfluidic pumps employing surface acoustic waves generated in ZnO thin films

ZnO thin film based surface acoustic wave (SAW) devices have been utilized to fabricate microfluidic pumps. The SAW devices were fabricated on nanocrystalline ZnO piezoelectric thin films deposited on Si substrates using rf magnetron sputtering and use a Sezawa wave mode for effective droplet motion. The as-deposited ZnO surface is hydrophilic, with a water contact angle of ∼75°, which prevents droplet pumping. Therefore, the ZnO surface was coated using a self-assembled monolayer of octadecyltrichlorosilane which forms a hydrophobic surface with a water contact angle of ∼110°. Liquid droplets between 0.5 and 1 μl in volume were successfully pumped on the hydrophobic ZnO surface at velocities up to 1 cm s−1. Under acoustic pressure, the water droplet on an hydrophilic surface becomes deformed, and the asymmetry in the contact angle at the trailing and leading edges allow the force acting upon the droplet to be calculated. These forces, which increase with input voltage above a threshold level, are found to be in the range of ∼100 μN. A pulsed rf signal has also been used to demonstrate precision manipulation of the liquid droplets. Furthermore, a SAW device structure is demonstrated in which the ZnO piezoelectric only exists under the input and output transducers. This structure still permits pumping, while avoiding direct contact between the piezoelectric material and the fluid. This is of particular importance for biological laboratory-on-a-chip applications.

Response of RF Networks to Transient Waveforms: Interference in Frequency-Hopped Communications

The long-tail transient responses of a bandpass network to pulsed and switched-tone stimuli are examined and a time-domain closed-form expression of the envelope response is developed. It is shown that the long-tail response leads to interference in frequency-hopping communication systems. Interference, and in particular co-site interference, can result in any radar, communication, or RF sensor system becoming exposed to unintentional pulsed RF signals. In the experimental study, 900-MHz Chebyshev bandpass filters are considered.

Measurements Under Pulsed-RF and Complex Modulated Signals Using Six-Port Reflectometers

This paper presents the design and characterization of simple and low-cost zero-bias Schottky diodes used as power detectors operating under pulsed-radio-frequency (pulsed-RF) or complex modulated signals in six-port-reflectometer network analyzers. Measurement results obtained at 1.8 GHz for quadrature-phase-shift-keying (QPSK) modulated signals and pulsed-RF signals for pulse durations of down to 300 ns are reported.

Extraction of nonlinear parameters of dispersive avalanche photodiode using pulsed RF measurement and quasi-DC optical excitation

A measurement system using a pulsed RF signal is presented for extraction of nonlinear parameters of a large-signal model (LSM) of a dispersive avalanche photodiode. Nonlinear model of the avalanche photodiode was considered as two-port network and vector reflection measurement was carried out using a microwave transition analyzer in pulsed RF mode in conjunction with synchronized pulsed optical stimulus on the photodiode. Square-wave optical stimulus of 5-/spl mu/s width (full width at half maximum) and 5-kHz pulse-repetition frequency (quasi-dc) were synchronized with the pulsed RF excitation using a synchronization circuit. High-frequency dispersion effects were taken into consideration for deriving the current through the photodiode and the theoretical background was given for the derivation of optical and bias-dependent parameters. Nonlinear parameters of LSM of the avalanche photodiode were extracted from the small-signal vector reflection measurement at different bias points and optical conditions. Thermal impedance of the device limits the continuous-wave measurement up to 0.1 mW of optical power, whereas when using the current method, it was possible to characterize the device up to 1.3 mW of peak optical power.

Quasi-Optimal Detector of Pulsed RF Signals in Conditions of Narrow-Band Interference

Quasi-Optimal Detector of Pulsed RF Signals in Conditions of Narrow-Band Interference

Real-time spectrum analysis in microstrip technology

We report on a time-domain analog in microwave lines to the spatial Fraunhofer (far-field) diffraction in paraxial conditions. Microstrip lines are used to design filtering configurations acting as spectrum analyzers. They are based on linearly chirped distributed Bragg coupling between the fundamental microstrip mode and the same but counterpropagating mode. Linearly chirped continuous impedance modulation in a microstrip line with varying upper plane strip-width is shown to yield a mode-coupling location and group delay linearly distributed in frequency. Under the condition of a temporal equivalent to the spatial Fraunhofer inequality, the energy spectral density of the input signal is directly recoverable from the average output (reflected) power. It is only necessary to take into account a linear axis-change, given by the dispersion coefficient (group-delay slope) of the structure, from time to Fourier frequency. Both pulsed and nonpulsed RF signals are studied. Sequential time-gated segments of the input have to be processed in the nonpulsed case. The maximum frequency resolution achievable in this situation is discussed. The devices developed here could have important potential applications in the field of temporal signal processing, such as filtering using time-division techniques.

Modeling the electromagnetic response of hearing aids to digital wireless phones

Interference produced in hearing aids by the pulsed RF signal from digital wireless phones has become an increasingly important issue to wireless phone manufacturers and service providers, hearing aid manufacturers and users, and government regulatory agencies. Development and validation of a comprehensive model of the interaction would greatly benefit the efforts to achieve mutual electromagnetic compatibility (EMC). In order to develop reliable accurate methods to measure hearing aid immunity, an exact mathematical relationship must be demonstrated between the interference generated in hearing aids using a dipole with a standardized test signal [the input referenced interference level (IRIL)] and that produced by actual wireless phones with various signal formats [the overall input referenced interference level (OIRIL)]. A set of theoretical conversion factors has been developed and applied to predict OIRIL interference from the standard IRIL, measured immunity value. A square-law relationship exists within the linear response region of the hearing aid such that each 1 dB increase in RF power (or field strength in decibels V/m) results in a 2 dB sound pressure level (SPL) increase in acoustic power (or sound pressure level). Hence, the IRIL for any given field strength is obtained by doubling (in decibels) the change in field strength and adding the result to the reference IRIL (in decibels SPL). Subtracting 7.60 dB [for time-division multiple access (TDMA)-50 Hz] or 10.68 dB [for TDMA-217 Hz or code-division multiple access (CDMA)] from the IRIL predicts the corresponding OIRIL. The lower and upper limits of the predicted OIRIL are constrained by the measured ambient sound level and the amplifier saturation, respectively. The model predictions are valid when comparable field strength gradients and distributions, separation distances and orientations are maintained between the hearing aid and the RF emitter.

How fast can radio messages be transmitted?

In 1991, experiments were reported by Ishii and Giakos which led the authors of those papers to the conclusion that radio messages can be transmitted faster than light. Such an idea is an apparent contradiction to the theory of relativity, and has provoked rebuttals, e.g. from Tichy-Racs (1992) and Marks (1992). The experimental evidence which followed, showed that an RF-pulse signal cannot travel faster than light. A paper by Stephan (see IEEE Antennas and Propagation Magazine, vol.35, no.3, p.13, 1993) has revealed that the controversy has not yet been resolved. This article should clarify how a misinterpretation of the observation could be understood as transmission faster than light.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>