Radio Frequency Measurement System Research Articles

Characterization of RF System for MIR/THz Free Electron Lasers at Chiang Mai University

The establishment of the mid-infrared and terahertz free-electron laser (MIR/THz FEL) facility is ongoing at the PBP-CMU Electron Linac Laboratory (PCELL) in Chiang Mai University. The facility utilizes an S-band radio-frequency (RF) gun and a linear accelerator (linac) to generate and accelerate electron bunches. These electron bunches are accelerated in the RF gun and the linac using RF pulses with a frequency of 2856 MHz. Measuring the RF properties becomes essential, as the RF pulse information can be utilized to estimate the electron beam properties. To achieve the measurement results, we employed an RF measurement system comprising directional couplers, coaxial cables, attenuators, a crystal detector, and an oscilloscope. Prior to conducting measurements, the crystal detector and RF equipment were calibrated and characterized to ensure precise and reliable results. The electron beam energy estimation using the measured RF power was compared with the measured beam energies. The gun and the linac were operated with an absorbed RF power of 1.52 MW and an input power of 1.92 MW, respectively. The estimated electron beam energies were found to be 2.18 MeV and 15.0 MeV, respectively, closely aligning with the measured beam energies of 2.1 MeV and 14.0 MeV after the gun and linac acceleration. These consistent energy values support the reliability of our RF power measurement system and procedure.

Precise dynamic characterization of microcombs assisted by an RF spectrum analyzer with THz bandwidth and MHz resolution.

The radio frequency (RF) spectrum of microcombs can be used to evaluate its phase noise features and coherence between microcomb teeth. Since microcombs possess characteristics such as high repetition rate, narrow linewidth and ultrafast dynamical evolution, there exists strict requirement on the bandwidth, resolution and frame rate of RF measurement system. In this work, a scheme with 1.8-THz bandwidth, 7.5-MHz spectral resolution, and 100-Hz frame rate is presented for RF spectrum measurement of microcombs by using an all-optical RF spectrum analyzer based on cross-phase modulation and Fabry Perot (FP) spectrometer, namely FP-assisted light intensity spectrum analyzer (FP-assisted LISA). However, extra dispersion introduced by amplifying the microcombs will deteriorate the bandwidth performance of measured RF spectrum. After compensating the extra dispersion through monitoring the dispersion curves measured by FP-assisted LISA, the more precise RF spectra of microcombs are measured. Then, the system is used to measure the noise sidebands and line shape evolution of microcombs within 2s temporal window, in which dynamic RF combs variation at different harmonic frequencies up to 1.96 THz in modulation instability (MI) state and soliton state are recorded firstly. Therefore, the improved bandwidth and resolution of FP-assisted LISA enable more precise measurement of RF spectrum, paving a reliable way for researches on physical mechanism of microcombs.

A Crane-Based Portable Antenna Measurement System—System Description and Validation

A portable near-field (NF) antenna measurement system for frequencies up to Ka -band is presented and evaluated in detail. The system follows the idea to collect measurement samples on arbitrary scan surfaces in the NF, where strong irregularities of the sample distribution may be tolerated as long as appropriate sampling criteria are fulfilled. The radio frequency (RF) equipment is integrated in a gondola, which is positioned by a standard overhead crane. During an NF scan, the exact position and orientation of the probe antenna are measured by a 6-D laser tracking system with high accuracy. The RF measurement system works with a phase-coherent measurement loop, where the signal transmission from the ground station to the RF equipment within the portable gondola is performed by an optical fiber transmission system with three optical fibers, realizing magnitude as well as phase compensation. The NF measurement samples are merged with the position and orientation data and, finally, transformed into the far-field by a flexible and highly efficient equivalent source algorithm. The complete setup of this measurement system is presented and discussed in detail, focusing on both hardware and software aspects. A series of validation and practical antenna measurement results is presented to demonstrate the feasibility of this approach.

Radiofrequency method for measurement of liquefied petroleum gas mass in the tank of a gas tank truck

Radiofrequency method for measurement of liquefied petroleum gas mass under overload from gas tank trucks into tanks of automotive gas-filling stations and gas-holders is considered. Experience of application of radiofrequency measurement system SU-5D-MASS for mass measurement of various liquids and gas condensates under their storage in reservoirs and pumping through pipelines is taken into account. Optimization of measurement system is suggested implying equipment of 1–2 gas tank-cars by Coriolis flow-meters and radiofrequency sensor of liquefied petroleum gas mass in the tank of a gas tank-car while other gas tank-cars are equipped only such a mass sensor. New approach of calibration of tanks of gas tank trucks and automotive gas-filling stations is suggested.

Engineering magnetoelectric composites towards application as tunable microwave filters

Tunable microwave devices are widely used in radar, telecommunication and radio frequency measurement systems. In recent years, a promising technology for tunable microwave devices, which combines the advantages of using the magnetic and electrical properties of materials as well as their magnetoelectric coupling, has been developed. In the present work, xMnFe2O4-(1 − x)Pb0.988(Zr0.52Ti0.48)0.976Nb0.024O3 ferrite-ferroelectric composites have been prepared and their functional properties were investigated, in order to be designed as components in tunable microwave devices. Structural, microstructural, dielectric and magnetic investigations confirmed the formation of composite ceramics with valuable dielectric and magnetic properties at room temperature. The complex permittivity and permeability of the investigated magnetoelectric ceramics, measured in the frequency range of 1 MHz to 1 GHz, show as a combination of the properties of Pb(Zr,Ti)NbO3 ferroelectric and magnetic MnFe2O4 phases. Experimental measurements and the numerical simulations were done using a high frequency structure simulator (HFSS) which revealed that the investigated composite disk placed on a microstrip line acts as an electromagnetic resonator and it could be consider as a filter with tunable stop-band capabilities controlled by an external magnetic field. It was found that the central stop-band frequency of the designed filter can be tuned with 18 MHz by changing the magnetic field from 0 to 2 kOe.

Unfolding the frequency spectrum for undersampled wideband data

In this letter, we discuss the problem of unfolding the frequency spectrum for undersampled wideband data. The problem is of relevance to state-of-the-art radio frequency measurement systems, which capture repetitive waveform based on a sampling rate that violates the Nyquist constraint. The problem is presented in a compact form by the inclusion of a complex operator called the CN operator. The ease-of-use problem formulation eliminates the ambiguity caused by folded frequency spectra, in particular those with lines standing on multiples of the Nyquist frequency that are captured with erroneous amplitude and phase values.