Modeling the frequency response of microwave radiometers with QUCS

Abstract

Characterization of the frequency response of coherent radiometric receivers is a key element in estimating the flux of astrophysical emissions, since the measured signal depends on the convolution of the source spectral emission with the instrument band shape. Laboratory Radio Frequency (RF) measurements of the instrument bandpass often require complex test setups and are subject to a number of systematic effects driven by thermal issues and impedance matching, particularly if cryogenic operation is involved. In this paper we present an approach to modeling radiometers bandpasses by integrating simulations and RF measurements of individual components. This method is based on QUCS (Quasi Universal Circuit Simulator), an open-source circuit simulator, which gives the flexibility of choosing among the available devices, implementing new analytical software models or using measured S-parameters. Therefore an independent estimate of the instrument bandpass is achieved using standard individual component measurements and validated analytical simulations. In order to automate the process of preparing input data, running simulations and exporting results we developed the Python package python-qucs and released it under GNU Public License . We discuss, as working cases, bandpass response modeling of the COFE and PLANCK Low Frequency Instrument (LFI) radiometers and compare results obtained with QUCS and with a commercial circuit simulator software. The main purpose of bandpass modeling in COFE is to optimize component matching, while in LFI they represent the best estimation of frequency response, since end-to-end measurements were strongly affected by systematic effects.-1 -arXiv:1011.6363v2 [astro-ph.IM]

Parameter Optimization of Noise-Reduction Filters of Hi-Performance Power Supplies

“…In order to find out the reasons for the discrepancy between real and required filter parameters, we combined laboratory tests, real component measurements and computer modeling for a qualitative analysis of the interaction of components. The open source QUCS software [1] was chosen for modeling purposes due to verbatim results [2], convenient filter modeling [3], and possibility to measure the S-parameters of a quadripole, which is useful for designing high-frequency circuits. The only disadvantage is the impossibility to simulate the electrical circuits in real-time mode.…”

A coherent polarimeter array for the Large Scale Polarization Explorer (LSPE) balloon experiment

“…We have developed a numerical model of the 43 GHz STRIP polarimeter using QUCS ("Quite Universal Circuit Simulator", http://qucs.sourceforge.net/) an open source electronics circuit simulator software already used in the framework of the Planck-LFI project. 16,17 QUCS allows us to simulate the noise behavior of the circuit also when non linear devices are included.…”

A Digital-Simulation Model for a Full-Polarized Microwave Radiometer System and Its Calibration

“…A simulation model for a total-power radiometer was established through simulink, which only gave some qualitative simulation results [13]. A modeling method for comprehensive simulation of radiometer channel response is proposed in [14], this method is based on quashing universal circuit simulator (QUCS), which gives the flexibility of choosing among the available devices. A pseudo-random number was used to simulate the waveform of the input noise signals to the integrator output signals (before A/D conversion), and the linearity of the simulation model was validated [15].…”