Jacques Sombrin

Direct electromagnetic optimization of microwave filters

This article explores an optimization procedure for microwave filters and multiplexers. The procedure is initialized by a classical filter synthesis based on a segmented electromagnetic synthesis that provides the basic dimensions of the structure. The optimization loop, which combines a global electromagnetic analysis and a coupling identification, improves the structure response compared to an empirical optimization.

Extraction of coupling parameters for microwave filters: determination of a stable rational model from scattering data

We present a method to derive a rational model from scattering data for electrical parameter extraction. Unlike other methods, the stability and the MacMillan degree of the rational approximation are guaranteed. In order to improve the usability of our method in computer-aided tuning, we also present an algorithm performing automatic reference plane adjustment. Results obtained on a 10/sup th/ order dual mode IMUX filter are presented.

Coupled Pade approximation-finite element method applied to microwave device design

In this paper, a fast and rigorous analysis method is presented, combining the Pade approximation and a finite element method. The method is applied to the design of two microwave devices: a narrow band bandpass filter and a broadband microwave module. The accuracy of this approach is demonstrated by the good agreement between the coupled Pade approximation-finite element analyses and the standard finite element ones, and also between the coupled Pade approximation-FE analysis and the experimental filter response.

A Novel Experimental Noise Power Ratio Characterization Method for Multicarrier Microwave Power Amplifiers

The linearity characterization of multicarrier power amplifiers in terms of Noise Power Ratio (NPR) is now well adopted. The use of an analog band pass noise source with a notch in the center bandwidth is currently used for this purpose. We present in this paper a novel NPR measurement technique based on a numerical generation of a gaussian noise. This experimental noise generation is similar to the technique used in non linear circuit level or system level simulations using the envelope transient technique. The measurement principle is based on the use of a baseband arbitrary waveform generator (AWG) and an upconverter chain from baseband to L or S band. The large signal Noise stimuli drive the amplifier under test. The output signal of the amplifier is downconverted back to baseband and the resulting complex envelope is recorded with a sampling scope and computed for NPR extraction. A comparison of NPR measurements obtained with our method and with the conventional analog noise source technique is presented. Other possible applications of our measurement system are also mentioned and emphasize the capabilities of the proposed characterization tool.

Efficient simulation of NPR for the optimum design of satellite transponders SSPAs

It is now well known that the prediction of intermodulation distortions at the system level using the AM-AM and AM-PM characteristics of power amplifiers may be of very poor accuracy if amplifiers exhibit nonlinear low frequency dispersion effects (memory effects). This paper presents a new cost effective method for computing the noise power ratio (NPR) of power amplifiers at the circuit level, hence providing a more accurate prediction and the possibility to include the NPR as a direct optimisation objective in the design of amplifiers. The method is particularly well suited to the design of high efficiency solid state power amplifiers.

A new satellite repeater amplifier characterization system for large bandwidth NPR and modulated signals measurements

Power consumption and dissipation of satellite payloads for space telecommunication systems are mainly due to power amplifiers. To increase system capacity with limited bandwidth, multicarrier operations are required. Linearity is specified to limit the signal distortion by the nonlinear power amplifiers. In order to minimize power consumption under those linearity requirements, accurate measurements have to be performed. The NPR is well known as the figure of merit for the intermodulation distortion performance of amplifiers in telecommunications. In this paper, the development of an accurate large bandwidth NPR measurement system is presented. It enables characterizations up to Ka band (17-21 GHz and 27-31 GHz for space telecommunications applications with typically 250 MHz bandwidth). Measurements made on power amplifiers have been used to optimize operating conditions.

A novel behavorial model of power amplifier based on a dynamic envelope gain approach for the system level simulation and design

This paper presents a novel and non quasi static behavioral ( black box) model of power amplifiers. It takes into account nonlinear memory effects for an accurate prediction of signal distortions and power budget in communication systems. The model topology and the model extraction procedure are described. The model proposed in this paper can be derived either from envelope simulation results of a PA circuit design or from time domain envelope measurements of a PA driven by modulated stimuli. Examples of new measurements (i.e. : dynamic AM/AM conversion characteristics) highlight nonlinear memory of SSPAs. The behavioral model proposed is very well suited for an efficient implementation in system level software packages because it consists of an extension of the complex envelope gain function. The proposed complex gain which depends on the input envelope and its first time derivatives provides a great enhancement as compared to the memoryless static complex gain derived from classical AM/AM and AM/PM conversion characteristics.

A test set-up for the analysis of multi-tone intermodulation in microwave devices

This paper proposes a multi-tone signal pattern designed for accurate and easy measurements of nonlinear devices linearity factors of merit. The stimulus signal we propose ensures that DUTs third order intermodulation products wont overlap. Thus, the relative phases of source tones do not affect the amplitudes of intermodulation products. The usual metrics for linearity factors, ACPR (Adjacent Channel Power Ratio) or NPR (Noise Power Ratio), can be acquired with a greater accuracy only with amplitude measurements. This work has been carried out with a sampler-based receiver, using FFT (Fast Fourier Transform) filtering for tone separation.

Simplified design of microwave filters with asymmetric transfer functions

This paper presents the design of a microwave bandpass filter having an asymmetric transfer function and a symmetric geometry. The purpose is to demonstrate that an efficient synthesis can provide simpler solutions for the hardware implementation. An example of a 6th order dual mode filter in circular waveguide technology is presented. Considering the desired topology, the initial synthesis from the Chebyshev transfer function leads to two solutions with an asymmetric electrical network. A symmetric network is then synthesised increasing the number of couplings. For one of the solutions, weak couplings can be neglected so that the transfer function is only slightly affected. The modified symmetric electrical network leads then to a simpler hardware implementation of the dual mode filter. The electrical network synthesis is described, then the optimal geometrical dimensions of the filter are determined applying an electromagnetic based optimisation method. An experimental realisation is finally compared to the theoretical results.

Continuous-time modeling of a Traveling-Wave Tube amplifier

This paper deals with the modeling of a Traveling-Wave Tube (TWT) amplifier. The continuous-time modeling approach is presented and the model is used to capture the carrier memory effect of the TWT amplifier. Some processing on measurements are described and an assessment of the model under 2-tone signals is achieved for validation.