Reinhard Knoechel

Improvement of power amplifier efficiency by reactive Chireix combining, power back-off and differential phase adjustment

An interesting effect of output power back-off (OPBO) efficiency improvement is presented which is present if 2 power amplifiers (PA) utilizing a reactive output Chireix coupling are combined with input power back-off and differential phase adjustment for maximum efficiency peaking. The capability of significant efficiency improvement at power backoff is demonstrated and validated by means of simulations and measurements. The new design method delivers a power added efficiency (PAE) of 48% at 6dB OPBO and 35% at 10dB OPBO for a 25.7W Si-LDMOS PA at 2.14 GHz for a WCDMA basestation application

Improved Design of Outphasing Power Amplifier Combiners

This paper presents a novel and improved design of signal combiners for highly efficient outphasing power amplifiers. Additional shunt reactances for an output power back off efficiency peaking, as they are required for the standard Chireix combiners, are eliminated. The circuits are based on two transmission lines with different line lengths and allow compact implementations. Analytical design equations are derived and formulas describing the operation of the new combiners are presented. Several design examples are given for combiners equivalent to the standard Chireix and to new circuits and compared with respect to their physical implementation. Design trade offs are discussed.

LINC digital component separator for single and multicarrier W-CDMA signals

An implementation of a digital component separator for a linear amplification using nonlinear components (LINC) system on a field-programmable gate array is presented. It employs a flexible upconversion architecture, which can be easily configured as an image-reject or direct-upconversion architecture for transmission of single or combined multicarrier wireless code-division multiple-access (W-CDMA) signals and uses the phase-modulation method. Four direct digital synthesizers are applied as phase modulators, operating first on a low IF carrier varying from 0 to 1/4 of the sampling frequency. The sampling frequency can be chosen up to 32 times (122.88 MHz) the symbol rate of the W-CDMA chip rate of 3.84 Mbit/s. The system allows a flexible frequency assignment and spacing of one or two independent W-CDMA channels. This paper outlines how the envelope and phase information of two combined W-CDMA channels may be pre-calculated in real time. This information may be used for the generation of two phase-modulated signals, which are then supplied to a single LINC transmitter. The achieved performance is demonstrated for single and multicarrier application utilizing direct and/or image-reject upconversion including simulated and experimental data (adjacent channel power ratio, complementary cumulative distribution function, error vector magnitude).

Systematic design of reconfigurable quadrature directional couplers

This paper presents an approach for the systematic design of reconfigurable quadrature directional couplers. From even-odd-analysis of four-ports with two-fold symmetry four eigenreflections are derived. The scattering-parameters are linear combinations of them. The eigenreflections can be positioned deliberately with tuning reactances to create directional couplers which are reconfigurable in coupling ratio, operating frequency or the arrangement of the output ports. Two exemplary couplers, a LC-bridge and a modified branchline-coupler, are presented and measurement results are shown. Directional couplers with adjustable coupling ratio can also be created with cascaded couplers and additional phase shifters or discontinuities. A compact directional coupler using this principle is presented together with measurement results.

Sequential power amplifiers with adaptable combiners

This paper discusses design aspects of sequential power amplifiers (SPAs). After derivation of theoretical performance limits, an optimum practical realisation is suggested, using an FPGA-circuit at the input and an adaptable directional coupler as the signal combiner at the output. Design trade-offs between the optimum coupling and the output power capability of the involved amplifiers are outlined. Using SPAs efficiencies of more than 50% can be achieved under up 10dB back-off from maximum power. The combining characteristics of the adaptable combiner are investigated. Off-the-shelf power amplifiers may be employed, which can be linearized in a conventional manner. The paper closes with measurement results.

Novel transmission line combiner for highly efficient outphasing RF power amplifiers

A novel transmission line (TL) combiner is proposed having the same functionality as a Chireix-combiner with respect to its load impedance and combiner efficiency, but without the need of additional parallel compensating elements, which are necessary to improve the power backoff efficiency in highly efficient outphasing rf power amplifiers. Thus the design complexity is reduced and an alternative approach to Chireix-combiners becomes available. A detailed mathematical analysis of this TL- combiner is presented and design equations are derived. Its different physical operation and performance is demonstrated by a design example.

Rapid monitoring of selected food properties using microwave dielectric spectra

In this paper, a novel microwave measurement approach is presented, which is capable of determining selected food properties from the dielectric spectrum. Such properties could be the water content, a possible amount of additionally added water, the content of conducting ions or the percentage of other constituents, having a noticeable influence on the effective complex permittivity versus frequency. The approach is based on measured dielectric data across a significant bandwidth of one or two octaves (or more), and on data analysis using the multi-variate statistical method of Principal Component Analysis (PCA) and Principal Component Regression (PCR). The prototype of a dedicated microwave instrument is described and as an experimental example the viability of the new approach is demonstrated by the exact determination of the percentage of deliberately added water in fruit juices.

New UWB free-space method for the classification and characterization of dielectric objects

This paper presents a new approach for the accurate free-space characterization of irregularly shaped and arbitrarily oriented dielectric objects. The objects under test are illuminated by UWB-pulses and the scattered pulses are collected by an array of receiving antennas. The scattered pulses contain information about the geometrical properties as well as the dielectric properties; a multivariate calibration method is supposed to be able to separate these properties. A classification algorithm is applied prior to the multivariate calibration. It provides a classification into two classes, low or high permittivity. The statistical calibration method is then applied separately in each class. This leads to a significant improvement of the accuracy of the determination of the dielectric properties compared to processing without classification.

Aerosol particle sensor based on millimeter wave coherent radar with high spatial resolution

The near range measurement of water content in aerosols by coherent radar in the millimeter wave band is discussed. For bistatic radar an effective illuminated area of volume scatterers is determined taking into account the illumination tapering of the volume due to the radar power pattern shape. Procedures for the measurement of mass loading and for the calibration of the radar are outlined and calculated expressions are presented. A coherent radar in the 3 mm range and a workbench for testing the sensor are described. The proposed measurement procedure may be used if the parameters of the particle distribution law are known; otherwise a calibration procedure has to be applied.

Multi Stage Switched Sequential Amplifier

This paper presents two and three stage switched sequential amplifiers (SSA) using switched directional couplers as power splitters and combiners. The SSA concept allows matching of the SSA efficiency characteristics to the amplitude probability density distribution of the applied modulated signal. Therefore the back-off efficiency can be increased significantly, e.g. a three stage SSAs can achieve a -10 dB back-off efficiency of more than 50% theoretically. The paper presents the circuit concept for two and three stage SSAs, theoretical considerations for possible efficiency enhancements and experimental results for a two stage SSA.