D.K. Paul

Analysis and design of broadband, high efficiency feedforward amplifiers

A novel analysis of feedforward linearizers providing design procedures for determining circuit parameters required for specified linearity and achieving high efficiency, is presented. Experimental results are reported for a C band feedforward linearized amplifier demonstrating a minimum of 20 dB intermodulation distortion suppression across the 5.9-6.4 GHz satellite band.

MMIC tunable bandpass filter using a ring resonator with loss compensation

Ring resonators incorporating negative resistance circuits for loss compensation are studied for use as high Q tunable MMIC resonators. The design of a 13 GHz MMIC bandpass filter together with a background theoretical analysis, are presented. Simulation results indicate unloaded Q-factors of 1000 over 1 GHz tuning bandwidth.

Microwave oscillators and filters based on microstrip ring resonators

Tunable microstrip ring resonator oscillators and filters are described. Two alternative techniques for suppression of unwanted higher order modes are reviewed. The practical oscillator has a tuning bandwidth of nearly 30%, and phase noise better than -90 dBc, 10 kHz from carrier. This is encouraging performance for a compact planar device.<<ETX>>

A semidistributed HEMT model for accurate fitting and extrapolation of S-parameters and noise parameters

A model is described for a low noise millimeter-wave HEMT device. It takes account of the distributed nature of the gate and drain electrodes by dividing the active region of the device into a number of slices. Each slice is modeled as an intrinsic HEMT with thermal noise sources and the slices are connected together through lossy reactances. The parameters of the first slice are made different from those of the remaining slices, in order to account for the inevitable differences in the field distribution in the gate feed region. The model parameters have been optimized numerically to fit the manufacturers measured S-parameters and all four noise parameters, for a commercially available HEMT chip. A good fit has been achieved simultaneously to all of these parameters, and the model therefore provides a reasonable basis for extrapolation to higher frequencies. The significance of the distributed gate effect and the unequal slice effect is assessed by comparing the best fit achievable when these effects are not included. >

HEMT models for S-parameter and noise parameter extrapolation

Four models have been developed and assessed for fitting the measured noise parameters up to 26 GHz and S-parameters up to 400 GHz for a commercial HEMT (high electron mobility transistor) chip. The first treats the intrinsic noise sources as uncorrelated thermal sources. The second is an extension of this, allowing a better fit to be achieved by including the distributed nature of the gate and drain electrodes using a semidistributed, sliced model. The third model neglects the distributed effect but takes into account the partial correlation of the gate and drain noise sources. This causes a larger improvement in the quality of fit, allowing the model to fit the measured data within reasonable measurement limits. The addition of the distributed effect to the correlated model gives the fourth model, which allows a further marginal improvement, but the conditioning of the problem and the accuracy of the data appear to be insufficient to allow accurate extraction of the additional parameters needed.<<ETX>>

Computer-aided design and optimisation of broadband stripline circulators for 18-30 GHz and 18-40 GHz

Computer programs have been written for the design and optimization of tracking stripline circulators, and used to predict the performance of broadband designs, 18-30 GHz and 18-40 GHz, using ferrites with 4 pi M/sup s/ approximately=5000 G. Initial results show agreement between predicted and experimental performance, and an undesirable insertion-loss spike has been identified as due to inherent mismatch associated with circulator modes. The design and location of matching transformers are discussed, and it is noted that the programs can be used with commercial design software.<<ETX>>