Colin S. Aitchison

Improvement of third-order intermodulation product of RF and microwave amplifiers by injection

This paper discusses the improvement in the third-order intermodulation product (IM3) performance obtainable from RF and microwave amplifiers by two alternative injection techniques. The first is the addition to the amplifier input of the second harmonics of the input spectrum and the second is the addition to the amplifier input of the difference frequencies between the spectral components of the input signal. Both techniques are considered in theory, by simulation and in practice. Both techniques give useful improvements in two-tone IM3 performance. The second harmonic technique reduced the IM3 level by 43 dB in an amplifier at 835 MHz. The difference-frequency technique gave a reduction of 48 dB in an amplifier at 880 MHz. The difference-frequency technique also gives a greater improvement for complex spectra signals.

Improved analysis and design of coupled-line phase shifters

An analysis of coupled-line microstrip phase shifters is presented which shows that significant differences in theoretical performance are obtained by using an exact analysis in terms of odd and even mode propagation velocities rather than the approach in which the velocities are averaged, measured data are presented and compared with theory over the frequency range 8-12 GHz and the agreement with theory is good. >

Analysis and practical performance of a difference frequency technique for improving the multicarrier IMD performance of RF amplifiers

This paper presents a difference frequency technique for IMD improvement in power amplifiers. The technique is based on feeding the original two tone signals and a signal which frequency is the difference frequency of the fundamental signals in to the amplifier. Theory, simulation and practical measurement are presented. The result of the related experiment which gave a two tones measurement of more than 40 dB reduction in the level of the third order IMD is reported.

Second harmonic injecting technique for low intermodulation RF-microwave amplifiers

An amplifier where the third order IM distortion has been reduced is proposed. If two signals at different carrier frequencies are incident at the input of an amplifier, due to the nonlinearity, these signals will interact with each other and the output will contain additional signals at all combinations of sum and difference of these frequencies, which are IM products. The injection of the second harmonics of the two input in the amplifier together with the fundamental signals will produce additional IM products at the output. By proper selection of phase and amplitude of the injected second harmonics, it is possible to make the third order IM products produced by the second harmonics and the original third order IM products out of phase and equal in amplitude. As a result third order IM products will be eliminated, in principle. Theory and simulation results obtained at 2.5 GHz are presented which supports the suggestion.

Design of Novel Multilayer Microwave Coupled-Line Structures using Thick- Film Technology

A novel octave band DC block (2.5 -10.5GHz) and a broadband 3dB directional coupler (3-8GHz) have been designed, fabricated and tested using a new multilayer format. The multiple layers of thick-film dielectric and metal were printed on an alumina base and an etching technique used to form the final conductor pattern. The tight coupling required between the coupled lines was realized by overlapping these lines in a multilayer structure. Very good agreement was obtained between measured and simulated data. The results demonstrate that multilayer thick-film techniques provide an efficient method of achieving small size, low cost components having good microwave performance. In particular, the new multilayer approach has been shown to overcome the problem of fabricating very small gaps between coupled lines in a traditional single layer structure.

Design of directional couplers using multilayer thick-film technology

The performance of multilayer directional couplers using a range of different thick-film dielectrics has been investigated. The properties of multilayer coupled lines are examined using their coupled-mode parameters. It is found that the optimum performance of multilayer directional couplers is largely affected by the thick-film dielectric used. A practical design strategy for multilayer directional couplers is developed, which overcomes the problem of excessive computation that is normally associated with the optimization of multilayer circuit designs. The methodology has been verified through the design and measurement of wide bandwidth 2 dB and 3 dB directional couplers that were fabricated using multilayer thick-film technology.

A simple technique for improving the IM3/C and PAE performance of MESFET amplifiers

This paper shows by simulation that a shunt short -circuited ¿ 4 line placed across the drain terminals of a microwave MESFET amplifier significantly improves both the IM3/C and 2-tone PAE performance by a maximum of 14dB and 3%(from 24.5% to 27.5%), respectively. Practical confirmation with both WCDMA and GSM-EDGE input signals is obtained with a microstrip amplifier at 2GHz demonstrating an average improvement in ACPR of 12.5dB and a reduction in EVM from 5.0% to 1.3% respectively. The technique is novel, simple and practical and will be of direct interest to designers of base station amplifiers.

Third Order Intermodulation Improvement in Distributed Amplifiers

The paper considers the third order intermodulation behaviour of a distributed amplifier (with loss in gate and drain lines) in which the principle non linearity is due to gm and shows theoretically that in a two tone intermodulation test at constant output power, C/IM3 increases as the number of sections in the distributed amplifier is increased. A similar result is obtained by the simulation of a n stage distributed amplifier. An improvement in C/IM3 of about 25dB is obtained by increasing the number of stages in a distributed amplifier, with loss, from one to five.

MQW electroabsorption optical modulator performance enhancement using an artificial transmission line configuration

This paper compares the simulated modulation bandwidth and return-loss performance of InP multi-quantum-well (MQW) electroabsorption (EA) optical modulators using an artificial transmission line (ATL) structure with the corresponding performance obtained in a 50-/spl Omega/ environment from a single EA device of the same total capacitance for the same modulating voltage. The comparison simulation includes the effects of loss at the modulation frequency in the EA devices and of the loss at the modulation frequency associated with the series inductors of the ATL fabricated on two alternative substrate configurations. The paper shows that with a three section ATL modulator, the 3-dB electrical bandwidth (3-dBe) improves by a factor of 2.3 without optimization of the ATL line parameters and by a factor of 3.4 with optimization. In addition, a much improved return-loss performance is obtained with the ATL configuration. The paper also illustrates the effect of EA device loss, ATL series inductor loss, and ATL group-delay variation on the modulation bandwidth.

Multi‐layer thick‐film microwave components and measurements

The trend in wireless and mobile communications for broader bandwidth microwave circuitry, coupled with high packaging density and low cost fabrication has triggered investigations of new circuit configurations and technologies that meet these requirements. We have addressed these issues through the study of multilayer microwave structures using advanced thick‐film technology. The techniques described employ several layers of metal sandwiched by thick‐film dielectric. This leads to an efficient solution for system miniaturisation. The significance of this work is that it shows the multilayer approach to microwave structures, coupled with new thick‐film technology, offers a viable and economic solution to achieve high‐density, high‐performance microwave circuits.