Acoustic-wave amplification in high-mobility semiconductors at microwave frequencies

The use of high-mobility piezoelectric semiconductors for acoustic-wave amplification at microwave frequencies is considered.     

The epHEMT gate at microwave frequencies

This paper examines the high-frequency behavior of the enhancement-mode pseudomorphic high electron-mobility transistor (epHEMT) gate. During this study, no bias was applied between the drain and source. Rather, the gate was forward biased with either the drain, source, or channel (drain and source connected together) grounded. While applying positive voltage V/sub g/ to the gate, one-port S-parameters were measured from 0.1 to 10 GHz and then converted to Z-parameters. Plotting the real part R of the impedance reveals two sharp peaks. The first peak occurs near the device threshold voltage for conduction in the InGaAs well. A second peak occurs at higher voltages where conduction begins to occur in the surface AlGaAs layer. An equivalent-circuit model is proposed to account for the epHEMT gate's high-frequency behavior and the proposed model is shown to be in good agreement with the experimental data.     

The silicon cryosar at microwave frequencies

Microwave and low-frequency measurements are reported onn^{+}-v-n^{+}silicon cryosars fabricated with narrow intrinsic region widths. The low-frequency measurements includeV-Idata with and without incident microwave power. The electric field required to cause impact ionization of the donors was found to be greater than 10⁵V/m. The microwave measurements include a demonstration of mixing, harmonic mixing, and harmonic generation. Small-signal impedance measurements as a function of bias are reported at 1.33 and 3.05 GHz, and the diode noise temperature was measured to be 16 000 or 3000 K depending on bias polarity. Mobile electron lifetime is 10^-10s.     

`Source-pull? technique at microwave frequencies

A technique to produce a variable and controlled source impedance is described in order to evaluate the performance of microwave devices under source impedance variable conditions. The procedure for a systematic error correction is also presented.     

Cable shielding measurements at microwave frequencies

A matched triaxial device is developed and constructed to measure the transfer impedance of braided coaxial cables at microwave frequencies. Full-design principles of the device have been developed and given in detail in the paper. The device is particularly suited for shielding measurements at frequencies up to 3.5 GHz, for which no comparable technique exists. The performance of the device is fully evaluated both theoretically and by measurements. The accuracy of the device is studied by comparing the results against those obtained from the low-frequency International Electrotechnique Committee triple-coaxial apparatus, and using well-known theoretical models.     

Measurement of surface impedance at microwave frequencies

A technique for measuring the surface impedance of a plane stratified media at microwave frequencies is given, and preliminary tests are made for a variety of situations ranging from capacitive impedances to surfaces, which display a purely inductive reactance. The technique utilises a modulated scatterer to measure the elliptically polarised electric field of a TM wave propagation over the surface.     

Continuous-time integrated FIR filters at microwave frequencies

We discuss adaptive integrated finite-impulse response (FIR) filters operating in the continuous time domain. These filters become attractive to implement at microwave frequencies. An important topological property of the traveling wave FIR filter is presented, and its advantages when used as an adaptive equalizer are pointed out. Design considerations and modeling aspects of compact on-chip delay lines are given. Simulation results for an adaptive equalizer operating at a data rate of 10 Gb/s are presented.     

Inverse black body radiation at microwave frequencies

The inverse black body radiation, which is the problem of determining the area-temperature distribution of a black body from its measured radiated power spectrum, was recently solved by Bojarski. His solution employs the inverse Laplace transform to reconstruct the area-coldness distribution from an integral equation based on Planck's law. Our solution is similar but restricted to microwave frequencies and employs the Rayleigh-Jeans approximation to yield the corresponding portion of the area-coldness distribution using the inverse Laplace transform but avoiding the iterative procedure of Bojarski.     

Measurement of ferrite parameters at microwave frequencies

A method for determining, at microwave or millimetre-wave frequencies, the relative permittivity and the saturation magnetisation of a ferrite is described. The method is based on the measurement of the guide wavelength in a rectangular guide completely filled with the ferrite and magnetised transversely. Tentative results are presented.     

Magnetoresistance of the Corbino disk at microwave frequencies

The behavior of a Corbino disk of InSb in a static, transverse magnetic field and a high frequency electric field is investigated. Measurements and analysis show that, owing to an internal magnetic field effect, the impedance of the Corbino disk shows a frequency dependence even at microwave frequencies. Measurements performed on rectangular samples show the same effect even more pronounced. It is concluded that, in the case of medium to high Hall angles, this effect may determine an upper frequency limit of Hall-effect devices which is considerably lower than the dielectric relaxation frequency.     

Nonlinear effects in coaxial cables at microwave frequencies

A study of the generation of intermodulation products due to nonlinearities in braided coaxial cables at L-, S-and C-band frequencies is in progress and some results are presented. The different cable parameters responsible for intermodulation products at microwave frequencies have been examined and their relative contributions towards the total nonlinearities assessed.     

Electrical characteristics of polypyrrole composites at microwave frequencies

The microwave absorption and reflection characteristics of composites of polypyrrole with paper, cotton cloth and polyester fabrics have been evaluated. Refiectivity measurements in the range 2–18 GHz and plane wave modelling have revealed impedance charateristics with a common transition rgion. Relationships between substrate material, polymer loading and electrical performacne have been explored. Polarisation characteristics have alos been measured. The electrical model has been successful in predicting the performance of both Salisbury screen and Jaumann multilayer designs of radar-absorbing material.     

Electronic tuning of a dielectric resonator at microwave frequencies

This aper deals with electronic tuning of a 950MHz shielded dielectric resonator by using a varactor-loop circuit. A theoretical investigation based on an accurate model circuit is resented. henomena such as jumps in frequency and amplitude, and degradation of the DR qualities are described     

Characterization of bump arrays at RF/microwave frequencies

A systematic procedure for the characterization of complex bump configurations at RF and microwave frequencies, is presented. Beginning with simple arrangements—single- and two-coupled bumps—full-wave electromagnetic (EM) field analysis, circuit simulations and RF measurements were used for the development and validation of their respective equivalent circuit models. These models were then extended to characterize three-coupled bumps, both in linear and triangular configurations. Finally, a combination of all the electrical parameters obtained from these simple bump configurations was used to characterize a complete bump array, taking into consideration that for pitches used in most high-speed packages, EM coupling between a bump and its “next but one” neighbor can be neglected.     

Resistive parametric mixing in GaAs oscillators at microwave frequencies

Resistive mixing in GaAs between a suitably biased microwave pump signal and a small signal at the first subharmonic of the pump is shown to result in an effective negative mobility at the signal frequency. The implications are discussed.