`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.     

An experimental technique for in vivo permittivity measurement ofmaterials at microwave frequencies

A procedure for making in vivo dielectric measurements with an open-ended coaxial line probe is discussed. The theory behind the technique is discussed, along with a correction method to account for the system imperfections. Experimental results are compared with data for the lumped parameter model approach and a mathematically sound integral equation method available in the literature. The results show good agreement, with the exception of the lumped parameter technique, which deviates at higher frequencies. The limitations of this technique are considered     

Active load technique for load-pull characterisation at microwave frequencies

The letter describes a load-pulling method that allows an extension of the two-signal approach to applications where the output frequency spectrum is different from the input one, as in the case of power devices operating with multicarrier input signals.     

Novel technique for measuring the Q factor of thin-film lumped elements at microwave frequencies

Using higher-order resonances, it is possible to determine the Q factors of thin-film lumped elements at microwave frequencies. This technique avoids any perturbation of the experimental arrangement which normally arises from insertion and removal of the unknown.     

Secondary-emission amplification at microwave frequencies

Two types of photomultipliers exhibiting flat base-band response to ∼4 Gc/s are described. One photomultiplier employs crossed electric and magnetic fields, the other is purely electrostatic. At present both devices consist of eight Cu-Be secondary emission stages and an internally situated, opaque-backed S-1 photocathode. Current gain exceeds 10⁵, and the transit time dispersion is less than7 times 10^{-11}s. Frequency response measurements have used heterodyning between the modes of the Zeeman-split Doppler profiles of a 6328 Å He-Ne laser, and also shot noise in the current from a steadily illuminated photocathode as sources of microwave modulated currents. Transient response measurements have been made using sub-nanosecond light pulses from phase-locked He-Ne and argon ion lasers, the results being consistent with the measured frequency response. A calculation of the frequency response to be expected fromnidentical stages of secondary emission when only the secondary electron emission velocities contribute to electron transit time differences, as is true of the geometries used in the experiments, gives results in agreement with experiment, assuming a value of 3 eV for the most probable secondary electron emission energy from BeO. This value is consistent with direct observations by others.     

A new resistance measurement technique applicable tohigh-temperature superconducting materials at microwave frequencies

A two-gap electrically floating resonant strip was used for surface resistance measurements of the high-temperature superconductor YBa₂Cu₃O_7-δ. The method is simple, has no electrical contact, operates at various resonant frequencies, and requires only a small sample. An analysis that allows for the accurate design of the strip dimensions to produce a desired resonant frequency was used. Experimental measurements on resonant frequencies in X- and Ku-band (8-18 GHz) agree well with the calculations. The method allows one to extract the normalized surface resistance of the sample from transmission coefficient measurements at the resonant frequency. These normalized values compare favorably to the Mattis-Baredeen theory taken in the local limit. The resonant strip in waveguide should have applications in high-temperature superconductive material characterization and in the development of waveguide superconductive filters     

An improved model for the dielectric constant of sea water at microwave frequencies

The advent of precision microwave radiometry has placed a stringent requirement on the accuracy with which the dielectric constant of sea water must be known. To this end, measurements of the dielectric constant have been conducted atS-band andL-band with a quoted uncertainty of tenths of a percent. These and earlier results are critically examined, and expressions are developed which will yield computations of brightness temperature having an error of no more than 0.3 K for an undisturbed sea at frequencies lower thanX-band. At the higher microwave and millimeter wave frequencies, the accuracy is in question because of uncertainties in the relaxation time and the dielectric constant at infinite frequency.     

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.     

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.     

An automated approach for implementing GTD to model 2-D terraineffects at microwave frequencies

The impetus for the work described arose out of the need to model absolute signal strength for a microwave landing system (MLS) operating in the presence of irregular terrain. A complete, automated approach for predicting absolute signal strength at microwave frequencies for sites involving irregular, 2-D terrain profiles is presented. The approach involves two computer models: one to convert raw terrain elevation data into a linear profile; the other to estimate path loss using the geometrical theory of diffraction. The linearization of a terrain profile is accomplished by mapping raw terrain data into a phase domain and then identifying significant terrain features from the stationary phase points as defined by Fermat's principle. Since the entire modeling process is automated, little expertise on the part of the user is required. Validation of the approach is given by comparisons of measured and modeled signal strength data for representative sites. While the model described is limited to 2-D terrain, the approach is applicable to 3-D terrain as well     

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.     

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.     

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.     

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.