Electrically cascaded surface-acoustic-wave resonator filters

Three nearly identical surface-acoustic-wave resonator filters at ? 35 MHz have been fabricated with aluminium metallisation on yz LiNbO3 substrates. The filters are electrically cascaded to yield a combined frequency response that exhibits 80 dB sidelobe suppression, Q ? 3000, no spurious responses in the range 1?500 MHz and an insertion loss in a 50 ? system of only 13 dB.     

Fine tuning of surface-acoustic-wave resonator filters with metallisation thickness

Two-port surface-acoustic-wave resonator filters with Q factors in excess of 3000 and a sidelobe suppression of 30 dB have been fabricated from yz LiNbO3 with aluminium metallisation. The dispersion of the centre frequency with aluminium thickness has been found to be 70?10 kHz/?m at 35 MHz. The ability to fine tune with metal thickness has been used to compensate inherent substrate inhomogeneities and to fabricate a high-Q factor flat-top filter.     

Rigid-plastic collapse of compression-bent shallow shells

Limit analysis solutions are given for simply supported shallow spherical shells under combined external loading. The effect of transverse shear on collapse loads is examined in the paper. Lower bound and exact load interaction curves at collapse are given for several shell configurations. The shell material is assumed rigid-plastic and yields according to the von Mises criterion. The results indicate that the lower bound approach gives acceptable results when extremely shallow shells are considered. It is also shown that the reduction of collapse loads due to transverse shear is of the same order as found for circular plates.     

Spatial periodic modulation of the high-field domain in cadmium sulphide

It is shown that there exists a maximum oscillation frequency for the current oscillations in semiconducting CdS. Below the corresponding minimum sample length, current oscillations do not exist. This maximum oscillation frequency may be exceeded with long samples by modulating the electric field along the sample. The technique presented is applicable to transferred-electron devices.     

Plastic shallow shells under combined loads

Details of an experimental program, concerned with shallow spherical shells under combined lateral and inplane pressure loading, are described. The available theoretical analyses are reviewed and their predictions are compared to the experimentally obtained results. Yield point and post-yield behavior of the shells is discussed and some recommendations regarding the analysis and design of these shells are made.     

Apodised surface-wave transducers

A new method of fabricating surface-wave interdigital transducers is presented. The method allows a quick and simple variation of the apodisation, and many apodisation functions can be investigated on the same transducer. Results with a filter on yz lithium niobate are presented.     

Exact Mises limit loads for cylindrical shells

Numerical solutions for limit loads of pressurized cylindrical cantilever shells are given for the exact Il'yushin yield surface. It is suggested that the numerical approach can be used for more complex problems for which the exact solution based on equation (2) has not been obtained to date.     

On the use of vias in conductor-backed coplanar circuits

Ground planes of conductor-backed coplanar waveguides (CBCPWs) behave like overmoded patch antennas supporting parallel-plate modes and show numerous resonances. For typical monolithic-microwave integrated-circuit chip sizes, these unwanted resonance frequencies lie within the microwave and millimeter-wave frequency region. Due to this feedback mechanism, today's coplanar millimeter-wave amplifiers operating up to 250 GHz require special packaging techniques for stable operation. The use of vias is one method of suppressing parallel-plate modes. The effect of via-holes within a ground plane and the effect of an open or a shorted ground-plane periphery on the parallel-plate modes of CBCPWs were investigated in depth up to 200 GHz for quartz and GaAs substrates. It is shown that the placement of the vias within the coplanar-waveguide structure is crucial for the suppression of parallel-plate modes. If properly placed, vias are an effective means to suppress these unwanted modes over a chosen frequency range     

Harmonic operation of GaAs millimetre wave transferred electron oscillators

Harmonic operation of GaAs millimetre wave transferred electron (TE) oscillators has been identified using a wideband waveguide system. The harmonic number was determined by precisely measuring the frequency as well as the frequency variations of the harmonic components when the oscillator was tuned mechanically or electrically. We find that GaAs TE oscillators at 94 GHz, matched to a waveguide circuit by means of a resonant disc, operate at the second or third harmonic frequency, depending on the length of the active GaAs region, which was between 1.8 and 2.6 ?m.     

Coplanar millimeter-wave ICs for W-band applications using 0.15μm pseudomorphic MODFETs

A small signal S-parameter and noise model for the cascode MODFET has been validated up to 120 GHz, allowing predictable monolithic microwave integrated circuit (MMIC) design up to W-band. The potential of coplanar waveguide technology to build compact, high performance system modules is demonstrated by means of passive and active MMIC components. The realized passive structures comprise a Wilkinson combiner/divider and a capacitively loaded ultra miniature branch line coupler. For both building blocks, very good agreement between the measured and modeled data is achieved up to 120 GHz. Based on the accurate design database, two versions of compact integrated amplifiers utilizing cascode devices for application in the 90-120 GHz frequency range were designed and fabricated. The MMICs have 26.3 dB and 20 dB gain at 91 GHz and 110 GHz, respectively. A noise figure of 6.4 dB was measured at 110 GHz. The 90-100 GHz amplifier was integrated with an MMIC tunable oscillator resulting in a W-band source delivering more than 6 dBm output power from 94 to 98 GHz