Ian D. Robertson

Fabrication, RF Characteristics and Mechanical Stability of Self-Assembled 3D Microwave Inductors

Abstract We present a method for the fabrication of vertical inductors for radio-frequency and microwave applications. This process uses five levels of lithography and electroplating, with no substrate removal, high temperatures or serial process steps. Rotation of the inductors perpendicular to the substrate is achieved by surface tension driven self-assembly, giving separation from the substrate and therefore increasing substantially the Q and self-resonant frequencies. Meander and spiral air-bridged inductors of up to 5.5xa0nH are demonstrated. The Q of 2xa0nH inductors shows an increase from 4 to 20 after having undergone the self-assembly process. Mechanical sensitivity is evaluated through finite element modelling, and the maximum displacements indicated are below 10xa0nm for 1xa0g of loading. Mechanical resonance frequencies are found within the 6–15xa0kHz range.

High Q Achieved in Microwave Inductors Fabricated by Parallel Self-Assembly

We present microwave frequency characteristics of meander inductors fabricated in a fully parallel low temperature self-assembly process. This technique enhances the inductor performance by rotating the coil into an upright position, which significantly reduces substrate losses and parasitic capacitance. A peak Q of 20 has been measured for a 2 nH inductor at 3 GHz on a 1–10 Ω·cm silicon substrate, compared to a Q of 4 for an equivalent conventional planar coil. Fabrication of vertical airbridged spiral inductors is also demonstrated, and the high resistance of these vertical structures to mechanical shock is shown by a simple model.

Rigorous network representation of microwave components by the use of indirect mode matching

This paper presents a new method for the analysis of a wide variety of microwave components like posts, circular junctions, or corners in rectangular waveguides. The method gives the impedance or admittance matrix of the microwave component by applying discrimination between the localized and accessible modes in the indirect mode matching (IMM) formulation. In this way, the method is more simple and versatile than previous modeling techniques where IMM is involved, since no use of a Greens function is required for the coupling between different ports. Furthermore, additional obstacles, like posts at the center of a circular junction, can be considered as different terminations of the corresponding transmission lines. The formulation is given for a two-port as well as a multiport system, and in the present paper numerical demonstration is provided for an abrupt and a step H-plane transition from a rectangular to a radial waveguide, a centrally located H-plane circular post in a rectangular waveguide, and a two-port circular junction between rectangular waveguides. The results are compared with the High Frequency Structure Simulator. In all of the aforementioned cases, the method proved to be fast, very accurate, and easy to implement.

Feedforward linearisation applied to a direct carrier modulation transmitter

A feedforward system for direct carrier modulation transmitters is proposed and experimental results are presented. The advantage of this architecture over the conventional one using a feedforward amplifier is that the overall distortion resulting from the modulator is also reduced. The feedforward structure needs a reference signal to compare and cancel distortions: this is achieved using a second modulator which is operated at very low input level to obtain a signal with a negligible distortion. Simulation results suggest that the effect of LO feedthrough which can deteriorate the signal quality is also reduced. Experimental results on a 900 MHz feedforward transmitter with 192 kbps BPSK modulation and Nyquist filtering (/spl alpha/=0.35) show that adjacent channel interference is reduced by as much as 30 dB.

Multilayer CPW lowpass filters on GaAs/Si MMICs

A multilayer coplanar waveguide lowpass filter, fabricated on GaAs and Si substrates using MMIC technology, is presented and the performance investigated experimentally and with electromagnetic simulations. The filter is a Chebyshev type employing three low impedance sections and two high impedance sections. The low impedance sections have a characteristic impedance of 3 /spl Omega/. The high impedance lines use a narrow centre conductor mounted on top of the polyimide layers in order to achieve as high an impedance as possible (100 /spl Omega/).

FDTD modeling of an InP traveling-wave HPT

The development and application of a three-dimensional finite-difference time-domain (FDTD) model for a traveling-wave heterojunction phototransistor (TW-HPT) are presented. The model is enhanced using effective permittivity schemes at the dielectric interfaces and special techniques for the treatment of very thin material sheets. The 3D full-wave electgromagnetic model allows the numerical calculation of the output photocurrent, electrical characteristic impedance, light absorption, microwave losses as well as microwave and optical dispersion. Run in a fast, parallel processing, machine the simulation herein allowed (for the first time, to the best of the authors knowledge) the simultaneous investigation of the optical and microwave characteristics of the traveling-wave structure. This is in contrast to the approach followed by other researchers in the past, as well as by popular simulation packages, based on which results only for the microwave property can be obtained. Snapshots of the field propagation inside the device provide valuable insight into its passive behavior and clearly demonstrate the devices velocity mismatch between the optical signal and the photogenerated electrical pulse. Numerical results for the effective refractive indices of the optical and electrical wave quantify the difference in the velocities of the two waves.

Sideband noise reduction in transposed gain oscillators

This paper presents an analysis of the local oscillator noise reduction mechanism in transposed gain oscillators. The transposed gain oscillator is used for low phase noise signal generation. The results of the analysis show that the degree of LO noise reduction depends solely on the delay mismatch between the low frequency and local oscillator signal paths and that these delays also determine for which of the output frequencies the sideband noise is suppressed.

Reduced spurious signals in an injection-locked oscillator by using combining technique

An injection-locked oscillator technique has been used in order to improve phase noise in the oscillating signal. A single-ended injection-locked oscillator in subharmonic mode provides the unwanted signals due to the nonlinear properties. These unwanted signals can be suppressed by using power combiner technique. A cascaded oscillator using power combining technique was tested. As a result, it is found that the spurious signals caused by the injection locking phenomenon in subharmonic mode reduce by more than 25 dB

Linearised Mixer System Using a Simplified Feedforward Technique for Digital Mobile Communication

This paper presents a simplified system of feedforward mixer which can be applied to digital mobile communication. The complexity of the proposed system is reduced from the two-loop structure originally proposed in the modified feedforward system to a single loop only. Compared with a single mixer, two-tone measurement results at 2.0 and 2.0001 GHz demonstrates up to 33 dB IM3 distortion reduction. The spectrum of a downconverted 900 MHz 16-QAM signal to 70 MHz IF using the proposed system illustrated improves a mixer linearity.