D.P. Steenson

Fabrication and characterization of micromachined rectangular waveguide components for use at millimeter-wave and terahertz frequencies

The fabrication and characterization of micromachined reduced-height air-filled rectangular waveguide components suitable for integration is reported in this paper. The lithographic technique used permits structures with heights of up to 100 /spl mu/m to be successfully constructed in a repeatable manner. Waveguide S-parameter measurements at frequencies between 75-110 GHz using a vector network analyzer demonstrate low loss propagation in the TE/sub 10/ mode reaching 0.2 dB per wavelength. Scanning electron microscope photographs of conventional and micromachined waveguides show that the fabrication technique can provide a superior surface finish than possible with commercially available components. In order to circumvent problems in efficiently coupling free-space propagating beams to the reduced-height G-band waveguides, as well as to characterize them using quasi-optical techniques, a novel integrated micromachined slotted horn antenna has been designed and fabricated, E-, H-, and D-plane far-field antenna pattern measurements at different frequencies using a quasi-optical setup show that the fabricated structures are optimized for 180-GHz operation with an E-plane half-power beamwidth of 32/spl deg/ elevated 35/spl deg/ above the substrate, a symmetrical H-plane pattern with a half-power beamwidth of 23/spl deg/ and a maximum D-plane cross-polar level of -33 dB. Far-field pattern simulations using HFSS show good agreement with experimental results.

A new micro-machined millimeter-wave and terahertz snap-together rectangular waveguide technology

A novel technique for micro-machining millimeter and submillimeter-wave rectangular waveguide components is reported. These are fabricated in two halves which simply snap together, utilizing locating pins and holes, and are physically robust, and cheap, and easy to manufacture. In addition, S-parameter measurements on these structures are reported for the first time and display lower loss than previously reported micro-machined rectangular waveguides.

Self-sustained current oscillation above 100 GHz in a GaAs/AlAs superlattice

A GaAs/AlAs superlattice with a large miniband (120 meV) showed self-sustained current oscillation at a frequency of 103 GHz giving rise to microwave emission (power 0.5 mW). The emission line had a linewidth of about 1 MHz and was tuneable by about 800 MHz. An analysis suggests that the transport in the superlattice was mainly due to electrons in the lowest miniband and that the oscillation was caused by traveling dipole domains. We also observed frequency locking of the current oscillation attributed to a synchronization of domain propagation by the external high-frequency field.

Microfabrication of channels using an embedded mask in negative resist

A technique has been developed which allows the fabrication of channels within the body of multiple layers of negative resist. Previously this was only possible in the positive resist system but with the transfer to negative resist, higher and more clearly defined channels are now possible. Thick negative resists are also easier to process than their positive counterparts, allowing multiple crossing channels. The physical structure of a full height W-band waveguide with an integrated E-plane filter has been fabricated with this technique. The fabrication procedure presented in this paper is quick, reproducible and easily implemented using standard photolithography equipment.

Electrical and radiation characteristics of semilarge photoconductive terahertz emitters

We present experimental characterization of semilarge photoconductive emitters, including their electrical/photoconductive parameters and terahertz spectra. A range of emitters were studied and fabricated on both LT-GaAs and SI-GaAs, having a variety of electrode geometries. The spatial cone of terahertz radiation was defined. The dependencies of the photocurrent and the terahertz power on the bias voltage and the laser power were determined. A Fourier-transform interferometer is used to determine the terahertz spectra and to clarify the effects of the substrate and electrode geometry.

Membrane-supported CPW with mounted active devices

This paper reports the fabrication of printed circuit lines on a 5 /spl mu/m thick membrane that minimizes dielectric loss and effectively eliminates surface modes, both of which are important for operation at millimeter-wave and submillimeter-wave frequencies. The relatively low-cost low-temperature process uses a photosensitive resin (SU-8) to form the membrane and enables devices to be mounted on it.

A balanced self-oscillating mixer

A balanced self-oscillating mixer is proposed. It consists of a pair of AlGaAs/GaAs 10×45 μm pHEMTs, oscillating at 7.53 GHz and uses the extended resonance effect. The circuit exhibits a conversion gain of 3.6 dB and reduces the second-order intermodulation products by 18.3 dB. The balanced nature of the oscillators also provides good LO to RF isolation of 40.5 dB when used as an upconverter. This approach relaxes the filtering requirements for generating single-sideband AM.

Laser Prototyping of Microwave Circuits in LTCC Technology

In this paper, a process for direct laser structuring of microwave circuits in low-temperature co-fired ceramic (LTCC) technology is reported. An efficient alternative to screen printing is proposed for prototyping circuits by laser patterning the conductors on the unfired tape. A line width and gap of 50 ¿m are achieved with laser machining. A range of samples has been studied using a scanning electron microscope in order to optimize the process parameters. The surface roughness of laser-treated samples is measured with a surface profiler and compared with the untreated samples. A method of creating microvias and trenches in thick LTCC substrate is also demonstrated. For 254 ¿m thick green tape, vias with a diameter and separation of 50 ¿ m are realized along with trenches having a width as small as 30 ¿m. The method of optimizing the laser machining process is described in detail. A band-stop mushroom resonator and a microstrip ring resonator filter are fabricated and their results compared against simulations.

A resonant tunnelling diode self-oscillating mixer with conversion gain

An 11-GHz self-oscillating microwave mixer using a resonant tunneling diode is described. Operating in a nonoptimized system, a maximum conversion gain of 10 dB with an associated noise figure of 11.5 dB has been observed. As a result of the conversion gain and self-oscillating configuration, a simpler construction with fewer components than conventional circuits is obtained. The local oscillator can be injection locked and swept over a frequency range of 200 MHz.<<ETX>>

Measurements to 320 GHz of millimetre-wave waveguide components made by high precision and economic micro-machining techniques

A new technique for the fabrication and integration of various waveguide components together with an integrated E-plane circuit to form a compact millimetre-wave subcomponent has been produced. These waveguide components were fabricated in two halves using SU-8 such that the circuits can be placed in the E-plane of the waveguide and accommodated in a specially designed metal block for measurement. This technique is sufficiently flexible and repeatable so as to permit complex 3-D waveguide components with low loss and excellent surface finish to be realised at low cost. Various rectangular waveguide sections with operating frequencies from 110 to 320 GHz have been fabricated and measured to evaluate this approach.