L. Azcona

Manufacturing Tolerance Analysis, Fabrication, and Characterization of 3-D Submillimeter-Wave Electromagnetic-Bandgap Crystals

The sensitivity of the characteristic band edge frequencies of three different 500-GHz electromagnetic-bandgap crystals to systematic variations in unit cell dimensions has been analyzed. The structures studied were square bar woodpiles made with dielectric having epsiv rap12 and epsivr=37.5 and two wide bandgap epsivr=37.5 crystals designs proposed by Fan and Johnson and Joannopoulos. These epsivr values correspond to high-resistivity silicon and a zirconium-tin-titanate ceramic, respectively. For the woodpiles, the fractional frequency bandgap varied very little for dimensional deviations of up to plusmn5% from the optimum. The bandgaps of the Fan and Johnson and Joannopoulos structures were affected to a greater extent by dimensional variations, particular sensitivity being exhibited to the air-hole radius. For all crystals, the effect of increasing the amount of dielectric in the unit cell was to shift the bandgap edges to lower frequencies. Both silicon and ceramic woodpiles, along with a ceramic Fan structure, were fabricated and dimensionally characterized. Mechanical processing with a semiconductor dicing saw was used to form the woodpiles, while the Fan structure required both dicing and UV laser drilling of circular thru-holes. Good agreement with predicted normal incidence transmissions were found on the low-frequency side of the bandgap in all cases, but transmission values above the upper band edge were lower than expected in the ceramic structures

A 250 GHz Subharmonic Mixer Design Using EBG Technology

The design, manufacture and characterization of a sub-harmonic mixer operating in the millimeter wavelength range is described. The mixer combines for the first time electromagnetic band gap (EBG) technology (which improves the radiation features of the dipole antenna used to couple radiation to the mixer), with conventional local oscillator (LO) waveguide circuitry. The mixer is designed to operate in an RF frequency band around 250 GHz when supplied with a LO frequency between 115 and 135 GHz. The fixed IF frequency spans 2.5-3.5 GHz. Performance predictions were made using a combination of the finite elements (FE) method to compute the embedding impedance of the diodes and the harmonic balance analysis (HBA) to predict the noise temperature. A prototype mixer has been fabricated and tested. Best mixer performance (double side band (DSB) mixer noise temperature and conversion loss of 3000 K and 11.5 dB, respectively) was measured with a LO power level of about 5 mW. Good agreement is observed with the predicted performance.

Application of 1.55 /spl mu/m photomixers as local oscillators & noise sources at millimetre wavelengths

Ultrafast commercial photodiodes have been incorporated into mm-wave waveguide mounts. A method of rapidly characterizing the frequency response of these photomixers using spontaneous-spontaneous beating of light from an erbium doped fibre amplifier (EDFA) is described. The combination of photomixer and EDFA forms a bright, single mode, continuum source suitable for spectroscopy. Results show that the available power is significantly greater than that from a mercury arc lamp. A new photomixer design, featuring a combined probe and filter structure, impedance matched over the W-band to both the coplanar output line on the photodiode chip and to reduced height milled waveguide, is also presented.

Optimization of a 500 GHz Receiver Using EBG Technology

The optimization of a 500 GHz receiver based on Electromagnetic Band Gap (EBG) technology is presented. The conguration consists of a dipole antenna placed on top of a woodpile structure and utilises a Schottky diode as the detecting element. The inuence of the diode and its substrate chip on the radiation performance has been studied, with the nding that it has to be placed as close as possible to the dipole antenna to avoid distorting the radiation pattern. Measurements are presented which conrm our simulations.

Integrated 1.55 μm photomixer local oscillator sources for heterodyne receivers from 70 GHz to beyond 250 GHz

Photomixing is a flexible and efficient method of providing both local oscillator signals for heterodyne receivers and high frequency phase reference signals. Ultrafast, 70 GHz bandwidth, λ = 1.55 μm, photodiodes from u2t Photonics AG have been incorporated into three designs of mm-wave waveguide mounts. The photomixers utilise a thin freestanding gold foil, or a gold on dielectric, probe to couple power into the waveguide and to deliver the photodiode bias. The frequency coverage of the designs is from 70 GHz to 300 GHz. A method of rapidly characterizing the frequency response of these photomixers using spontaneous-spontaneous beating of light from an EDFA is described. Recent work has been directed at increasing the degree of integration of the photodiode with the waveguide probe and choke filter to reduce the frequency dependence of the output power. A simplified photomixer block manufacturing process has also been introduced. A combined probe and filter structure, impedance matched to both the coplanar output line on the photodiode chip and to 0.4 height milled waveguide, is presented. This matching is achieved over the W-band with a fixed waveguide backshort. We present modelled and experimental results showing the increased efficiency and smoother tuning. The design and frequency response of such a probe is reported. We also present the performance of a simpler mount, operating in the frequency range from 160 GHz to 300 GHz, which generates powers of around 10 μW up to 250 GHz.

A 250 GHz sub-harmonic mixer design implemented in EBG technology

The design that is presented in this paper corresponds to a sub-harmonic mixer with an RF frequency around 250 GHz and combines conventional and EBG technologies. In this design an EBG woodpile structure was used as substrate for a dipole antenna, improving its radiation features, whereas the local oscillator (LO) feeding waveguide is a metallic rectangular waveguide. Although in order to take full advantage of this technology and to avoid losses resulting from the transitions between different technologies, the whole system should be completely realised using EBG technology, this is a first step towards a fully integrated EBG receiver.

Integrated 1.55 μm photomixer local oscillators for heterodyne receivers at mm wavelengths

Photomixing is a flexible and efficient method of providing both local oscillator signals for heterodyne receivers and high frequency phase reference signals. Ultrafast, 70 GHz bandwidth, = 1.55 m, photodiodes from u2t Photonics AG have been incorporated into mm-wave waveguide mounts. The photomixers utilise a thin gold probe to couple power into the waveguide and a gold-on-quartz choke filter to deliver photodiode bias. A method of rapidly characterizing the frequency response of these photomixers using spontaneous-spontaneous beating of light from an EDFA is described. Recent work has been directed at increasing the degree of integration of the photodiode, waveguide probe and choke filter to reduce the frequency dependence of the output power. A simplified photomixer block manufacturing process has also been introduced. A combined probe and filter structure, impedance matched to both the coplanar output line on the photodiode chip and to 0.4 height milled waveguide, is presented. This matching is achieved over the W-band with a fixed waveguide backshort. We present modelled and experimental results showing the increased efficiency and smoother tuning. Subsequent integration steps could use the InP photodiode substrate to support the waveguide probe and rf filter. The design and frequency response of such a probe is presented.