Abstract
We present antenna-pattern measurements obtained from a double-metal supra-terahertz-frequency (supra-THz) quantum cascade laser (QCL) mounted within a mechanically micro-machined waveguide cavity and dual diagonal feedhorn assembly. With the QCL operating in continuous-wave mode at 3.5 THz, and at an ambient temperature of ∼60 K, emission from both laser facets has been simultaneously directed to a suitable supra-THz detector mounted on a multi-axis linear scanner. Comparison of simulated and measured far-field antenna patterns shows an excellent degree of correlation between beamwidth (full-width-half-maximum) and sidelobe content. Furthermore, when compared with unmounted equivalents, very substantially enhanced QCL beam profiles are observed. Our novel device demonstrates the effectiveness of diagonal feedhorns intended for use in future spaceborne Earth-observing supra-THz heterodyne radiometers.
Highlights
The Earth’s upper atmosphere plays an important role in influencing weather and future climate change
Integration with a mechanically fabricated waveguide and feedhorn antenna structure offers the possibility of enhancing the quantum cascade laser (QCL) output signal by constraining it to a propagation mode that results in improved beam quality, and simultaneously allows coupling to a mixer diode mounted within the same waveguide
In addition to using reduced waveguide and feedhorn dimensions that approach fundamental-mode operation, our novel dual feedhorn allows signal emission from each facet of the QCL to be propagated into free-space and the resulting antenna patterns to be measured
Summary
The Earth’s upper atmosphere plays an important role in influencing weather and future climate change. The mesosphere and lower thermosphere (MLT) are strongly affected by both natural and anthropogenic inputs from the surface, and by solar and space-weather impacts from the space environment above. By measuring the global distribution of chemical species (O, NO, OH) that exist within the MLT, climate models can be enhanced and the prospect of climate change better understood. Observations within the MLT are best performed by supraTHz high-spectral-resolution heterodyne radiometers as these allow full characterisation of related spectral signatures. In order to avoid the attenuation of Earth’s lower atmosphere, and provide global coverage, deployment in space is required
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