Abstract
We report on the development of two 874 GHz receiver channels with orthogonal polarizations for the International Submillimetre Airborne Radiometer. A spline horn antenna and dielectric lens, a Schottky diode mixer circuit, and an intermediate frequency (IF) low noise amplifier circuit were integrated in the same metallic split block housing. This resulted in a receiver mean double sideband (DSB) noise temperature of 3300 K (minimum 2770 K, maximum 3400 K), achieved at an operation temperature of 40 °C and across a 10 GHz wide IF band. A minimum DSB noise temperature of 2260 K at 20 °C was measured without the lens. Three different dielectric lens materials were tested and compared with respect to the radiation pattern and noise temperature. All three lenses were compliant in terms of radiation pattern, but one of the materials led to a reduction in noise temperature of approximately 200 K compared to the others. The loss in this lens was estimated to be 0.42 dB. The local oscillator chains have a power consumption of 24 W and consist of custom-designed Schottky diode quadruplers (5% power efficiency in operation, 8%-9% peak), commercial heterostructure barrier varactor (HBV) triplers, and power amplifiers that are pumped by using a common dielectric resonator oscillator at 36.43 GHz. Measurements of the radiation pattern showed a symmetric main beam lobe with full width half maximum <5° and side lobe levels below -20 dB. Return loss of a prototype of the spline horn and lens was measured using a network analyzer and frequency extenders to 750-1100 GHz. Time-domain analysis of the reflection coefficients shows that the reflections are below -25 dB and are dominated by the external waveguide interface.
Highlights
Ice clouds in the upper troposphere are important for the hydrological cycle and have a big impact on radiative transfer processes, which act to both cool and warm the Earth’s atmosphere.1 Yet, there is a lack of measurement data on ice clouds, which can help to improve current weather and climate models
The 874 GHz receivers of ISMAR are based on GaAs membrane Schottky diode mixers that are integrated with spline horn antennas and intermediate frequency (IF) low noise amplifier (LNA) monolithic microwave integrated circuits (MMICs) in a common gold-plated aluminum split block (Fig. 2)
A single dielectric resonator oscillator (DRO) (Atlantic Microwave, model EDRO-1000 Series) at 36.433 GHz is used as a fundamental source for the local oscillator (LO) chains that consist of power amplifiers (Spacek Labs, model SP384-25-29, coaxial to waveguide), heterostructure barrier varactor (HBV) frequency triplers (Wasa Millimeter Wave, model WX3-864#05), and custom-designed Schottky frequency quadruplers
Summary
Ice clouds in the upper troposphere are important for the hydrological cycle and have a big impact on radiative transfer processes, which act to both cool and warm the Earth’s atmosphere. Yet, there is a lack of measurement data on ice clouds, which can help to improve current weather and climate models. Ice clouds in the upper troposphere are important for the hydrological cycle and have a big impact on radiative transfer processes, which act to both cool and warm the Earth’s atmosphere.. There is a lack of measurement data on ice clouds, which can help to improve current weather and climate models. Satellite-borne instruments that operate at sub-mm wavelengths are suitable to gather these data due to strong interaction with ice particles and the capability to produce long-term data sets. A number of satellite missions utilize sub-mm radiometers to monitor the atmosphere.. A number of satellite missions utilize sub-mm radiometers to monitor the atmosphere.2–4 None of these are specialized for retrievals of ice clouds. The Ice Cloud Imager (ICI) is a new satelliteborne instrument that will address this issue..
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