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W-Band radiometers using intermediate frequency down-conversion (super-heterodyne) and direct detection are compared. Both receivers consist of two W-band low noise amplifiers and an 80-to-101 GHz filter, which conforms to the reception frequency band, in the front-end module. The back-end module of the first receiver comprises a subharmonic mixer, intermediate frequency (IF) amplification and a square-law detector. For direct detection, a W-Band detector replaces the mixer and the intermediate frequency detection stages. The performance of the whole receivers has been simulated requiring special techniques, based on data from the experimental characterization of each subsystem. In the super-heterodyne implementation a local oscillator at 27.1 GHz (with 8 dBm) with a x3 frequency multiplier is used, exhibiting an overall conversion gain around 48 dB, a noise figure around 4 dB, and an effective bandwidth over 10 GHz. In the direct detection scheme, slightly better noise performance is obtained, with a wider bandwidth, around 20 GHz, since there is no IF bandwidth limitation (~15 GHz), and even using the same 80-to-101 GHz filter, the detector can operate through the whole W-band. Moreover, W-band detector has higher sensitivity than the IF detector, increasing slightly the gain. In both cases, the receiver performance is characterized when a broadband noise input signal is applied. The radiometer characteristics have been obtained working as a total power radiometer and as a Dicke radiometer when an optical chopper is used to modulate the incoming signal. Combining this particular super-heterodyne or direct detection topologies and total power or Dicke modes of operation, four different cases are compared and discussed, achieving similar sensitivities, but better performances in terms of equivalent bandwidth and noise for the direct detection radiometer. It should be noted that this conclusion comes from a particular set of components, which we could consider as typical, but we cannot exclude other conclusions for different components, particularly for different mixers and detectors. [ABSTRACT FROM AUTHOR]

This paper presents and discusses three different low-cost microstrip implementations of Schottky-diode detectors in W Band, based on the use of the Zero Bias Diode (ZBD) from VDI (Virginia Diodes, Charlottesville, VA, USA). Designs are based on a previous work of modeling of the ZBD diode. Designs also feature low-cost, easy-to-use tooling substrates (RT Duroid 5880, 5 mils thickness) and even low-cost discrete SMD components such as SOTA resistances (State Of The Art TM miniaturized surface mount resistors), which are modeled to be used well above commercial frequency margins. Intensive use of 3D EM simulation tools such as HFSS TM is done to support microstrip board modeling. Measurements of the three designs fabricated are compared to simulations and discussed. [ABSTRACT FROM AUTHOR]

This paper presents and discusses the careful modeling of a Zero Biased Diode, including low-frequency noise sources, providing a global model compatible with both wire bonding and flip-chip attachment techniques. The model is intended to cover from DC up to W-band behavior, and is based on DC, capacitance versus voltage, as well as scattering and power sweep harmonics measurements. Intensive use of 3D EM (ElectroMagnetic) simulation tools, such as HFSSTM, was done to support Zero Biased Diode parasitics modeling and microstrip board modeling. Measurements are compared with simulations and discussed. The models will provide useful support for detector designs in the W-band. [ABSTRACT FROM AUTHOR]