Ernst Weissbrodt

W-band radiometer system with switching front-end for multi-load calibration

A W-band Dicke type radiometer with an MMIC single pole-five-throw (SP5T) switch front-end and a Schottky diode detector is presented. The radiometer is intended to test active W-band loads as well as to generate passive millimeter wave imagery. By applying active or conventional hot and cold loads to the spare input ports of the SP5T, the radiometer can switch between the antenna, the external reference loads, and a monolithic integrated 50 Ω load. Hence, accurate radiometric multi-load calibration can be performed as well as standard Dicke operation.

Active load modules for W-band radiometer calibration

An active cold load (ACL) and an active hot load (AHL) circuit were developed in W-band (75 - 110 GHz) and manufactured in IAFs metamorphic high electron mobility transistor (mHEMT) technology. The millimeter-wave monolithic integrated circuits (MMICs) were radiometricly characterized with a dedicated hot cold on wafer noise measurement setup and packaged into waveguide modules. The active load modules were then again characterized, to be used as reference loads in radiometry systems with switching front-ends [1].

A

For application in radiometry or noise measurement systems, an integrated active hot-cold load (AHCL) operating in the W-band (75-110 GHz) is presented and realized as monolithic millimeter-wave integrated circuit (MMIC). It makes use of a novel circuit topology that employs only a single active noise source and monolithic integrated switches to provide a cold and a hot noise reference temperature. The AHCL provides a measured cold temperature of only 230 K and a hot temperature of 860 K around 94 GHz, thus enabling two-point radiometric calibration and absolute power measurements. The noise source of the AHCL has been fabricated as a two-port test structure too. In that configuration, it has been measured as a low-noise amplifier with a noise figure of 2.5 dB at 94 GHz proving its good noise performance. As a standalone active cold load (ACL), an excellent noise power of only 190 K at 93 GHz is achieved. The AHCL and ACL MMICs have been fabricated in 100-nm gate-length metamorphic high electron-mobility transistor technology.

W

At this paper we report on a W-band direct detection radiometer cascading a single-pole four-throw switch with integrated 50 Ω load as a reference noise source, a 3 x 20 dB low-noise amplifier chain, and a broadband Schottky-diode detector. All components are designed and fabricated in 100 nm metamorphic high electron mobility transistor (mHEMT) technology and use waveguide packaging. By using 2 channels of the switch module the Dicke-principle is implemented to drastically reduce the inherent amplifier noise. The multi-throw switch insertion loss is less than 3.5 dB on the chip level and 4.4 dB on the module level. The entire W-band direct detection radiometer chain is also integrated on a single chip and packaged into a waveguide module, which was successfully tested and is now ready for system integration.