Abstract
This paper presents a transmitter (TX) and a receiver (RX) with bowtie-antenna and silicon lens for gas spectroscopy at 222-270 GHz, which are fabricated in IHP’s $0.13~\mu \text{m}$ SiGe BiCMOS technology. The TX and RX use two integrated local oscillators for 222 – 256 GHz and 250 – 270 GHz, which are switched for dual-band operation. Due to its directivity of about 27 dBi, the single integrated bowtie-antenna with silicon lens enables an EIRP of about 25 dBm for the TX, and therefore a considerably higher EIRP for the 2-band TX compared to previously reported systems. The double sideband noise temperature of the RX is 20,000 K (18.5 dB noise figure) as measured by the Y-factor method. Absorption spectroscopy of gaseous methanol is used as a measure for the performance of the gas spectroscopy system with TX- and RX-modules.
Highlights
High-resolution spectroscopy at millimeter-wave /terahertz (THz) frequencies is a very powerful tool for gas sensing, because many molecules have rotational transitions in the mmW/THz range [1], [2], [3]
A transmitter (TX) and receiver (RX) in 65 nm CMOS have been reported [6], [7], [8], with gas spectroscopy results at 225 - 255 GHz, [9]. They were compared to results obtained by a solid state multiplier TX and RX made by Virginia Diodes Inc. (VDI) using GaAs Schottky diodes [10]
Considering corrections due to the (1 – 2) dB loss of the transmitted signal caused by the insertion loss of the balun, which connects the doubler output with the differential bowtie antenna, the radiation efficiency of the antenna (65 %), and the selfheating of the TX, the measured radiated power agrees with the local oscillator (LO) power obtained by on-wafer measurement
Summary
High-resolution spectroscopy at millimeter-wave (mmW) /terahertz (THz) frequencies is a very powerful tool for gas sensing, because many molecules have rotational transitions in the mmW/THz range [1], [2], [3]. This paper describes the implementation of a single bowtieantenna with silicon lens for a 2-band TX and RX to increase their performance parameters considerably compared to the previous 2-band TX and RX with two separate LBE on-chip antennas. We will show that our TX/RX spectroscopy system provides a significantly higher sensitivity for high resolution gas spectroscopy compared to our previous system This results from the high directivity of the bowtie antenna with silicon lens and from using a single antenna for both channels which allows better alignment across the entire frequency band. The paper ends with the conclusion including an outlook concerning further improvement of our gas spectroscopy system
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