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We demonstrate a full-cycle breath gas sensor system based on terahertz/millimeter-wave gas spectroscopy. The sensor consists of a transmitter and receiver working around 250 GHz based on SiGe BiCMOS technology. Typical detection thresholds are in the ppm range depending on the respective molecule. The data analysis provides partial pressures of the investigated molecules by fitting of spectra which are measured by wavelength modulation. Beside the spectroscopic measurement and the data analysis, a full cycle of breath analysis includes the sampling and the conditioning of the sample tubes. The full cycle takes about 35 min per sample in average. As the system is compact and easy to operate, it allows for on-site analysis of breath samples in medical laboratories or hospitals.

This letter presents a four-way combined frequency multiplier chain (FMC), which converts a single-ended 110–135-GHz input signal to a differential 440–540-GHz output signal. The four-way combined FMC uses four identical FMCs, which consist of two amplification and two frequency doubling stages. These blocks are designed with optimized parameters to be used as the transmitter of a gas spectroscopy system at 440–540 GHz. The four-way combined FMC has 0.5 dBm measured maximum output power at 450 GHz and −4.5 dBm at 500 GHz.

A subharmonic mixer (SHM), which is measured within the RF range 450–500 GHz, is presented. The SHM uses a single-balanced topology with optimized parameters for gas spectroscopy at 440–540 GHz. The differential RF input of the mixer core is transformed to a single-ended input using a Marchand balun. The mixer is designed using a 130-nm SiGe BiCMOS technology. The mixer shows a measured conversion loss of 8.5 dB and an estimated noise figure of 33 dB at 480 GHz, using −1 dBm local oscillator (LO) power. The conversion loss was quantified to be in the range of 7.5–12.5 dB at 450–500 GHz.

The analysis of human breath is a very active area of research, driven by the vision of a fast, easy, and non-invasive tool for medical diagnoses at the point of care. Millimeter-wave gas spectroscopy (MMWGS) is a novel, well-suited technique for this application as it provides high sensitivity, specificity and selectivity. Most of all, it offers the perspective of compact low-cost systems to be used in doctors' offices or hospitals. In this work, we demonstrate the analysis of breath samples acquired in a medical environment using MMWGS and evaluate validity, reliability, as well as limitations and perspectives of the method. To this end, we investigated 28 duplicate samples from chronic obstructive lung disease patients and compared the results to gas chromatography-mass spectrometry (GC-MS). The quantification of the data was conducted using a calibration-free fit model, which describes the data precisely and delivers absolute quantities. For ethanol, acetone, and acetonitrile, the results agree well with the GC-MS measurements and are as reliable as GC-MS. The duplicate samples deviate from the mean values by only 6% to 18%. Detection limits of MMWGS depend strongly on the molecular species. For example, acetonitrile can be traced down to 1.8 × 10−12 mol by the MMWGS system, which is comparable to the GC-MS system. We observed correlations of abundances between formaldehyde and acetaldehyde as well as between acetonitrile and acetaldehyde, which demonstrates the potential of MMWGS for breath research. Deutsche Forschungsgemeinschafthttp://dx.doi.org/10.13039/501100001659 Deutsches Zentrum für Lungenforschunghttp://dx.doi.org/10.13039/501100010564

This article presents a reflectometer-based on-chip dielectric sensor with integrated transducers at 240 GHz. The chip simplifies the measurement of a vector network analyzer (VNA) to sense the incident and reflected waves by using two heterodyne mixer-based receivers with a dielectric sensing element. Radio frequency (RF) and local oscillator (LO) submillimeter waves are generated by two frequency multiplier chains, respectively. Two back-to-back identical differential side-coupled directive couplers are proposed to separate the incident and reflected signals and couple them to mixers. Both transmission line and coplanar stripline transducers are proposed and integrated with reflectometer to investigate the sensitivity of dielectric sensors. The latter leads to a larger power variation of the reflectometer by providing more sufficient operating bands for the magnitude and phase slope of $S_{11}$ . The readout of the transducers upon exposure to liquids is performed by the measurement of their reflected signals using two external excitation sources. The experimental dielectric sensing is demonstrated by using binary methanol–ethanol mixture placed on the proposed on-chip dielectric sensor in the assembled printed circuit board. It enables a maximum 8 dB of the power difference between the incident and reflected channels on the measurement of liquid solvents. Both chips occupy an area of 4.03 mm2 and consume 560 mW. Along with a wide operational frequency range from 200 to 240 GHz, this simplified one-port-VNA-based on-chip device makes it feasible for the use of handle product and suitable for the submillimeter-wave dielectric spectroscopy applications.

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.

Molecular spectroscopy of gases is an important method for various applications on Earth and in space. In the millimeter-wave / terahertz range, many molecules have rotational transitions and are distinguishable by their spectral fingerprint. We analyze the performance of a heterodyne receiver fabricated in SiGe BiCMOS technology, which operates at room temperature and is tunable from 225 GHz to 255 GHz. At 241 GHz, the double sideband noise temperature of the receiver is approximately 20,000 K at 1.5 GHz intermediate frequency and the Allan time is 1 s. First heterodyne measurements of methanol emission lines were successfully performed in laboratory experiments.

This work gives an overview of integrated microwave to millimeter wave sensors and their applications covering frequencies from 28 GHz to 240 GHz. The designs are capable to address versatile application fields from liquid compound measurements to plaque detection and classification in arteries, glucose detection in continuous glucose monitoring (CGS) systems and virus detection in the context of respiratory diseases. The demonstrated approaches represent powerful and miniaturized solutions for highly sensitive contactless sensing of sample properties. Exploiting millimeter wave frequencies enables highest levels of integration to implement miniaturized sensing solutions including on-chip readout systems.

This paper presents a reflectometer with an integrated transducer as a high-integration miniaturized sensor for dielectric spectroscopy at 240 GHz in SiGe BiCMOS technology. The reflectometer consists of a signal generation component using 240-GHz multiplier chains, side-coupled directive couplers and a two-channel heterodyne receiver. Readout of the transducer upon exposure to liquids is performed by the measurement of its reflected signal using an external excitation source. The experimental dielectric sensing is demonstrated by using a binary methanol-ethanol mixture placed on the proposed on-chip dielectric sensor in the assembled printed circuit board.

This paper presents a high-integration miniaturized dielectric spectroscopy system for sensing the change of permittivity at 240 GHz in the SiGe BiCMOS technology. The sensor features a transducer with a resonator to perform bandpass frequency response, whose complex value of $S_{21}$ is varied with the permittivity of the sample under test. This variation can be detected and recorded as the change of amplitude and phase of the 240-GHz in-phase and quadrature direct conversion mixer. An external 30-GHz source is employed with cascade frequency multiplier chain to deliver a signal through the system with a wide tuning range of 215–245 GHz. An additional probe is employed to carry the sample and implement chip measurements on the probe station. The sensing function of this system is performed with the leaded wire as a metallic sample to be placed on the top of the transducer. Based on the measured dc output voltage changes, the calculated magnitude and phase of IQ signal in the 215–245-GHz range are used to estimate the complex permittivity change of MUTs. This dielectric spectroscopy system is also suitable for sensing the complexy permittivity change at higher frequencies in the future terahertz Lab-on-Chip measurements.

The unique fingerprint spectra of volatile organic compounds for breath analysis and toxic industrial chemicals make an mm-wave (mmW)/THz gas sensor very specific and sensitive. This paper reviews and updates results of our recent work on sensor systems for gas spectroscopy based on integrated transmitter (TX) and receiver (RX), which are developed and fabricated in IHP’s $0.13~\mu \text{m}$ SiGe BiCMOS technology. In this paper, we present an mmW/THz spectroscopic system including a folded gas absorption cell of 1.9 m length between the TX and RX modules. We discuss the results and specifications of our sensor system based on integrated TX and RX. We demonstrate TXs and RXs with integrated antennas for spectroscopy at 238–252 GHz and 494–500 GHz using integer- $N$ phase-locked loops (PLLs). We present a compact system by using fractional- ${N}$ PLLs allowing frequency ramps for the TX and RX, and for TX with superimposed frequency shift keying or reference frequency modulation. In another configuration, the voltage controlled oscillators of the TX and RX local oscillator are tuned directly without PLLs by applying external voltages. Further developments of our system are aimed at realizing an even wider frequency span by switching between frequency bands, and to use a more compact gas absorption cell.

Millimeter-wave/terahertz (mmW/THz) spectros-copy is a promising tool for gas sensing applications, such as breath analysis or the detection of toxic chemicals, which require compact portable systems. Long gas cells that are needed for high sensitivities are often bulky and limit the portability of the system. We present a compact mmW/THz circular multipass gas cell with an optical path length of 1.9 m and an outer diameter of only 21.5 cm. The beam is refocused at each internal reflection as a consequence of the large divergence of the mmW/THz beams. We determined the losses of the cell to about 3 dB around 250 GHz and demonstrated sensitive gas spectroscopy with a detection limit of 14 ppm/√Hz for acetaldehyde in a mixture with methanol.

We present broadband gas spectroscopy based on SiGe BiCMOS technology. A bandwidth of about 222 -270 GHz is achieved by a combination of two frequency bands on single transmitter and receiver chips. The antennas of transmitter and receiver for both bands are closely placed on a single chip such that coupling into the same optical system can be realized. We coupled the beams into a compact custom-made multi-pass ring cell with an optical path length of 1.9 m. We demonstrate sensitive gas spectroscopy capabilities by a full bandwidth spectrum of methanol.

A novel 245 GHz 4thindex harmonicpush-push VCO is presented in IHP SiGe: C BiCMOS technology with f T and f max of 300 and 500 GHz respectively. The VCO utilizes the 4thharmonic index in the push-push oscillating core to obtain 245 GHz signals. The VCO comprises of a 4thharmonic oscillating core with 1/64 divider and a 245 GHz common base (CB) LNA buffer stage. The output power of the VCO reaches -18 dBmat 251 GHz with a phase noise of -86 dBc/Hz at 1 MHz offset frequency. The VCO has a tuning range of 18 GHz, occupies an area of 0.45 mm2 and dissipates 179 mW with divider, or 95 mW without divider.

Breath gas analysis is a promising tool for medical research and diagnosis. A particularly powerful technological approach is millimeter-wave/terahertz (mmW/THz) spectroscopy, because it is a very sensitive and highly selective technique. In addition, it offers the potential for compact and affordable sensing systems for wide use. In this work, we demonstrate the capability of a mmW/THz spectrometer for breath analysis. Samples from three volunteers and a sample from ambient air were analyzed with respect to 31 different molecular species. High-resolution absorption spectra were measured by scanning two absorption lines from each species. Out of the 31, a total of 21 species were detected. The results demonstrate the potential of mmW/THz spectroscopy for breath analysis. Deutsche Forschungsgemeinschaft

This letter presents a wideband 240-GHz direct-conversion receiver manufactured in a 130-nm SiGe:C BiCMOS technology with $f_{T}/f_{\text {max}}=300$ /500 GHz. A mixer-first receiver is implemented, with a new dc offset cancellation loop architecture to compensate for the mixer dc offsets and biasing purposes. A transimpedance amplifier is utilized as a load for the mixer, optimized with the dc offset cancellation loop to maximize the bandwidth. A local oscillator (LO) chain that multiplies by 8 a 30-GHz input signal drives the mixer. The proposed receiver achieves the widest 3-dB bandwidth among the published works of 55 GHz, with a conversion gain of 13 dB. The measured average single-sideband noise figure is 18 dB. It dissipates 500 mW, while occupying 1.25 mm2, requiring LO input signal of only −10 dBm.

This work describes an electrical interferometer for contactless permittivity measurements working at 120 GHz. It was fabricated in a 130 nm SiGe process featuring an ft and fmax of 240 and 330 GHz. The on-chip system contains a 120 GHz VCO with a tuning range of 7 GHz featuring a divide-by-64 circuit to enable external PLL operation. The subsequent buffer provides 7 dBm of output power at 120 GHz. Additionally, the IC contains high-precision and high-resolution phase shifters based on a slow-wave transmission line approach with digital control for direct readout ability. A 120 GHz LNA with 17 dB gain and a power detector to provide DC output signals were realized on chip. It enables sample emulation capability by phase shift inducement in the measurement as well as a reference transmission line. In terms of phase detection, the system shows a sensitivity of 907.36 MHz/°.

This paper presents two scalable resonator-based transducers (RBTs) at terahertz (THz) frequency range to realise THz spectroscopy for dielectric sensing. First, the design of 0.24 THz RBT is described by scaled a 0.12 THz sensing structures which utilises a wavelength-long closed-ring resonator to place inside of the Coplanar stripline (CPS) to make a high-selective bandpass response and combines with short-ended strips to create the bandstop behavior. Its scattering parameter can have a very large magnitude change and resonance frequency shift for the loaded samples. Next, a ring structure is also presented to implement 0.48 THz sensing by scaled a low frequency RBT, which employs ring resonator with an asymmetrically loaded stubs to perform a high analytic sensitivity and selectivity for loaded samples. Both presented scalable transducers, possessing the high integration capability of silicon circuits, are proved to be the promising employments in THz spectroscopy.

This paper for the first time prototypes and compares the homodyne and heterodyne terahertz dielectric sensors for lab-on-chip applications. The homodyne sensor consists of a multiplier chain, a balun-based power divider, an on-chip transducer, and IQ mixers. Differently, the heterodyne sensor requires an additional multiplier chain; however, it waives one mixer and a power divider, leading to reduced losses and alleviated power consumption. Fabricated using 0.13 µm SiGe BiCMOS technology, the homodyne and heterodyne sensors take 4 mm2 and 5.2 mm2, and consume 400 mW and 499 mW, respectively. By experiments, both designed homodyne and heterodyne sensors can effectively sense the dielectric parameters of the samples. Moreover, the heterodyne sensor can address the DC offset issues with merely 99 mW additional power.

In this paper, a fully integrated wideband 240-GHz transceiver front-end, supporting BPSK modulation scheme, with on-chip antenna is demonstrated in SiGe:C BiCMOS technology with $f_{\text {T}}/f_{\text {max}}\,\,=$ 300/500 GHz and local backside etching option. Within the transmitter, the upconversion is provided by fundamental mixing using a modified Gilbert cell mixer driven by a multiplier-by-eight local oscillator (LO) chain. The transmitter achieves a 3-dB RF bandwidth of 35 GHz with a saturated output power of −0.8 dBm. The down converter is equipped with a mixer first architecture. The mixer is designed utilizing a transimpedance amplifier as load for enhanced noise and bandwidth performance. For dc-coupled receiver, two dc offset cancellation loops are implemented within the receiver chain. It achieves a 3-dB RF bandwidth of 55 GHz, minimum single-sideband noise figure (SSB NF) of 13.4 dB, and a gain of 32 dB with 25-dB gain control. A wideband on-chip double-folded dipole antenna and an on-board optical lens are utilized to demonstrate a wireless link achieving 20- and 25-Gb/s data rates at bit error rates (BERs) of $6.3 \times 10^{-6}$ and $2.2\times 10^{-4}$ , respectively, across a distance of 15 cm. The transmitter and receiver consume 375 and 575 mW, respectively, which correspond to power efficiencies of 15 pJ/bit for the transmitter and 23 pJ/bit for the receiver. They occupy a silicon area of 4.3 and 4.5 mm2, respectively.

This work describes a dielectric sensing system applying a 120 GHz electrical interferometer for contactless permittivity measurements. The applied IC was fabricated in a 130 nm SiGe process featuring an ft and fmax of 240 GHz and 330 GHz. The on-chip system contains a 120 GHz VCO with a tuning range of 7 GHz featuring a divide-by-64 circuit to enable external PLL operation. An important feature of the IC is high-precision and high-resolution phase shifting based on a slow-wave transmission lines approach with digital control. This allows for direct digital readout ability. The on chip power detector provides DC output signals giving the opportunity to record transfer functions of the interferometer. It enables sample emulation capability by phase shift inducement in the measurement as well as a reference transmission line. The motherboard of the system provides PLL stabilization for frequency sweeps. The proposed approach is capable of automated dielectric monitoring by phase compensation.

In this report we propose a sensor architecture and a corresponding read-out technique on silicon for the detection of dynamic capacitance change. This approach can be applied to rapid particle counting and single particle sensing in a fluidic system. The sensing principle is based on capacitance variation of an interdigitated electrode (IDE) structure embedded in an oscillator circuit. The capacitance scaling of the IDE results in frequency modulation of the oscillator. A demodulator architecture is employed to provide a read-out of the frequency modulation caused by the capacitance change. A self-calibrating technique is employed at the read-out amplifier stage. The capacitance variation of the IDE due to particle flow causing frequency modulation and the corresponding demodulator read-out has been analytically modelled. Experimental verification of the established model and the functionality of the sensor chip were shown using a modulating capacitor independent of fluidic integration. The initial results show that the sensor is capable of detecting frequency changes of the order of 100 parts per million (PPM), which translates to a shift of 1.43 MHz at 14.3 GHz operating frequency. It is also shown that a capacitance change every 3 μs can be accurately detected.

We describe a spectrometer consisting of a vector network analyzer, a gas absorption cell, and a quasi-optical bench that acquires terahertz spectra of gaseous substances and mixtures. We tested volatile organic compounds that are medical biomarkers or chemicals which can be found on the US Environment Protection Agency list of harmful substances. Absorption spectra at gas pressures between 10 Pa and 5000 Pa were recorded. A subsequent multivariate data analysis demonstrated excellent qualitative and quantitative identification of pure substances and complex mixtures. The applied multivariate algorithms are principal components analysis, partial least square regression and soft independent modelling of class analogy.

This work presents a fully-differential wideband and low power 240 GHz multiplier-by-8 chain, manufactured in a 130 nm SiGe:C BiCMOS technology with f T /f max = 300/500 GHz. A 30 GHz input signal is multiplied by 8 using a Gilbert cell based quadrupler and doubler and then amplified with 3-stage cascode amplifier. To achieve wide bandwidth and optimize for power consumption, the power budget has been designed in order to operate the frequency multipliers and the output amplifier in saturation. With this architecture the presented circuit achieves a 3 dB bandwidth of 40 GHz, with a relative 3 dB bandwidth of 17%, and a peak saturated output power of 0 dBm. It dissipates 255 mW from 3 V supply which results in drain efficiency of 0.4%, while occupying 1.2 mm2. With these characteristics the presented circuit suits very well as a frequency multiplier chain to drive balanced mixers in 240 GHz transceivers for radar, communication and sensing applications.

We present a 245 GHz gas spectroscopy system with a transmitter array and a receiver based on SiGe BiCMOS technology. Beam profiles of the transmitter array and noise sources of the system were analyzed. We demonstrate the detection of a 50 ppm mixture of ethanol in ambient air after preconcentration. With the maximum signal-to-noise ratio of 190 the resolution can be estimated to 260 ppb.

We present a gas sensor system based on 245 GHz SiGe transmitter and receiver chips and a carbon molecular sieve gas concentrator. A gas mixture of 100 ppm methanol in ambient air at atmospheric pressure can be detected with high SNR of up to 430 at a pressure of 7.7 Pa after thermal desorption of the gas, which corresponds to a sensitivity of 230 ppb.

This paper presents a highly selective integrated dielectric sensor with read-out circuit at 240 GHz in SiGe BiCMOS and back-side etching technology. The sensor features with a resonator to perform bandpass frequency response which varied in accordance to the dielectric change of the sample under test. This variation can be sensed and recorded as the change of output voltage of an integrated 240 GHz IQ receiver. The demonstration of aforementioned function is verified by measuring the output of mixer when a sample is placed over the resonator.

The implementation of an integrated mm-wave transmitter (TX) and receiver (RX) in SiGe BiCMOS or CMOS technology offers a path towards a compact and low-cost system for gas spectroscopy. Previously, we have demonstrated TXs and RXs for spectroscopy at 238 -252 GHz and 495 - 497 GHz using external phase-locked loops (PLLs) with signal generators for the reference frequency ramps. Here, we present a more compact system by using two external fractional-N PLLs allowing frequency ramps for the TX and RX, and for TX with superimposed frequency shift keying (FSK) or reference frequency modulation realized by a direct digital synthesizer (DDS) or an arbitrary waveform generator. The 1.9 m folded gas absorption cell, the vacuum pumps, as well as the TX and RX are placed on a portable breadboard with dimensions of 75 cm x 45 cm. The system performance is evaluated by high-resolution absorption spectra of gaseous methanol at 13 Pa for 241 - 242 GHz. The 2f (second harmonic) content of the absorption spectrum of the methanol was obtained by detecting the IF power of RX using a diode power sensor connected to a lock-in amplifier. The reference frequency modulation reveals a higher SNR (signal-noise-ratio) of 98 within 32 s acquisition compared to 66 for FSK. The setup allows for jumping to preselected frequency regions according to the spectral signature thus reducing the acquisition time by up to one order of magnitude.

In this paper, an integrated dielectric sensor with a read-out circuit in an unmodified SiGe BiCMOS technology at 125 GHz is presented. The sensor consists of a 500- $\mu{\hbox {m}}$ shorted half-wave coplanar-waveguide transmission line in the uppermost metal layer of the silicon process, while the read-out is obtained by reflection coefficient measurement with an integrated reflectometer and a signal source. The reflectometer is verified with a circuit breakout including an integrated dummy sensor. The reflectometer is able to measure the phase of the reflection coefficient from 117 to 134 GHz with a resolution of 0.1 $^{\circ}$ and a standard deviation of 0.082 $^{\circ}$ . The integrated sensor with the reflectometer circuit have been fabricated in a 190-GHz ${ f}_{ T}$ SiGe:C BiCMOS technology. It spans an area of 1.4 ${\hbox {mm}}^{2}$ and consumes 75 mA from a 3.3-V supply. The circuit has been assembled on a printed circuit board for characterization by immersion into test liquids. The sensor is controlled by a controller board and a personal computer enabling a measurement time of up to 1 ms per frequency point. Functionality of the sensor is demonstrated from 118 to 133 GHz with immersion of the sensor into different binary methanol–ethanol mixtures, showing good correlation between theory and measurement. The sensor shows a standard deviation of the measured phase of 0.220 $^{\circ}$ and is able to detect a difference in $\epsilon_{r}^{\prime}$ of 0.0125.

A compact gas spectroscopy sensor system based on a 245 GHz transmitter (TX) and receiver (RX) fabricated in SiGe technology is presented. The frequencies of the TX and RX are tuned by applying external voltages at the voltage-controlled oscillators. For 2f spectroscopy, a frequency modulation is also applied at the TX. As a result, methanol spectra are presented, that exhibit a high signal-to-noise ratio of up to 560 and an acquisition time as short as 39 s, respectively.

This paper presents a four stage all-transmission-line 220 GHz differential LNA in SiGe BiCMOS technology. Cascode topology is chosen for each stage. The amplifier takes advantage of microstrip transmission lines to realize the inductive load, Marshand balun, input, output, and inter-stage matching of the LNA. The LNA has a gain of 21 dB at 224 GHz, a 3 dB bandwidth of more than 6 GHz. It has a supply voltage of 3V and power dissipation of 234 mW. The amplifier is intended for the use in communication, security scanning, imaging and remote sensing at 220 GHz.

A 245-GHz transmitter (TX) array with an integrated antenna-array for a gas spectroscopy system has been realized. It consists of a push–push VCO with a 1/64 frequency divider, power amplifiers, frequency doublers, and on-chip antennas with localized backside etching. The TX-frequency is tunable in the range from 238 to 252 GHz. The TX-array has been fabricated in a 0.13- $\mu\hbox{m}$ SiGe:C BiCMOS technology with ${\rm f} _{\rm T} /{\rm f} _{\max}$ of 300 GHz/500 GHz. Its output power is approximately 7 dBm at 245 GHz, and the effective isotropically radiated power (EIRP) reaches 18 dBm at 245 GHz. The main components of the gas spectroscopy system are a TX and a receiver (RX) in SiGe BiCMOS as well as a gas absorption cell. The sensitivity of this spectroscopy system is demonstrated by measuring the high-resolution absorption spectrum of gaseous methanol ( $\hbox{CH}_{3}\hbox{OH}$ ). Due to the increased power provided by the TX-array, the sensitivity of the spectrometer can be increased significantly.

A four-stage common-base (CB) 245-GHz low-noise amplifier (LNA) and a fourth subharmonic 245-GHz transconductance mixer are presented. An integrated subharmonic receiver for sensing applications in the 245-GHz industrial-scientific-medical band is proposed. The receiver consists of a single-ended CB LNA, a fourth transconductance subharmonic mixer, a 60-GHz push-push voltage-controlled oscillator with a 1/32 divider, and an IF amplifier. It is fabricated in an SiGe: C BiCMOS technology with f T and fmax of 300 and 500 GHz, respectively. Its measured single-ended gain is 21 dB at 243 GHz with a tuning range of 12 GHz, and a noise figure of 33 dB. The input 1-dB compression point is -37 dBm . The receiver dissipates at 358 mW.