A compact 128-element Schottky diode grid frequency doubler generating 0.25 W of output power at 183 GHz

This paper presents a compact varactor grid frequency doubler encapsulated in a waveguide environment, thus providing single mode (H₁₀) waveguide connection at both input and output. Schottky diodes are used as varactors in this 128-element grid frequency doubler. By packaging the grid and its embedding network together with a stepped waveguide taper on the output, a module measuring 9 mm x 19 mm by 19 mm is created. A peak output power of 0.25 W is produced at 183 GHz with 1.32 W of input power and a corresponding conversion efficiency of 19%. The peak conversion efficiency is 23% at 183 GHz with 666 mW of input power

Low kinetic inductance superconducting MgB2 nanowires with a 130-picosecond relaxation time for single-photon detection applications

Properties of superconducting nanowires set the performance level for Superconducting Nanowire Single Photon Detectors (SNSPD). Reset time in commonly employed large area SNSPDs, 1-10ns, is known to be limited by the nanowire\u27s kinetic inductance to the load impedance ratio. On the other hand, reduction of the kinetic inductance in small area (waveguide integrated) SNSPDs prevents biasing them close to the critical current due to latching into a permanent resistive state. In order to reduce the reset time in SNSPDs, superconducting nanowires with both low kinetic inductance and fast electron energy relaxation are required. In this paper, we report on a study of kinetic inductance in narrow (15-100nm) and long (up to 120m) superconducting MgB2 nanowires made from 5 nm-thick films, offering such combination of properties. Such films were grown using Hybrid Physical Chemical Vapor Deposition, resulting in a critical temperature of 32K, and a switch current density of 5107A/cm2 (at 4.8K). Using microwave reflectometry, we measured a kinetic inductance of Lk0(4.8K)=1.3-1.6 pH/ regardless of the nanowire width, which results in a magnetic field penetration depth of 90 nm. These values are very close to those in pristine MgB2. We showed that after excitations by a 50 fs pulsed laser the reset time in 35nm120m MgB2 nanowires is 130 ps, which is more than a factor of 10 shorter than in NbN nanowires of similar length-to-width ratios. Depending on the bias current, such MgB2 nanowires function as single-, double , or triple- photon detectors for both visible (= 630 nm) and infrared (= 1550 nm) photons, with a dark count rate of <10 cps. Although the apparent photon detection efficiency seems so far to be low, further technological advances (uniform nanowire width, smaller thickness, increasing the switching current closer to the pair-breaking current) may improve this figure of merit

Transmission Loss in Coplanar Waveguide and Planar Goubau Line between 0.75 THz and 1.1 THz

In many cases, metallic planar waveguides are required in the design of integrated circuits. However, at terahertz frequencies, metallic planar waveguides present high losses, which make necessary the use more efficient waveguides to avoid power limitations. In this work, the attenuation constant of two popular planar waveguides for terahertz frequencies, Coplanar Waveguide (CPW) and Planar Goubau Line (PGL), are compared between 0.75 THz and 1.1 THz. To measure the PGL, its transition is deembeded using a multiline Thru-Reflect-Line calibration standard. Measurement results show a lower attenuation constant across the band for a PGL (0.13 mm-1 < α < 0.39 mm-1) than for a CPW (0.68 mm-1 < α < 0.99 mm-1) when an ultra-thin substrate is used suspended in air, which greatly reduces the substrate mode coupling from the PGL. These results put the PGL as a less lossy metallic planar waveguide for terahertz applications

A Capacitive-Gap Coupled Terahertz Planar-Goubau-Line Power Divider

The planar Goubau line is a single-conductor waveguide with a low attenuation constant at terahertz frequencies compared to other planar waveguides. However, its single-conductor nature complicates the design of circuit elements compared to multi-conductor waveguides, especially when impedance transformation is needed, like in the case of power dividers. In this paper, we present a power divider for a planar Goubau line based on capacitive-gap coupled lines, providing a matched input port. A 900-GHz equal power divider was fabricated on a suspended silicon membrane and was characterized with a Vector Network Analyzer and terahertz probes between 0.5 THz and 1.1 THz. Simulations and measurements are in good agreement, the measured input return loss is lower than 15dB at the design frequency, and the average coupler loss is estimated to be lower than 1 dB when de-embedding the feeding lines

A Corrugated Planar-Goubau-Line Termination for Terahertz Waves

The planar Goubau line is a promising low-loss metal waveguide for terahertz applications. To enable advanced circuits and multi-port measurements based on planar Goubau lines, there is a strong need for broadband impedance-matched loads, which can be used to absorb the energy and minimize standing waves in a system. In this work, we propose a termination for planar Goubau lines based on an exponentially-tapered corrugated line, gradually increasing conductor losses while maintaining small reflections. The corrugation density is high enough to increase conductor losses without requiring an auxiliary low-conductivity material. A 400-\ub5m long planar Goubau line load was fabricated on a 10-\ub5m thick silicon substrate suspended in the air. Simulations of the load show excellent agreement with calibrated reflection measurements in the frequency range 0.5 THz – 1.1 THz. Above the cut-off frequency of around 580 GHz, the measured reflections are less than -19 dB, below the noise floor of the characterization setup

On-Chip Characterization of High-Loss Liquids Between 750 and 1100 GHz

Terahertz spectroscopy is a promising tool for analyzing the picosecond dynamics of biomolecules, which is influenced by surrounding water molecules. However, water causes extreme losses to terahertz signals, preventing sensitive measurements at this frequency range. Here, we present sensitive on-chip terahertz spectroscopy of highly lossy aqueous solutions using a vector network analyzer, contact probes, and a coplanar waveguide with a 0.1 mm wide microfluidic channel. The complex permittivities of various deionized water/isopropyl alcohol concentration are extracted from a known reference measurement across the frequency range 750–1100 GHz and agrees well with literature data. The results prove the presented method as a highsensitive approach for on-chip terahertz spectroscopy of high-loss liquids, capable of resolving the permittivity of water

Terahertz Planar Goubau Line Components on Thin Suspended Silicon Substrate

The planar Goubau line is a low-loss planar single-conductor waveguide that holds promise for terahertz applications,\ua0where power efficiency is crucial. We present three circuit elements for planar Goubau line: a stopband filter, a matching\ua0load, and a power divider, which have been fabricated in a high-resistivity silicon membrane. Simulation results are presented for\ua0the matching load and the power divider. The filter’s performance is validated by comparing measurement results with simulations,\ua0showing good agreement

Capacitively-coupled resonators for terahertz planar-Goubau-line filters

Low-loss planar Goubau lines show promising potential for terahertz applications. However, a single-wire waveguide exhibits less design freedom than standard multi-conductor lines, which is a significant constraint for realizing standard components. Existing filters for planar Goubau line lack clear design procedures preventing the synthesis of an arbitrary filter response. In this work, we present a design for a bandpass/bandstop filter for planar Goubau line by periodically loading the line with capacitively-coupled \u1d706∕2 resonators, which can be easily tuned by changing their electrical length. The filter’s working principle is explained by a proposed transmission-line model. We designed and fabricated a passband filter centered at 0.9 THz on a 10-\u1d707m silicon-membrane substrate and compared measurement results between 0.5 THz and 1.1 THz to electromagnetic simulations, showing excellent agreement in both \u1d44611 and \u1d44621. The measured passband has an insertion loss of 7 dB and a 3-dB bandwidth of 31%. Overall, the proposed filter design has good performance while having a simple design procedure

A 183-GHz Schottky diode receiver with 4 dB noise figure

Atmospheric science based on space-borne\ua0millimeter wave measurements require reliable and state-of-the art\ua0receivers. In particular, the water vapor line at 183.3 GHz\ua0motivates the development of sensitive mixers at this frequency.\ua0Traditional assembly techniques employed in the production of\ua0Schottky diode receivers involve flip-chip mounting and soldering\ua0of discrete dies, which prohibit the implementation of reliable and\ua0repeatable production processes. In this work, we present a\ua0subharmonic 183 GHz mixer implementing a repeatable assembly\ua0method using beamlead Schottky diodes. The mixer was\ua0integrated with a InP HEMT MMIC low noise intermediate\ua0frequency amplifier resulting in a record-low receiver noise\ua0temperature of 450 K at 1 mW of local oscillator power measured\ua0at room-temperature. The measured Allan time was 10 s and the\ua0third order local oscillator spurious power was less than -60 dBm.\ua0The proposed assembly method is of particular importance for\ua0space-borne missions but also applicable to a wide range of\ua0terahertz applications