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Abstract:

Simultaneous multi-band observations with heterodyne receivers offer significant advantages for astronomical applications requiring broad spectral coverage or frequency phase-transfer calibration, such as very-long-baselineinterferometry (VLBI) observations conducted by the Event Horizon Telescope (EHT). However, simultaneous multi-band operation is typically achieved using free-space optical diplexers, which introduce additional loss and noise when implemented in ground-based cryogenic receiver systems.

In this work, we present a novel band-splitting diplexing-hybrid architecture that enables simultaneous dual-band observations while preserving the sideband-separating (2SB) functionality of modern superconductor–insulator–superconductor (SIS) receivers. The proposed concept extends the simultaneous-observing multiband receiver (SOMBR) approach by integrating frequency-selective diplexing functionality directly into the RF quadrature-hybrid network required by a conventional 2SB receiver. As a demonstration, a dual-band architecture covering ALMA Bands 5 and 6 (163–275 GHz) is investigated.

A broadband superconducting quadrature-hybrid chip based on a three-section branch-line coupler was designed and analysed using full-wave electromagnetic simulations. The hybrid was combined with straight rectangular waveguide sections as high-pass filters to realise an integrated diplexing-hybrid network capable of routing Band 5 and Band 6 signals to independent receiver chains while simultaneously providing the quadrature power division required for sideband separation. Simulation results demonstrate the feasibility of the proposed architecture, achieving broadband power division and frequency-selective routing across the combined Band 5+6 frequency range. Although further optimisation is required to improve amplitude balance and return-loss performance, particularly at the lower edge of Band 5, the results establish the viability of integrating simultaneous dual-band and 2SB functionality within a compact superconducting circuit. The proposed architecture provides a potential pathway towards low-loss, cryogenically compatible multi-band SIS receivers for future astronomical instrumentation.

Abstract:

Most Josephson junction Travelling Wave Parametric Amplifiers (JTWPAs) developed so far have been focused on operation below 20 GHz, primarily driven by the choice of the qubit resonance frequency used in quantum computation research. Consequently, there is a lack of effort to extend their operation to higher frequency ranges. However, millimetre (mm)- wave JTWPAs could offer potential significant advantages for astronomy, but their operation in this regime is largely unexplored. In this paper, we describe the design considerations for extending JTWPAs operation to the W-band range. We present two JTWPA designs, one with and one without phase matching elements, and we discuss the design methodology of both approaches, before showing their predicted performance respectively.

Abstract:

Josephson-junction-based parametric amplifiers (JPAs) are key enabling technologies in superconducting quantum electronics, supporting applications ranging from dark-matter detection to quantum-computing readout. However, conventional JPAs are intrinsically narrowband, motivating the development of broadband architectures such as impedance-matched parametric amplifiers (IMPAs), which enhance bandwidth through the incorporation of auxiliary passive resonators.

In this work, we present the design and fabrication of a three-pole kinetic-inductance impedance-matched parametric amplifier (KIMPA) based on a niobium titanium nitride (NbTiN) nonlinear nanowire and implemented using an inverted microstrip architecture. The amplifier is synthesised using the multipole filter-design framework of Naaman and Aumentado and targets a 10% fractional bandwidth centred at 6 GHz with 20 dB gain. The device employs a multilayer architecture consisting of a 30 nm NbTiN wiring layer, a 150 nm amorphoussilicon dielectric layer, and a 200 nm niobium sky plane, enabling compact parallel-plate capacitors and improved fabrication robustness compared with conventional coplanar-waveguide implementations.

The design methodology is presented from the graph-based filter-synthesis model through circuit-level implementation and physical layout generation. Harmonic-balance simulations predict approximately 20 dB gain across a 6.0–6.4 GHz operating band, demonstrating the feasibility of broadband kinetic-inductance parametric amplification in an inverted microstrip platform. Fabricated devices have been completed and are currently being prepared for cryogenic characterisation.

Abstract:

Kinetic inductance travelling-wave parametric amplifiers (KITWPAs) have emerged as promising quantum-limited amplifiers for large-format detector arrays and quantum sensing applications. Extending this technology to millimetre-wave frequencies could enable ultra-low-noise pre-amplification for astronomical heterodyne receivers, potentially improving receiver sensitivity and mapping speed. In this work, we present the preliminary design of a W-band three-wave mixing (3WM) KITWPA based on a high-kinetic-inductance niobium-titaniumnitride (NbTiN) inverted microstrip transmission line.

The proposed architecture incorporates waveguide-coupled radial-probe transitions and a DC-bias network adapted from established superconducting mixer technologies to enable 3WM operation at millimetre-wave frequencies. Electromagnetic simulations are combined with coupled-mode analysis to evaluate the amplifier performance. Simulations predict an intrinsic gain exceeding 20 dB over a broad frequency range from 30 to 110 GHz. When integrated within a WR-10 waveguide environment, the effective operating bandwidth is predicted to extend from 75 to 110 GHz with more than 15 dB gain. The proposed design demonstrates the feasibility of implementing DC-biased 3WM KITWPAs in the W-band and represents a potential route towards low-noise pre-amplifiers for future mm-wave and submm-wave heterodyne receiver systems.