We present a Josephson traveling-wave parametric amplifier (JTWPA) based on a low-loss lumped-element coplanar waveguide architecture. By employing open-stub capacitors and Manhattan-pattern junctions, our device achieves an insertion loss below 1 dB up to 12 GHz. We introduce windowed sinusoidal modulation for phase matching, demonstrating that a smooth transition in the impedance-modulation strength effectively suppresses intrinsic gain ripples. Using Tukey-windowed modulation with 8% impedance variation, we achieve 20–23-dB gain over 5-GHz bandwidth under ideal matching conditions. In a more practical circuit having impedance mismatches, the device maintains 17–20-dB gain over 4.8-GHz bandwidth with an added noise of 0.18 quanta above standard quantum limit at 20-dB gain and $-99$-dBm saturation power, while featuring zero to negative backward gain below the band-gap frequency.

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• Optoelectronics
• Quantum fluctuations & noise
• Quantum information with solid state qubits
• Superconducting quantum optics
• Optical parametric oscillators & amplifiers
• Superconducting devices
• Traveling waves
• Microwave techniques