We investigate the required embedding networks to enable ideal performance
for a high-gain travelling-wave parametric amplifier (TWPA) based on three-wave
mixing (3WM). By embedding the TWPA in a network of superconducting diplexers
and hybrid couplers, the amplifier can deliver a high stable gain with
near-quantum-limited noise performance, with suppressed gain ripples, while
eliminating the reflections of the signal, the idler and the pump as well as
the transmission of all unwanted tones. We demonstrate a configuration where
the amplifier can isolate. We call this technique Wideband Idler Filtering
(WIF). The theory is supported by simulations that predict over 20 dB gain in
the band 4-8 GHz with 10 dB isolation for a single amplifier and 30 dB
isolation for two cascaded amplifiers. We demonstrate how the WIF-TWPAs can be
used to construct switchable isolators with over 40 dB isolation over the full
band 4-8 GHz. We also propose an alternative design where the WIF can be
implemented without diplexers. Finally we show how, with small modifications,
the technique can be implemented for four-wave mixing (4WM) TWPAs as well.Comment: 13 pages, 22 figures, 3 table