  We investigate the required peripheral circuits 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,
hybrid couplers and impedance matching networks, 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 also 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 4-8 GHz band 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 controllable isolators with over 40 dB
isolation over the full 4-8 GHz band.
