  Superconducting resonator parametric amplifiers achieve ultra-low-noise
amplification through the nonlinear kinetic inductance of thin-film
superconductors. One of the main challenges to the operation of these devices
is the separation of the strong pump tone from the signal tone after
amplification has been achieved. In this paper, we propose and experimentally
demonstrate a pump separation method based on operating a half-wave
superconducting resonator amplifier behind a cryogenic circulator. Our pump
separation scheme does not involve post-amplification interference, and thereby
avoids the delicate phase matching of two different pump paths. We demonstrate
the scheme using two-port half-wave resonator amplifiers based on
superconducting NbN thin-films. We present measurements of gain profiles and
degrees of pump separation for amplifiers having different coupling quality
factors. On an amplifier having a coupling quality factor of $\sim2000$, we
measured a peak signal gain of $15\,\mathrm{dB}$ whilst achieving pump
separation of $12\,\mathrm{dB}$. The amplifier was stable for continuous
measurements, and the gain drift was measured to be $0.15\,\mathrm{dB}$ over an
hour. The same amplifier was operated at $3.2\,\mathrm{K}$ and achieved a peak
signal gain of $11\,\mathrm{dB}$ whilst having a pump separation factor of
$10.5\,\mathrm{dB}$. The pump separation scheme, and these promising results,
will advance the development of superconducting resonator amplifiers as an
important technology in quantum sensing.
