  The microwave radio dynamic spectra of the Crab pulsar interpulse contain
fine structures represented via narrowband quasiharmonic stripes. The pattern
significantly constrains any potential emission mechanism. Similar to the zebra
patterns observed, for example, in type IV solar radio bursts or decameter and
kilometer Jupiter radio emission, the double plasma resonance (DPR) effect of
the cyclotron maser instability may allow for interpretion of observations of
pulsar radio zebras. We present electromagnetic relativistic particle-in-cell
(PIC) simulations of the electron-positron cyclotron maser for cyclotron
frequency smaller than the plasma frequency. In four distinct simulation
cycles, we focused on the effects of varying the plasma parameters on the
instability growth rate and saturation energy. The physical parameters were the
ratio between the plasma and cyclotron frequency, the density ratio of the
"hot" loss-cone to the "cold" background plasma, the loss-cone characteristic
velocity, and comparison with electron-proton plasma. In contrast to the
results obtained from electron-proton plasma simulations, we find that the
pulsar electron-positron maser instability does not generate distinguishable X
and Z modes. On the contrary, a singular electromagnetic XZ mode was generated
in all studied configurations close to or above the plasma frequency. For low
density ratios, the highest peak of the XZ mode is at double the frequency of
the highest peak of the Bernstein modes, indicating that the radio emission is
produced by a coalescence of two Bernstein modes with the same frequency and
opposite wave numbers. Our estimate of the radiative flux generated from the
simulation is up to $\sim$30 mJy from an area of 100 km$^2$ for an observer at
1 kpc distance without the inclusion of relativistic beaming effects, which may
account for multiple orders of magnitude.
