  Linear acceleration emission is one of the mechanisms that might explain
intense coherent emissions of radio pulsars. This mechanism is not well
understood, however, because the effects of collective plasma response and
nonlinear plasma evolution on the resulting emission power must be taken into
account. In addition, details of the radio emission properties of this
mechanism are unknown, which limits the observational verification of the
emission model.
  By including collective and nonlinear plasma effects, we calculate radio
emission power properties by the linear acceleration emission mechanism that
occurs via the antenna principle for two instabilities in neutron star
magnetospheres: 1) the relativistic streaming instability, and 2) interactions
of plasma bunches.
  We used 1D electrostatic relativistic particle-in-cell simulations to evolve
the instabilities self-consistently. From the simulations, the power properties
of coherent emission were obtained by novel postprocessing of electric
currents.
  We found that the total radio power by plasma bunch interactions exceeds the
power of the streaming instability by eight orders of magnitude. The wave power
generated by a plasma bunch interaction can be as large as $2.6\times10^{16}$
W. The number of bunch interactions that are required to explain the typical
pulsar power, $10^{18}$-$10^{22}$ W, depends on how the coherent emissions of
bunches are added up together. Although $\sim$$4\times (10^1-10^5)$
simultaneously emitting bunches are necessary for an incoherent addition of
their radiation power, $\gtrsim 6-600$ bunches can explain the total pulsar
power if they add up coherently. The radio spectrum of the plasma bunch is
characterized by a flatter profile for low frequencies and by a power-law index
up to $\approx-1.6 \pm 0.2$ for high frequencies. The plasma bunches
simultaneously radiate in a wide range of frequencies.
