  Mergers of compact objects (binary neutron stars, BNS, or neutron star-black
hole, NSBH) with a substantial mass ratio ($q>1.5$) are expected to produce a
mildly relativistic ejecta within $\sim20^\circ$ from the orbital plane. We
present a semi-analytic approach to calculate the expected synchrotron emission
observed from various viewing angles, along with the corresponding radio maps,
that are produced by a collisionless shock driven by such ejecta into the
interstellar medium. This method is supported by 2D numerical calculations of
the full relativistic hydrodynamics with an agreement in the observed emission
of $\sim30\%$. We consider a toroid ejecta with an opening angle of
$15^\circ\leq\theta_ \text{open}\leq30^\circ$ and broken power-law mass
distribution, $M(>\gamma\beta)\propto(\gamma\beta)^{-s}$ with $s=s_{\rm KN}$ at
$\gamma\beta<\gamma_0\beta_0$ and $s=s_{\rm ft}$ at
$\gamma\beta>\gamma_0\beta_0$ (where $\gamma$ is the Lorentz factor). While the
peak flux is dimmer by a factor of $\sim$2-3, and the peak time remains roughly
the same (within $20\%$), for various viewing angles compared to isotropic
equivalent ejecta ($\theta_\text{open}=90^\circ$) considered in preceding
papers, the radio maps are significantly different from the spherical case. The
semi-analytic method can provide information on the ejecta geometry and viewing
angle from future radio map observations and, consequently, constrain the
ejection mechanism. Due to the larger ejected mass in NSBH merger, this late
non-thermal signal can be observed to distances of $\lesssim 200$Mpc for
typical parameter values.
