  The present work introduces a robust way to generate attosecond pulses with
tunable ellipticity via high-order harmonic generation by co-rotating $\omega -
2\omega$ bicircular laser fields. The total electric field of the laser fields
exhibits an absence of rotational symmetry, which leads to the generation of
high harmonics of the same helicity across a broad range of spectral bandwidth.
High-harmonics with the same helicity offer the opportunity to synthesize
attosecond pulses with tunable ellipticity. The polarisation properties of the
generated harmonics are robust against the variations in driving fields'
parameters, such as wavelength, intensity ratio, and the sub-cycle phase
between $\omega-2\omega$ fields. Our work opens an avenue to study
chiral-sensitive light-matter ultrafast processes on their intrinsic timescale.
