  We demonstrate a photonic radio frequency (RF) transversal filter based on an
integrated optical micro-comb source featuring a record low free spectral range
of 49 GHz yielding 80 micro-comb lines across the C-band. This record-high
number of taps, or wavelengths for the transversal filter results in
significantly increased performance including a QRF factor more than four times
higher than previous results. Further, by employing both positive and negative
taps, an improved out-of-band rejection of up to 48.9 dB is demonstrated using
Gaussian apodization, together with a tunable centre frequency covering the RF
spectra range, with a widely tunable 3-dB bandwidth and versatile dynamically
adjustable filter shapes. Our experimental results match well with theory,
showing that our transversal filter is a competitive solution to implement
advanced adaptive RF filters with broad operational bandwidths, high frequency
selectivity, high reconfigurability, and potentially reduced cost and
footprint. This approach is promising for applications in modern radar and
communications systems.
