  Quantum dots are frequently used as charge sensitive devices in low
temperature experiments to probe electric charge in mesoscopic conductors where
the current running through the quantum dot is modulated by the nearby charge
environment. Recent experiments have been operating these detectors using
reflectometry measurements up to GHz frequencies rather than probing the low
frequency current through the dot. In this work, we use an on-chip coplanar
waveguide resonator to measure the source-drain transport response of two
quantum dots at a frequency of 6 GHz, further increasing the bandwidth limit
for charge detection. Similar to the low frequency domain, the response is here
predominantly dissipative. For large tunnel coupling, the response is still
governed by the low frequency conductance, in line with Landauer-B\"uttiker
theory. For smaller couplings, our devices showcase two regimes where the high
frequency response deviates from the low frequency limit and
Landauer-B\"uttiker theory: When the photon energy exceeds the quantum dot
resonance linewidth, degeneracy dependent plateaus emerge. These are reproduced
by sequential tunneling calculations. In the other case with large asymmetry in
the tunnel couplings, the high frequency response is two orders of magnitude
larger than the low frequency conductance G, favoring the high frequency
readout.
