We have used coplanar resonators to provide a sensitive measure of the
ab-plane microwave complex conductivity sigma = sigma(1)f - i sigma(2
) at 8 and 16 GHz of high quality, patterned thin films of YBa2Cu3O7-d
elta on MgO substrates, No BCS coherence effects were observed in sigm
a(1)(T) below T-c. Instead, we observe a broad peak centred between 40
and 50 K, which was present in all of the samples, The T dependence o
f the magnetic penetration depth lambda(T) = (omega mu(0) sigma(2)(T))
(-1/2) also differed from that expected for a BCS superconductor in th
e London limit, This difference is most noticeable at low T, where ins
tead of the usual exponential T dependence, we observe a term in T-2 f
or every sample, We discuss briefly the effects of sample oxygenation
bn these results.