An experimental investigation of large nonlinear dipole arrays is pres
ented, using a diode-loaded dipole placed between two parallel conduct
ing plates. Using this topology we were able to demonstrate enhanced c
onversion efficiency into the second harmonic and obtain spontaneous p
arametric oscillation for certain array geometries. Parametric oscilla
tion was achieved by strongly driving the antenna at a single pump fre
quency and adjusting the cavity length for resonance at a subharmonic.
A pump threshold for parametric down-conversion was observed, below w
hich no sub-harmonics were produced. These results suggest using quasi
-optical techniques for frequency multiplication and parametric up-con
version or amplification.