The microwave microstrip ring resonator (MRR) is perturbed by a flexible, nondestructive method of keeping cross and partial overlays of Al2O3 strips. The splitting of the resonance curve is observed with amplitude variations as expected theoretically, but is not observed below a critial perturbation. Further empirical relations are reported for the first time, for the odd-mode frequency (fro) and even-mode frequency (fre) variations, giving fre changes proportional to the perturbation, but fro being independent of the same. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 168–171, 1998