A technique of dielectric perturbation in a dielectric resonator antenna (DRA) has been explored with specific application to filter out higher resonating modes causing unwanted radiations. This is especially conceived and conjectured for microstrip-fed cylindrical DRA (CDRA). Creating a protruded cavity in it filled with dielectric material of varying \varepsilon-{r} is the primary mechanism. Effect of such perturbation has been experimentally demonstrated establishing air ( \varepsilon-{r}=1) as the simplest and most promising one for a specific application in weakening \text {HEM}-{21\delta} mode in it, recently identified as the source of cross-polar radiations. Physical insight into this new technique is also clarified. As much as 10 dB reduction in the principal plane cross-polarized values without affecting the primary radiations has been documented. © 2002-2011 IEEE.