Abstract: A multiple frequency tag in one embodiment comprises a generally flat dielectric substrate having first and second generally opposite principal surfaces. A first resonant circuit including a first inductor coil is located on the first surface of the substrate, the first resonant circuit having a first predetermined resonant frequency. A second resonant circuit including a second inductor coil is located on the second surface of the substrate. The second resonant circuit has a second predetermined,resonant frequency which preferably is different from the first predetermined resonant frequency. The first inductor coil is positioned on the substrate to partially overlie the second inductor coil in a manner which minimizes the magnetic coupling between the first and second coils. The tag may be employed in an electronic article security system for protecting articles or may be employed in any other type of system for detecting the presence of a tag and possibly an item attached to the tag.

Abstract: A microwave oscillator with TM01.delta. dielectric resonator is disclosed. The oscillator operates with a TM01.delta. mode as contrasted with prior art techniques of TE01.delta. mode. This provides for an improved tuning range in excess of 10% of the operating frequency.