An electromagnetic antenna apparatus exhibits a generally continuous signal
response between a first frequency and a second frequency, and further
exhibits a deviation from the signal response in a frequency region
centered substantially at a selected frequency between the first frequency
and the second frequency. The apparatus includes: (a) an antenna
transceiving element; (b) a feed structure coupled with the antenna
receiving element for communicating transceiving signals with the antenna
transceiving element; and (c) a discontinuity structure in the antenna
transceiving element coupled with the feed structure. The discontinuity
structure is configured for effecting return of selected transceiving
signals to the feed structure as return signals. The return signals effect
the deviation.
