3. TRIPLE BAND OPERATION
Corresponding to cavity perturbation theory, when a resonant cavity is perturbed, i.e., when a
foreign object with distinct material properties is introduced into the cavity or when a general
shape of the cavity is changed, electromagnetic fields inside the cavity change consequently. The
underlying assumption of cavity perturbation theory is that electromagnetic fields inside the cavity
after the change differ by a very small amount from the fields before the change. But the change inProgress In Electromagnetics Research Symposium Proceedings, Stockholm, Sweden, Aug. 12-15, 2013 1431
cavity causes significant change in resonant frequency. The concept of cavity perturbation theory
has been used in proposed antenna to introduce the novel concept of additional modified TM0δ0
mode and to derive the antenna for triple band operation.
Again, according to cavity model, the first three modes that can be excited in the cavity are
usually denoted by TM010, TM020 and TM030. These modes correspond to longitudinal currents
distributed on the patch which have nulls at the radiating edges. The TM010 is the most used
in realistic purposes since the TM020 mode has a broadside-null radiation pattern and the TM030
produces grating lobes. Modes higher than TM030 mode are quite unusual and show substandard
radiation performance as TM020 mode (broadside null).
Due to etching slots adjacent to radiating edges of antenna, the currents of TM030 resonant
frequency circulate around the slot and become similar to the TM010 mode; thus the slot also
modify three lobe shape of TM030 mode to regular behavior, but they do not perturb TM010 mode
significantly [11]. In this paper, loaded F slot near one of the radiating edges introduces modified
TM0δ0 (1 < δ < 3) mode. Figures 5 & 6 show the 3D and polar plot of modified TM0δ0 (1 < δ < 3)
mode for the proposed antenna. In addition, the slot modifies the grating lobe shape of TM030
mode to regular behavior (as Figures 7 & 8) and derives the antenna for triple band operation.
Figure 3: 3D radiation pattern of TM010 mode at
3.907 GHz.
Figure 4: Polar plot of TM010 mode at 3.907 GHz