Mode Mixing in DRA
(A method to increase impedance bandwidth)
Various methods have been derived to increase the bandwidth of DR antennas
1) Stacking two cylindrical DRs of different sizes to merge their resonant bands
2) Attaching parasitic metal strips on a DR surface to induce additional resonance
3) Leaving air gaps between stacked DRs or between a DR and the ground plane to enhance radiation
4) Adjusting the aspect ratio of a DR to reduce its Q factor
5) Using structural discontinuities in DRs may also reduce their Q
factor, for example, embedding dielectric resonators of different
permittivities, carving a notch, or drilling a series of holes.
Large impedance bandwidth can also be achieved by merging multiple
resonance bands eg. Using a truncated tetrahedron with narrow base
attached to a ground plane has a 40% bandwidth in terms of input and
output impedance and radiation pattern
MODE Mixing ( Different mode of DRs with same radiation patterns are coupled to create a wide bandwidth)
In this we use TE111 , TE112 , TE113 modes to merge-
Obstacles in merging these modes –
1) TE112 mode is having different radiation pattern in comparison of
TE111. TE113 for Eθ(TE112) is minimum at θ=90 while for TE111 and TE113
having maxima at θ=90
2) And f112 lies between f111, f113
Method to remove these obstacles-
To adjust the radiation pattern of TE112 mode
Using assymetrical moat carved off-------
Figure shows a DRA with asymmetric Moat -- by adjusting the gap g1,
g2 and g3 we can adjust the radiation pattern of the TE112 mode.
Effect of aspect ratio on resonant frequencies (a/b)
As aspect ratio is increased the f111,f112 and f113 become closer so we use large aspect ratio for mode mixing
Effect of d/b ratio
As d/b ratio increases the f111,f112 and f113 become far, so we use less d/ ratio for mode mixing
Field pattern for TE111, TE112, TE113
TE111
TE112
TE113
for more information visit DRA(dielectric resonator antenna)
