International Journal of Advances in Engineering & Technology, May 2011. ©IJAET
Figure.2 shows two gap coupled annular ring antennas in which inner one is feeded at point(c, 0) by a coaxial cable (a1<c<b2) where a1 and b1 is inner and outer radius of the inner ring and a2 and b2 is inner and outer radius of the outer ring. The inner ring is fed with the coaxial cable while the outer ring is kept parasitic. The thickness of the substrate h is small as compared to the difference between the inner and outer radius of the inner ring. The analysis is done using only one parasitic antenna.
The equivalent circuit for gap coupled ARMSA is shown in figure 3 and 4.
Figure3: Modified equivalent circuit of gap-coupled ARMSA for odd mode
Figure4: Modified equivalent circuit of gap-coupled ARMSA for even mode
It can be expressed as the parallel combination of Y1, L1, C1 and Y2, L2, C2 where the subscript 1 represent for inner ring and 2 for the outer parasitic ring. The component L represents the stored magnetic energies while C represents electric energies, which occur at below patch metallization and the fringing fields around the radiating apertures of inner and outer ring. The admittance Y shows the power loss through coupling and radiating apertures. The parasitic patch is excited by the gap coupling whereas the feed patch is excited by the coaxial probe feeding technique. The value of Y1, L1, and C1 is calculated using cavity model as,
L = 1
π n m,k µh
[ ][J (k c)Y (k a ) Y (k c)J (k a ) '
n C = 1 1 µε Lk n 1 e
0 ε r 2
1 ----------(2) − ' n 1 n 1 e ] 2 ----------(1)
Vol. 1,Issue 2,pp.151-158
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