Biomedical Engineering Reference
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Fig. 10 Geometry of three different L-probe patch antenna arrays with or without the soft-surface
structure. a Array without the soft-surface structure, b Array with the soft-surface structure of one
layer, c Array with the soft-surface structure of each layer (from [ 10 ], reprinted with permission
from IEEE)
the soft-surface structure of the metal strip only on the top layer. Design III shown
in Fig. 10 c is the L-probe patch antenna array with the proposed soft-surface
structure of the metal strips on each layer to guarantee the good connection of
the vias at different layers. To simplify the simulation, all the metal strips have
the identical width of w p = 1.4 mm on each layer. To demonstrate the effectiveness
of the proposed novel soft-surface structure inserted in the antenna array for the
impedance and radiation performance improvement, simulated results for the above
three cases were presented for comparison.
The simulated results show that the impedance and radiation performance are
almost the same for Designs II and III, which indicates that only the top metal strip
has the primary influence on the performance. The metal strips at the other layers
which are used to guarantee the good connection of the vias have little effect as long
as the width of those strips are not bigger than that of the top metal strip ( w p ).
Figure 11 a compares the simulated | S 11 | of the antenna arrays with or without the
soft-surface structure. The bandwidths of the arrays without and with the soft-surface
structure for | S 11 | < 10 dB are 27 % (Design I) and 29 % (Design III), respectively.
The impedance bandwidth of the antenna array seems not sensitive to the soft-surface
structure, and the bandwidth is improved for the array with the soft-surface structure
slightly. From Fig. 11 b, the simulated peak gain around 60 GHz of the antenna array
with the soft-surface structure (Design III) is near 18 dBi, which is about 4 dBi higher
than that of the array without the soft-surface structure (Design I). Also, compared
with the antenna array without the soft-surface structure (Design I), a more stable
peak gain is achieved by adding the soft-surface structure in the operation band.
The radiation patterns of different antenna arrays with or without the soft-surface
structure in two principal planes at 60 GHz are compared in Fig. 12 . It is seen that
the antenna array without the soft-surface structure (Design I) has a worse sidelobe
radiation due to the contribution from the surface wave diffraction. As we know, the
L-probe patch antenna has a poor cross polarization at the H-plane. By introducing the
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