60-GHz LTCC Antenna Arrays - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 220

Fig. 19 Geometry of two antenna elements with different feeding technology. a Element A: “single
feed” approach, b Element B: “differential feed” approach

approach. Two orthogonal L-probes as two input ports excite the patch to achieve
dual polarization characteristic. In Fig. 19 b, Element B illustrates the “differential
feed” approach. Four mutual orthogonal L-probes are employed to excite the patch.
Probes A and C along x -axis connected to the balun with 180 ◦ phase difference of
two outputs as Port I are used to excite horizontal polarization, and Probes B and D
along y -axis connected to the balun with 180 ◦ phase difference of two outputs as Port
II are used to excite vertical polarization. Here, we define that horizontal polarization
is the polarized direction along the x -axis and vertical polarization is the polarized
direction along the y -axis. The signal via of the L-probe is surround by a circle of
shielding vias which are composed of six vias connected the top and bottom ground
of the SL structure. The shielding vias positioned around the apertures can achieve
an optimum coaxial effect to ensure a low transmission loss of the signal via [ 30 , 31 ].
Figure 20 shows the simulated S parameters of the proposed two antenna elements.
For the element A, as Fig. 20 a shows, the simulated impedance bandwidth in the
frequency range is from 51.5 to 70 GHz for Port I (| S 11 | < 10 dB) and from 53.5

GHz to simulation upper limit frequency 75 GHz for Port II (| S 22 | <

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10 dB). For
Element B, as Fig. 20 b shows, the simulated 10-dB bandwidth is about 25.4 % with
respect to the center frequency of 60.5 GHz from 52.5 to 68.5 GHz for Port I (| S 11 |)
and about 30.2 % with respect to the center frequency of 63 GHz from 53.5 to 72.5
GHz for Port II (| S 22 |), respectively.

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