Crossover 0dB
The key feature of the crossover in BM is to avoid overlapping signals
at crossings and maintain a reasonable level of isolation between
signals at crossing lines. It means crossover allows two signals to
cross each other while retaining a high degree of isolation [31].
The signal flowed to port 3 when port 1 was excited in contrast to the
signal flowed to port 2 when port 4 was excited. Theoretically,
crossover should be 0dB for the insertion loss. A 50Ω microstrip
transmission line was used to design the crossover. It was fabricated by
using a single layer Rogers
RT5880LZ
with relative permittivity (εr) 1.96, a thickness of 0.25mm, and loss
tangent ð of 0.0009, respectively.
The
insertion loss S13 and S24 and as well as the phase difference S13 and
S24 were implemented by compact two 3-dB BLC. The simulated return loss
(S11) characteristics were achieved below -10dB within the range between
2.76GHz to 4.16GHz frequency band. For the selected compact design
crossover for the development of the BM, the insertion loss to simulated
and measured results were -0.16 dB and -0.5 dB, at the centre frequency
of 3.5 GHz. The comparison between the S-parameters’ response compact
0dB crossover is as shown in Fig. 4(a). Meanwhile, the phase differences
between the simulated and measured results were similar to S13 and S24
is 0o, as shown in Fig. 4(b). The overall dimension
for the fabricated of this work was 40mm × 21mm, as shown in Fig.
5(a).The proposed design under test of the S-parameters is illustrated
in Fig. 5(b). The loss extra between simulated and measured induced by
the SMA and coaxial cables.