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.