12704_SCTE_Broadband_Nov2016_COMPLETE_lowres

technical

To construct the 1-to-4 power divider, three 1-to-2 power dividers were used. The final structure has been optimised for the best S-parameter values: optimised isolation, insertion and return loss are shown in Fig. 3 below. The output ports of the first stage, with impedance 50Ω, have been stretched to connect to the second stage. The impedance value was unchanged, as it depends upon the microstrip width and substrate thickness as in Equation 2. There was a slight effect on reducing the return loss, subsequently corrected by optimisation. Fig. 3 below shows that the achieved return loss is below 20dB over the band for this small 1-to-4 power divider structure (60.16mm x 19.94mm). The insertion loss is between 6.2 to 7.2dB, and the isolation between output ports is below 16dB over the UWB band. Fabrication and measurements To validate simulated results, the 1-to-4 power divider was fabricated as above on RO3035 substrate dielectric, of 0.75mm thickness, relative permittivity 3.5 and tangent loss of 0.0015. Surface-mounted resistors were 100Ω for the first and second sections and 432Ω for the third section. The resistors were

Figure 2:

The final layout for the 1-to-2 UWB power divider is shown in Fig. 2, with overall size of 12.52mm x 19.56mm. The proposed power divider is one of the smallest size power dividers in comparison with UWB power dividers from previous work, and with very good performance as shown in Table 2 [3, 4, 15-17]. After optimisation, the return loss improved by 7.5dB, with a 1.5dB minimum improvement for isolation over the band. The insertion loss did not change, as it is depends on the substrate tangent loss and metal surface roughness [18] which were not changed by the optimisation.

Reference No

S11

S21

S32

Size

[3] [4]

>12dB >13dB >10dB >17dB >11dB >20dB

>3.5dB >3.5dB >3.5dB >3.5dB >3.5dB >3.5dB

>10dB >10dB >10dB

16mm x 18mm 16mm x 32mm 21mm x 34mm 15.5mm x 22mm

[15] [16] [17]

>6dB

>14dB >17dB

16mm x 17mm

Present work

12.6mm x 19.6mm

Table 2. Simulated parameters for power dividers in this and previous work

Figure 3:

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Vol. 38 No. 4 - November 2016 Issue