12704_SCTE_Broadband_Nov2016_COMPLETE_lowres

technical

Power dividers are important for impedance matching in many microwave and RF systems.

I

Z(i) / Ω R(i) / Ω W(i) / mm L(i) / mm

Input (port 1)

50

-

1.381

6.656 6.768 6.714 6.671

1 2 3

90.52 96.1 0.851 70.71 94.3 1.079 55.24 527 1.298

Output (ports 2 & 3) 50 6.656 Table 1: Geometry parameters for The UWB 1-to-2 power divider - 1.381

The circuit was fabricated on a 0.75mm thick RO3035 substrate with permittivity ( ε r ) of 3.5. This substrate is chosen in consideration of equation (2), showing that the line width is directly related to the substrate thickness and inversely related to the substrate permittivity. The resulting line width must be thick enough to comply with fabrication tolerance [14]. Additionally, this substrate has a low tangent loss of 0.0015, thus reducing insertion loss. Simulation and optimisation The simulation of the UWB power divider was performed using CST microwave studio 2015. Initially, the return loss was below 12.5dB, the isolation was less than 14dB and the insertion loss was between 3.2 and 3.8dB over the band. After optimising widths, resistor values and ports and section lengths, a better return loss and isolation were achieved (see the optimised S-parameter values in Fig. 1 below).

where (Z) is the microstrip impedance, ( ε e ) is the effective permittivity, (W) is the microstrip width, (t) substrate thickness, (L) is the microstrip length and ( λ e ) is the effective wave length. ( f o ) is the central frequency, equal to 6.85GHz. The centre line of ports and sections is taken to be the equivalent microstrip length to simplify design and a 50% mitering method is used to minimise the effect of reflections from microstrip bending [13].

Figure 1:

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Vol. 38 No. 4 - November 2016 Issue