User Guide

ME910G1 HW Design Guide
1VV0301593 Rev.7 Page 60 of 98 2021-02-02
Transmission line design
When designing the ME910G1 interface board, the placement of components was chosen
properly, in order to keep the line length as short as possible, thus leading to the lowest
possible power losses. A Grounded Coplanar Waveguide (G-CPW) line was chosen, since
this kind of transmission line ensures good impedance control and can be implemented
in an outer PCB layer as needed in this case. A SMA female connector has been used to
feed the line.
The interface board is made on a FR4, 4-layers PCB. The substrate material is
characterized by relative permittivity εr = 4.6 ± 0.4 @ 1 GHz, TanD= 0.019 ÷ 0.026 @ 1 GHz.
A characteristic impedance of nearly 50 Ω is achieved using trace width = 1.1 mm,
clearance from a coplanar ground plane = 0.3 mm each side. The line uses the reference
ground plane on layer 3, while copper is removed from layer 2 below the line. The height
of the trace above ground plane is 1.335 mm. Calculated characteristic impedance is 51.6
Ω, the estimated line loss is less than 0.1 dB.
The line geometry is shown below:
Figure 18: Line geometry
Transmission Line Measurements
An HP8753E VNA (Full-2-port calibration) was used in this measurement session.
A calibrated coaxial cable was soldered to the pad corresponding to RF output; a SMA
connector was soldered to the board in order to characterize the losses of the