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40 GHz and 70 GHz Launch limitation DifferencesThe launch design will have its own frequency range. The sizing and spacing launch geometry is proportional to the wavelength of the energy that is traveling through the transition. Having the smaller geometry is a challenge to the limitations of board fabrication processes and leads more inconsistency in the performance of the high frequency boards after fabrication. The lower frequency boards are not as sensitive to the variations inherent in board processing and perform more consistently between individual boards after fabrication.On the left are 40 GHz and 70 GHz bandwidth grounded coplanar waveguide (GCPW) and microstrip test boards. These are standard Signal Microwave boards test made using 8mil thick Rogers RO4003 material with an FR-4 stiffener. Shown in the close-ups are comparisons of the 40 GHz launch designs and 70GHz launch designs. The 70 GHz launch has different size vias, notably the first vias on either side of the trace, and they are spaced closer to the trace and the edge of the board. The 40GHz launch designs have larger vias and are not spaced as tight.
40 GHz and 70 GHz launch differential launch designs will have their own frequency range limitations. The size and spacing of the launch geometry is proportional to the wavelength of energy that crosses the transition. Having smaller geometries challenges the limitations of the board manufacturing process and results in more inconsistent performance of high-frequency boards after manufacturing. Low-frequency boards are less sensitive to variations inherent in board processing and have more consistent performance from board to board after manufacturing. On the left are 40 GHz and 70 GHz bandwidth grounded coplanar waveguide (GCPW) and microstrip test boards. These are standard Signal Microwave test boards made of 8-mil thick Rogers RO4003 material with FR-4 stiffeners. Shown in the close-up is a comparison of the 40 GHz launch design and the 70 GHz launch design. The 70 GHz launch has different sized vias, especially the first via on either side of the trace, which are spaced closer to the trace and board edge. The 40 GHz launch design has larger vias and is not as tightly spaced.
Top Ground Launch for Multi-Layer BoardsTop Ground LaunchFor both microstrip and GCPW transmission lines, when implemented in a multi-layer board configuration, the ground layer for the microwave transmission line is buried. The connector will not have access to it no matter how the connector is configured.The launch designs developed by Signal Microwave incorporate a short section to transition the ground connection from the top of the board to the buried ground layer.The small set of vias at the edge of the microstrip board is a GCPW section used to transfer the energy from the connector to the board using only the top ground connection of the connector.Signal Microwave Board ConstructionThe 8 mil RO4003 top layer is processed seperately including vias and plating. Then the RO4003 layer is laminated to the FR-4 layer which acts as a stiffener. The FR-4 layer does not have through vias that can cause resonances and no back drilling is For microstrip and GCPW transmission lines, when implemented in a multilayer board configuration, the ground plane of the microwave transmission line is buried. It is not accessible to the connectors regardless of the connector configuration. The launch design developed by Signal Microwave includes a short section that transitions the ground connection from the top of the board to the buried layer. A small group of vias at the edge of the microstrip board is the GCPW section used to make the top ground connection using only the connector. Energy is transferred from the connector to the board. Signal Microwave Board Structure 8 mil RO4003 top layer is processed separately, including vias and plating. The RO4003 layer is then laminated with the FR-4 layer as a reinforcement layer. The FR-4 layer has no Through hole, no need for back drilling
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