C_AIR Coplanar Air-Bridge Parameters Notes Equivalent Circuit
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Coplanar Air-Bridge C_AIR represents a single bridge as the connection of ground planes. Such bridges are necessary in CPW-circuits in order to suppress the higher order modes. The bridge dimensions are defined using the line type addressed by C_LTYP and the bridge type addressed by C_BTYP.

Parameters  

Notes

• For C_AIR, TYPE=0 and TYPE=- 1 in selected C_BTYP is not allowed.
• The parameter TYPE in selected C_BTYP and the parameter CEN_MET in selected C_LTYP can not have the same value.
• If L in applied C_BTYP is set to a positive non-zero value, two coplanar lines of length L are connected to the bridge. Note that the distance between the reference planes is given by 2L+2BG+BW.
• The parameters of the dielectric material under the bridge is defined C_TECH. The index DIE_IDX in selected C_BTYP indicates, which dielectric layer (0, 1 or 2) is used for the bridge (see C_AIRTYP in chapter 4 for more information).
• If L1 and L2 in selected C_GRID are not set to –1 or –2 (auto sizing), the minimum values for L1 and L2 are:

  L1min=W+2S+2GW

  L2min=8DL+BW+2BG

Equivalent Circuit  

For the modeling of the C_AIR element, a p-network is used. The parasitic electric field due to the air-bridge is represented by the lossy shunt capacitance Cp. The inductance L is used for the modelling of the current disturbance in the area of the bridge. The metallic losses within the bridge itself are taken into account by the use of a frequency dependent resistance R.

The equivalent circuit parameters are derived from quasi-static FD-calculations. The connected lines at ports are modeled as C_LIN elements and are represented by their characteristic impedance ZL and phase constant b. There is no limitation due to the length of connected lines (L in selected C_BTYP).