CST – Computer Simulation Technology

Coax to CPW Transition

Image of the Coax to CPW transition. Image of the Coax to CPW transition.

The conventional method of connecting a coaxial cable to CPW is co-planar, i.e. end fed. Problems arise with this connection method when a large dimensional discrepancy between the coaxial inner conductor and the inner conducting strip of the CPW exists.

The coax to CPW transition addition to Antenna Magus has a different topology to the above mentioned. The coaxial connector is mounted on the underside of a substrate with the center conductor extending through the substrate and is attached in a perpendicular manner to the central conducting strip of the CPW. To overcome the dimensional difference between the center conductors of the CPW and the coax, a small tab like structure is used to form a linear taper between the two. The outer conductor of the coax is modified, and only a section of it extends through the substrate and is attached to the groundplane....

Modified coaxial connector and tab structure (substrate is removed for clarity) Modified coaxial connector and tab structure (substrate is removed for clarity)

The perpendicular connection allows the high-frequency electric field of the coax to directly couple, in a uniform manner, on the same plane with the high-frequency electric field in the gap between the CPW center conductor and the groundplane. This modification in physical geometry allows minimal mismatch and ultra-wideband (where S11 < -10 dB and S21 > -1 dB) with the upper limit dependent on the exact physical parameters and geometry of the coaxial connector used. Antenna Magus has coaxial connector two design options: a practical coax, for designs below 20 GHz, and a frequency scaled connector.

Typical S-parameter response versus frequency. Typical S-parameter response versus frequency.

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