The Co-Conical Field Generation System-a 40 GHz antenna calibration cell

A prototype test cell for generating standard fields suitable for antenna calibration from DC to 40 GHz has been developed and tested. A 1 meter scale model of the Co-Conical Field Generation System (CFGS), an expanding, constant impedance coaxial transmission system has been constructed. By maintaining symmetry throughout the cell, a uniform and calculable wavefront is established. This symmetry also maintains the dominant TEM mode structure and more importantly, allows for the gradual and efficient termination of the incident energy. Simple termination schemes have generally provided better than 20 dB absorption of the injected energy with complex designs showing much more promise. The field structure within the test volume has been mapped by measuring the reflections by a small passive scatterer. The measurement results agree well with transmission line theory and show no significant signs of mode degradation as energy propagates down the cell. Various numerical techniques agree well with the measurement results and transmission line equations, allowing for further study of scattering effects within the cell.