Demonstrated low radiative loss of a quadrupole ultrashort electrical pulse propagated on a three strip coplanar transmission line

We present an approach for reducing the absorption and dispersion due to Cherenkov radiation on coplanar transmission lines, which does not require the reduction of the permittivity mismatch between the substrate and the superstrate of the optoelectronic chip. Exciting only the odd mode of a three strip coplanar transmission line, a quadrupole ultrashort electrical pulse is generated and propagates with very low radiative loss over long distances (>5 mm). The quadrupole's measured frequency dependent absorption and dispersion, are compared to those measured for the even mode (dipole) pulse on the same transmission line. The radiative loss for the quadrupole pulse is shown to be <1/10 that of the dipole pulse, and for equal transverse dimensions it is <1/10 the radiative loss of the two strip transmission line and of the two slot coplanar waveguide. (C) 1997 American Institute of Physics. [S0003-6951(97)01945-1].