Transitioning between microstrip and inverted microstrip

A broadband microstrip to inverted microstrip transition is described in which field matching between microstrip and inverted microstrip is obtained by gradually removing the dielectric at the transition so the E-field has a region over which to redistribute itself as it propagates from microstrip to inverted microstrip or vice versa. The method that yielded the least reflection (<-10 dB) and the most transmission (<0.5-dB ripple) entailed removing the dielectric in a particular radial pattern. The inverted microstrip metal and dielectric is further trimmed in a specific way. Empirical testing was conducted at K alpha -band (26.5-40.0 GHz). The substrates used were 254- and 381- mu glass-reinforced teflon with a dielectric constant of 2.2. The empirical testing of this structure indicates that the thinner the dielectric substrate supporting the inverted microstrip line, the better the measured performance of the transition. Minimizing the attachment overlap of the inverted microstrip to microstrip transition reduces reflection greatly; this occurs since overlap acts as excessive lumped capacitance. A few applications for this design are mentioned.<>