Designs for broadband cavity-coupled microstrip vertical transitions

Two designs for broadband cavity-coupled microstrip vertical transitions were proposed in this paper. The cavity in the first design functions as a section of a waveguide whereas the second design has the cavity operating in non-resonant modes. Examples of such designs centered at C-band and X-band were presented for practical applications. The finite element method was selected to perform the required numerical simulations. It is shown that the 1-dB fractional bandwidth of these cavity-coupled vertical transitions is more than 100%, which is greater than the reported fractional bandwidth provided by the slot-coupled microstrip vertical transitions.