Double ridged structures mode study for broadband antennas design

Knowledge of the cutoff frequencies of modes in nonstandard double ridged waveguides is extremely important for determination of operation bandwidth for design of broadband structures. It is shown that for nonstandard dimensions of the ridged waveguide the TE30 mode doesn?t exist or is degenerated or the higher mode skips the TE30 mode. Strategy of the complex broadband double ridged horn antennas design (coaxial ? waveguide transitions, impedance transformers, radiated ridged and horn structures etc.) is mentioned and as an example the 4?40GHz antenna is presented.