Transmission line to waveguide transformer having differential feed pins spaced a common distance from a closed waveguide wall

A transformer between a waveguide and a transmission-line, comprising:

• a high-frequency circuit module having differential-pair terminals through which a differential signal is input or output;
• said transmission-line including a pair of transmission-lines, each one of the pair of transmission-lines being connected to a respective one of the differential-pair terminals;
• a waveguide including first and second metal walls parallel to each other and ends of the first and second metal walls are connected to each other through a third metal wall, the high-frequency circuit module provided on the waveguide;
• and
• feed pins arranged inside of the waveguide, each feed pin being connected to a respective one of the pair of transmission-lines, each transmission-line of the pair of transmission lines including a drawn line connecting to the high-frequency circuit module through the respective one of the differential-pair terminals and a derived line connected to the drawn line at a first end and extending in a direction parallel to the third metal wall and connected to the feed pin at a second end, the feed pins having a second distance of approximately (λg*(1+2α)/4) away from the third metal wall, λg is a wavelength in the waveguide, and α is an integer which is equal or larger than 0,
• wherein each of the feed pins has a third distance of approximately (a/4) away from a respective one of the first wall and the second wall, a is length of the waveguide along the third metal wall.