Waveguide-to-microstrip line coupling arrangement and a frequency converter having the coupling arrangement

A microwave frequency converter comprising:

• (a) a waveguide having a pass band covering an RF signal frequency and a cutoff band covering a local oscillator signal frequency which is lower than that of said RF signal frequency, one end of said waveguide being short-circuited;
• (b) a microwave integrated circuit attached to an outer surface of a wall of said waveguide, said microwave integrated circuit having a microstrip line including a ground plane, a dielectric substrate and a center strip conductor which are stacked in sequence, said center strip conductor having a semicircular end whose radius corresponds to one half the width of said center strip conductor, said microstrip line extending along said outer surface of said wall, extending from the short-circuited end of said waveguide such than said ground plane, is in contact with said waveguide;
• (c) a metallic post having cylindrical portions, said post having one end adjacent to and connected to said center strip conductor, said metallic post extending from a center of a circle defined by said center conductor, said circle having a half portion which corresponds to said semicircular end of said center conductor, to the inside of said waveguide via circular through-holes made in said dielectric substrate, said ground plane, and said wall of said waveguide, said circular through-holes being coaxial with said metallic post, and the diameter of said circular through-hole made in said ground plane being made smaller than that of said circular through-hole made in said wall of said waveguide, said
• cylindrical portions of said metallic post including a large-diameter portion interposed between first and second small-diameter portions;
• (d) an annular cylindrical dielectric member fitted in said circular through-hole of said wall of said waveguide such that said first small-diameter portion of said metallic post penetrates said annular cylindrical dielectric member and said annular cylindrical dielectric member is supported by one end surface of said large-diameter portion;
• and
• (e) a local oscillator and a mixer both formed within said microwave integrated circuit for converting said RF signal from said waveguide into an IF signal.