Multi-mode filter

A method of manufacturing a dielectric resonator body for a multi-mode cavity filter, the method comprising:

• providing a piece of first dielectric material, said piece of first dielectric material having a substantially flat face for mounting said piece of first dielectric material on a substrate and a plurality of external sides in addition to said substantially flat face, the piece of first dielectric material having a first dielectric constant and a shape supporting at least a first resonant mode and a spurious response generated at least partially by a higher-order resonant mode of the first resonant mode;
• providing at least one region of a second dielectric material, said at least one region of said second dielectric material being located on one of said plurality of external sides of said piece of first dielectric material and not covering all of said one of said plurality of external sides, said second dielectric material having a second dielectric constant different from said first dielectric constant;
• and
• providing a layer of conductive material at least partially coating an outer surface of said piece of first dielectric material and said at least one region of second dielectric material, said substantially flat face being substantially not covered by said layer of conductive material,
• whereby the presence of the at least one region of second dielectric constant alters the frequency separation between the first resonant mode and the spurious response.