Microwave ovens with infrared rays heating units

A microwave oven comprising a cooking compartment having side walls, a floor, and a ceiling, and an infrared heating unit mounted on said ceiling, said infrared heating unit comprising a lamp envelope of electrically insulative material having two opposite ends, an electrical lead disposed at each of said ends, and a heating coil disposed within said lamp and having two ends connected to respective ones of said leads, said coil including a series of coil loops extending along a length of said coil, said series of loops including two end groups of loops located at respective end sections of said coil, and an intermediate group of loops located between said end groups of loops, wherein radiant heat reflected off said side walls, floor, and ceiling tends to be concentrated at said intermediate group of loops, said loops of said intermediate group having a larger pitch interval than the loops of either of said end groups.