In the 1940s, Percy Spencer, a engineer, paused in front of a magnetron - a device that powers a radar tube - in a Raytheon laboratory. The candy bar in his pocket melted. Intrigued, Spencer reached for another item to replicate the effect - popcorn. Within seconds, the microwave - and microwave popcorn - had been discovered. In 1947, the first oven – a "Radarange" – was demonstrated. Spencer and Raytheon devised the first appliances, which were so enormous, the could only be sold for commercial kitchens. They also cooked very unevenly. In 1967, Raytheon aquired Amana Refrigeration. Shortly after, the Amana Radarange, priced at under $500 and kitchen-sized, began its debut as a daily convenience.
Source: MIT, Raytheon, Scientific American Inventions and Discoveries by Rodney Carlisle (Wiley, 2004)