A waveguide filter is an electronic filter that is constructed in waveguide technology. Waveguides are hollow metal tubes inside which an electromagnetic wave may be transmitted. Filters are a basic component of electronic engineering designs and have numerous applications. Waveguide filters are most useful in the microwave band of frequencies, where they are a convenient size and have lowloss. Examples are found in satellite communications, telephone networks, and television broadcasting. Waveguide filters weredeveloped during World War II for radar and electronic countermeasures, but afterwards soon found civilian applications. Post-war development was concerned with reducing size, first with new analysis techniques that eliminated unnecessary components, then by innovations such as dual-mode cavities and ceramic resonators. Waveguides can support a variety of electromagnetic wave modes: both a disadvantage, spurious modes frequently cause problems, and an advantage; dual-mode designs can be much smaller. The chief advantages of waveguide filters are ability to handle high power and low loss. The chief disadvantages are bulk and cost compared to technologies like microstrip.