A waveguide filter is an electronic filter that is constructed with waveguide technology. Waveguides are typically hollow metal tubes inside which an electromagnetic wave may be transmitted. Filters are devices used to allow signals at some frequencies to pass (e.g., the passband), while others are rejected (e.g., the stopband). Filters are a basic component of electronic engineering circuits and have numerous applications. These include selection of signals and reduction of noise. Waveguide filters are most useful in the microwave band of frequencies, where they are a convenient size and have low loss. Examples of microwave filter use are found in satellite communications, telephone networks, and television broadcasting, for example. When employed as filters, air cavity waveguide filters have the ability to handle high power and low loss at a fixed frequency. To serve systems with multiple channels, several cavity filters are integrated with switches into a switched filter bank. With the addition of each channel however, the size increases, the cost increases and performance is lowered. These are three of the key performance distracters to air cavity waveguides. Another conventional waveguide filter is a Hititte tunable filter formed as a monolithic microwave integrated circuit (MMIC). This is a single MMIC with multiple tunable filter channels. While compact, these filters have very poor insertion loss (e.g., −30 to −8 dB) making them unusable for most filter bank applications.
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