Researchers at the University of California, Davis have developed absorptive bandpass filters that enable improved passband flatness and good impedance matching both in-band and out-of-band.
In radio frequency and microwave systems, filters are used to improve signal clarity and remove or reject undesired “noise.” Conventional filters function by producing mismatched impedance to out-of-band signals. However, this approach can also simultaneously deteriorate the performance of nearby non-linear devices - such as analog-to-digital converters, mixers, and high-gain amplifiers. Therefore, an alternate, technical solution is an isolator. But, too often, these types of devices are bulky, expensive, bandwidth-limited and difficult to integrate into holistic communications systems. Due to these limitations, a more effective, less expensive, absorptive (reflectionless), filter would have broad scientific and commercial applications.
Researchers at the University of California, Davis have developed absorptive bandpass filters that have good impedance match not only in the passband but also in the stopband. These filters integrate absorptive stubs. The absorptive stubs absorb both the out-of-band reflection signals and the close-to-passband signals, resulting a reflectionless stopband and enhanced passband selectivity. As a result, this design for an absorptive filter is both more effective and efficient than other absorptive filters - and also offers much better performance than conventional filters.