Portland State University. Department of Electrical and Computer Engineering
Term of Graduation
Date of Publication
Master of Science (M.S.) in Electrical and Computer Engineering
Electrical and Computer Engineering
Passive electric filters -- Mathematical models, Passive electric filters -- Design, Electrical engineering
1 online resource (x, 69 pages)
For many applications requiring some sort of signal filtering or signal conditioning, the filter requirements are usually approached with a single purpose in mind, which is to maximize both passband signal amplitude and stop band signal attenuation to the load with little to no thought given to what happens to the stop band signal energy. Many conventional filters have very poor impedance matching in the stopband resulting in reflected energy or large return loss (S11). This reflected energy can then cause interactions with adjoining system components which do not in general respond well to spurious reflected energy and can result in degradation of system performance or other unintended consequences .
This thesis implements and verifies the design procedure and examines the frequency scaling of a novel passive filter design methodology proposed by Morgan and Boyd  which the authors claim results in an easy to realize reflectionless filter which has stopband reflection response superior to conventional passive filters. Following the proposed design methodology, a reflectionless filter was simulated and then realized in a hardware prototype and good agreement observed between simulation and measurement results. To determine the quality of stopband response, the reflectionless filter response was compared to a Butterworth admittance complimentary diplexer designed using accepted techniques , , . The reflectionless filter showed similar measured stopband response to the diplexer but this was gained with a much simpler design process than was required for the diplexer.
To verify the ability of the procedure to scale the design requirements, a filter with a decade wider bandwidth was also designed and the measured response compared to a similarly scaled Butterworth diplexer. For this frequency range of interest, the reflectionless filter exhibited superior stopband rejection when compared to the diplexer. Simulation and measured results were in good agreement for both filters.
In conclusion, this work was able to realize a reflectionless filter using Morgan and Boyd's design procedure and the measured results were in good agreement with simulation results. The stopband of the reflectionless filter was comparable to a similar diplexer but with much less design effort required. The scaling of design parameters for reflectionless filters was also demonstrated.
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Lemire, Guy Barry, "Absorptive Reflectionless Filters" (2020). Dissertations and Theses. Paper 5501.