This study presents options for the implementation of high-frequency filters using microwave photonics in the incoherent regime. The discussion is therefore limited to systems with longer delay times, implying the use of transmission paths of hundreds of meters to many kilometers in length, or systems with an equivalent dispersion. Microwave photonic filters are, in accordance with systems and signals theory, presented as two-port systems with high-frequency microwave electrical signals at the input and output ports. For filters with a discrete aperiodic impulse-response function, an analytical derivation of the transfer function was carried out using the example of discrete systems, both for filters with a finite impulse response as well as for those with a quasi-infinite impulse response. Following this is the definition of a general microwave photonic system and a description of its building blocks. In the third section, the designs for building various types of photonic filters are presented together with the customized mathematical formulations, allowing for direct calculations of the transfer functions. The next section is dedicated to measurements and measurement equipment, giving an empirical insight into the reality of photonic filters based on manufactured prototypes, corresponding to the previously presented designs. A comparison between the measured and computed results is made, reporting on the correspondence between the real filter and the applied model, and thus justifying the use of analytical approaches to calculate the transfer functions for the purpose of a generic filter design, using the approaches and tools for discrete filter design. Finally, an example of a photonic filter in a hybrid configuration with an electrical microwave filter for an improved combined response is presented.
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