## 1 Introduction
Segmenting the structure into simple blocks is a common strategy used by many authors to speed up the analysis of complex microwave devices [13; 14; 15; 16]. Each building block (i.e., inverters, resonant posts, empty transmission lines, etc.) is characterized by its generalized (multimode) scattering or admittance matrix, and then all these matrices are cascaded with well-known methods such as the ones presented in [17; 18; 19; 20]. Once all the circuital matrices have been cascaded, a global circuital matrix that characterizes the whole structure, is obtained. The segmentation procedure is independent of the electromagnetic solver used for the characterization of each building block. Even different solvers can be used for characterizing different individual building blocks. In this work, we present a simple, non-intrusive, and solver independent fast frequency sweep technique, which takes profit of the segmentation of the structure under analysis into simple constitutive blocks. Each one of these simple blocks typically presents a simple frequency response that can be easily interpolated with very few frequency points. In [1], the structure was already segmented into simple blocks. However, the fast frequency sweep (either using AWE or CFH) was applied to the complex and quickly changing frequency response of the whole filter. Thus, if the device was a filter with a high number of cavities, the frequency response became more complex, and the approximation with only one frequency point with AWE became less accurate. Thus, CFH needed to be used, and the number of sub-domains and frequency points where the exact solution had to be computed increased with the complexity of the frequency response (i.e., with the number of filter cavities). The same would have happened if vector fitting would have used. In this work, a different strategy is proposed. The idea is to take profit of the fact that the individual building blocks (inversors, empty lines, resonant posts, etc.) have simple frequency responses regardless of the number of building blocks that compose the whole structure, and therefore regardless of the complexity of the frequency response of the whole device. Thus, the strategy consists of applying a simple fast frequency sweep scheme, such as spline interpolation, to the computation of the frequency response of each one of the elements of the multimodal circuital matrix. Thus, an approximated, but very accurate, mutimodal circuital matrix of each building block is obtained in as many frequency points as desired. Finally, all these matrices are cascaded, and the scattering parameters of the whole device is obtained. With this procedure, the total simulation time is significantly reduced. To the best knowledge of the authors, this is the first time that the segmentation of the structure into simple building blocks is used to implement a fast frequency sweep. The result is a technique that can be applied to accelerate any simulation technique; that is not intrusive, and thus does not require access to the frequency dependent part of the simulator; and that is simple to implement, regardless of the complexity of the whole frequency response of the device, since the simple building blocks will always present simple frequency responses. To test the performance of this new fast frequency sweep technique, it was applied to the computation of the frequency response of several devices: an all-metallic coupled cavities filter in rectangular waveguide, a coupled cavities filter in rectangular waveguide with dielectric posts loading each resonator, and finally a coupled cavities filter in substrate integrated waveguide (SIW). These devices were selected to have a wide variety of possible simple building blocks (irises, dielectric posts, and metallic vias), in order to ensure that the method produces good results in all cases. All this type of building blocks present simple frequency responses, but some simpler than others.