In the field of numerical simulations of electromagnetic devices, we are often interested not only in the electric and magnetic fields themselves, but also in secondary quantities like Q-values, scattering parameters, or impedances. As the latter typically are frequency dependent quantities, a set of values for a given frequency range is to be calculated. One popular approach to perform such calculations is the simulation in time-domain: The structure is excited by a broadband pulse, some output signals (e.g. field components or wave amplitudes) are monitored, and finally the frequency domain parameters are obtained by a discrete Fourier transform (DFT). If efficient simulation algorithms as the FDTD-method are applied, this approach covers a wide range of applications as the current "state of the art"-technique. Its major drawback, however, is the limitation of the time step due to the Courant-criterion: Especially for low-frequency applications (with long time periods), and if resonances with high Q-factors appear (leading to long settling times), the simulation time may become unacceptably long. An alternative is the classical frequency domain approach, where the fields at each frequency point are calculated by solving an algebraic system of equations. However, as for large and possibly complex systems the algebraic solvers are still not very robust, usually this classical frequency domain technique is only competitive for some special applications. In a new type of frequency domain approach we do not solve the inhomogeneous equation at each frequency point, but use some solutions of the eigenvalue problem of the structure to describe its electromagnetic behavior. In this presentation, we apply the Finite Integration Technique, which supplies a general theoretical basis for both time and frequency domain formulations, sharing the same matrix operators and thus the same system matrix. The eigenmodes of this matrix can be proven to have some orthogonality properties, and therefore can be used for a modal approach: A set of dominant modes of the structure is calculated once, and the fields at arbitrary frequencies within a given range can be described by a superposition of these modes. Hence we are able to compute frequency domain quantities like scattering parameters (of both lossfree and lossy devices) with an arbitrary resolution of the frequency axes. From the description of the structure by its eigensolutions, also a formula for the calculation of external Q-values of waveguide-coupled cavities is derived. Some examples demonstrate the applicability and the properties of the new method.