Communication equipments help processing the coded information by electric signals. The connection between two points is realized by transmission lines or waveguides. Frequency, power of the signal, reflection coefficient and noise of the environment must be taken into consideration, when designing these transmission lines or waveguides. Coaxial cables are widely used in radio frequency systems, but the dielectric in cable causes power loss with increasing frequency. Therefore it is worth using a microwave waveguide. This device is a pipe, that has a rectangular or circular cross section. The last one is a flexible cable and it is used to transmit electromagnetic waves with circular polarization. The first one is a rigid metal waveguide and it is used to transmit electromagnetic waves with vertical or horizontal polarization. In microwave engineering waveguides are used for filters, combiners, waveguide resonators, and directional couplers. I would like to show in my thesis that it is possible to design a filter and a combiner from a rectangular waveguide over the 14,5-15,35 GHz frequency band. Our goal is to prove, that some structural modifications improve the reflection coefficient of the filter and the bandwith of the combiner.