Design and fabrication of new microwave multiplexing structures for electronic communications are presented in this thesis report. They are based on directional filters over the planar microstrip technology, and operate for several standard bands for wireless communications. In this report, they are classified into four proposals, starting from the design and demonstration of multi-pole directional filters for multiplexing networks, following with a dual-band multi-pole directional filter, a wide band and narrow band diplexer and ending with a differential-signals diplexer for noise suppression. All the structures present low dimensions, light weight and ease of fabrication, making them good solutions for easy integration into existing systems. To support the novelty of the projects, two of the proposals have been presented in high-standard conferences and the other two have been accepted for publication in indexed journals. Starting from the design proposal of multi-pole directional filters, the circuit schematic model and design equations of multi-pole directional filters is presented for the first time. Following the proposed theory, two microstrip two-pole directional filters are designed and fabricated for different bands: GSM 850 and the Radiolocation and Space Research band. A two-channel multiplexing network based on the designed structures is implemented, demonstrating the capacity of the multi-pole directional filters to be used for channelization of several bands, following a modular concept, with good filter selectivity for each channel.