Design of fully integrated 4x4 and 8x8 Butler matrices in microstrip/slot technology for ultra wideband smart antennas

The paper presents the design of ultra wideband (UWB) 4times4 and 8times8 Butler matrices in multi-layer microstrip-slot technology that are aimed for inclusion in UWB switched-beam smart antennas. The design exploits the multi-layer microstrip/slot technology to accomplish UWB 3 dB couplers and differential phase shifters that form these two devices. The choice of this technology helps to overcome the problem of crossovers, which is the main challenge in practical realizations of Butler matrices.