Recently, substrate integrated waveguide (SIW) technology attracts more and more attentions in the development of millimeter-wave integrated beamforming network (BFN) depending on its inherent advantages. However, the SIW-based BFN usually has a relative large circuit size. To overcome this weakness, we propose a novel multi-folded SIW Butler matrix at the center frequency of 60 GHz. Such a structure can reduce the circuit area more than 75% compared with the conventional single-layer version. Two different full-wave simulation tools are employed to validate our design. This folded BFN offers a number of benefits, such as highly compact configuration, low couplings between adjacent paths, and wide operation bandwidth. For convenient use, the SIW ports can be converted to the microstrip line ports arranged in order through a special broad-band two-layer transition network. Such a miniaturized SIW Butler matrix presents an excellent candidate in the development of compact intelligent millimeter-wave communication system.
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