A compact 24–26 GHz IPD-based 4×4 Butler matrix for beam forming antenna systems

A compact 24-26 GHz low loss 4×4 Butler matrix is implemented in an IPD (integrated passive device) technology and presented in this paper. A modified coplanar waveguide (M-CPW) branch line coupler is utilized as the core element of the Butler matrix. The proposed Butler matrix occupies a chip area of 2.2 × 1.9 mm2 (excluding the I/O test pads). The measured results showed output relative phase errors of less than 5% over a frequency range of 26-29 GHz and less than 13% over 24-25 GHz, and output amplitude imbalances of less than 1.3 dB over a frequency range of 24-27 GHz. The proposed Butler matrix is well suited for use in microwave low-cost, high performance beam forming wireless communications systems.