On-chip miniaturised wideband rat-race coupler using integrated passive device technology

In this study, a miniaturised wideband rat-race coupler using glass integrated passive device (GIPD) technology is studied. The circuit miniaturisation is achieved using slow-wave synthesised coplanar waveguides (CPWs). For wideband operation, a compact CPW phase inverter is developed and integrated. At the centre frequency, 12 GHz, the proposed rat-race coupler is only 6.5% the size of a conventional 1.5-λ_g ring coupler with the same GIPD technology; the fractional bandwidths, on the other hand, reach 65 and 32%, respectively, at the sum and difference ports. The coupler shows good amplitude and phase balances, with the transmission loss around 0.7-1.1 dB at the centre frequency.