This paper presents the design and implementation of a compact 2.4/5.2-GHz rat-race coupler on a glass substrate. Due to the low-loss substrate and thick metal layers, the process provides high-Q capacitors and inductors, and therefore the lumped rat-race coupler is practical. The coupler consists of three bandpass and one bandstop networks to achieve dual-band operations. The measured insertion losses at 2.4 GHz and 5.2 GHz are less than 2.7 dB and 1.9 dB, respectively. The measured return losses at the frequencies of interest are better than 20 dB. Moreover, the phase imbalances at the in-phase and anti-phase output ports are less than 3.9o and 4o at 2.4 GHz and 5.2 GHz, respectively. The chip size including all testing pads is merely 2.87 × 2.1 mm2 which is comparable to on-chip levels.
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