| dc.description.abstract | In this paper, differential bridge-T coils and phase inverter are employed as basic building blocks to realize rat-race couplers with features, like wide bandwidth, dual-band operation, miniaturization and unequal power division ratios. To demonstrate the performance achieved, several design examples are implemented in the integrated passive device (IPD) and 0.18-μm CMOS technology, including wideband rat-race coupler, dual-band rat-race coupler, and dual-band rat-race coupler with unequal power division ratios.
First, by using differential bridge-T coils and phase inverter, a 2.5 GHz miniaturized wideband rat-race coupler is implemented in IPD. The circuit size is only 1.13 × 1.19 mm2 and the corresponding electrical size is 0.0190 0.02750 at 2.5 GHz. The 15-dB return loss bandwidth is 69.2%. It outperforms the conventional rat-race coupler in terms of circuit size and operation bandwidth.
Secondly, by using the same structure of the proposed miniaturized wideband rat-race coupler while replacing the original differential bridge-T coils by dual-band differential bridge-T coils, miniaturized dual-band rat-race couplers are achieved. A 2.45/5.5 GHz dual-band rat-race coupler is realized in IPD, and the circuit size is only 2.73 × 4.17 mm2. The corresponding electrical size is 0.0223λ0 × 0.0341λ0 at 2.45GHz, and it is 0.0501λ0 × 0.0765λ0 at 5.5 GHz. Its 10-dB return loss bandwidth is 81.2% at 2.45 GHz while it is 27.3% at 5.5 GHz. In addition, a 10/24 GHz dual-band rat-race coupler is impemented in 0.18-μm CMOS technology, the circuit size is only 0.871 × 1.18 mm2. The corresponding electrical size is 0.029λ0 × 0.0393λ0 at 10 GHz and it is 0.0697λ0 × 0.0944λ0 at 24 GHz. The 10-dB return loss bandwidth is 99.8% at 10 GHz while it is 30.38% at 24 GHz.
Finally, by varying the equivalent characteristic impedances of the dual-band differential bridge-T coil at the two bands, miniaturized dual-band rat-race coupler that is capable of achieving different power division ratios over the two bands can also be achieved. As an example, a proposed dual-band rat-race coupler having 3dB power division ratio at 2.45 GHz and 0dB power division ratio at 5.5 GHz is realized in IPD. The circuit size is only 3.1 4.4 mm2. The corresponding electrical size is 0.0697λ0 × 0.0944λ0 at 2.45 GHz and it is 0.0697λ0 × 0.0944λ0 at 5.5 GHz. The bandwidth of ±0.5dB amplitude error is 42% at 2.45 GHz and it is 7.5% at 5.5 GHz. Also, the design limitations, of using dual-band differential bridge-T coils for dual-band rat-race coupler designs, including the power division ratio and frequency ratio of the two center frequencies, are thoroughly investigated. | en_US |