Compact impedance-transforming 3-dB three-port power dividers with modified asymmetric impedance transformers (MCCTs)

For further size reduction and design flexibility, a modified asymmetric impedance transformer, a modified constant-conductance-type transmission-line impedance transfor-mer (MCCT) is proposed. The MCCT consists of two different transmission-line sections connected in cascade and a shunt open stub. Several MCCTs are compared to the conventional asymmetric constant-conductance-type transmission-line impedance transformers (CCTs) and the comparison verifies that the MCCTs have advantage over the conventional CCTs in terms of size reduction. One of MCCTs is also compared to the conventional Π- and T-type compact impedance transformers and the compared results show that the bandwidth of the MCCT is 78.5%, while those of the conventional ones are 40% and 42.5%, respectively. Using the MCCTs, impedance-transforming 3-dB MCCT power dividers are built and it is illustrated that the isolation circuits of the MCCT power dividers should be made of not only resistances but also capacitances. To validate the MCCT power dividers, one microstrip impedance-transforming MCCT power divider is fabricated and measured at a center frequency of 1 GHz. The measured results are in good agreements with prediction, showing measured power divisions of S₂₁ = S₃₁= -3.08 dB, matching of S₁₁ = -23.8 dB, S₂₂ = -39.67 dB, S₃₃ = -49.5 dB and isolation of S₂₃ = -24.07dB at 1GHz.