Design of a direct Ku-band linear subharmonically pumped I/Q vector modulator in multi-layer thin-film MCM-D

The design of a direct Ku-band linear subharmonically pumped I/Q vector modulator in a multi-layer thin-film MCM-D process is described. The modulator consists of a Wilkinson power divider, a CPW Lange coupler and 2 sub-harmonically pumped mixers. Three distributed designs have been realized for the 7 GHz Wilkinson power divider: a fully distributed design, a meandered design with capacitively loaded transmission lines and a design with high-impedance lines and capacitive compensation at the ends. An excellent correspondence has been obtained between the measured and simulated results, indicating the high accuracy that can be obtained using the integrated passives design-library. Over the 6.5-7.6 GHz band, the Wilkinson has a measured return loss better than -22 dB, an isolation better than -25 dB with only 0.3 dB losses. Over the 10.5-14.5 GHz band, the Lange coupler has a measured return loss and isolation better than 20 dB, an amplitude balance below 0.13 dB and a phase balance of (90 +/- 1) deg. A beam-lead anti-parallel diode pair is mounted onto the MCM using thermocompression. The diode model has been verified using non-linear network analyzer measurements. An excellent agreement has been obtained between the measured and simulated powers and phases for more than 9 harmonics. It is shown that an optimal reactive termination for the third harmonic of the LO exists such that a very flat mixer conversion loss can be obtained over the 6.8-7.45 GHz band. The IF-, RF- and LO-input impedances are also flat, such that a good and constant matching can be achieved, required to obtain a modulator with a good amplitude and phase balance.