| dc.description.abstract | Phase shifter is an essential component in a phased array. The function of a phase shifter is to provide a tunable insertion phase. In phased array applications, phase shift up to 360° is usually necessary. If the amount of phase shift provided by a single stage of phase shifter can be increased, the number of cascaded stages can then be reduced, which may lead to the reduction of insertion loss and circuit area. In this thesis, a 2.4-GHz analog phase shifter is designed at 2.4 GHz based on magnetically coupled all-pass network (MCAPN). The design goal is to achieve a phase shift up to 180° using only a single-stage network.
In this work, we use the ferroelectric varactor technology based on BSTO thin film developed by our lab and combine it with the integrated passive process offered by WIN Semiconductors (the WIPD process) by flip-chip bonding to realize the proposed magnetically coupled all-ass phase shifter. The coupled inductors in the MCAPN are realized using the WIPD process on a GaAs substrate. The polarity of the two intertwined inductors is designed to produce a positive coupling coefficient, which helps increase the amount of phase shift. Simulation results show that, at 2.45 GHz, a coupling coefficient of 0.8 can be achieved. If the tunability of the varactors is 2.3, the simulated phase shift is as high as 191°.
The ferroelectric varactors in the phase shifter are fabricated on a sapphire substrate. Measurement results of the varactors show that tunability of 2.3 is achieved under 10-V bias. The construction of the phase shifter is finalized by flip-chip mounting the GaAs chip onto the sapphire carrier. Measurement results of the phase shifter show that, under 10-V bias, maximum phase shift of 161° occurs at 2.35 GHz, with return loss greater than 11.3 dB and insertion loss less than 15.8 dB.
From the measurement results of the test varactors on the same carrier, it is found that the quality factor of the varactors is lower than what is used in the simulation, leading to the higher insertion loss. Moreover, we suspect that, the temperature for flip-chip bonding may be too high so that the characteristics of the ferroelectric thin film has changed, resulting in lowered tunability and thereby the reduced phase shift, which is less than 180°. Nevertheless, since the measured phase shift is as high as 161°, we successfully demonstrate that phase shifters with large amount of phase shift can be realized using MCPAN. | en_US |