A tunable slot loop antenna loaded with interdigitated ferroelectric varactors at multiple positions is designed, fabricated, and measured. Measurement results show that the resonant frequency of the proposed antenna can be tuned from 15.18 GHz to 15.36 GHz as the bias voltage is increased from 0 V to 39 V.

A frequency-reconfigurable antenna based on periodically loading ferroelectric MIM capacitors along a slot loop is designed, fabricated, and measured. The antenna is fabricated on a 430-m-thick sapphire substrate with a total area of 1×1 cm 2 . The size of the slot loop is 2.5×2.5 mm 2 . By changing the bias voltage of the ferroelectric varactors from 0 V to 7 V, the resonant frequency of the varactor-loaded antenna can be tuned from 5.57 GHz to 7.33 GHz, corresponding to a tuning range of 27.3%, while keeping the return loss greater than 10 dB. At 5.57 GHz, the size of the slot loop is 0.046×0.046 0 2 . When biased at 7 V, the antenna gain is À10.8 dBi at 7.35 GHz. Under 0-V bias, the P in,1 dB of the tunable antenna is 18.8 dBm at 5.6 GHz.

All-pass phase shifters using ferroelectric varactors are designed, fabricated, and measured. The design equations for the allpass phase shifter are presented. The fabrication process of the ferroelectric varactors is described. Measurement results of singlestage all-pass phase shifters show that phase shift greater than 85ﾟ can be achieved under 10-V bias. At the frequency where maximum phase shift occurs, the insertion loss is less than 2 dB and the return loss is greater than 12 dB. Simulations based on the measured S parameters of the single-stage phase shifters show that, by cascading four stages of individually biased single-stage phase shifters, maximum phase shift of 180ﾟ can be achieved with a phase error as low as ±3ﾟ between 2.1 GHz and 3.25 GHz, corresponding to a 43% bandwidth.

Tuning element is essential for the design of tunable and reconfigurable RF circuits. Ferroelectric thin-film integrated capacitor is proposed in this work as the tuning element for MCM-D SiP technology. The proposed ferroelectric capacitors are fabricated on a sapphire substrate. The fabrication process is described. Measurement results show that the capacitance density is about 19 fF/ m 2 at 0-V bias. The tunability of the ferroelectric capacitor reaches 2:1 as the bias voltage is increased from 0 V to 7 V. The quality factor at 2.4 GHz is 15.5 under 0-V bias and reaches 30 when the bias voltage is 8 V. The proposed ferroelectric capacitor is applied to a RF phase shifter design for the purpose of demonstrating the potential of using the proposed thin-film ferroelectric technology for realizing MCM-D SiP. All-pass network is adopted as the circuit topology for the phase shifter. The design of the phase shifter is explained. To implement the phase shifter, surface mount components are mounted on the substrate on which the ferroelectric capacitors are fabricated. Measurement results show that, for bias voltage ranging from 0 V to 10 V, the phase shifter exhibits an insertion loss less than 2.6 dB and a return loss greater than 9.5 dB from dc to 6 GHz. Maximum phase shift of 98.8° is achieved at 3.15 GHz.