Planar Tunable RF/Microwave devices with magnetic, ferroelectric and multiferroic materials
Modern ultra wideband communication systems and radars, and metrology systems all need reconfigurable subsystems that are compact, lightweight, and power efficient. At the same time, isolators with a large bandwidth are widely used in communication systems for enhancing the isolation between the sensitive receiver and power transmitter. Conventional Isolators based on the non-reciprocal ferromagnetic resonance (FMR) of microwave ferrites in waveguide. However, these approaches are usually bulky. This presentation focuses on theoretical study, numerical evaluation and measurement verification of novel planar RF/microwave devices with magnetic substrates and superstrates, demonstrating tunable and non-reciprocal characteristics, so that size, weight and cost of systems can be reduced.
The combination of ferrite thin films and planar microwave structure constituted a major step in the miniaturization of such a non-reciprocal devices. A novel type of tunable isolator was presented, which was based on a polycrystalline yttrium iron garnet (YIG) slab loaded on a planar periodic serrated microstrip transmission line that generated circular rotating magnetic field. The non-reciprocal direction of circular polarization inside the YIG slab leads to over 19dB isolation and < 3.5dB insertion loss at 13.5GHz with 4kOe bias magnetic field applied perpendicular to the feed line. Furthermore, the tunable resonant frequency of 4 ~ 13.5GHz was obtained for the isolator with the tuning magnetic bias field 0.8kOe ~ 4kOe.
The non-reciprocal propagation behavior of magnetostatic surface wave in microwave ferrites such as YIG also provides the possibility of realizing such a non-reciprocal device. A new type of non-reciprocal C-band magnetic tunable bandpass filter with ultra-wideband isolation is presented. The BPF was designed with a 45o rotated YIG slab loaded on an inverted-L shaped microstrip transducer pair. This filter shows an insertion loss of 1.6~2.3dB and an ultra-wideband isolation of more than 20dB, which was attributed to the magnetostatic surface wave. The demonstrated prototype with dual functionality of a tunable bandpass filter and an ultra-wideband isolator lead to compact and low-cost reconfigurable RF communication systems with significantly enhanced isolation between the transmitter and receiver.