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.