The USAF Research Laboratory – Sensors Directorate (AFRL RY) has developed an advance tunable high isolation RF circulator that is capable of providing enhanced radar detection ranges and improved communications reception by reducing signal leakage and undesirable internal reflections between ports. At the tuned frequency of interest isolation values are better than 70 dB which far exceed the isolation of typical 3-port circulators that provide an isolation of about 20 dB.
The AFRL circulator was invented to address shortcomings in monostatic radars, which have traditionally been restricted to pulse mode operation due to false target detection caused by internal leakage, and reflections in conventional circulators. The invention eliminates these internal artifacts and thus allows monostatic systems to operate in continuous mode, improving long-range detection and overall signal purity. The benefits offered by this system for radar can be extended to other applications that use RF circulators including communications, spectrum management, and e-warfare.
This tunable, high isolation circulator relies on destructive interference between two conventional circulators connected in parallel to cancel the internal reflections and signal leakage between ports. First, a power splitter is utilized to divide the incoming signal into two identical channels. By matching the load on each circulator, nearly identical internal reflections and leakage are generated in each circulator.
Each circulator is further connected to a phase trimmer so that the phase offset between the two circulators may be adjusted to cancel the internal leakage and reflections, which occurs once the two channels are recombined in a power combiner. The resulting signal purification occurs solely in the analog regime, providing increased effectiveness relative to known isolation methods that require digital conversion and subsequent post-processing.
Some notable benefits of the high isolation RF circulator:
- Reduces leakage signals and internal reflections resulting in improved noise floor and reduced false alarms
- Allows continuous mode operations translating to more time on target
- Enables much weaker signals to be detected at longer ranges
- Offers extensive system flexibility: scalable to different frequency ranges and power levels, wideband, tunable; compatible with both new builds and retrofits
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