Frequency-Selective Limiters Using Triple-Mode Filters

Abstract

This paper presents the first frequency-selective limiter (FSL) with both power-activation and user-prompted override that also features a reconfigurable threshold power and frequency tuning with closed-loop feedback. The FSL is based on a tunable absorptive bandstop-to-all-pass filter topology with integrated electronics. Three distinct modes are available: user-defined bandstop, power-activated bandstop, and all-pass mode. In the user-defined bandstop mode, the FSL presents a measured notch of 45−55 dB at an user-defined center frequency within 1.5−2 GHz tuning range. The out-of-band insertion loss is less 0.8 dB. In the power-activated mode, the FSL switches intrinsically between its bandstop and all-pass responses based on the incident power level at any user-defined power threshold and frequency within the 1.5−2 GHz range. In the all-pass mode, the measured loss is less than 3.1 dB at the user-defined center frequency and less 0.8 dB elsewhere. The measurements are conducted including the two SMA connectors and the associated connector-to-microstrip transitions. The threshold power level is tunable in the −45 to +8 dBm range. The filter is designed and fabricated with high-quality substrate-integrated cavities with an extracted resonator unloaded quality factor (Qu) of 300. The unique features and the measured RF performance of the presented FSL are state-of-the-art results. INDEX TERMS Frequency-selective limiter, FSL, power-activated filter, tunable filter, absorptive bandstop-to-all-pass filter, evanescent-mode cavity filter.

Multi-Octave Interference Detectors with Sub-Microsecond Response

“…This instability can be resolved with various methods including reflectionless filters [14], [18], [19], and isolators [20], [21]. The bandwidth of these technologies, however, is typically limited to one octave.…”

“…Such power-dependent responses typically have limited power dynamic range (10-20 dB). A wider dynamic range can be achieved with active coupling techniques [14], which, similar to [9], [10], requires prior knowledge of the interfering signal frequency. Spectrum scanning methods in [15], [16] are effective in locating the interferer in the band of interest, at the cost of extended response time.…”

Reflective Parametric Frequency Selective Limiters with sub-dB Loss and $μ$Watts Power Thresholds

“…Yet, the fully-passive diode-based FSLs reported to date exhibit much higher power thresholds than those attained by the state-of-the-art (SoA) ferrite-based counterparts [9], thus not being adequate to protect the majority of the integrated front-ends used by IoT systems. Just recently, a diode-based FSL relying on an active feedback-loop, using a board-level power detection and an electromechanically tunable cavity resonator has been reported [20]. Yet, due to the required intense operations allowing to reconfigure its transmission characteristics and regardless of its exceptionally low threshold granted by the use of a sensitive power detector, this reported FSL is not ideal when miniaturized radios with a low-power consumption are needed.…”