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DIRECTED ENERGY PROFESSIONAL SOCIETY

Abstract: 24-Systems-207

UNCLASSIFIED, PUBLIC RELEASE

Auto-tune Filters for Mitigation of HPM Effects

Radio frequency communication systems, because of their requirement for an aperture/antenna to transmit and receive, are inherently susceptible to High Power Microwave (HPM) Directed Energy Weapons (DEW). Ideally, any Counter-DEW (CDEW) technology employed for this type of ‘front door’ attack would not only protect the communication system from damage, but also allow the system to function simultaneous with the DEW attack. An Auto-tune Filter (AtF) can help to mitigate the effect of a DEW attack by automatically creating a high insertion loss ‘notch’ at the frequency of the DEW, while maintaining an essentially unchanged insertion loss over the remainder of the passband, thus allowing the communication system to continue to function.
AtFs are passive microwave components that provide a frequency-selective, power-limiting function in response to strong RF signals. The AtF is passive in that it automatically adapts to power-limit received high-power signals at the specific frequency of those high-power signals without apriori frequency information and without any feedback or control loop. The frequency-specific power limiting is dynamic in frequency and power, and the AtF can react to multiple high-power inputs simultaneously.
There are two types of Auto-tune Filters – absorptive and reflective – which differ in their basic mode of operation as well as their performance. The Absorptive type of AtF, as the name implies, absorbs high power signals that exceed the power threshold (P(th)) of the device. Any RF signal above P(th) will experience an insertion loss that increases with increasing power, creating a high loss ‘notch’ centered at the frequency of that high power signal. RF signals at frequencies outside of that notch are transmitted with only the relatively small amount of low-power insertion loss. The reflective type of AtF will reflect any high power signal that exceeds the designed P(th) of the AtF and create an insertion loss notch similar to that of the absorptive AtF.
The two basic types of AtFs together with the various design parameters, including ferrite type, ferrite dimensions, waveguide design, and magnetic biasing, allow for a wide range of power thresholds. AtFs can be designed for power thresholds as low as -40 dBm to as high as +50dBm, or possibly higher. Peak power handling has been measured as high as 1.5 kW.
This paper examines how a range of strong, unwanted signals can be countered using a mix of Auto-tune Filters, taking into account power threshold, bandwidth, and dynamic range of power limiting.

UNCLASSIFIED, PUBLIC RELEASE