[Goose]

Seems to me the widespread use of anti-radiation drones would be a game changer. It seems like a perfect use case for them, as they can loiter/wait for radar or jamming sites to turn on and then home in, as opposed to needing an aircraft in position to launch a HARM. 


There look to be several available. The Harpy made by Israel. Turkish KARGI. Chinese ASN301 (copy of the harpy). Taiwanese Chien Hsaing. Sadly no US option I could see.

As far as I can tell, these loitering drones are unsuited to attack GPS jammers. GPS jammers need to be on all the time, or close to it, to be effective. The potential targets can't know when they will be attacked, so they have to assume it can be at any time. By the time the HIMARS/JDAM is inbound, it is basically too late, even assuming you can detect the threat at all. These drones are listed as targeting SAM radars, which can operate intermittently. The radars that are SAM associated operate at 2 GHz or above (a few exceptions like the P-15 and successors). Radars also are generally high peak power. GPS jammers are almost exclusively continuous signals (CW) with lower peak power. Since they are "always on", loitering is unnecessary. If the drone can receive the signal, there is no reason to wait. If it can't receive and DF the signal, it will never find the jammer anyway, except by chance.

The problem with "small" drones is that getting a "good" initial line of bearing to the target becomes more difficult as the frequency gets lower. The antenna gain is lower and the beamwidths are wider. The HARM operates against 1.5 GHz GPS jammers, but it has similar (or worse) limitations. The HARM however can be targeted to a particular location by either the launch platform or based on prior ESM data. It only has to use it's on-board antennas when it is already close to the target. However, it can tune to 1.5 GHz and have antennas that work. Unlikely these drones can, given their original purpose. Certainly the original HARMs could not.

It is easily possible to build a drone that would be able to receive and DF GPS jammers. However it needs to be a purpose-built device. It would be nice to have the ability to launch it along a basic target vector provided by prior ESM work, as otherwise most missions would come up empty. Such a drone would undoubtedly have the ability to use an adaptive antenna assembly to "null out" the GPS jammer from the drone's own GPS receiver. A real small drone/missile will have trouble doing this, but something of the size of Chien Hsaing drone could.

[Goose]

Seems to me the widespread use of anti-radiation drones would be a game changer. It seems like a perfect use case for them, as they can loiter/wait for radar or jamming sites to turn on and then home in, as opposed to needing an aircraft in position to launch a HARM. 


There look to be several available. The Harpy made by Israel. Turkish KARGI. Chinese ASN301 (copy of the harpy). Taiwanese Chien Hsaing. Sadly no US option I could see.

As far as I can tell, these loitering drones are unsuited to attack GPS jammers. GPS jammers need to be on all the time, or close to it, to be effective. The potential targets can't know when they will be attacked, so they have to assume it can be at any time. By the time the HIMARS/JDAM is inbound, it is basically too late, even assuming you can detect the threat at all. These drones are listed as targeting SAM radars, which can operate intermittently. The radars that are SAM associated operate at 2 GHz or above (a few exceptions like the P-15 and successors). Radars also are generally high peak power. GPS jammers are almost exclusively continuous signals (CW) with lower peak power. Since they are "always on", loitering is unnecessary. If the drone can receive the signal, there is no reason to wait. If it can't receive and DF the signal, it will never find the jammer anyway, except by chance.

The problem with "small" drones is that getting a "good" initial line of bearing to the target becomes more difficult as the frequency gets lower. The antenna gain is lower and the beamwidths are wider. The HARM operates against 1.5 GHz GPS jammers, but it has similar (or worse) limitations. The HARM however can be targeted to a particular location by either the launch platform or based on prior ESM data. It only has to use it's on-board antennas when it is already close to the target. However, it can tune to 1.5 GHz and have antennas that work. Unlikely these drones can, given their original purpose. Certainly the original HARMs could not.

It is easily possible to build a drone that would be able to receive and DF GPS jammers. However it needs to be a purpose-built device. It would be nice to have the ability to launch it along a basic target vector provided by prior ESM work, as otherwise most missions would come up empty. Such a drone would undoubtedly have the ability to use an adaptive antenna assembly to "null out" the GPS jammer from the drone's own GPS receiver. A real small drone/missile will have trouble doing this, but something of the size of Chien Hsaing drone could.