Billy T all I have to say to you is Sergeant York.
All off the shelf systems that worked well for their assigned missions, yet when put together as another system, they tracked, targeted and destroyed a Latrine Fan, along with the latrine, instead of the incoming drone.
And again, rockets are not a high angle weapon, their trajectory is much lower and faster than a mortar round.
BM-21 "Grad"
Caliber 122.4 mm (4.81 in)
Barrels 40
Rate of fire 2 rounds/s
Muzzle velocity 690 m/s (2,264 ft/s)
Maximum range 20,400 m (22,310 yds)
Sights PG-1M panoramic telescope
A mortar is a muzzle-loading indirect fire weapon that fires shells at low velocities, short ranges, and high-arcing ballistic trajectories.
81mm M1 Mortar
FM 23-91:Mortar Gunnery
General Data
Weight: 136 lbs assembled; tube 44.5 lbs; mount 46.5 lbs; base plate 45 lbs.
Overall Length: 3 ft 9.5 in.
Muzzle velocity (HE): 700 f.p.s.
There is a hell of a difference in hitting a Mortar round at 700 fps, and a rocket at 2,264 fps.
That is a Mach 2.03 for the BM 21, rocket, a Mortar is Mach .6275, one hell of a difference in preformance profile.
Plus here is a little something I found, this is the range fans of the BM-21 system rockets. The rockets have a range of 12.7 miles / 20.4 km, now just how big will your proposed system have to be to defend the impact areas of the range fans?
The Katyusha Rocket "Multiple Rocket Launcher" BM-21 could be easily taken apart and smuggled into a "demilitarized" Palestinian state. Individual Katyushas can be launched from a pipe using just a car battery.
The speckled region to the left is the Tel Aviv metropolitan area, which houses some 70% of Israel's Jewish population and 80% of the country's industrial base. The West Bank is a mountainous region overlooking the Mediterranean coastal plain and Gaza is a seaside district with its own port. If Israel relinquishes military control over these regions, it will be impossible to prevent the smuggling of weapons such as the Katyusha. The potential implications are clear.
Rockets are not mortars, and their flight profile is much lower and faster than a mortar round.