Deploying UAVs as Jammers in the Aegean Se
By Dimitris Natsiopoulos, Electrical and Computer Engineer
In the dawn of 21st Century, one of the new achievements for the military aviation that saw extensive use was the deployment of UAVs (Unmanned Aerial Vehicles) in war theaters around the Globe. These aircrafts come to replace conventional manned aircrafts especially in supporting missions.
Used in ISR (Intelligence, surveillance and reconnaissance) missions like the Nothrop Grumman RQ-4 Global Hawk or armed with Hellfire missiles like the MQ-9 Reaper for ground support, UAVs plays an important role in todays defence capabilities. With rapid advancements in technology, nowdays it is possible for a relatively small aerial platform to participate in almost every task of aerial combat.
In a possible conflict between Greece and Turkey, the Greek Forces must find a way to neutralize the 2nd largest army in NATO. This task isn’t easy but with careful plans and focusing on force multipliers it is higly possible. Apart from the conventional warfare where armed forces using brute force try to eliminate each other, there is another method that can bring havoc to the command of hostile forces.
Electronic Warfare, using many cheap aerial platforms that can cover long distances in short time is the answer.
Electronic warfare can be used not only for defensive puproses but also for offensive missions inside enemy territory. These missions can be stand alone or part of a bigger air raid. Rather than operating expensive (to aqcuire and maintain) one-role aircrafts such as EA-6B Prowler (used in electronic warfare by the US Navy) deploying UAVs with electronic attack pods can be a strong alternative.
The realtively small geographical area of the Aegean Sea and Minor Asia (part of Turkey) means that a UAV can stay for many hours in the war theater. Its flight autonomy along with its flight path could cover a large area jamming the enemy communications. Taking off from any of the dozens Greek islands (either using a ground catapult or a small airport) it can fly in friendly airspace or in a small distance inside enemy territory.
The Advantages of using a UAV as an ECM platform are listed below:
- Flexible to operate at different locations covering large areas
- Can fly at medium to high attiltudes, growing the affected area of jamming compared to stationary ground jammers. It is crucial especially for the desirable geographical region (Greece and Minor Asia) which consists of many hills and mountainous landscapes. These obstacles can block the line of site between the transmitter/jammer and reduce the desired artificiall noise level.
- Not expensive. Easy to operate and maintain. Can program many different UAVs to follow certain waypoints so that the enemy Integrated Air Defence System can be saturated and jammed causing interference and severe noise level to the enemy radars. That will result in reduced radar capabillity and will create blind sectors giving the friendly aircraft fighters the backdoor to fly unoticed inside the enemy’s airspace. These offensive ECM operations coupled with SEAD/DEAD aircrafts (armed with anti-radiation missiles like AGM-88E HARM) can easily neutralize the enemy’s air defences.
- UAVs can be launched either from ground catapults or using short airstrips
- Electronic attack pods are lighter than a missile making them possible to be carried in the external pylons
- Can easily disrupt UHF military communication even with a simple spark-gap transmitter
- A pilot/operator of a UAV can handle a group of them.
- After the insertion in the enemy airspace there is no need for constant communication between the friendly ground control station and the UAV. From that point on it can fly in pre-programmed flight path.
An exemplary UAV that can be taken into consideration as a baseline is the MQ-9 Reaper. Many other UAVs from various companies have the same or better flight characteristics.
- Crew: 0 onboard, 2 in ground station
- Length: 36 ft 1 in (11 m)
- Wingspan: 65 ft 7 in (20 m)
- Height: 11 ft 10 in (3.6 m)
- Empty weight: 4,901 lb (2,223 kg)
- 7 Hardpoints.4 of them certified for Electronic Warfare attacking pods
- Max takeoff weight: 10,494 lb (4,760 kg)
- Fuel capacity: 4,000 lb (1,800 kg)
- Payload: 3,800 lb (1,700 kg)
- Internal: 800 lb (360 kg)
- External: 3,000 lb (1,400 kg)
- Powerplant: 1 × Honeywell TPE331-10 T76 turboprop, 900 hp (671 kW) with Digital Electronic Engine Control (DEEC)
- Maximum speed: 300 mph; 260 kn (482 km/h)
- Cruising speed: 194 mph; 169 kn (313 km/h)
- Range: 1,151 mi; 1,852 km (1,000 nmi)
- Endurance: 14 hours fully loaded
- Service ceiling: 50,000 ft (15,240 m)
- Operational altitude: 25,000 ft (7.5 km)
The desired autonomy, flight ceiling and electrical supply are totally covered. Keep in mind that each Electronic Warfare attack pod requires about 1-10 kW of electrical power to effectively operate. The Honeywell TPE 331-10 powerplant as shown above can cover this requirement while the UAV can fly at cruise speed.
Jamming the UHF/VHF military communication
The primary mission of the UAV ECM is to disrupt enemy communication. Most millitary radios use the C-band (500-1000 MHz). These radios are mainly used by the military to transmit voice messages. Disrupting the tranmited signal can cause a part of it to fade. Those interruptions would make communication impossible to understand. This can be done even with less sophisticated and inexpensive jammers like a spark gap trasnmitter.
In the above drawing the coil L and the capacitor C2 is the wanted resonant circuit. The energy which can be created by a high voltage source is stored in the capacitor C1, and is created on every spark. And that makes the resonant circuit ring.
This circuit will then wait for the capacitor C1 to charge up again through the resistance R, and then ignite another spark. The spark frequency is about f=1 / R*C1
For UHF frequencies the antenna itself is the resonant circuit, tuned to the above frequency f.
After the release of every spark the created signal has a wide bandwidth centered on this frequency. Throwing big amounts of noise in a wide spectrum from the jammer perspective is desirable.We can use multiple spark gap transmitters centered in different frequencies to disrupt different channels. Keep in mind that most military radios work in low power levels.
A UHF steerable antenna can be used covered by radome material. An electronic warfare attacking pod can be equiped with two antennas each one of them covering a 180 degree sector.
Disrupting enemy X-Band radar would require more advanced designs. Constructing an X-band jammer may be more complex but the final result is more compact (less volume) due to the fact that the operating frequency would lead to smaller dimensions of the antenna.
Power requirement of the Jammer
Taking the Friis equation into account for a 2-point communication
This equation gives the power received by one antenna under idealized conditions given another antenna some distance away transmitting a known amount of power.
We can see that the distance R between the 2 objects is weighed by a ^2 factor.
That means that the closer the two objects are (aircrafts, ground stations, infantry units etc) the greater is the Pr (power of the received antenna).
In the case of radar the transmiting and receiving antenna are the same. The scattering object is an aircraft. Then the transmiting wave travels the same distance two times and the equation (after a few modifications) that gives us the Power of the radar’s receiver is
Pr= Pt*(G^2)*(λ^2)* σb /((4*π)^3)*(R^4) (II)
Where σb=radar cross section factor
In the case of the jammer transmitting to the enemy radar/receiver there is no backscatter path and thus the needed equation is that of the Friis Equation.
From the two cases (I,II) it can be assumed that for the same distance the jammer need approximately 100 times less power to achieve the enemy radar’s power level.
With this in mind it can be possible for a 1kW jammer to effectively disrupt most common radars and create an adequate noise level.
Of course jamming radar isn’t as simple as that. Most modern radars have ECCM (Electronic counter countermeasures) that can separate the signal from the noise (jamming+interference+common enviroment noise). But in the case of multiple jammers emitting from different directions that would be difficult. The total noise would be very random in time and space and also difficult to recognize and isolate.
Advanced jamming methods can be also used.
RANGE GATE PULL OFF
One quite useful method is the Range Gate Pull Off or RGPO.
If the UAV has been detected and tracked by an enemy radar range gates will be “placed” to either side of it, by the enemy radar. The radar concetrates on a range interval, a narrow window of a few hundred meters which encloses the target’s location and no longer is looking for other targets. The RGPO technique consists of the following steps:
a) At first, a sample of the illuminating pulse signal is captured and the radar’s pulse repetition frequency (PRF) is determined. This sample is amplified and sent back immediately when more singals are received.This procedure repeats until the falsed signal from the transmitter is much stronger than the echo from the aircraft’s body (the ‘skin echo’). Then the sensitivity of the tracking radar’s receiver needs to be reduced in order to avoid overload. On the other hand, this has the consequence that the ‘skin echo’ drops below the noise threshold.
b) After that another replica is transmitted after each of the ‘dummy’ skin echoes.The jammer increases the power of the second replica signal while the ‘dummy’ skin signal is getting weaker.
c) Then the radar tracker has locked on the delayed replica and at the same time the ‘dummy’ has sunk down into the noise. With consideration to each of the radar’s pulses, the replica is now being delayed by small, but increasing amounts of time. The range gates, of course, follow the dummy target which appears to be dropping. This continues until the range gates have been moved away from the target’s real position. The result is that the radar is tracking a false ghost target and the skin echo is being blanked out by the range gates.
d) Phase four is a simple one. The jammer is switched off and leaves the radar with just nothing but noise inside the window between its range gates.
To sum up, deploying an adequate Electronic Warfare squadron of UAVs will give the upper hand to the Hellenic Air Force. Electronic warfare is a form of ‘soft kill’, disabling and neutralizing the core of the enemy’s capabilities. With the enemy’s higher command having trouble passing the right orders, this could give the edge to the allied forces. Cyberwarfare and Electronic Warfare are the new ‘weapons’ of the 21st Century. EW is a weapon of great impact which can play a decisive role in today’s conflicts. It can force the Turkish army to fight blinded, disoriented and with no consistency. Unlike the use of lethal force, EW can change more rapidly the course of a war and end it sooner. Controlling and manipulating the RF Spectrum can bring victory which in other cases seems extremely difficult.
It always seems impossible until it is done…