The planned transition from the AN/APG-81 to the AN/APG-85 marks a fundamental technology shift in the semiconductor basis of the transmit/receive modules [20]:
| Property | GaAs (APG-81) | GaN-on-SiC (APG-85) | Improvement |
|---|---|---|---|
| Bandgap | ~1.4 eV | ~3.4 eV | 2.4x |
| Breakdown Field Strength | ~0.4 MV/cm | ~3.3 MV/cm | ~8x |
| Power Density | ~1.5 W/mm | 5–12 W/mm | 3–8x |
| Power Added Efficiency | 25–40% | 50–65% | ~1.5–2x |
Sources: Qorvo GaN/GaAs Analysis [21], Military Embedded Systems [22]
The AN/APG-85, also developed by Northrop Grumman, is planned for F-35 Lot 17 and subsequent production batches [23]:
The full potential of the AN/APG-85 depends on the successful integration of the Technology Refresh 3 (TR-3) computer infrastructure. The TR-3 software stabilisation will continue until at least 2026 [24].
The Chinese J-20 features the Type 1475 AESA radar with an estimated 2,000–2,200 TRMs in a larger aperture [25]. The AN/APG-85 is the answer to this physical disadvantage: since the F-35 cannot enlarge its nose cone, it must increase power per module.
The Swiss F-35A aircraft will, according to current knowledge, be delivered with the AN/APG-81, not with the AN/APG-85 [26]. This results in an estimated 33% shorter first-detection range compared to APG-85-equipped allies.
The radar is the most important sensor system of a modern fighter aircraft – comparable to the eyes and ears of the jet. It transmits electromagnetic waves and analyses their reflections to detect, track and identify enemy aircraft, ships, vehicles and ground objects. Modern fighter aircraft radars can simultaneously track dozens of targets, map the ground and even jam enemy radars [19].
Both the AN/APG-81 and the AN/APG-85 are so-called AESA radars (Active Electronically Scanned Array). With this technology, the radar antenna does not consist of a single large transmitter with mechanical steering, but of approximately 1,600 tiny, independent transmit/receive modules (TRMs). Each of these modules functions as an independent mini-radar station [9].
The advantage: the radar beam can be steered electronically in any direction within microseconds – without mechanical movement. This enables the radar to perform multiple tasks virtually simultaneously: track air targets, map the ground and jam enemy radar systems [10].
The AN/APG-81 by Northrop Grumman is the standard radar of all F-35s to date. It is based on gallium arsenide semiconductors (GaAs) – a material proven since the 1980s for high-performance microwave applications [12]. The AN/APG-81 represents a significant performance leap over predecessor systems (such as the F-16's AN/APG-68) and masters the following modes [19]:
The limitations of the AN/APG-81 are determined by the physical properties of gallium arsenide: the power density of GaAs is approximately 1.5 W/mm, which limits maximum transmission power and thus detection range [13].
The AN/APG-85 uses gallium nitride (GaN) on silicon carbide substrates – a semiconductor technology that offers fundamental advantages over GaAs. GaN enables a 3- to 8-fold increase in power density (5–12 W/mm) with simultaneously higher efficiency (over 50% compared to 25–40% with GaAs) [13, 14].
In practice, this means:
The Swiss F-35A aircraft will, according to current knowledge, be delivered with the AN/APG-81 and not with the AN/APG-85 [26]. There are several reasons for this:
Switzerland thus receives a radar that, whilst significantly superior to the F/A-18 predecessor system, is no longer state-of-the-art upon delivery. The estimated first-detection range against conventional targets is approximately 150 km for the AN/APG-81 compared to an estimated 225 km for the AN/APG-85 – a disadvantage of approximately 33% [6].
Mission Data Files (MDF) are extensive, highly complex databases that explain to the F-35's onboard computer what its sensors perceive. They form the sensory and cognitive centre of the aircraft [27]. Without current MDFs, the F-35 is massively restricted in its effectiveness in a modern electronic battlefield: it can fly, but it cannot reliably distinguish friend from foe, classify threats or effectively deploy its electronic countermeasures [27].
The MDFs contain parametric data – so-called electronic signatures – on a multitude of enemy and allied systems [27, 29]:
The AN/ASQ-239 Barracuda – the F-35's electronic warfare system – and the aircraft's sensor fusion are completely dependent on current MDFs. Without them, the onboard computer lacks the reference database to classify received signals. This has concrete operational consequences [27]:
The MDFs define the so-called "Blue Line" – the optimal route and tactics by which the aircraft can penetrate hostile airspace without being detected. This route calculation is based on the fusion of a large amount of factors: detection ranges of enemy radars, their scan patterns, gaps in coverage and the F-35's own stealth characteristics in various flight attitudes [27].
The existing Swiss F/A-18 fleet and the F-35 differ fundamentally in the question of who may integrate electronic signatures into the threat library:
| Aspect | F/A-18 Hornet | F-35A Lightning II |
|---|---|---|
| Signature Integration | Switzerland can integrate signatures autonomously in Emmen | Signatures must be programmed in the USA |
| Responsible Authority | Swiss Air Force / RUAG (Emmen) | 350th Spectrum Warfare Group, Eglin AFB, Florida [30] |
| Response Time | Days to a few weeks | Months (according to GAO reports [31]) |
| Data Sovereignty | Switzerland retains full control over threat analysis | Switzerland must disclose threat scenarios to the USA [27] |
| Crisis Capability | Autonomous – even without external support | Dependent on US prioritisation and willingness |
This difference is of central importance for a neutral state: the F/A-18 can continue to operate autonomously with updated threat data in a crisis, the F-35 cannot.
Within the F-35 programme, there is a clear hierarchy in access to MDF resources [27, 30]:
Switzerland, as an FMS customer, falls into the lowest category. It receives standardised data packages but has no influence on their prioritisation, content or update rhythm.
Only Israel has, through massive political pressure and its special strategic partnership with the USA, fought for the right to operate its own cyber infrastructure in parallel and to modify MDFs independently [27]. Switzerland lacks this option. Whilst the Swiss Federal Department of Defence argues that Switzerland receives the same standards as all other partners – "same standard" in this context means: same dependency on the US database and no national autonomy in electronic warfare [29].
The F-35 is designed as a "software-defined platform" – it is dependent on permanent connection to the manufacturer's infrastructure. In the event of withdrawal of US support, the following degradation would occur [27, 33]:
| Phase | Timeframe | Effects |
|---|---|---|
| Initial | Days 0–10 | Limited impact; routine maintenance possible with locally cached data. Mission capability at approximately 70–75%. |
| Accelerated | Days 10–30 | Predictive maintenance algorithms (ODIN) no longer available. Unplanned failures accumulate. Spare parts orders no longer system-supported. |
| Critical | From Day 30 | Software updates and MDF updates cease. Tactical relevance declines. More complex repairs impossible as diagnostic functions depend on server validation. |
| Long-term | From Day 60+ | Fleet "cannibalises" itself – technicians must remove parts from other jets. Mission capability drops to a fraction. |
To create tailored MDFs for Switzerland, the USA must know exactly what Switzerland wants to defend against. Switzerland must therefore disclose its intelligence data, strategic threat scenarios and operational doctrines to the manufacturer country [27]. For a neutral state that should keep its defence planning confidential vis-à-vis all parties, this is problematic.
The USA could theoretically refuse to include certain targets in the Swiss MDFs – for example if they involve systems of US allies. The question of whether the F-35 would recognise an aircraft of a NATO partner as a threat if the USA has not programmed it remains open and is of critical importance for a neutral state [27].
The creation and validation of new MDFs can, according to reports from the US Navy and the GAO, take months [31]. In a rapidly escalating conflict, the Swiss Air Force is dependent on prioritisation by the US Air Force. Does Switzerland – as an FMS customer without its own reprogramming capabilities – stand on the priority list behind the US armed forces, Israel or NATO?
That the USA uses arms cooperation as a political lever is not a theoretical consideration but historical reality [27, 34]:
The comparison illustrates the fundamental difference in operational capability:
| Scenario | F/A-18 Hornet | F-35A Lightning II |
|---|---|---|
| US support withdrawn | Continued autonomous operation possible; Switzerland can maintain threat data independently | Progressive degradation; no independent updating of threat library possible |
| New threat emerges | Signature integration within days in Emmen | Dependent on US analysis and return delivery (months) |
| Deployment against non-US allies | No restriction | Theoretical restriction through MDF contents possible |
| Long-term operation without manufacturer | Possible (proven over decades) | Not envisaged in system architecture |
[6] Radartutorial: AN/APG-85 – Technische Spezifikationen
[7] Lockheed Martin: Block 4 Capabilities Sharpen the F-35's Edge
[9] Active Electronically Scanned Array – Technologieübersicht
[10] Qorvo: X-Band Radar – Driving Defense Applications with Beamforming
[12] Elite RF: GaN vs GaAs – Key Differences in RF Power Amplifiers
[13] RayPCB: GaAs vs. GaN Radar – What is the Difference
[14] MSE Supplies: Differences Between GaN and GaAs RF Power Amplifiers
[19] Northrop Grumman: AN/APG-81 AESA Fire Control Radar
[20] Military Embedded Systems: GaN Technology in AESA Radar Systems
[21] Qorvo: X-Band Radar: Driving Defense Applications with GaN and GaAs Technology
[22] Military Embedded Systems: GaN vs. GaAs for Next-Gen AESA Radar
[23] Northrop Grumman: Developing the Next Generation Radar for the F-35. 2023
[24] Defense News: Key tests for latest F-35s will begin in 2026. 2025
[25] Air University / CASI: A Look at the J-20 AESA Radar. 2025
[26] Breaking Defense: Eyeing risk of radar delays, Lockheed proposes new F-35 fuselage design. 2025
[27] The War Zone: You Don't Need A Kill Switch To Hobble Exported F-35s. 2025
[28] Synthetic-Aperture Radar – Technologieübersicht
[29] Lockheed Martin: Switzerland Can Use the F-35A Independently
[30] 350th Spectrum Warfare Wing: F-35 Partner Support Complex
[31] GAO-24-106703: F-35 Sustainment – Costs Continue to Rise While Planned Use and Availability Have Decreased
[32] Eglin AFB: RAF, RAAF reactivate squadron for F-35 reprogramming mission. 2024
[33] Aerospace Global News: The F-35 (probably) doesn't have a physical kill switch – but it doesn't need one! 2025
[34] Aerospace Global News: Why some countries are banned from buying F-35 fighter jets