Radar Systems – AN/APG-81 vs. AN/APG-85

¶ 4. Radar Systems – AN/APG-81 vs. AN/APG-85

¶ The Technology Leap: GaAs to GaN

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]:

Sources: Qorvo GaN/GaAs Analysis [21], Military Embedded Systems [22]

¶ AN/APG-85 – Operational Improvements

The AN/APG-85, also developed by Northrop Grumman, is planned for F-35 Lot 17 and subsequent production batches [23]:

• Detection Range: Estimated ~50% increase over APG-81
• SAR Resolution: Sub-metre capability through ultra-wideband operation
• Electronic Warfare: Massively increased burn-through capacity
• LPI: Ultra-wideband spreading reduces spectral power density

¶ TR-3 Dependency

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].

¶ Strategic Context

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.

¶ Implications for Switzerland

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.

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¶ Radar Explained in Plain Language

¶ What Does a Fighter Aircraft Radar Do?

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].

¶ AESA Technology: Thousands of Mini-Transmitters Instead of One Large Antenna

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].

¶ AN/APG-81: The Current Generation

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]:

• Air-to-Air: Long-range detection with track-while-scan
• Air-to-Ground: SAR mapping and ground moving target indication (GMTI)
• Electronic Warfare: Directed energy for jamming enemy radars
• LPI Mode: Frequency agility to avoid own detection

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].

¶ AN/APG-85: The Next Generation

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:

• ~50% More Range: Enemy aircraft are detected significantly earlier [6]
• Better Image Resolution: Sub-metre resolution in ground mapping – individual vehicle types can be distinguished from great distance [28]
• Stronger Jamming Capability: The higher transmission power enables overcoming enemy radar systems from a safe distance (burn-through) [22]
• Harder to Detect: The signal can be spread across a broader frequency band, making detection by enemy reconnaissance more difficult [20]

¶ Why Switzerland Receives the AN/APG-81

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:

• Production Lot Assignment: The Swiss aircraft originate from production lots prior to full APG-85 integration (Lot 17+)
• Export Restrictions: GaN technology for military applications is subject to strict US export controls [7]
• Prioritisation: US armed forces and close allies (Five Eyes) receive new technologies first

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].

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¶ Mission Data Files – The F-35's Brain

¶ What Are Mission Data Files?

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].

¶ What Signatures Do the MDFs Contain?

The MDFs contain parametric data – so-called electronic signatures – on a multitude of enemy and allied systems [27, 29]:

• Radar Systems: Frequency bands, pulse repetition rates, scan patterns of enemy ground and airborne radars
• Surface-to-Air Missile Systems: Guidance and fire control radar profiles (e.g. S-300, S-400, Patriot)
• Air-to-Air Missiles: Seeker head characteristics and guidance signatures
• Cruise Missiles and Drones: Radar and IR signatures of cruise missiles and UAVs
• EW Systems: Electronic warfare systems and their frequency profiles
• IFF Data: Friend-or-foe identification codes of allied forces

¶ Why Are MDFs Critical?

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]:

• No automatic threat classification (the pilot sees signals but cannot classify them)
• No effective electronic warfare (countermeasures require signature-specific responses)
• No optimised route guidance through hostile airspace

¶ The "Blue Line": Optimal Route Through Hostile Airspace

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].

¶ F/A-18 vs. F-35 – The Critical Difference in Signature Integration

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:

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.

¶ Partner Hierarchy: Switzerland Stands at the End of the Queue

Within the F-35 programme, there is a clear hierarchy in access to MDF resources [27, 30]:

1. US Armed Forces (USAF, USN, USMC): Highest priority, own reprogramming laboratories
2. ACURL Partners (Australia, Canada, United Kingdom): Operate their own reprogramming laboratory with personnel in Florida; have a certain degree of autonomy [32]
3. NIRL Partners (Norway, Italy): National reprogramming capabilities under development [32]
4. FMS Customers (Switzerland, Finland, Poland, etc.): Receive standardised MDF packages; no own reprogramming capabilities [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 Its Own MDF Autonomy

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].

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¶ Consequences of US Support Withdrawal

¶ Degradation Process

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]:

¶ Information Disclosure and Transparency Requirement

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.

¶ Political Filters

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].

¶ Time Delays in MDF Updates

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?

¶ Historical Precedents

That the USA uses arms cooperation as a political lever is not a theoretical consideration but historical reality [27, 34]:

• Turkey (2019): As a Level 3 partner of the F-35 programme, Turkey was completely excluded from the programme after purchasing the Russian S-400 system. Deliveries were cancelled, system access blocked, Turkish industry removed from the supply chain.
• United Arab Emirates: The USA suspended the F-35 sale due to concerns about Huawei 5G technology and proximity to China. The UAE broke off negotiations, citing unacceptable sovereign restrictions.
• Pakistan (F-16): Although Pakistan possesses F-16 jets, these are subject to strict operational restrictions and end-use monitoring that limit their use against certain targets.

¶ F/A-18 vs. F-35 in a Crisis Scenario

The comparison illustrates the fundamental difference in operational capability:

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¶ References

[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