The CAPTOR radar family provides the main sensor for the Eurofighter Typhoon fighter aircraft. This article gives a deeper insight into the second iteration: CAPTOR-E. This is the second of a two-part series of articles. The first article focuses on the development and capability of the original mechanically steered CAPTOR versions. We recommend reading the previous article first.
As early as 1993, a European program for developing an AESA radar demonstrator for combat aircraft was initiated in the France and the United Kingdom, with Germany joining the effort two years later. Since then, a consortium comprising the companies EADS (now Hensoldt), Selex (now Leonardo) and Thales had been working on AMSAR (Airborne Multirole Solid State Active Array Radar), a generic demonstrator for developing the technology required for an AESA fighter radar. AMSAR had an array with a diameter of 60cm equipped with 1000 T/R (Transmit/Receive) modules on a Gallium-Arsenide (GaAs) basis.
AMSAR’s objective was an airborne AESA technology demonstrator with real-time operation, including Adaptive Beam Forming (ABF) techniques. The target platforms for these new technologies were fast jet aircraft, in particular the Rafale and Eurofighter. The first purpose was to mature E-scan (Electronic scan) technology and demonstrate all operationally-significant attributes and functions of an AESA airborne radar. AMSAR focused on air-to-air performance, including Electronic Counter-Counter Measures (ECCM), and Ground Moving Target Indication (GMTI).
Integration and evaluation of the AESA antenna was carried out between 2005 and 2006 at EADS Defence Electronics in Germany. In 2006 and 2007 the entire radar system was integrated at EADS. The assembled radar was subsequently put through its paces in France against targets and jammers in a simulation environment, followed by ground trials against aerial targets and jammers. During this testing, the radar met or exceeded all required performance thresholds. The ground trials were followed by demonstrator flights, installed on the QinetiQ BAC 1-11 test bed aircraft. A total of 22 flights were performed in 2008 over land and sea in France, Germany, and the UK. The radar performance for air-to-air and air-to-ground modes was assessed against aerial targets (Tornado and Alpha Jet aircraft) and various ground objects. The technologies developed and the data gathered still form a significant basis of both the CAPTOR-E on the Eurofighter and the RBE-2 AA radar on the Rafale.
In addition to AMSAR, a number of government and industry funded technology programmes had been initiated in each of the four Eurofighter nations (United Kingdom, Germany, Italy and Spain) to develop and de-risk key elements of AESA technology including system concepts, processing algorithms and critical components. In 2002, a bilateral effort between the UK and Germany was initiated, named CECAR (CAPTOR E-Scan Risk Reduction). This project aimed to develop an AESA derivative of the existing CAPTOR radar, mounting a new AESA antenna front end to the existing CAPTOR-M back end whilst retaining the interface and some of the hardware of the original system in order to reduce risk and costs. Italy and Spain were also included later on in the program. After some progress with initial concept studies, the resulting radar was to be named CAESAR (CAPTOR AESA Radar).
The CAESAR system was fully integrated and tested in rooflab trials prior to being installed in the aforementioned BAC 1-11 test aircraft. Equal priority was given to robustness and performance to ensure that useful results could be obtained from the earliest flights. Significant effort was expended by all members of the Euroradar consortium to optimise the system in order to satisfy these objectives. Flight tests on a Eurofighter (Development Aircraft DA5) followed in the spring of 2007 in Germany. The bulk of this work was funded by the German MoD and supported by all Euroradar partners as an adjunct to the CECAR programme. These were focused on a set of functional modes of the CAPTOR system. In late 2007, the antenna was remounted on the BAC 1-11 to test advanced waveforms against air and ground targets. In 2008, the radar was primarily tested in Synthethic Aperture Radar (SAR) and simultaneous air-to-air and air-to-ground operations.
While CAESAR offered a low-risk path to upgrade all existing Eurofighters with an E-Scan antenna, historically low budgets and some of the radar’s insufficient performance metrics led to a failure for any nation to adopt the system. The technical concerns mainly revolved around the antenna being a vertically mounted, fixed aperture which would have resulted in an increase in Radar Cross Section (RCS) of the aircraft and lower detection performance at higher off-boresight angles.
These complications delayed significant progress until November 2014, when a €1 billion development and integration contract was signed by the four core Eurofighter partners. The chosen radar standard now included a repositioner (as opposed to the fixed plate of CAESAR). The radar’s name now also was changed to CAPTOR-E. Final test flight campaigns in the following years were funded by Kuwait and Qatar, the first customers of the baseline CAPTOR-E Mk0 radar. The first series production radar sets were delivered to the Kuwait Air Force in late 2021.
Due to greater capability requirements, the core nations had decided to opt for more advanced systems to be fielded for their Eurofighters. Germany and Spain have initiated a cooperation for a further upgrade of the radar, called CAPTOR-E Mk1/ECRS Mk1, whilst the United Kingdom and Italy have chosen a second development route via the ECRS Mk2 for their respective fleets. Details of these upgrade plans will be covered in a seperate article.
In order to manage cost and risks associated with an E-Scan upgrade for the CAPTOR radar, the baseline CAPTOR-E Mk0 retains a significant portion of the original hardware. Both the radar processor and multi channel receiver are kept with slightly modified software.
The E-Scan Antenna is mounted on a repositioner that allows a wider field-of-regard in terms of angular coverage (azimuth) compared to a fixed-plate antenna. Traditional fixed-plate phased array radars are roughly limited to a +-60° scan area, whereas this setup allows for surveillance and detection at an angular coverage of around 180 degrees. This is achieved by the use of Leonardo-developed swashplates. The repositioner features two coupled swashplates which can also change the radar’s elevation from -30° to +30° degrees. It should be noted the repostioner adapts its movement pattern and location based on the currently selected radar mode.
The antenna assembly also houses all relevant connections between the radar’s frontend and it’s backend. This entails all cables and the tubing of the radar’s evaporative cooling circuit, which is routed through the entire backplate of the antenna.
Fighter radar AESA antennas are assembled with hundreds, or even thousands, of T/R modules. The CAPTOR-E radar makes use of modified Hensoldt SMTR modules. SMTR was the result of a development with particular effort into maximising cost-effectiveness with regards to materials, processes and production constraints with efforts starting in the year 2000. The module covers core requirements for various applications such as fighter radars, surveillance radars or for advanced spaceborne SAR satellite systems (TerraSAR-X).
The T/R module’s components are housed on a hermetically sealed PCB. The compact dimensions of 64.5 x 13.5 x 4.5mm result in a weight of less than 15 grams. On the PCB there is an integrated circuit (ASIC) a GaAs-based high power amplifier (HPA), a circulator, a GaAs-based limiter, a GaAs based Low Noise Amplifier (LNA), a GaAs-based phase controller and a GaAs-based amplifier controller. Due its compact design, the power losses during signal processing are very low. However, air cooling is no longer sufficient for these devices and thus the T/R modules are liquid-cooled.
The module covers frequencies from 8GHz to 11GHz (X-Band). An output power of up to 39dBm (8W) can be delivered at the output. Relatively low power consumption leads to an overall efficiency of more than 20%. The typical noise figure of the complete module amounts to <3.0dB over the entire frequency range.