(Neptune) was the code name of a series of low-to-mid-VHF band airborne intercept radar devices developed by Germany in World War II and use in several types of aircraft. They were usually combined with a "backwards warning device", indicated by the addition of the letters "V/R" , meaning Forward/Backward). Working in the metre range, Neptun was meant as a stop-gap until scheduled SHF-band devices became available (for instance the FuG 240/E cavity magnetron-based FuG 240 Berlin AI radar).Aders, p. 269
Transceiving antennas used for on twin-engined night fighters usually used a (stag's antlers) eight-dipole array with shorter elements than the previous 90 MHz SN-2 radar had used or as an experimental fitment, the 90°-crossed twin-element set Yagi based single-mast-mounted array.
Variants
FuG 216: Experimental series to plan the further development. Installed in Fw 190 A-6/R11 and Bf 109 G-6 The aircraft were used by NJGr 10 until March 1944, after which some machines of 6./JG 300 () were equipped.Aders, S. 210 Manufacturer: (FFO, German for airborne radio research institut in Bavaria) R1 version (backwards warning device) Frequency: 182MHz Power: 1.0kW Transmitting and receiving antennas each consist of twin dipoles, mounted under and above the wings, respectively Single display device with distance readout V version (for single engined night fighters) Frequency: 125MHz Power: 1.2kW Range: 500 to 3,500m Antennas in the form of spikes or (Fw 190) as "antlers" on right and left wings
FuG 217: Installed mainly in Ju 88 G-6, only a few Bf 110 G-4, He 219 or Me 262 received the . It could be combined with the additional device to automatically measure the target distance and fire the guns at a set range.Aders, S. 268 Manufacturer: FFO R2 version (backward warning device) J2 version (for single-engined night fighters) V/R (combined night fighter and backward warning device for two-engined fighters) Two switchable frequencies: 158 and 187MHz Search angle: 120° Range: Spike or "antler" antennas
FuG 218: mass-produced Manufacturer: Siemens / FFO R3 version (backward warning device) J3 version (for single-engined night-fighters) V/R version (combined night fighter and backward warning device for two-engined fighters)
Six switchable frequencies: 158 to 187MHz Search angle: 120° Range: Weight: R3 and J3 with spike antennas and V/R with "antler" antennas. G/R version (combined night fighter and backward warning device for two-engined fighters) Only one single device built, replacing the 2kW transmitter with a 30kW transmitter. Range increased to up to . This device was intended for the Dornier Do 335. "Antler" antennas.
See also List of WW II Japanese airborne radar systems
References
(1) TME 11-219 Directory of German Radar Equipment Gebhard Aders: Geschichte der Deutschen Nachtjagd, Motorbuch publishing corporation, 1977, :File:Neptun FuG 217.pdf