www.radartutorial.eu www.radartutorial.eu Radar Basics

Van Atta Reflector Array

Figure 1: Passive linear Van Atta Array with incident wave (red) and back-radiated wave (blue)

Figure 1: Passive linear Van Atta Array with incident wave (red) and back-radiated wave (blue)

Van Atta Reflector Array

The Van Atta reflector array is realized in a flat design array in which the elements are interconnected to re-radiate received energy back in the direction of arrival. This array reflects over a wider angle than the typical corner reflector but is sensitive only to incident waves in the frequency band. It consists of several antenna elements (for example dipoles or patch antennas), which are symmetrically connected on the backside with lines of the same length. This ensures that the antenna element which first receives the incident wave then transmits the last one signal received by the opposite antenna element. As with a Phased Array antenna, this causes the re-radiated beam to be tilted in the direction of the incident wave.

Figure 2: Principle representation of a four-by-four Van Atta array of sixteen patches (the line lengths have not been adjusted).

Figure 2: Principle representation of a four-by-four Van Atta array of sixteen patches (the line lengths have not been adjusted).

The radar cross-section of a passive Van Atta array is:

(1)

  • σ = radar cross-section
  • n = number of antenna elements
  • λ = wavelength of the radar

The bandwidth is limited to the bandwidth of the antenna elements used. Circular polarization is possible if the antenna elements support it. However, patch antennas then require double the number of interconnect lines, which becomes possible only with multilayer printed circuit boards. Whole radiator groups can also be used as antenna elements. An areal distribution with centrally symmetrical cabling is also possible (see Fig. 2). This steers the incoming wave not only in the azimuth but also in the elevation angle.

Figure 3: Active Van Atta array with 4 antenna elements

Figure 3: Active Van Atta array with 4 antenna elements

Van Atta Arrays can also be used actively by inserting amplifiers into the cable connections. For this purpose, either the directions of the cables used bidirectionally in the passive variant must be split with circulators or separate antenna Arrays must be used.

Active Van Atta Arrays can be used for stealth and deception. Additional mixers in the amplifiers can also be used to modulate the returned signal and, for example, to fool the scanning radar into thinking it is flying at a very high radial speed or in the direction away from the radar. Additional phase shifters may also be used, which then make it possible to re-radiate a signal with a phase opposite to the passively reflected echo signals and thus reduce the effective backscatter area of the object to be camouflaged.

Lester Clare Van Atta (April 18. 1905 – March 16. 1994) technical Director of the Hughes Research Laboratories was the inventor and name giver of this retroreflector. He applied the retroreflector for a patent in 1955.