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Rotman Lens

Beam ports
Array ports

Figure 1: Rotman lens with waveguides

Beam ports
Array ports

Figure 1: Rotman lens with waveguides

Beam ports
Array ports

Figure 1: Rotman lens with waveguides

Rotman Lens

A Rotman lens is a passive phase-shifting network for phased array antennas. It consists of a large waveguide system, several feed points (beam ports), and several antenna connections (array ports). The phase shift to the antenna ports is made in real-time by delay differences in the waveguide system. The steering of the antenna pattern can be selected by choosing the port, the number of which determines the possible main directions that are fixed to this beam port. Thus, continuous phase shifting is not possible. The Rotman lens can be constructed by a waveguide system in which the ports are horn radiators. The choice between “E-plane” or “H-plane” sectorial horns decides the polarization direction in the waveguide system. The bandwidth of the Rotman lens is determined by the design of the ports and can be several octaves.

Figure 2: Rotman lens in stripline technology

Figure 2: Rotman lens in stripline technology

Figure 2: Rotman lens in stripline technology

Rotman lenses can also be realized in stripline technology on a dielectric substrate material. However, the thickness of the substrate material should be small compared to the port widths to keep the line widths small and avoid cross-coupling between the lines. This technology is suitable for very high frequencies between 20 and 120 MHz.

The straight wall in Figure 1 one can also be continuously fitted with ports that are wired with a terminating resistor (dummy ports) to avoid interfering reflections on the wall. The length of the supply lines of the beam ports is not critical, but those of the array ports should all have the same length, which is why detour lines are added.

The Rotman lens is a popular beam-forming device, widely employed in the radar industry since its unveiling in 1963 by W. Rotman and R.F.Turner[1]. Sometimes it is also called Rotman-Turner lens after both inventors.

Source:

  1. Patent US3170158A