The invention relates to a panei, paπicuiariy a panel for use in building.

.Air traffic control and the_ difficulties inherent in an increasingly densely packed commercial aircraft environment have been widely discussed internationally. Aircraft are controlled by ground personnel using what are known as "Primary Radars '. These operate in X-Band and are manufactured by many companies. Their main function is to plot the position and height of an aircraft; information which, using software, is convened into a permanently updated three dimensional track and is then presented to Air Traffic Controllers on the ground.

The need to identify each aircraft individually has been achieved through the use of "Secondary Radar ^" operating at a much lower frequency (between 1 and 1.1 ghz) . This radar transmits on one requency and receives on another and again through using software, is able to display automatically the individual track number of the aircraft alongside the three dimensional position known through the Primary Radar. This system is generally known by the acronym IFF. Together these two systems provide course, speed, height and identity of all airborne contacts.

Serious problems have arisen with Secondary Radars due to interference from structures, vehicles and other solid objects which are irradiated naturally during operations. False and at times multiple radar returns are presented to the operator which, in some instances can be reduced by the incorporation of very expensive software. The effects of these unwanted radar returns are to confuse the operator ^' s picture and at times through multipath effects to misidemify aircraft in the air traffic control system. The dangers inherent from these effects are obvious.

It is an object of the invention to seek to mitigate these disadvantages.

According to a first aspect of the invention there is provided a panei for use in building, comprising a moulded body and an absorber for incident electromagnetic energy in the radar range of frequencies incorporated with the body during moulding thereof.

The absorber may comprise a film of material for absorbing the incident energy.

The film may be incoφorated within the body.

The film may be about 20mm from a boundary surface of the panel.

The body may comprise a concrete body.

The body may be formed by casting.

The film may comprise through apeπures whereby to provide a key for the concrete.

There may also be reinforcement means in the body.

The reinforcement means may suitably comprise a stainless steel mesh.

The reinforcement means may further comprise stainless steel bards.

According to a second aspect ox the invention there is provided a panel as hereinbefore defined, connected with a substantially similar panei whereby to provide at least pan of a building structure.

According to a third aspect of the invention there is a building incorporating a plurality of paneis as hereinbefore defined connected together.

According to a fouπh aspect of the invention there is provided a method of making a panel for building, comprising providing a mould, providing a mouidable material for providing a moulded body of the panel, providing an absorber for incident electromagnetic energy in the radar range of frequencies, placing the absorber in the mould and moulding the material to provide a panel with the absorber incorporated in situ in the body.

A panel embodying the invention is hereinbefore described, by way of example, with reference to the accompanying drawings.

Fig.l is a section through pan of atypical panel used in building: and

Fig.2 is a section showing schematically a panel according to the invention.

Referring to the drawings, there is shown a panel 1 for use in building, comprising a moulded body 2, in the embodiment of cast concrete, and an absorber 3 uch as a sheet, film or the like of a material such as bavfoil, for absorbing incident electromagnetic energy in the radar range of frequencies, the absorber 3 being incoφorated in the body 2 during moulding of the body.

The panel 1 is typically cast, by pouring the concrete into a mould (not shown ⁾ and letting it set or cure. The absorber 3 is laid in the mould and incorporated as an integral pan of the panel 1 by pouring in the concrete. To provide for passage of the concrete during pouring to all pans of the mould so that the formed panel 1 has the desired external shape as determined by the mould, and to act as a kev, there are through aϋeπures tnot shown) in the film.

The poured concrete can then pass through the apertures and when it sets it keys the film 3 in the body 2 of the panel. The film 3 is set about 20mm from a boundary face 4 of the panel which in use is a front external surface of the panel

1.

Reinforcement means 5 such as a stainless steel mesh and/or bar can be incoφorated during moulding too.

In use, a plurality of similar panels 1 are assembled using fixings 6, 7 (which may also be cast in during moulding) to form say a wall of a building, with the suriace 4 being an external suπace. Incident electromagnetic energy is then absorbed, and does not inteπere with ground radar such as is used in air traffic control operations.

Placing the absorber film 3 within the body 2 of the panei 1 so that it becomes integral with the panei 1 beiow an external surface 4 thereof protects the film against damage and ensures that it is in a desired position in relation to the building. It will be understood that the panel ^er se acts as an absorber without the need to use additional mosaics of absorber tiles.