Flat-Panel Grid Antenna

1. Flat-Panel Grid Antenna R Struzak

2. This antenna offers ~18 dBi gain, VSWR <1.5, and bandwidth ~10% • It consists of 19 vertical half-wave (L/2) and 18 horizontal full-wave (L) radiators located a quarter-wave above a flat reflector. At large distances, the fields of vertical radiators add in-phase, and the fields of the horizontal conductors cancel. (patented by Kraus, http://www.elmag5.com/gridflat.htm, accessed 21-02-2003) R Struzak

3. 19 ‘real’ elements + 19 elements representing the reflector give a total number of 38 antenna elements • At the direction at which all signals add in phase, the resultant field strength is 38 greater than that produced by a single element. Thus, the array multiplication factor = 10* log(38) = ~16 dB • With individual antenna gain ~ 2dB added, it gives the total antenna gain of about 18 dB R Struzak

4. Schematic diagram of the radiating grid. The array is fed at one point (marked by a circle) by a 50 ohm coaxial cable. Its inner conductor traverses the ground plane through a hole. The outer conductor is bounded to the ground plane. R Struzak

5. The total dimensions of the radiating grid are 4L x 2.5L (L = the wavelength) • At 2.4 GHz (L=12.5 cm) it gives 50 cm x 31.75 cm. (Physical radiator dimensions may be shorter if a dielectric is applied between the grid and reflector) In that case, the dimensions of the reflector must be larger, but Kraus (on the webpage quoted) does not give any indications. If we add L to each side of the grid, the radiator dimensions are 75 cm x 57 cm R Struzak

6. Individual radiator lengths:(L/2): 19 x 6.25cm = 118.75 cm(2L): 2 x 25cm = 50 cm(3L): 2 x 37.5cm = 75 cm (4L): 2 x 50cm = 100 cm • Total length: 343.75 cm R Struzak

7. Proposed construction • Kraus does not give any indications on how to fix mechanically the radiating grid over the reflector • For simplicity, I propose using a standard thermo-isolation plate (polyester or similar foam), glued (or fixed in another way) to the reflector • I propose also to use another (identical) plate as the external cover of the grid R Struzak

8. Main components 1: 2: 3: Length ~75cm Width ~60cm Height ~3cm Dielectric cover (foam) Dielectric substrate (foam) The supporting metal sheet (ground plane). The coaxial cable and the fixture are not hown. The fold along 2 sides is to assure a rigidity. • Notes • The dielectric material is to be checked in a microwave oven against losses • The radiating grid is fixed between the cover and the substrate plates • All the components shown have approximately the same dimensions Note: R Struzak

9. Cut across the antenna • Flat reflector (metal sheet) 75x60 cm + L/4 flanges • Cover (dielectric foam) 75x60 cm • Substrate (dielectric foam) • 75x60 cm • Radiators (cupper wires or paper-thin strips ~4mm wide) • Coaxial cable connection (amplifier output) Note: fixtures are not shown 4 2 3 1 5 R Struzak

10. Wires: • ‘0’ frame 9L: 112.5cm x 1 = 112.5 cm • ‘U’ frame 4L: 50cm x 2 = 100 cm • ‘U’ frame 3L: 37.5cm x 2 = 75 cm • ‘I’ wire L/2: 6.25cm x 9 = 56.25 cm • Total length: 343.75 cm R Struzak

11. Material list 1x metal sheet ~81x~67cm (could be simulated by a cardboard plate covered by a thin copper foil) 2x thermo-isolation foam plate 75x60x2.5cm 1x quality coaxial cable (or connector) 3.5m copper wire 1mm (or copper tape) Cost: ~10-20 euro (material, except fixation & cable/ connector) + cost of ~1 hour work R Struzak