Shaped Sector Antennas for LMDS and MMDS Hubs

REMEC Magnum Inc.
San Jose, CA

A line of hub sector antennas for the 24 to 42 GHz local multipoint distribution system (LMDS) and 2.1 to 2.7 GHz multichannel multipoint distribution system (MMDS) wireless access frequency bands has been recently introduced. The goal of the designs is to provide the most uniform coverage possible within a sector while minimizing interference in adjacent cells. An exact electromagnetic formulation has been combined with artificial intelligence (AI) and a set of mechanical constraints to obtain the best possible antenna solution. The production constraints guarantee a cost-effective form factor. The addition of AI allows the electromagnetic formulation to be transformed from an antenna analysis tool to a design synthesis tool. The result is a family of antennas with previously unimaginable mechanical and performance characteristics.

Fig 1 Elevation pattern characteristic Each antenna’s elevation pattern electric field follows an approximately cosecant-shaped distribution in order to provide uniform coverage as a function of distance from the hub mounting. Hence, a relative high field is directed toward the horizon relative to the field aimed at locations closer to the hub, as shown in Figure 1 . The patterns have uniform coverage in azimuth throughout the sector. Additionally, the units reduce the radiation spillover into adjacent cells and, hence, lessen interference.

Fig 2 Azimuth pattern characterisitcs Because the antennas do not waste power by directing it in unwanted directions they exhibit high gain relative to comparable products. This advantage is especially prevalent when comparing the worst-case performance within the sector to that of previously offered hub antennas, as shown in Figure 2 . The new hub antennas are available in both vertical and horizontal polarizations. They typically provide better than 50 dB of cross-polar rejection over the entire cell. As the popularity of wireless broadband increases, these antenna characteristics offer dramatically improved carrier-to-interference ratios when compared to more conventional solutions. The antennas are available in a variety of azimuth standard beamwidths, including 45º, 60º and 90º. Custom beamwidth and form factors are available upon request.

Fig 3 The LMDS hub antenna's radiation pattern raster scan Due to the physical nature of the antenna, the patterns in regions off the principle planes are simply the product of the patterns on the principle planes; that is, the azimuth and elevation angles are separable, such that

E(q,f) = E(q) x E(f)

where

q = elevation angle

f = azimuth angle

Hence, the antenna maintains its desirable azimuth patterns for all elevations angles, regardless of the distance from the hub. Figure 3 shows a raster scan of a 90º LMDS hub.

Fig 4 The MMDS hub antenna The LMDS versions of the antenna have a form factor similar to a typical LMDS radio in order to provide a compact integrated solution. The antennas are available with UL-registered heated radomes. (A photograph of the LMDS hub antenna was shown previously.) The MMDS versions are constructed out of lightweight sheet metal, and the brackets allow pole mounting by a single installer. In addition, the antenna provides the 3 kW CW power handling commonly required for video distribution hubs. The MMDS hub geometry is shown in Figure 4 . The antennas are particularly effective when used with the company’s line of low sidelobe CPE antennas. Additional information may be obtained via e-mail at sales@remecmagnum.com.