S4-2.3 Antenna Arrays

Work through these

• Concept of antenna array; two-element array of infinitesimal dipoles

  Two antennas fed together already produce a pattern neither has alone, because their fields add in some directions and cancel in others. That interference is the entire principle behind every array that follows.

• N-element uniform array and the array factor

  The array factor is the abstraction that makes arrays tractable: the total pattern is the single element's pattern multiplied by a factor depending only on the arrangement and the feeding. Get this and the rest of the unit is arithmetic.

• Broadside and end-fire arrays; directivity calculation

  Feeding the elements in phase points the beam sideways to the line of antennas; feeding them with a progressive delay points it along the line. This is beam steering with no moving parts, and directivity follows from the geometry.

• Non-uniform arrays: binomial and Tschebyscheff distributions (qualitative)

  Feeding the elements unequally trades a wider main beam for smaller sidelobes, and the binomial and Tschebyscheff distributions are two named points on that trade. The trade itself is the design decision, not the distributions.

• Phased antenna arrays (qualitative)

  Changing the phase fed to each element electronically steers the beam in real time, which is what radar and modern cellular base stations do. This item is where the unit connects to hardware people are building right now.