A well-known method of increasing the gain and lower the half-power beamwidth of the radiation pattern is to replace the single radiator by an antenna array. Its application in communications is interesting if, for example, a point-to-point connection is to be established. It is of special interest in MIMO systems, where a channel capacity might be increased if multiple radiators, either on the transmit or the receive side (or both) are used [75]. In radar systems an application of arrays is more common in order to achieve lower half-power beamwidths, which in general are used to increase the angular resolution.

In this chapter, specific design issues of UWB antenna arrays are described. According to the methods previously described, the frequency and time domain models are explained and used for the practical array design. In the second part of the chapter an extension of the monopulse technique to UWB systems is described, based on the array theory.

Array factor in UWB systems

The resulting array radiation pattern depends on the following parameters:

1. • number of array elements N

2. • distance between the elements d

3. • frequency f

4. • excitation coefficients – amplitude and phase

5. • radiation pattern of a single array element EF(f, ψ).