Timed Arrays

2RF SIGNALS

Antenna arrays started as very narrow band antennas, in fact continuous wave (CW or single frequency). Historically, this approach worked well, because signals and hardware were narrow band and methods of analyzing and synthesizing arrays were also narrow band and steady state. Many simple analytical expressions exist for narrow band RF systems and work well for pedagogical purposes. In today’s world, however, signals are very complex, fast switching, and broadband. Correspondingly, antenna arrays are huge, adaptive, broadband, and complex. The approach to designing and analyzing these new antenna array systems requires numerical simulations as well as experimental measurements that surpass the simpler analytical, steady-state approaches of the past.

This chapter lays the foundation for wide-band signals. Normally, antennas and signals do not appear in the same book, but timed arrays are designed for realistic time-varying signals and scenarios, so the signal is a critical part to understanding the antenna. The first part of this chapter covers the basics of baseband and passband RF signals. The last part of the chapter deals with polarization and bandwidth.

2.1 THE CARRIER AND MODULATION

This section presents two types of signals: a carrier signal that is a high-frequency sinusoid and a lower frequency information (baseband) signal that modulates the carrier. The carrier converts the baseband signal with its low-pass frequency content to a passband signal with ...