Wideband frequency synthesis for broadband communications

To mitigate intentional and unintentional in-band interference problems in today's navigation and communication frequency bands, spread-spectrum techniques such as direct sequence (DS) or frequency hopped (FH) systems are frequently used. ^{1 2} A key component of an FH spread-spectrum system is the frequency hop synthesizer used to generate the hop frequencies. Spreading of the communication or the navigation signals is done over a wider transmission bandwidth to lessen the impact of any intentional or unintentional interference. Typically, frequency synthesizers are driven by a secure code generator called Transec (transmission security) to avoid follow-on interference. The wideband frequency synthesizers must be designed to support wideband communication data rates and waveforms employed with adequate margin to close the link. In this paper, issues related to FH synthesizer implementation in modern survivable communications such as the required frequency step size, hop rate, hop bandwidth, phase noise, spreading process gain, and the settling time are addressed. A typical FH synthesizer implementation and the associated link analysis example is given in this paper. FH spread spectrum helps in the link closure in interference condition.