Duty cycle (or duty factor) is a measure of the fraction of the time a radar is transmitting. It is important because it relates to peak and average power in the determination of total energy output. | DUTY CYCLE Duty cycle or duty factor is a measure of the fraction of the time a radar is transmitting. It is important because it relates to peak and average power in the determination of total energy output. This in turn ultimately effects the strength of the reflected signal as well as the required power supply capacity and cooling requirements of the transmitter. Although there are exceptions most radio frequency RF measurements are either continuous wave CW or pulsed RF. CW RF is uninterrupted RF such as from an oscillator. Amplitude modulated AM frequency modulated FM and phase modulated PM RF are considered CW since the RF is continuously present. The power may vary with time due to modulation but RF is always present. Pulsed RF on the other hand is bursts pulses of RF with no RF present between bursts. The most general case of pulsed RF consists of pulses of a fixed pulse width PW which come at a fixed time interval or period T . For clarity and ease of this discussion it is assumed that all RF pulses in a pulse train have the same amplitude. Pulses at a fixed interval of time arrive at a rate or frequency referred to as the pulse repetition frequency PRF of so many pulse per second. Pulse repetition interval PRI and PRF are reciprocals of each other. PRF 1 T 1 PRI 1 Power measurements are classified as either peak pulse power Poraveragepower Pave. The actual power in pulsed RF occurs during the pulses but most power measurement methods measure the heating effects of the RF energy to obtain an average value of the power. It is correct to use either value for reference so long as one or the other is consistently used. Frequently it is necessary to convert from Pp toPave or vice versa therefore the relationship between the two must be understood. Figure 1 shows the comparison between Pp andPave. pp o Ph 1 PRF ---- PRI p AVE PW or J T or PRI TIME Figure 1. RF Pulse Train The average value is defined as that level where the pulse area above the average is equal
