Recommendation ITU-R SM.1138, to which the RR makes reference, provides formulas to be used to calculate the necessary bandwidth when required by the RR. However, the only formula applicable to radar gives results that can vary by a factor of ten based on a constant chosen by the user. Recommendation ITU-R SM.853, considering that the formulas in Recommendation ITUR SM.1138 are incomplete, recommends numerous supplemental formulas. 2.1 Un-modulated radar pulses Recommendation ITU-R SM.853 provides guidance for determining the necessary bandwidth (20 dB below the peak envelope value) for rectangular and trapezoidal pulses. For these systems, the necessary bandwidth is the smaller of: BN (35) where is the pulse duration (at half amplitude) and is the rise time, both in seconds. t 2.2 Other modulations Necessary bandwidth formulas for frequency modulated pulse radars, frequency hopping radars, and CW radars, both un-modulated and frequency modulated are presented below. For frequency modulated pulse radars, the necessary bandwidth (20 dB bandwidth) formula exceeds the symmetrical trapezoidal pulse case (equation (35)) by twice the frequency deviation Bc: (36) The formula for frequency hopping radars has an additional term the maximum range over Bs, which the carrier frequency will be shifted: (37) Although Recommendation ITU-R SM.1138 gives no formula under the heading of “continuous wave emission” (here meaning a carrier without modulation) a realistic value of necessary bandwidth for un-modulated continuous wave (CW) radars depends on the frequency tolerance and noise. For frequency modulated CW radars, the necessary bandwidth is twice the maximum Bd, frequency deviation: (38) 2.3 Typical values of necessary bandwidth Table 23 shows typical necessary bandwidths, followed by the ranges of the necessary bandwidth values, for four types of radars. 23 Typical BN Type of radar Range of BN (MHz) Fixed radiolocation radar 6 20 kHz to 1.3 GHz Mobile radiolocation radar 5.75 250 kHz to 400 MHz Airport surveillance radar 6 2.8 MHz to 15 MHz Weather radar 1 250 kHz to 3.5 MHz
Recommendation ITU-R SM.1138, to which the RR makes reference, provides formulas to be used to calculate the necessary bandwidth when required by the RR. However, the only formula applicable to radar gives results that can vary by a factor of ten based on a constant chosen by the user. Recommendation ITU-R SM.853, considering that the formulas in Recommendation ITUR SM.1138 are incomplete, recommends numerous supplemental formulas. 2.1 Un-modulated radar pulses Recommendation ITU-R SM.853 provides guidance for determining the necessary bandwidth (20 dB below the peak envelope value) for rectangular and trapezoidal pulses. For these systems, the necessary bandwidth BN is the smaller of: (35) where t is the pulse duration (at half amplitude) and is the rise time, both in seconds. 2.2 Other modulations Necessary bandwidth formulas for frequency modulated pulse radars, frequency hopping radars, and CW radars, both un-modulated and frequency modulated are presented below. For frequency modulated pulse radars, the necessary bandwidth (20 dB bandwidth) formula exceeds the symmetrical trapezoidal pulse case (equation (35)) by twice the frequency deviation Bc: (36) The formula for frequency hopping radars has an additional term Bs, the maximum range over which the carrier frequency will be shifted: (37) Although Recommendation ITU-R SM.1138 gives no formula under the heading of “continuous wave emission” (here meaning a carrier without modulation) a realistic value of necessary bandwidth for un-modulated continuous wave (CW) radars depends on the frequency tolerance and noise. For frequency modulated CW radars, the necessary bandwidth is twice Bd, the maximum frequency deviation: (38) 2.3 Typical values of necessary bandwidth Table 23 shows typical necessary bandwidths, followed by the ranges of the necessary bandwidth values, for four types of radars. 23 Type of radar Typical BN (MHz) Range of BN Fixed radiolocation radar Mobile radiolocation radar Airport surveillance radar Weather radar 6 5.75 6 1 20 kHz to 1.3 GHz 250 kHz to 400 MHz 2.8 MHz to 15 MHz 250 kHz to 3.5 MHz
R-REC-SM.1541-5-201308-S!!MSW-E.docx