JED - February 2009 - 51

This is less than the 500-meter jamming link distance, so two-ray propagation applies. The jammer ERP is 37 dBm (5 Watts). The jamming link loss is: LOSS J = 120 + 40 log (dist) – 20 log (hT) – 20 log (hR) LOSS J = 120 + 40 log(0.5) – 20 log(0.5) – 20 Log (2) = 120 - 12 + 6 – 6 = 108 dB The J/S ratio is: J/S = ERPJ – ERPS – LOSS J + LOSSS = 37 - 32 – 108 + 136 = 33 dB A high J/S is achieved with a low-power jammer because the jammer is very close to the target receiver. LOSSS = 32.4 + 20 log(dist) + 20 log(frequency) = 32.4 + 20 log(20) + 20 log(5000) LOSSS = 32.4 + 26 + 74 = 132.4 dB The jammer is 10 km from the UAV, so the jamming link loss is: LOSS J = 32.4 + 20 log(dist) + 20 log(frequency) = 32.4 + 20 log(10) + 20 log(5000) LOSS J = 32.4 + 20 + 74 = 126.4 dB Because the receiving antenna on the UAV is a whip, it will have equal gain toward the ground station and the jammer. Thus, the jamming-to-signal ratio is given by: J/S = ERPJ – ERPS – LOSS J + LOSSS = 60 - 50 – 126.4 + 132.4 = 16 dB The Journal of Electronic Defense | February 2009 Jam Microwave UAV Link Next, we consider jamming UAV links from the ground. A UAV must have a command link (uplink) from the control station and a data link (downlink) back to the control station. We will cover the jamming of each link. Both links operate at approximately 5 GHz. Figure 3 shows the UAV command link. The control station has a 20-dBi dish antenna that has 20-dBi gain and 15-dB side lobe isolation. That is, the average side lobe is 15 dB below the main beam boresight gain (which is the gain toward the UAV). The uplink transmitter has 1 Watt transmitter power. The UAV is 20 km from the ground station and has a 3 dBi whip antenna. The downlink transmitter (on the UAV, in Figure 4) outputs 1 Watt into its antenna. The jammer has a 10-dBi log periodic antenna and has 100 Watts of jamming power into its antenna. Figure 4: Jamming a UAV down link requires transmission to the ground station location. 51 Data Link Now consider jamming the data link as shown in Figure 4. The jammer is 20 km from the control station and its antenna is directed into a side lobe of the control station antenna. What J/S is achieved? The data link transmitter has 1-Watt transmitter power and a 3-dBi antenna. The desired signal link ERP is 30 dBm (1 Watt) + 3 dBi = 33 dBm. The desired signal link loss is the same as calculated for the command link, 132.4 dB. The jammer ERP as calculated above is 60 dBm. Because the jammer is 20 km from the control station, the jamming link loss is the same as the desired signal loss (132.4 dB). The control station antenna is directional. Its gain toward the UAV (GR) is 20 dBi, but its gain in the direction of the jammer (GRJ) (which is in a side lobe) is 15 dB less, or 5 dBi. Thus, the jamming-to-signal ratio is given by the formula: J/S = ERPJ – ERPS – LOSS J + LOSSS + GRJ – GR J/S = 60 - 33 – 132.4 + 132.4 + 5 -20 = 12 dB Figure 3: Jamming a UAV up link requires transmission to the UAV. Because both links operate at microwave frequencies, line of sight propagation applies. Command Link First consider jamming the command link, with the jammer antenna directed toward the UAV as shown in Figure 3. What J/S is achieved? The desired signal ERP is 30 dBm (1 Watt) + 20 dB = 50 dBm The jammer ERP = 50 dBm (100 Watts) + 10 dB = 60 dBm Since the command station is 20 km from the UAV, the command link loss is: What’s Next Next month, we will look at jamming cell phones. For your comments and suggestions, Dave Adamy can be reached at dave@lynxpub.com. a

JED - February 2009

Table of Contents for the Digital Edition of JED - February 2009

JED - February 2009
Contents
The View From Here
Calendar
From the President
The Monitor
Washington Report
World Report
Charting the Course of Indian EW
What's Next in Data Recorders?
Technology Survey: RWR/ESM Systems
EW 101
2009 AOC Industry and Institute/University Member Guide
JED Sales Offices
Index of Advertisers
JED Quick Look
JED - February 2009 - JED - February 2009
JED - February 2009 - Cover2
JED - February 2009 - 3
JED - February 2009 - Contents
JED - February 2009 - 5
JED - February 2009 - The View From Here
JED - February 2009 - 7
JED - February 2009 - Calendar
JED - February 2009 - 9
JED - February 2009 - 10
JED - February 2009 - 11
JED - February 2009 - From the President
JED - February 2009 - 13
JED - February 2009 - 14
JED - February 2009 - The Monitor
JED - February 2009 - 16
JED - February 2009 - 17
JED - February 2009 - 18
JED - February 2009 - 19
JED - February 2009 - 20
JED - February 2009 - 21
JED - February 2009 - Washington Report
JED - February 2009 - 23
JED - February 2009 - World Report
JED - February 2009 - 25
JED - February 2009 - Charting the Course of Indian EW
JED - February 2009 - 27
JED - February 2009 - 28
JED - February 2009 - 29
JED - February 2009 - 30
JED - February 2009 - 31
JED - February 2009 - 32
JED - February 2009 - What's Next in Data Recorders?
JED - February 2009 - 34
JED - February 2009 - 35
JED - February 2009 - 36
JED - February 2009 - 37
JED - February 2009 - 38
JED - February 2009 - Technology Survey: RWR/ESM Systems
JED - February 2009 - 40
JED - February 2009 - 41
JED - February 2009 - 42
JED - February 2009 - 43
JED - February 2009 - 44
JED - February 2009 - 45
JED - February 2009 - 46
JED - February 2009 - 47
JED - February 2009 - 48
JED - February 2009 - 49
JED - February 2009 - EW 101
JED - February 2009 - 51
JED - February 2009 - 52
JED - February 2009 - 2009 AOC Industry and Institute/University Member Guide
JED - February 2009 - 54
JED - February 2009 - 55
JED - February 2009 - 56
JED - February 2009 - 57
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JED - February 2009 - 85
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JED - February 2009 - 87
JED - February 2009 - 88
JED - February 2009 - Index of Advertisers
JED - February 2009 - JED Quick Look
JED - February 2009 - Cover3
JED - February 2009 - Cover4
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