JED - October 2017 - 67

E W101
continued from page 46
GM is the main beam boresight gain of the radar antenna in dB

Jammer
88 dBm
ERP

Radar
being
jammed

RCS = 10 m2
15 km

XMTR

Radar's target

If we add a loss factor for 1° pointing error by the jamming antenna on the satellite, there is an additional loss
of 5.6 dB (using the formula developed in last month's "EW
101" column, but at the higher frequency of the radar).
This makes the J/S = -19.3 dB

THE JAMMING ADEQUACY

It must be said that -19.3 dB J/S is a pretty sad job of
Fig. 2: The jamming geometry and the ERPs of the desired signal and jamming
2: The jamming
geometry
theratio.
ERPs of the desired signal and jamming jamming. Now, let's look a few changes in the problem that
transmitters
determineand
the J/S
would improve the quality of the jamming:
One more consideration is that the radar is aimed at its target - not at the satellite. Thus, the satellite must jam into the
side lobes of the radar antenna.
For this problem, let the radar cross section (RCS) of the
radar's target be 10 m2.

What if we are protecting a low RCS asset: If the radar's target has a 10-4 meter RCS (i.e. a stealth aircraft): The satellite
jammer would provide a very comfortable 30.7 dB J/S.
What if the satellite jammer has 10 dB more tube power: The
J/S would be increased by 10 dB.

THE JAMMER
Let's use the same 2-meter jamming antenna we used last
month. At 5 GHz, this antenna would have 38 dB gain (using
the formula employed above for the target radar).
If the jammer transmitter has an output power of 100 Watts,
the ERP of the jammer will be:
50 dBm + 38 dB = 88 dBm

THE JAMMING EQUATION
Figure 2 shows the jamming geometry.
From several earlier "EW 101" columns (for example December 2009), the jamming-to-signal ratio for remote radar jamming is given by the formula:
J/S = 71 + ERPJ - ERPS + 40 log RT -
20 log R J + GS - GR - 10 log RCS
Where: J/S is the jamming to signal ratio in dB
ERPJ is the ERP of the jammer in dBm
ERPS is the ERP of the radar in dBm
RT is the range from the radar to its target in km
R J is the range from the jammer to the radar in km
GS is zzthe side-lobe gain of the radar antenna in dB

What if the satellite jamming antenna were increased to 4
meters in diameter: The jamming antenna gain would increase
by 5. 8 dB, providing an additional 5.8 dB of J/S.

DURATION OF JAMMING
Remember that the jammer is over the horizon to the
jammed radar for only 19.3 minutes. This may be adequate for
some tactical situation, but continuous jamming would require
several satellites. What if we use a synchronous satellite? The
problem is that a synchronous satellite would be about 37, 000
km from the jammed radar.
This will reduce the jamming signal (hence the J/S) by 33
dB relative to jamming from a satellite in low Earth orbit.

WHAT'S NEXT
Next month, we will start a new series of columns. (No
more spherical trig for a while.) We will discuss the newgeneration surface-to-air missiles and guns and their associated radars. We will look at the specifications available
from open literature and associate the new threat capabilities with the EW techniques and systems they will dictate.
For your comments and suggestions, Dave Adamy can be
reached at www.lynxpub.com. a

The Journal of Electronic Defense | October 2017

J/S = 71 + 88 dBm - 131.3 dBm +
40 log (15) - 20 log (828) +
21.3 dB - 41.3 dB - 10
= 71 + 88 - 131.3 + 47 - 58.4 + 21.3 - 41.3 - 10 = -13.7 dB

828 km

131.3 dBm
ERP

Again, RCS is the radar cross section of the radar's target in square meters
Plugging in our given values, the jamming to signal
ratio is:

67


http://www.lynxpub.com

Table of Contents for the Digital Edition of JED - October 2017

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Maximizing EW Capabilities Within the Brigade Combat Team
Homing Senses: Anti-Ship Seekers Show New Diversity
The Heat is On
EW 101
Technology Survey: COMINT/DF Receivers
2018 EW/SIGINT Resource Guide
AOC News
Index of Advertisers
JED Quick Look
JED - October 2017 - intro
JED - October 2017 - cover1
JED - October 2017 - cover2
JED - October 2017 - 3
JED - October 2017 - 4
JED - October 2017 - 5
JED - October 2017 - The View From Here
JED - October 2017 - 7
JED - October 2017 - Conferences Calendar
JED - October 2017 - 9
JED - October 2017 - Courses Calendar
JED - October 2017 - 11
JED - October 2017 - From the President
JED - October 2017 - 13
JED - October 2017 - 14
JED - October 2017 - insert1
JED - October 2017 - insert2
JED - October 2017 - The Monitor
JED - October 2017 - 16
JED - October 2017 - 17
JED - October 2017 - 18
JED - October 2017 - 19
JED - October 2017 - 20
JED - October 2017 - 21
JED - October 2017 - Washington Report
JED - October 2017 - 23
JED - October 2017 - World Report
JED - October 2017 - 25
JED - October 2017 - Maximizing EW Capabilities Within the Brigade Combat Team
JED - October 2017 - 27
JED - October 2017 - 28
JED - October 2017 - 29
JED - October 2017 - 30
JED - October 2017 - 31
JED - October 2017 - 32
JED - October 2017 - 33
JED - October 2017 - 34
JED - October 2017 - 35
JED - October 2017 - Homing Senses: Anti-Ship Seekers Show New Diversity
JED - October 2017 - 37
JED - October 2017 - 38
JED - October 2017 - 39
JED - October 2017 - 40
JED - October 2017 - 41
JED - October 2017 - 42
JED - October 2017 - 43
JED - October 2017 - The Heat is On
JED - October 2017 - 45
JED - October 2017 - EW 101
JED - October 2017 - 47
JED - October 2017 - 48
JED - October 2017 - 49
JED - October 2017 - 50
JED - October 2017 - Technology Survey: COMINT/DF Receivers
JED - October 2017 - 52
JED - October 2017 - 53
JED - October 2017 - 54
JED - October 2017 - 55
JED - October 2017 - 56
JED - October 2017 - 57
JED - October 2017 - 58
JED - October 2017 - 59
JED - October 2017 - 60
JED - October 2017 - 61
JED - October 2017 - 62
JED - October 2017 - 63
JED - October 2017 - 64
JED - October 2017 - 65
JED - October 2017 - 66
JED - October 2017 - 67
JED - October 2017 - 2018 EW/SIGINT Resource Guide
JED - October 2017 - 69
JED - October 2017 - 70
JED - October 2017 - 71
JED - October 2017 - 72
JED - October 2017 - 73
JED - October 2017 - 74
JED - October 2017 - 75
JED - October 2017 - 76
JED - October 2017 - 77
JED - October 2017 - 78
JED - October 2017 - 79
JED - October 2017 - 80
JED - October 2017 - 81
JED - October 2017 - 82
JED - October 2017 - 83
JED - October 2017 - 84
JED - October 2017 - 85
JED - October 2017 - 86
JED - October 2017 - 87
JED - October 2017 - 88
JED - October 2017 - 89
JED - October 2017 - AOC News
JED - October 2017 - 91
JED - October 2017 - 92
JED - October 2017 - Index of Advertisers
JED - October 2017 - JED Quick Look
JED - October 2017 - cover3
JED - October 2017 - cover4
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