# JED - February 2018 - 33

```E W101

The Gun Dish radar antenna is 1 meter in diameter,
so its boresight gain at 15 GHz will be:
G = -42 + 20 log D + 20 log F = -42 + 20 log(1) + 20
log (15,000) = -42 + 0 + 83.5
= 41.5 dBi
The effective radiated power is found from the return power formula for a 1 square meter target at 20 km.
Re-arranging the formula:

Note: the above analysis only presents a set of reasonable estimates of threat system parameters to support
the following jamming discussion. Accurate parameters
can be found in classified threat data bases.

NOW LET'S JAM THE GUN DISH RADAR
The engagement at maximum lethal range is shown in
Figure 1. A self-protection jammer on an aircraft with
10 square meters RCS has a 100 Watt transmitter and 3
dBi antenna gain (i.e., ERP = 53 dBm). The maximum
lethal range of the ZSU-23-4 is 2,500 meters. At that
range, the self-protection jamming formula yields the
following jamming-to-signal ratio.
J/S = ERPJ - ERPS + 71 + 20 log R - 10 log RCS
= 53 - 104 + 71 + 20 log(2.5) - 10 log (10) = 53 -
104 + 71 + 8 - 10 = 18 dB
At the maximum acquisition range (20 km), the J/S is:

FORMULA FOR THE GAIN OF A SYMMETRICAL
PARABOLIC ANTENNA
G = -42 + 20 log D + 20 log F
Where: G is the boresight gain of the antenna in dBi, D is
the diameter of the antenna in meters and F is the
operating frequency in MHz

S = -114 dBm + 10 log BW + NF + Req RFSNR
Where: BW is the effective receiver bandwidth in MHz,
NF is the receiver noise figure in dB
Req RFSNR is the required pre-detection signal to
noise ratio

PR = ERP + G -103 - 20log F- 40 log R + 10 log RCS
dBm
G is the boresight gain of the radar antenna
F is the operating frequency in MHz
RCS is the radar cross section of the target

J/S = 53 - 104 + 71 + 20 log(20) - 10 log (10) = 53 -
104 + 71 + 26.0 - 10 = 36 dB

SELF-PROTECTION JAMMING-TO-SIGNAL RATIO

BURN-THROUGH RANGE

J/S = ERPJ - ERPS + 71 + 20 log R - 10 log RCS

As shown in Figure 2, the target aircraft is at the
maximum range from the radar at which its jammer can
protect it. For this problem, we will assume that burnthrough occurs at a J/S ratio of 2 dB.
The two step process for calculation of the burn
through range is:

Where: J/S is the jamming to signal ratio in dB
ERPJ is the effective radiated power of the jammer in
dBm\
dBm\
R is the range from the radar to the target in km
RCS is the radar cross section of the target

20 log R BT = ERPS - ERPJ - 71 + 10 log RCS + J/S Req
R BT = Anti-log {[20 log R BT] / 20}
Plugging our values into this equation gives:
20 log R BT = 104 dBm - 53 dBm - 71 + 10 log 10 + 2
dB = -8
R BT = Anti-log {-8 / 20} = 398 meters

WHAT'S NEXT
Next month, we will move our discussion to the new
generation EW threats and countermeasures. For your
at www.lynxpub.com. a

SELF-PROTECTION JAMMING BURN-THROUGH RANGE
First solve the J/S formula for the range term, then solve
for the actual range.
20 log R BT = ERPS - ERPJ - 71 + 10 log RCS + J/S Req
R BT = Anti-log {[20 log R BT[ / 20}
Where: RBT is the range from the radar to the target at burnthrough in km
J/S Req is the J/S value at which the jammer can no

The Journal of Electronic Defense | February 2018

ERP = PR + 103 + 40 log R + 20 log F - 10 log RCS - G
= -93 + 103 + 52 + 83.5 - 0 - 41.5 = 104 dBm

Handy formulas for estimating

33

```
http://www.lynxpub.com

# JED - February 2018

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
Tactical CEMA for the Mechanized Force
New Products
EW 101
AOC News
JED Quick Look
JED - February 2018 - intro
JED - February 2018 - cover1
JED - February 2018 - cover2
JED - February 2018 - 3
JED - February 2018 - 4
JED - February 2018 - 5
JED - February 2018 - The View From Here
JED - February 2018 - 7
JED - February 2018 - Conferences Calendar
JED - February 2018 - 9
JED - February 2018 - Courses Calendar
JED - February 2018 - 11
JED - February 2018 - From the President
JED - February 2018 - 13
JED - February 2018 - 14
JED - February 2018 - The Monitor
JED - February 2018 - 16
JED - February 2018 - 17
JED - February 2018 - 18
JED - February 2018 - 19
JED - February 2018 - World Report
JED - February 2018 - 21
JED - February 2018 - Big Challenges Ahead as DOD Tries to Address EMSO Implementation
JED - February 2018 - 23
JED - February 2018 - 24
JED - February 2018 - 25
JED - February 2018 - 26
JED - February 2018 - insert1
JED - February 2018 - insert2
JED - February 2018 - Tactical CEMA for the Mechanized Force
JED - February 2018 - 28
JED - February 2018 - 29
JED - February 2018 - 30
JED - February 2018 - New Products
JED - February 2018 - EW 101
JED - February 2018 - 33
JED - February 2018 - AOC News
JED - February 2018 - 35
JED - February 2018 - 36
JED - February 2018 - Index of Advertisers
JED - February 2018 - JED Quick Look
JED - February 2018 - cover3
JED - February 2018 - cover4
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