IEEE - Aerospace and Electronic Systems - August 2023 - 48

Industry Insights
DOI. No. 10.1109/MAES.2023.3266741
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An Overview of Radar Operation in the Presence of Diminishing Spectrum
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William L. Melvin , Georgia Tech Research Institute, Georgia Institute of
Technology, Atlanta, GA 30318 USA
INTRODUCTION
variations of the RRE exist. A common version yielding
output SNR is
Monostatic radar systems actively interrogate the environment
by transmitting a radiofrequency (RF) waveform
and then receiving and processing the reflected
signal to determine the presence of an object, its location,
and other important features (e.g., motion, object
type, or change in the object's location) [1], [2], [3].
Radar has many civilian and military applications,
including air traffic surveillance [4], severe weather
detection and tracking [5], Earth resources management
[6], automotive safety [7], missile defense [8],
and haptic user interface [9]. These radar systems
deploy on a plethora of platforms, including land-based
pedestals and towers, automobiles and trucks, manned
and unmanned aircraft and helicopters, marine vessels,
satellites, dirigibles, person-held devices, etc.
Several key factors determine the radar system's effectiveness
in a given operating environment: detection capability;
accuracy in estimating target parameters, such as
range, angle, and Doppler frequency; and the ability to discriminate
or characterize target type. The selection of operating
center frequency and bandwidth plays a substantially
important role in the radar's effectiveness. Radar operating
frequencies range from high frequency (HF), starting at 3
MHz, through millimeter wave (MMW) at over 100 GHz.
Bandwidths vary greatly, with typical values from hundreds
ofkilohertz to 1 GHz ormore. A number offactors influence
the selection ofradar operating frequency and bandwidth.
Radar detection, estimation, and characterization
capability monotonically depend on signal-to-noise
ratio (SNR). The radar range equation (RRE) characterizes
basic radar performance [1], [2], [3].Many
Authors' current addresses: William L. Melvin is with
Georgia Tech Research Institute, Georgia Institute of
Technology, Atlanta, GA 30318 USA (e-mail: william.
melvin@gtri.gatech.edu).
Manuscript received 19 March 2023; accepted 6 April
2023, and ready for publication 12 April 2023.
Review handled byMichael Brandfass.
0885-8985/23/$26.00 ß 2023 IEEE
48
SNRo ¼
cFp
PTGT
4pR2
sT
M
4pR2
M
GR2
4pkBT0BFnLsys
Gp
(1)
where PT is peak transmit power in Watts, GT is maximum
transmit antenna gain, RM is range to the target
in meters, sT is radar cross section (RCS) in square
meters, GR is maximum receive antenna gain,c
wavelength in meters, Fp is two-way propagation loss,
is
kB is Boltzmann's constant (J/K), T0 is standard temperature
(290 K), B is bandwidth in Hertz, Fn
receiver noise figure, Lsys is RF system loss, and Gp is
is
matched filtering gain from pulse compression and
Doppler filtering. Wavelength and frequency are
related as fcc ¼ c,where fc
is the center frequency
and c is taken as the speed of light. The maximum
antenna gain Gx
is nominally Gx ¼ 4pAe=2
c,with Ae
the effective antenna area. A number of factors in (1)
exhibit explicit frequency dependence, including
antenna gain, RCS, wavelength, and propagation loss.
We consider both explicit and implicit frequency selection
factors in more detail in the section " Frequency
Selection and Use in Radar. "
Noise-limited performance is given by (1). However,
radar systems necessarily operate in environments
where clutter and other interference degrades capability.
Clutter is any colored noise signal that is not the
target of interest, and possesses target-like qualities; it
is a form of interference impeding radar access to targets.
For example, ground clutter returns exhibit an
angle and Doppler response that spectrally competes
with moving target returns [10]. Radio frequency interference
(RFI) results from in-band signals emanating
from specific angle-of-arrivals, but otherwise appearing
uncorrelated in the temporal domain, thereby desensitizing
radar performance by increasing the uncorrelated
noise floor.
The signal-to-interference-plus-noise ratio (SINR)
captures radar performance in an interference-limited
IEEE A&E SYSTEMS MAGAZINE
AUGUST 2023
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IEEE - Aerospace and Electronic Systems - August 2023

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