IEEE - Aerospace and Electronic Systems - October 2021 - 17

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determination " details the initial orbit determination (IOD)
step, particularly focused on radar measurements, in orbit
determination. The " Results " section describes our results
from a short surveillance stare covering uncued detection.
" Conclusion " and " Future Work " conclude and discuss
planned future work, respectively.
PASSIVE RADAR
Passive radar is a type of radar that uses already existing
sources of radio frequency (RF) illumination, such as commercial
radio and television broadcasts, instead of a dedicated
or cooperative transmitter. The prime advantage ofnot
requiring a dedicated transmitter is that passive radars are
electromagnetically covert. However, by not having control
over the transmitted signal, a passive radar system is at the
mercy of the characteristics of existing transmitters. With a
larger amount ofthe electromagnetic spectrumbeing opened
up to commercial interests, there is a vast amount of energy
available for passive radar systems while traditional active
radar applications are losing spectrum access.
FM radio as the illuminator ofopportunity, for this article,
provides its own set of advantages and disadvantages.
FM radio typically occupies the 88-108 MHz band, with
analog signals of bandwidths less than 100 kHz. The lowbandwidth
results in poor range-resolution but also significant
flux-density. The use ofFM radio generally dictates a
OCTOBER 2021
large bistatic baseline distance. This is due to the radiative
characteristics oftypical transmitters and the fact that radio
telescopes are often located far away from potential sources
ofRF interference (RFI). This large standoff range has the
benefit of ensuring that even narrow elevation beam transmissions
will illuminate large volumes of space above the
radio telescope receiver.
An often overlooked benefit ofpassive radar processing is
its flexibility. Passive radar signal processing, essentially the
passive form ofcontinuous wave noise radar, allows ambiguity-free
velocity and delay ranges. Further, passive radar processing
allows the coherent processing interval (CPI) and the
pulse repetition frequency to be chosen arbitrarily as these factors
are not determined by transmitted signal. Received signals
can be processed inmultiple ways in parallel.
MURCHISON WIDEFIELD ARRAY
The Murchison Widefield Array (MWA) is a radio telescope
in the Western Australian desert [8]. It is the low-frequency
precursor to the Square Kilometre Array, operating in the frequency
range of 70-300 MHz. The main scientific goals of
theMWA are to detect radio emission from neutral hydrogen
during the so-called epoch ofreionization (EoR), to study our
Sun and heliosphere, the Earth's ionosphere, and radio transient
phenomena, as well as map the galactic and extragalactic
radio sky [9].
IEEE A&E SYSTEMS MAGAZINE
17
IEEE - Aerospace and Electronic Systems - October 2021

Table of Contents for the Digital Edition of IEEE - Aerospace and Electronic Systems - October 2021
