Aerospace and Electronic Systems Magazine March 2018 - 5

implemented at the receiver by only the single antenna. Under
this concept, even a small boat carrying a simple and cheap receiver can have the capability of over-the-horizon target detection, which is attractive in practical applications. In addition, the
shipborne receiver can be deployed in the center of the EEZ and
the overall length of the propagation path can be greatly reduced
compared with the conventional monostatic HFSWR system on
the coast. This will be helpful for the detection of some small
targets, e.g., fishing boats. But the coverage area of this bistatic
HFSWR system is still limited by the transmitter site and cannot
be too far from the coastline.
To further extend the coverage area of HFSWR to the open
sea, a more flexible solution is to deploy the transmitter and one
or multiple receivers on different ship platforms, which forms a
bistatic or multistatic shipborne HFSWR system. In summary, this
system has the following advantages:
a. It is a fully mobile system, and the radar coverage area can be
freely selected in the open sea by moving the positions of the
transmitter and the receiver.
b. As long as the transmitting antenna array can be deployed on a
large ship (e.g., a large barge), even a small boat carrying one
or two receiving antennas can have the capability of over-thehorizon target detection.
c. One transmitter can easily support the operation of multiple
distributed receivers to cover a large and wide area in the open
sea.
d. When one target is detected by multiple receivers, the detection probability can be significantly improved from the spatial diversity. The target localization can be implemented by

Figure 1.

System configuration of conventional HFSWR on the coast.

MARCH 2018

a multilateration technique using the detection results of multiple transmitter-receiver pairs, and potentially the localization
accuracy can be higher than that of monostatic HFSWR using
range and angular information.
e. The ship carrying the HFSWR receiver is covert and undetectable for the enemy's interception; thus, it can be deployed
nearer the target or area of interest to get better detection performance and accuracy.
Although many attractive advantages can be offered by the
bistatic or multistatic shipborne HFSWR system, the complexities of the system configuration and motions of the transmitter or
receiver will bring additional technical challenges to the associated signal processing, particularly for sea clutter suppression and
target detection. In monostatic shipborne HFSWR, the space-time
distribution of sea clutter caused by radar platform motion is quite
regular [9], and the standard STAP technique can effectively suppress it [10], [11]. In bistatic or multistatic shipborne HFSWR, the
radar transmitter and receiver or receivers are at different positions
with different moving directions, and the produced sea clutter is
complicated, with irregular space-time distributions. Conventional HFSWR transmits a single waveform and receives with a uniform linear array (ULA), which is a single-input, multiple-output
(SIMO) system. However, to implement the wide area coverage
and operation of a small shipborne receiving system with beamforming capability, bistatic or multistatic shipborne HFSWR needs
to deploy a transmitting array, transmit orthogonal waveforms, and
work in multiple-input, single-output (MISO) mode or multipleinput, multiple-output (MIMO) mode. This brings even more complexities to the signal processing. All these have not been analyzed
in previous studies.
In this article, the concept of bistatic or multistatic shipborne
HFSWR is investigated, particularly for its space-time sea clutter distribution characteristics and potential ship target detection performance. The advantages and disadvantages of different
shipborne HFSWR configurations (monostatic or bistatic; SIMO,
MISO, or MIMO; motions of the transmitter or receiver; etc.) are
analyzed and compared by numerical simulations. It is shown that
the sea clutter suppression and target detection performance highly
depend on the particular radar geometrical and systematical configuration. Compared to the SIMO and MISO modes, the MIMO
working mode has the most advantages and flexibilities and can
always be adapted to achieve good performance for various motions experienced by the transmitter and receiver.

IEEE A&E SYSTEMS MAGAZINE

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine March 2018