Aerospace and Electronic Systems Magazine March 2018 - 23

tenna in the field of target monitoring. To balance applications of
ocean current measurement and target monitoring, frequencies
higher than 10 MHz are used. This limits the detection range and
target monitoring performance. From this perspective, it is difficult
for compact HFSWR to replace large-array HFSWR.
It is necessary to investigate the feasibility of long-range target detection, monitoring, and tracking using compact HFSWR.
This work presents an integrated method for target detection and
tracking for compact HFSWR. The structure of this article is as
follows. The following section introduces the principles of target
monitoring using compact HFSWR. Next, the method of integrating detection and tracking and its process is described. The detection results are then presented with the measured high-frequency
(HF) data and verified with synchronous automatic identification
system (AIS) data. The final section is the conclusion.

TARGET MONITORING PRINCIPLE
CHARACTERISTIC ANALYSIS OF AREA TARGETS IN
RANGE-DOPPLER IMAGES
HFSWR can detect a target that has strong echoes and observable
radial velocities. It can also distinguish targets from one another
because of their different radial velocities and range information.
The range R and radial velocity Vral of the moving target can be
obtained from the range-Doppler (R-D) image of a single channel.
For a moving target, R can be calculated as follows:
R = cΔt / 2

(1)

Vral = Δf λ / 2

(2)

where Δt is the time delay of the radar transmit signal, c is the
speed of light, λ is the wavelength, and Δf is the Doppler shift.
To estimate the azimuth of the moving target using beam-forming
technology, multiple-channel data are required. For linear-array radar systems such as HFSWR, the larger the aperture, the narrower
the beam width and the better the azimuth resolution. Therefore,
large-array HFSWR of hundreds or thousands of meters can obtain
MARCH 2018

better azimuth resolution than that obtained by compact HFSWR.
However, the bandwidth of HFSWR is narrow in the high-frequency band, typically only about 30-100 kHz. Thus, the range resolution of HFSWR is limited. Even for HFSWR with an array of hundreds of meters, its azimuth resolution is larger than 1°. Moreover,
the larger the antenna aperture, the narrower the beam width. Thus,
HFSWR can also obtain higher SNR in one range-azimuth cell and
greater coverage. Only when higher SNR in one range-azimuth
cell is needed to improve detection range and greater coverage is a
larger array necessary.
Compared with microwave radar, HFSWR has coarser spatial resolution because of its poor range and azimuth resolution. However, HFSWR has higher Doppler resolution and can
achieve high radial velocity resolution by using a long coherent
integration time. In most cases, different targets can be distinguished from one another using R-D data even without the high
spatial resolution resulting from a large array. The range and velocity of a moving target cannot remain unchanged during a long
coherent integration time. By applying windowing functions in
radar data processing and variations of in range and velocity of
the target during a long integration time, the target echoes can
be spread over several adjacent cells in the R-D image. For a
maneuvering target, the spread width of its echo increases in
both velocity and range directions. The spread characteristics of
a moving vessel target make it show as an area target in HFSWR
R-D images. Compared with a CFAR point result, an area target
can illustrate more detailed changes in both range and velocity
of a moving target. Figure 2a shows an example of a singlechannel R-D image. The peak detection is marked by a plus sign.
When a target is detected, the CFAR point after peak detection
should locate within the extended region of an area target in the
R-D image, as shown in Figure 2b. Therefore, area targets can
provide more multidimensional features than single CFAR point
targets, which are helpful for distinguishing multiple moving
targets.
It can be concluded that most moving targets can be detected
and distinguished using a single-channel R-D image, and the
number of targets can also be estimated. Therefore, the smallaperture compact HFSWR can also be used to detect and track
moving targets.

IEEE A&E SYSTEMS MAGAZINE

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