Aerospace and Electronic Systems Magazine July 2018 - 37

Cheng et al.

Figure 4.

Distribution of array elements. (a) Overall array size. (b) Rectangular boundary grid.

process of a millimeter wave radar is as follows. First, the signal
is generated by a signal transceiver. Then, it is fed to a subarray
channel, and all subarray channel signals that are equal in phase
are fed to the (T/R) Transfrom/Receive module. Afterward, each
T/R signal is forwarded to a phase-shifting chip (VM) Virtual
Manufacturing and a (T/R) transceiver chip, wherein the signal
amplitude and phase are controlled and amplified. Finally, the
signal is emitted by the transmitting antenna. The antenna radiation pattern in a particular direction represents the synthesis of
electromagnetic radiation in that direction. Afterward, the scattered millimeter wave signal is received by a receiving antenna.
The received signal is amplified and downconverted to intermediate frequencies (IFs). The amplified IF signal is fed to a radar
signal processing unit. The quadrature demodulation of the IF
signal is performed according to radar operation mode, i.e., according to a high-resolution range and phase Doppler processing.
The obtained values are used to evaluate the target features. The
target features mainly include infrared image, target contour information, target location information, and distance information.
The infrared image is obtained by the infrared imaging system,
and the target contour information is acquired using millimeter
wave imaging technology in a W-band millimeter phased array
detector. The rest of the features are determined by the millimeter
detection system. The detection principle is similar to the working principle of the millimeter wave radar system. The evaluated
distance and angle of the target are sent to the missile control system. However, because of power supply requirements, two power
supplies should be used.
Because of the requirements for overall antenna array size, the
proposed design is based on a rectangular grid array. The sparse array is shown in Figure 4a. The dependence of array scanning range
on operational wavelength is defined by
d≤

λ
1 + sin θ max

(1)

where d represents the grid array spacing, λ represents the wavelength, and θmax denotes the maximum scanning angle.
JULY 2018

In this study, according to design requirements, the wavelength
of array was 3 mm, the beam scanning range was about 25°, and
the size and spacing of the grid were 40 × 40 and 0.67λ, respectively (Figure 4b).
The sparse array represents the array that consists of a certain
number of uniformly distributed elements, wherein elements are
in certain grid positions. The sparse array was used in this study
because its radiation pattern meets defined requirements. The element spacing was equal to the integer multiple of element spacing
in the original uniform array.
The rectangular grid of rectangular aperture array, shown in
Figure 4, represents a transverse distribution of M columns and
a vertical distribution of N rows. If, in the total radiation pattern
of the array, the 3-dB beam width θ3dB is not greater than θmax and
the 3-dB azimuth beam width ϕ3dB is not greater than the array elements, then the optimization model for the rectangular grid of the
rectangular aperture array is defined by
min ( PSLC )

0 ≤ m ≤ M , 0 ≤ n ≤ N
M N

  amn = N e
 m =0 n =0
θ 3dB ≤ θ max , φ3dB ≤ φmax

(2)

where PSLC represents the peak side-lobe level; m and n represent
the number of horizontal grid points and the number of longitudinal grid points, respectively; θ3dB is the 3-dB beam width, and ϕ3dB
represents the 3-dB azimuth beam width. The peak side-lobe level
represents the peak value of the side lobe in the antenna radiation
pattern. After optimization, the sparse array presented in Figure 5
is formed. In Figure 5, red dots represent 328 array elements and
black dots represent empty spaces in the array. During the optimization process, the sparse rate was about 20.5% and the minimal
element spacing was 0.67.
The peak side-lobe level in the array radiation pattern is calculated every 5°, and obtained values are presented Table 1. The

IEEE A&E SYSTEMS MAGAZINE

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