Fast and Accurate Near-Field Calibration Method for
Phased Array Antennas
Xin Jin, Shuai Wang, Yujie Lin, Xiangyuan Bu and Jianping An
School of Information and Electronics
Beijing Institute of Technology, Beijing, China
Email: {2120170774, swang, 3120130334, bxy, an}@bit.edu.cn
Abstract—The near-field calibration can be performed indoors,
avoiding to be affected by the environment and security concerns
which make it has important research value. Nevertheless, the
application is limited by the calibration efficiency and precision.
A near-field calibration method based on code division multiple-
access (CDMA) scheme is proposed in this paper to decrease
calibration time and improve the calibration precision. In the
proposed method, the calibrating signal associated with each an-
tenna is distinguished by a unique spread-spectrum code sequence
instead of the continuous wave (CW). The relationship between
calibration accuracy and signal to noise ratio (SNR) is obtained
by derivation, and the simulation results verify the correctness of
theoretical derivation results. If the SNR is higher than 15dB, the
calibration accuracy of the amplitude/phase can reach 0.1 decibel
(dB) and 1 degree (deg), respectively. The proposed method can be
good applied to the large-scale phased array antennas calibration.
Index Terms—phased array antennas, near-field calibration,
code division multiple-access(CDMA), spread-spectrum commu-
nication;
I. INTRODUCTION
Phased array antennas have been widely applied in the fields
of communication, radar, navigation and electronic counter-
measure due to their advantages such as fast beam scanning,
flexible beam pattern reconfiguration, and spatial orientation
ability [1]. Phased array antennas contain many active com-
ponents which performance can easily be affected by the
variation of temperature, environment or other factors [2,3].
Therefore, it is necessary to perform precise and periodic
calibration to ensure best performance for the phased array
antennas. The antennas can be measured in the near-field
or far-field radiation range. Traditional antenna calibration
method is far-field measurement. However, with the scale of
phased array antennas enlarging, it’s difficult to test in far-
field because of the open test condition and the remote test
distance. In contrast to the far-field measurement, the near-field
measurement technique can be conducted indoors, avoiding to
be affected by the weather, electromagnetic interference, and
security concerns. Meanwhile, by calculation the results of
near-field measurement can become the results of far-field. The
near-field measurement technique has become one of the key
techniques for higher frequency antennas and ultralow side-lobe
antennas.
This work is financially supported in part by NSFC under Contract No.
61471360, and in part by the Joint Foundation of NSFC and the General
Purpose Technology Research Program under contract U1636125.
The most common near-field measurement method is using
a vector network analyzer to obtain the amplitude and phase
of one antenna element with other elements closed [4]. This
method is low efficiency and can’t reflect the situation that all
antennas are working at the same time. W. Patton proposes a
method to perform near-field alignment of phased-array anten-
nas [5]. T. Laitinen uses fast Fourier transformation (FFT) and
Matrix inversion to measure the deviation degree of antennas
[6]. L. J. Foged realizes the spatial-filtering technology can
eliminate the near-field measurement errors [7].
In this paper, we propose a fast and accurate near-field
calibration method for phased array antennas based on code
division multiple-access (CDMA) [8]. With this method, each
antenna element can be divided by the unique signature code
easily, which means all the antennas under test (AUT) can
be calibrated simultaneously. Therefore, the calibration time
can be reduced. Moreover, the calibration accuracy and anti-
jamming capability can be improved as the CDMA scheme can
offer the processing gain.
In Section II, the proposed calibration method is described.
Section III derives the theoretical formulas of the calibration
precision with the proposed method. The comparison of system
simulation and the theoretical derivation results are showed in
Section IV, followed by conclusion in Section V.
II. PROPOSED CALIBRATION METHOD
The near-field calibration system for phased array antennas
is illustrated as Fig.1. It consists of K transmitting channels,
a control & data processing computer, a planar scanner, and a
system for measuring the amplitude and phase of the received
signal. A probe is installed on the fixed location [9] of the
planar scanner within the propagating near-field region, while
a reference antenna is located outside the sampling region in
order not to affect the signal received by probe.
Referring to Fig.1, we describe the procedure of calibration
process in detail as follows. First, the baseband calibration
signal generation module which showed in Fig.2 generates a
unique signature code sequence corresponding to each antenna
element. After interpolation and forming, all signature code
sequences become baseband calibration signals. Then the K-
band signals are processed by the T/R module and transmitted
by the phased array antennas. Simultaneously, the control &
data processing computer sends the scan instruction to the
locator on the planner scanner. After the probe moves to
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