In this paper, a 3D Helmholtz coil used for EMC (Electromagnetic Compatibility) test is proposed. The design consists of three paired orthogonal square Helmholtz coils. High-precision reconstruction of complex magnetic field environment can be achieved with audio frequency power amplifier and three-channel signal generator. It works at 0-400 kHz and weighs 30.5 kg. To verify the proposed design, both simulations and measurements are conducted. The results show that the coil has good performance at 0-400 kHz, which conclude coil factor, coil impedance, limit line compliance test and magnetic field uniformity.

For a continuous wave (CW) signal, the total radiated power (TRP) can be measured in a reverberation chamber (RC). In this paper, we show that the total radiated energy (TRE) can also be measured in an RC for transient signals, and observe that the proposed method has fast convergence speed for wideband signals. Measurements are performed to validate the proposed method.

The shielding effectiveness of a cable has been measured using two different methods in this paper. Results show that inconsistence exists and more investigations are required on these two methods.

The stirrer design is important in a reverberation chamber measurement system. Previous study shows that the rotating radius of the stirrer plays a key role for the stirrer performance. However, to identify the contribution from the structure, optimizing the stirrer structure while keeping the stirring volume unchanged is necessary. In this paper, when the stirring volume is kept invariant, we show that the detailed structure of stirrers can be optimized to improve the performance but the effect is not significant. A comparative study is given to confirm the effect of zigzag boundaries on the stirrers. Both simulations and measurements confirm the performance improvement, key performance indicators such as field uniformity and correlated angles are simulated and measured.

In a reverberation chamber, analytical solutions exist in very limited scenarios for the distribution of the boundary fields. For arbitrary-shaped objects, analytical solutions may not exist. To solve this problem, a general numerical method is proposed to obtain the mean field distribution near arbitrary-shaped objects in a random diffused-wave environment. The proposed method combines the full-wave method and the Monte-Carlo method; the numerical results are validated and compared with that from analytical equations. The proposed method can be applied to arbitrary-shaped objects with general material properties.

A frequency-modulated continuous-wave (FMCW) coherent lidar with downlink communication capability is proposed based on phase-diversity coherent detection, by which laser ranging, laser velocimetry and free-space optical downlink communications can be simultaneously achieved. In the local transceiver, a linear-frequency modulated (LFM) optical signal is generated and used as the lidar signal. The LFM optical signal is received by the remote transceiver and coded with data via amplitude modulation. Then, the light is transmitted back to the local transceiver, in which a phase-diversity coherent optical receiver is used to simultaneously extract the range, velocity, and communication data. The in-phase and quadrature outputs from the phase-diversity coherent optical receiver are simultaneously recorded to reform a complex signal. The data is extracted from the intensity of the complex signal, while the range and velocity are obtained from the argument of it. A demonstration experiment is carried out. Different digital baseband signals are encoded on the reflected signal via an intensity modulator, while the 80-MHz Doppler frequency shift is simulated by an acousto-optic modulator. The impact of the digital signal on lidar detection is removed. Meanwhile, the communication quality is little affected by the varied frequency of the de-chirped signal. Therefore, the lidar detection and the free-space optical communications are simultaneously implemented.

An intelligent radome utilizing composite metamaterial structures is presented and investigated in this article, which can realize energy isolation and asymmetric propagation of electromagnetic (EM) wave self-adaptively by controlling states of PIN diodes. The whole structure mainly consists of a broadband polarization-sensitive polarization converter (PC) and an active frequency selective rasorber (AFSR) switching between a transmission mode and absorption mode which is used as an energy-selective surface (ESS). Among them, the function of the PC is to make the EM waves transmit asymmetrically, and the purpose of AFSR is to make the high-power waves be reflected or absorbed, which depends on the polarization type of the wave. Thus, the radome can realize both asymmetric propagations of EM wave and electromagnetic shielding. The equivalent circuit models (ECM) and parametric studies are considered to explain the physical operating mechanism of PC and AFSR. The fabricated structure with 7*7 unit cells is experimentally demonstrated and the measured results agree with simulated results well. Considering the distinctive characteristic of self-actuation, the presented concept has the potential application in electromagnetic stealth and HPEMWs shielding to protect communication devices.

A compact all-fiber polarization coherent Lidar is demonstrated to simultaneously measure the velocity and depolarization ratio. In the Lidar system, a dual-polarization light beam is generated in a polarization modulator (PolM). The light beam consists of a linearly polarized optical carrier and an optical sideband with an orthogonal polarization state. If the light is depolarized, the polarization directions of the optical carrier and the sideband are rotated. Both of them can be detected along the polarization direction of the original optical carrier. In the receiver, the backscattered light along the polarization direction of the original optical carrier is selected and beats with a frequency-shifted optical local oscillator (LO) signal at a photodetector. A beat signal consisting of two single-frequency components will be generated. The velocity is extracted from the frequencies of the two single-frequency components, while the depolarization ratio can be extracted from the intensity ratio of the two single-frequency components. An experiment is carried out, in which a 159-MHz signal is applied to the PolM, and an 80-MHz signal is used to produce the frequency-shifted optical LO. Two single-frequency signals at 80 and 79 MHz are generated at the receiver and used to simultaneously measure the velocity and depolarization of a target in real time.

A frequency-modulated continuous-wave (FMCW) lidar is proposed to avoid signal aliasing in the measurement of distance and velocity. In the transmitter, a lightwave is amplitude-modulated in a Mach-Zehnder modulator by a linear-frequency modulated (LFM) waveform. The modulated light is used as a probe signal. The reflected optical signal beats with a local optical (LO) signal in a phase-diversity coherent optical receiver. The in-phase and quadrature components of the output signal are simultaneously recorded. The distance is extracted from the sum of the squares of the two components, while the velocity is calculated from the ratio of them. An experiment is carried out, in which the real-time distance and velocity of a spinning disk are measured. The proposed method can be used to solve the problems of signal aliasing which may lead to the ambiguity of distance and velocity measurements in traditional FMCW lidars. Moreover, the impacts of optical phase fluctuations are removed from the distance measurement in the proposed method.