Jingjian Huang

Method for inshore ship detection based on feature recognition and adaptive background window

Abstract Inshore ship detection in synthetic aperture radar (SAR) images is a challenging task. We present an inshore ship detection method based on the characteristics of inshore ships. We first use the Markov random field (MRF) method to segment water and land, and then extract the feature points of inshore ships using polygonal approximation. Following this, we propose new rules for inshore ship extraction and use these rules to separate inshore ships from the land in binary images. Finally, we utilize the adaptive background window (ABW) to complete the clutter statistic and successfully detect inshore ships using a constant false alarm rate (CFAR) detector with ABW and G 0 distribution. Experimental results using SAR images show that our method is more accurate than traditional CFAR detection based on K -distribution ( K -CFAR), given the same CFAR, and that the quality of the image obtained through our method is higher than that of the traditional K -CFAR detection method by a factor of 0.165. Our method accurately locates and detects inshore ships in complicated environments and thus is more practical for inshore ship detection.

A novel DOA estimation algorithm for a 5-element circular array

Under the influence of the radome of the active and passive radar, the uniform circular array (UCA) becomes non-uniform in the electromagnetic performance, so the accuracy of direction of arrive (DOA) estimation is not high. This paper presents a universal look-up table algorithm for 5-element circular array to solve the problem. Firstly, we traverse the view field of the radar to obtain the long baseline phase differences of each angle point and store them to obtain the lookup table. Then, we can solve the incoming signals long baseline phase differences on the array and compare them with the phase differences stored in the lookup table according to the maximum cosine value criterion. Finally, we can get the closest point and the corresponding angle is the angle of the incoming signal. Numerical simulation results and experimental results verify the effectiveness of the algorithm.

Compact dual-band microstrip bandpass filter using stub-loaded stepped-impedance resonator

In this paper, two dual-band microstrip bandpass filters (BPFs) based on the stepped-impedance resonator (SIR) and stub-loaded SIR (SL-SIR) are presented. The characteristics of the SL-SIR are studied by using the even-/odd-mode analysis method. The simulation results show the length of the loaded stub has no influence on the odd-mode resonant frequency, but it can affect the even-mode resonant frequency. In addition, the BPF based on the SL-SIR has higher frequency selectivity and stopband rejection than the one based on the SIR. Whats more, the loaded stub can reduce the size of the BPF. Therefore, the BPF based on the SL-SIR can be applied in the modern wireless communication systems.

2-D DOA ESTIMATION OF LFM SIGNALS FOR UCA BASED ON TIME-FREQUENCY MULTIPLE INVARIANCE ESPRIT

In order to improve the angle measurement precision with a low computational complexity, a 2-D direction of arrival (DOA) estimation algorithm UCA-TF-MI-ESPRIT is proposed in this paper. This algorithm is based on the mode space algorithm and the time-frequency (TF) multiple invariance rotational invariance technique (MI-ESPRIT). Firstly, a uniform circular array (UCA) is equivalent to a virtual uniform linear array (ULA) by utilizing mode-space algorithm. Then, the smoothed pseudo Wigner-Ville distribution (SPWVD) of the ULA output is calculated. The spatial time-frequency matrix can be obtained through the average of multiple time-frequency points in the time-frequency plane, and the signal subspace can also be obtained through using eigen decomposition. Then a simple and effective subarray dividing approach is proposed, and the multiple rotational invariant equation of the array is obtained by using the Bessel function. Finally, the closed-form solution is obtained using multi-leastsquares (MLS) criterion so that the 2-D DOA estimation of LFM signals in UCA is completed. The simulation results verify the effectiveness of the algorithm proposed by this paper.

Conformal LPDA antenna array for direction finding application

This letter introduces a wideband conformal log-periodic dipole array (LPDA) antenna array mounted on a foam cone for direction finding application. To miniaturize this conformal LPDA antenna array, the LPDA antenna with curvilinear dipoles is used. Simulated and measured results show the LPDA antenna with curvilinear dipoles has good radiation performances. Mounting on a ROHACELL foam cone, the LPDA antenna with curvilinear dipoles maintains its radiation characteristics. The measured results of the conformal LPDA antenna array show that it can be utilized for direction finding application.

An absorptive/transmissive FSS radome with lumped resistors loaded

Combing FSS technology with absorbing conception, an FSS radome with absorptive and transmissive characteristics is presented in the paper. It can transmit electromagnetic wave at around 20.5 GHZ. And below the transmission band, it can absorb energy at the frequency range of 5~15GHz with Sit and S21 both less than -10dB, and with the absorption rate more than 80% (even up to 95% at some frequency range). When the FSS radome is cooperated with a waveguide horn operating at K band, the mono-static RCS of antenna system can be dramatically reduced in the absorbing band by 10dB, which provides a possibility that this FSS radome can be utilized in the military field to reduce RCS and realize the stealthy capabilities. The unit cell is a hexagon format and is duplicated as a honeycomb formation. The pass band is obtained by a metallic FSS with a wide rejection band. The absorbing performance is realized by a lossy layer with metallic strips and lumped resistors, which utilizes the metallic FSS as the ground plane within the absorbing frequency range. The equivalent circuit is given briefly and the working principle is analyzed clearly.

Design of a random distribution frequency selective surface

In this paper, a novel frequency selective surface (FSS) using random distribution method is investigated. This FSS can diffuse the reflected wave analogy to array antenna. The reflectivity of three-layer stacked cross patches are studied at first. Then an array of 20×20 FSS is constructed and simulated. Finally a 300mmx300mm three-layer random surface is fabricated and measured. More than 5dB RCS reduction in 7-20GHz is obtained from measurement. Both the simulation and measurement results demonstrate the validity of this design.

Far-Field Symmetry Analysis and Improvement of the Cavity Backed Planar Spiral Antenna

The far-fleld pattern symmetry of the cavity backed planar spiral antenna is analyzed. We discover that the back radiation of the planar spiral and the cavity efiects degrade the pattern symmetry. To improve the pattern symmetry, an improved method to reduce the back radiation is proposed. Then a novel antenna conflguration is designed. The center section of the planar spiral is replaced with a conical spiral. So the back radiation at higher frequency band can be restrained. The broadside gain, axial ratio and pattern symmetry are compared. The results show that this novel conflguration can achieve better far-fleld symmetry at a wider band.