Hai-Han Sun

Bio: Hai-Han Sun is an academic researcher from Nanyang Technological University. The author has contributed to research in topics: Dipole antenna & Antenna (radio). The author has an hindex of 8, co-authored 36 publications receiving 193 citations. Previous affiliations of Hai-Han Sun include University of Technology, Sydney.

Suppression of Cross-Band Scattering in Multiband Antenna Arrays

Abstract: This paper presents a novel method of suppressing cross-band scattering in dual-band dual-polarized antenna arrays. The method involves introducing chokes into low-band (LB) elements to suppress high-band (HB) scattering currents. The experimental results show that by inserting LB-pass HB-stop chokes into LB radiators, suppression of induced HB currents on the LB elements is achieved. This greatly reduces the pattern distortion of the HB array caused by the presence of LB elements. The array considered is configured as two columns of HB antennas operating from 1.71 to 2.28 GHz interleaved with a single column of LB antennas operating from 0.82 to 1.0 GHz. The realized array with choked LB element has stable and symmetrical radiation in both HB and LB.

Underwater Image Enhancement via Minimal Color Loss and Locally Adaptive Contrast Enhancement

Abstract: Underwater images typically suffer from color deviations and low visibility due to the wavelength-dependent light absorption and scattering. To deal with these degradation issues, we propose an efficient and robust underwater image enhancement method, called MLLE. Specifically, we first locally adjust the color and details of an input image according to a minimum color loss principle and a maximum attenuation map-guided fusion strategy. Afterward, we employ the integral and squared integral maps to compute the mean and variance of local image blocks, which are used to adaptively adjust the contrast of the input image. Meanwhile, a color balance strategy is introduced to balance the color differences between channel a and channel b in the CIELAB color space. Our enhanced results are characterized by vivid color, improved contrast, and enhanced details. Extensive experiments on three underwater image enhancement datasets demonstrate that our method outperforms the state-of-the-art methods. Our method is also appealing in its fast processing speed within 1s for processing an image of size $1024\times 1024 \times 3$ on a single CPU. Experiments further suggest that our method can effectively improve the performance of underwater image segmentation, keypoint detection, and saliency detection. The project page is available at https://li-chongyi.github.io/proj

Scattering Suppression in a 4G and 5G Base Station Antenna Array Using Spiral Chokes

Abstract: This letter presents a novel distributed choking technique, the spiral choke, for scattering suppression in dual-band antenna arrays. The working principle and the scattering suppression capability of the choke are analyzed. The spiral chokes are implemented as low-band radiators in a colocated 4G and 5G dual-band array to suppress cross-band scattering while broadening the bandwidth of the choked element. The experimental results demonstrate that the cross-band scattering in the array is largely eliminated, and the realized dual-band array has very stable radiation performance in both well-matched bands.

A Wideband Base Station Antenna Element With Stable Radiation Pattern and Reduced Beam Squint

Abstract: This paper presents the design procedure, optimization strategy, theoretical analysis, and experimental results of a wideband dual-polarized base station antenna element with superior performance. The proposed antenna element consists of four electric folded dipoles arranged in an octagon shape that are excited simultaneously for each polarization. It provides ±45° slant-polarized radiation that meets all the requirements for base station antenna elements, including stable radiation patterns, low cross polarization level, high port-to-port isolation, and excellent matching across the wide band. The problem of beam squint for beam-tilted arrays is discussed and it is found that the geometry of this element serves to reduce beam squint. Experimental results show that this element has a wide bandwidth of 46.4% from 1.69 to 2.71 GHz with ≥15-dB return loss and 9.8 ± 0.9-dBi gain. Across this wide band, the variations of the half-power-beamwidths of the two polarizations are all within 66.5° ± 5.5°, the port-to-port isolation is >28 dB, the cross-polarization discrimination is >25 dB, and most importantly, the beam squint is <4° with a maximum 10° down-tilt.

Achieving Wider Bandwidth With Full-Wavelength Dipoles for 5G Base Stations

Abstract: A new method of designing full-wavelength dipoles (FWDs) is presented. A dual-polarized antenna is built based on FWDs for base station applications as an example. The antenna has four FWDs arranged in a square loop array form. The employed FWDs are bent upward to maintain a small aperture size, so that the realized element still fits in traditional base station antenna (BSA) array. The antenna is first matched across the band from 1.63 to 3.71 GHz, which can cover both the LTE band from 1.7 to 2.7 GHz and the 5G (sub-6 GHz) band from 3.3 to 3.6 GHz simultaneously. Then, band-stop filters are inserted in the feed networks of the antenna to suppress the radiation between 2.7 to 3.3 GHz. The antenna is fabricated and tested. Experimental results validate the simulation results. Comparing with the previously available FWD that has a bandwidth of 32%, the FWD proposed in this article exhibits a much wider bandwidth of 78%. Moreover, this bandwidth is also comparable to and wider than those of the state-of-the-art BSAs based on half-wavelength dipoles (HWDs). The bandwidth enhancement and footprint reduction of the FWD in this article demonstrate a high potential of FWDs to be used in other applications.

Suppression of Cross-Band Scattering in Multiband Antenna Arrays

Abstract: This paper presents a novel method of suppressing cross-band scattering in dual-band dual-polarized antenna arrays. The method involves introducing chokes into low-band (LB) elements to suppress high-band (HB) scattering currents. The experimental results show that by inserting LB-pass HB-stop chokes into LB radiators, suppression of induced HB currents on the LB elements is achieved. This greatly reduces the pattern distortion of the HB array caused by the presence of LB elements. The array considered is configured as two columns of HB antennas operating from 1.71 to 2.28 GHz interleaved with a single column of LB antennas operating from 0.82 to 1.0 GHz. The realized array with choked LB element has stable and symmetrical radiation in both HB and LB.

Ridge Gap Waveguide Multilevel Sequential Feeding Network for High-Gain Circularly Polarized Array Antenna

Abstract: This paper proposed a wideband, efficient, and high gain circularly polarized (CP) array antenna based on the gap waveguide technology for 30 GHz frequency band applications. The antenna subarray is a $2 \times 2$ slot groove gap waveguide-based cavity-backed antenna. The antenna is fed by a ridge gap waveguide (RGW). Two corners of the radiating slots are truncated to obtain CP radiation, and some corrugations are introduced to the radiating layer to suppress the surface waves between neighbor subarrays. The planar 16-way feeding network based on RGW is utilized to feed the subarrays. The feeding network is multilevel sequential phased with a quadrature phase shift. To validate the array antenna performance, a prototype of the antenna has been manufactured using standard milling technology. The measured reflection coefficient bandwidth is about 22% covering from 28.3 to 35.3 GHz, and a measured 3 dB axial ratio bandwidth of about 21.8% is achieved from 27.8 to 34.6 GHz. The maximum measured gain is 23.5 dBi which is occurred at 30.75 GHz.

Dual-Band Shared-Aperture Base Station Antenna Array With Electromagnetic Transparent Antenna Elements

Abstract: An electromagnetic transparent antenna element is proposed for dual-band shared-aperture fifth-generation (5G) MIMO base station antenna array developments. The antenna element that operates in the low-frequency band (LB) of 1.8–2.7 GHz is placed above the aperture of the antenna array that operates in the high-frequency band (HB) of 3.3–3.8 GHz. Because of this antenna array configuration, the antenna elements in the LB have to be transparent to the electromagnetic waves radiated by the HB antenna array. This kind of electromagnetic transparent antenna element allows the HB antenna array working properly in the dual-band shared-aperture antenna array configuration. In this work, the electromagnetic transparent antenna element is inspired by the element of a typical wide-angle bandpass frequency selective surface (FSS). The radiation performance of the electromagnetic transparent antenna element at the LB is realized by properly combining the wide-angle bandpass FSS elements. A dual-band dual-polarized shared-aperture antenna array is then developed to demonstrate the concept and design. The experimental result validates the stable radiation patterns of each antenna element in both LB and HB. It indicates the proposed approach is promising for 5G MIMO base station antenna array developments.

Compact Dual-Polarized Shared-Dipole Antennas for Base Station Applications

Abstract: Crossed-dipole (CD) antennas have been widely employed for dual polarization in wireless communication systems in recent years. In this paper, a novel design concept of dual-polarized shared-dipole (DPSD) antenna is presented. Different from the traditional CD antennas, the arms of the DPSD antenna are shared for two orthogonal polarizations. This design technique leads to significant size reduction and high isolation compared to the traditional CD antennas. The operation principle of the proposed antenna is theoretically analyzed. To validate the presented design concept, two novel DPSD antennas are designed, fabricated, and measured. The first design is a four-port DPSD antenna, which is a straightforward demonstration of the operation principle of the DPSD antenna. The second design is a highly integrated DPSD antenna, which avoids the use of a feed network and provides a simple configuration to design the dual-polarized antenna. Both of the DPSD antennas are designed to operate at 1.7–2.7 GHz for base station applications. The simulated and measured results confirm that the two DPSD antennas have wide bandwidth with VSWR 35 dB dB. In addition, stable gain and half-power beamwidth are obtained with the variance less than ±0.55 dB and ±3.5°, respectively.

Scattering Suppression in a 4G and 5G Base Station Antenna Array Using Spiral Chokes

Abstract: This letter presents a novel distributed choking technique, the spiral choke, for scattering suppression in dual-band antenna arrays. The working principle and the scattering suppression capability of the choke are analyzed. The spiral chokes are implemented as low-band radiators in a colocated 4G and 5G dual-band array to suppress cross-band scattering while broadening the bandwidth of the choked element. The experimental results demonstrate that the cross-band scattering in the array is largely eliminated, and the realized dual-band array has very stable radiation performance in both well-matched bands.