Neutralization Lines Research Articles

ISOLATION ENHANCEMENT TECHNIQUES IN MIMO ANTENNA SYSTEMS: A SURVEY

In this survey paper, we discuss various techniques that can be employed to enhance isolation between multiple-input and multiple-output (MIMO) antennas. In this modern world, the MIMO antenna system is an important technique used in wireless technology. The channel capacity in a multipath environment can be improved by deploying multiple antenna elements, i.e., the MIMO technique at both the transmitter and receiver terminals. To have an efficient MIMO technique, the isolation between the multiple antenna elements must be as high as possible. In the past decade, many research works have proposed techniques to enhance isolation in MIMO antennas. In this survey, we examined various mutual coupling reduction techniques employed to improve isolation in multiple antenna elements and compared them based on various performance metrics. Isolation enhancement techniques such as stubs, filters, defected ground structure, decoupling networks, orientation of the radiating elements, parasitic elements, periodic structures, neutralization lines, metamaterials, etc., are discussed in this paper.

Compact Millimeter-Wave Array With Wide-Angle Scanning for Mobile Phones

This paper describes a compact four-element wide-angle scanning millimeter-wave array for mobile phones. The wide-angle scanning array with four elements is achieved with a small element spacing of 0.3λ0. Two critical difficulties for the compact array with 0.3λ0 spacing are the realization of the small element and the mutual coupling reduction between each element. For the small antenna element, a modified quarter-wavelength shorted patch antenna element working at the 25.5-27.5 GHz is designed. The coupled shorted structure and coupled feeding structure of the element is designed to reduce the H-plane cross-polarization level (XPL) which is a key drawback of quarter-wavelength shorted patch antenna. For the mutual coupling of the four-element array with 0.3λ0 spacing, three compact neutralization lines (NLs) are applied to reduce the mutual coupling to better than -15 dB. Finally, the proposed compact four-element array only occupies a small size of 1.14λ0 × 0.3λ0, which is the smallest mm-wave four-element array in the open literature. Also, the proposed array can scan from -60° to 60° with a peak gain of 9 dBi, a gain fluctuation less than 1.3 dB, a good sidelobe level, and an acceptable cross-polarization level. The proposed mm-wave array with the superior performance of a small array size and wide beam scanning is promising for modern mobile phones.

Neutralization‐line‐based decoupling for miniaturized MIMO antenna array

AbstractIn this paper, a miniaturized multiple‐input, and multiple‐output (MIMO) antenna array is proposed based on quarter‐mode substrate‐integrated waveguide. The decoupling structure of composite neutralization lines (NLs) is used to improve the isolation of the MIMO antenna array. Each NL comprises a simple metal strip attached to each of the two antenna radiators to create an extra coupling path that opposes the primitive antenna coupling to reduce mutual coupling. Eventually, the 2 × 2 MIMO antenna array is fabricated and implemented to verify the design. The measured impedance bandwidth of S11 less than −10 dB ranges from 3.48 to 3.52 GHz, and the peak gain of the element is 4.87 dBi, the mutual coupling levels between the orthogonal and the parallel antenna elements are −19.2, −22.6, and −17.9 dB, respectively, making it a suitable candidate for MIMO systems.

Decoupling of MIMO antenna array based on half-mode substrate integrated waveguide with neutralization lines

This paper proposes a miniaturized multiple-input and multiple-output (MIMO) antenna array based on half-mode substrate integrated waveguide (HMSIW). Initially, quarter-mode on the conventional HMSIW is introduced to widen the operating bandwidth while enabling the antenna to remain miniaturized. Then, the quasi-electric wall characteristics of metal via are adopted to orthogonally arrange four antenna elements without a gap to reduce the array size further. Next, the decoupling structure of composite neutralization lines (NLs) is used to improve the isolation of the MIMO antenna array. Each NL comprises a simple metal strip attached to each of the two antenna radiators to create an extra coupling path that opposes the primitive antenna coupling to reduce mutual coupling. Eventually, the 2 × 2 MIMO antenna array is fabricated and implemented to verify the design. The simulated and measured results are in good agreement. The measured impedance bandwidth of S11 less than −10 dB ranges from 5.05 to 5.43 GHz, and the peak gain of the element is 7.93 dBi on the broadside at the center frequency of 5.35 GHz, and the array gain reaches 10.09dBi. The mutual coupling levels between the orthogonal and the parallel antenna elements are −19.2, −19.1, and −15.9 dB, respectively. The overall size of the antenna array is only 1.06λ0 × 1.06λ0 × 0.025λ0, making it a suitable candidate for fifth-generation MIMO systems.

A Design of Fractal Hilbert MIMO Antenna for 5G Mobile

This paper presented two new fractal Hilbert MIMO antenna designs with different two thicknesses (0.8mm and 1 mm) and used hybrid techniques between neutralization lines (NL) and defected ground structure (DGS), to enhance mutual coupling of the antenna for 5G applications. Higher isolation and smaller size are major advantages of this design. ​The proposed fractal Habrit curve MIMO antennas were fabricated for the 3800 - 5460 MHz and 3735-5390 MHz bands with a 49 dB and 40 dB return loss and high isolation of 19.67 dB and 18.5 dB, using FR4 with dimensions of (24 × 45 × 0.8mm3) and (24 × 45 × 1mm3) respectively. The results prove that the MIMO antenna is suitable for a sub-6 band that is qualified for 5G smartphone applications.

Space Efficient Meta-Grid Lines for Mutual Coupling Reduction in Two-Port Planar Monopole and DRA Array

Traditionally used mutual coupling (MC) reduction techniques such as electromagnetic bandgap structures, isolators and neutralization lines require extra space between radiators. Besides, metamaterial-based techniques require multi-layer arrangements. However, the proposed meta-grid lines overcomes the above demerits by integrating meta-grid lines in the ground plane itself. As a proof-of-concept, two-port CPW-fed monopole antenna array (TPCFMAA) and two-port DRA array (TPDRAA) are designed, fabricated and tested. It has been observed that the TPCFMAA has mutual coupling below −20 dB for frequency between 2.6 to 4.4 GHz. The envelope correlation coefficient reduces from 0.072 to 0.026 by integrating meta-grid lines in the ground plane of the TPCFMAA. At 3.5 GHz, the inter-element distance between the antennas is noted to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${0.015}\lambda _{\mathrm {h}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{\mathrm {h}}\,\,=$ </tex-math></inline-formula> highest operating wavelength). The TPDRAA’s operating frequency can be tuned by changing the parameters of the annular ring slot in the excitation patch. The bandwidth of TPDRAA can be further increased by merging the two resonances of the two annular ring slots in the excitation patch. For TPDRAA, the measured −10 dB impedance bandwidth is from 5.65 to 6.55 GHz. The mutual coupling between the antenna elements is seen to be below −16 dB for an inter-element spacing of 4.8 mm, which is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.090\lambda _{\mathrm {h}}$ </tex-math></inline-formula> . The measured gain of TPDRAA within the bandwidth is from 4.17 dBi to 5.2 dBi. The TPCFMAA can be used in 3.5 GHz Internet of Vehicles (IoV) multi-user MIMO service, whereas the TPDRAA can be used for satellite communication in the 5.925 to 6.425 GHz frequency band, WiMAX in the 5.7 to 5.85 GHz band, ISM in the 5.725 to 5.85 GHz band, and WLAN in the 5.8 GHz band.

Octaband WWAN/LTE Dual-Antenna System Decoupled by Two Neutralization Lines with Inductors for Smart Phones

A decoupled octaband WWAN/LTE dual-antenna system occupying a size of 80 mm × 15 mm × 6.8 mm for smart phones is proposed. The proposed antenna system consists of two antenna elements with symmetrical geometry, two neutralization lines (NLs) with embedded inductor, and an inverted-T branch. The two NLs mainly reduce the mutual coupling at the desired lower (704–960 MHz) frequency band, while the inverted-T branch mainly reduces the mutual coupling at the desired higher (1710–2690 MHz) frequency band. The fabricated prototype has a −6 dB impedance bandwidth of 0.3 GHz (0.69–0.99 GHz) and 1.2 GHz (1.66–2.86 GHz) which cover the LTE700, GSM850, GSM900, DCS, PCS, UMTS, LTE2300, and LTE2500 bands. Within these bands, the measured mutual couplings are lower than −10 dB. The measured antenna efficiencies are about 42.6%–60% and 58.3%–78.7% at the desired lower and higher frequency bands, respectively. The diversity performance and the SAR performance are also evaluated.

Dual-Band 2 × 2 MIMO Antenna with Compact Size and High Isolation Based on Half-Mode SIW

This paper presents a close-spaced dual-band 2 × 2 multiple-input multiple-output (MIMO) antenna with high isolation based on half-mode substrate integrated waveguide (HMSIW). The dual-band operation of the antenna element is achieved by loading a rectangular patch outside the radiating aperture of an HMSIW cavity. The HMSIW cavity is excited by a coaxial probe, whereas the rectangular patch is energized through proximity coupling by the radiating aperture of HMSIW. The antenna elements can be closely placed using the rotation and orthogonal arrangement for a 2 × 2 array. Small neutralization lines at the center of the MIMO antenna can increase the isolation among its elements by around 10 dB in the lower band and 5 dB in the higher band. A prototype of the MIMO antenna is fabricated and its performance is measured. The measured results show that the resonant frequencies are centered at 4.43 and 5.39 GHz with bandwidths of 110 and 80 MHz and peak gains of 6 and 6.4 dBi, respectively. The minimum isolation in both bands is greater than 35 dB. The envelope correlation coefficient is lower than 0.005 within two operating bands.

Compact 2 × 2 MIMO Antenna With Low Mutual Coupling Based on Half Mode Substrate Integrated Waveguide

This communication proposes a novel compact multiple-input multiple-output (MIMO) antenna with low mutual coupling based on a 2 ×2 dual-polarized half-mode substrate integrated waveguide (HMSIW). The antenna is printed on a single-layer substrate to provide a low profile and ease of integration with planar circuits. The proposed HMSIW antenna element operates in TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> mode and can be orthogonally arranged with two slots on the ground between the antenna elements, resulting in low mutual coupling. The edge-to-edge element space is only 0.033λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ( λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength). A new miniaturized decoupling structure of neutralization lines is proposed to further reduce the mutual coupling by -10 dB in comparison with the ground slot structure. The 2×2 MIMO antenna was fabricated and implemented to verify the design. The simulated and measured results were in good agreement. The measured impedance bandwidth of |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | less than -10 dB ranges from 5.025 to 5.135 GHz, and the peak gain is 5.6 dBi on the broadside at the center frequency of 5.08 GHz. The mutual coupling levels between the orthogonal and the parallel antenna elements are -45 and -36 dB, respectively. The envelope correlation coefficient is lower than 0.003 across the operating bandwidth. The overall size of the antenna is only 1.08λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×1.08λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.025λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , making the antenna a suitable candidate for upcoming fifth-generation MIMO systems.

Compact Uniform Circular Quarter-Wavelength Monopole Antenna Arrays With Wideband Decoupling and Matching Networks

Two novel decoupling and matching networks (DMNs) in microstrip technology for three-element uniform circular arrays (UCAs) are investigated and compared to a more conventional DMN approach with simple neutralization lines. The array elements are coaxially-fed quarter-wavelength monopole antennas over a finite groundplane. Three-element arrays are considered since UCAs with an odd number of elements are able to provide an almost constant maximum array factor over the whole azimuthal angular range. The new designs are explained from a theoretical point of view and their implementations are compared to four- and three-elements UCAs without DMN in terms of decoupling and matching bandwidth as well as beamforming capabilities. In addition to excellent decoupling and matching below -16 dB, a broader bandwidth is obtained by the two DMNs. The reasons for the enhanced bandwidth are similar in both cases: By introducing several circuit elements offering additional degrees of freedom, matching of the monopole input impedances at different frequencies becomes feasible. One of the presented designs offers a larger bandwidth, while the other design is able to provide a better total efficiency. Scattering parameters, radiation patterns, beamforming capabilities, and enhanced gain are all verified by measurements over the operating bandwidth.

Investigation of 2-port UWB MIMO diversity antenna design using characteristics mode analysis

In this research work, a 2-port UWB MIMO diversity antenna is designed to operate from 2.7 to 10.5 GHz with −10 dB impedance bandwidth of 118.18%. The proposed design has a total size of 0.57λ2.7×0.28λ2.7 (λ2.7 is lowest operating wave-length) consists of bi-planar printed fractal radiators whose feeds are contorted in geometry and are diametrically-fed. Characteristics mode analysis (CMA) is introduced to investigate antenna design, feeding technique and modal current distributions. The analysis includes study of modal dynamics, resonance mechanism, bandwidth potentials and modal radiation quality factor. The port-isolation is ⩾−15 dB when ground plane is truncated by rectangular slots via ellipsoid slot. With an end-connected ground thin neutralization lines, mutual coupling is further reduced by 7.5 dB (>−22.5 dB, measured). The diversity performance metrics are evaluated from ECC, CCL, DG, multiplexing efficiency, MEG and TARC. ECC is low <0.17 (from far-field magnitudes) and mean effective gain for both ports are |MEG| < 3 dB with MEG1MEG2 ≊ 1, which is serviceable for UWB multi-standard mobile/wireless/sensor ad-hoc diversity systems. An equivalent circuit model is also designed and the prototype of antenna is fabricated and measured to validate its performance.

A General and Systematic Method to Design Neutralization Lines for Isolation Enhancement in MIMO Antenna Arrays

A general and systematic approach is the first time proposed in this paper to design the neutralization line (NL) for isolation enhancement in multiple-input multiple-output (MIMO) antenna arrays. Each NL consists of a metal strip and a reactive component attached at its middle position. It is connected with every two antenna radiators to generate an additional coupling path against the original antenna coupling for isolation enhancement. A general network model that leads to a systematic design procedure is developed to meet the required isolation criteria. Three practical examples are presented and used to verify the proposed NL-based decoupling technique (DT). The measurement results align well with simulations. For all these examples, good impedance matching, isolation over 25 dB, total radiation efficiencies over 70%, and very low envelop correlation coefficients (ECCs) can be achieved simultaneously after adopting the proposed NL DT. Compared with previous decoupling works using parasitic elements, decoupling networks or NLs, the proposed method can achieve either a much wider decoupling bandwidth or a much smaller antenna separation distance while keeping a low design complexity along with systematic design procedure.

COMPACT DUAL-FREQUENCY MICROSTRIP ANTENNA ARRAY WITH INCREASED ISOLATION USING NEUTRALIZATION LINES

An effective technique utilizing neutralization lines to increase the isolation of a compact two-element dual-frequency microstrip antenna array is proposed in this paper. Two neutralization lines connect the two elements at the edge of each radiating patch. The positions and lengths of the two neutralization lines are studied to get the best performance of element isolation. A prototype of the proposed design was fabricated to validate the results. The measured results agree well with the simulated ones. It is shown that an increase of about 25 dB at the lower frequency and that of 17 dB at the upper frequency in isolation between the two antennas have been achieved.

Decoupled Dual-Antenna System Using Crossed Neutralization Lines for LTE/WWAN Smartphone Applications

A decoupled dual-antenna system for Long Term Evolution (LTE)/Wireless Wide Area Network (WWAN) smartphone applications is presented. The proposed dual-antenna system is composed of two symmetric antenna elements and two crossed neutralization lines. The antenna element of the proposed dual-antenna system consists of a driven branch and a parasitic ground branch, generating a couple of resonant modes. The dual-antenna system incorporates two crossed neutralization lines to reduce the mutual coupling between the two closely spaced antenna elements. A measured impedance bandwidth with S11 lower than -6 dB over 702-968, 1698-2216, and 2264-3000 MHz is obtained. Within the operating bands, the measured S21 is lower than 10 dB. Based on the measured 3-D radiation patterns, several important figures of merit for the diversity performance of the dual-antenna system are calculated, including the envelop correlation coefficient, the mean effective gain, and the diversity gain, and good results are obtained.

A Wideband Printed Dual-Antenna With Three Neutralization Lines for Mobile Terminals

A wideband printed dual-antenna for mobile terminals is studied. The dual-antenna, consisting of two symmetric antenna elements and three neutralization lines (NLs), is printed on a printed circuit board. The three NLs reduce the mutual coupling within a wide frequency band. The working mechanism of the three NLs is analyzed based on the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$S$</tex></formula> -parameters, the surface current distributions, and a simplified equivalent model which provides intuitive instructions to optimize the three NLs. A prototype shows that the measured <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$-$</tex></formula> 10 dB impedance bandwidth is 1.3 GHz (1.62–2.92 GHz) and the measured mutual coupling is lower than <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$-$</tex></formula> 15 dB at the 1.66–2.84 GHz band. It covers the GSM1800, GSM1900, UMTS, LTE2300, LTE2500, and 2.4-GHz WLAN bands. The radiation patterns are measured and the diversity performances are evaluated.

Comparison of Compact Monopole Antenna Arrays With Eigenmode Excitation and Multiport Conjugate Matching

The compactness of antenna arrays is highly restricted due to the mutual coupling between the radiation elements, which degrades the performance of impedance matching, radiation efficiency and antenna diversity. For this reason, networks based on eigenmode theory or conjugate matching methods have been introduced in a number of previous works to overcome these effects. With this objective, a matching and decoupling network is required between the input ports and the antenna array, whose function is to improve power matching and ports decoupling. In this paper, three designs with one-layer microstrip line structure of matching and decoupling networks based on a balun technique and neutralization lines are discussed. Two two-element monopole antenna arrays with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$0.1 \lambda $</tex></formula> separation and a four-element monopole array with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$0.07 \lambda $</tex></formula> separation operating around 2.5 GHz are fabricated and measured. The theoretical analysis is based on the scattering matrix. A comparison of the two approaches is illustrated in the paper. Good matching and decoupling behavior of the antenna arrays is found. Overall, it is found that arrays with only <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$0.1 \lambda $</tex></formula> element separation or even less can provide reasonable antenna performance.

Wideband Printed MIMO/Diversity Monopole Antenna for WiFi/WiMAX Applications

A novel printed diversity monopole antenna is presented for WiFi/WiMAX applications. The antenna comprises two crescent shaped radiators placed symmetrically with respect to a defected ground plane and a neutralization lines is connected between them to achieve good impedance matching and low mutual coupling. Theoretical and experimental characteristics are illustrated for this antenna, which achieves an impedance bandwidth of 54.5% (over 2.4-4.2 GHz), with a reflection coefficient <;-10 dB and mutual coupling <;-17 dB. An acceptable agreement is obtained for the computed and measured gain, radiation patterns, envelope correlation coefficient, and channel capacity loss. These characteristics demonstrate that the proposed antenna is an attractive candidate for multiple-input multiple-output portable or mobile devices.

Studies on the potency test of antiserum for Weils disease by the intracutaneous method.

A method for estimating the leptospiricidal activity of therapeutic antiserum for Weil's disease was improved by using the intracutaneous method in guinea pigs. The neutralization curves between the leptospiral suspensions for challenge and the antisera were shown to be linear over a wide range of the dosis of the pathogen. Although the reproducibility of the neutralization experiments was high, a significant divergence was observed among the slopes in various test samples. However, the trouble due to such a discrepancy in the slope may practically be reduced if such an antiserum preparation that has a regression coefficient close to the mean of those of various neutralization lines constructed by many different products is adopted as the reference. A practical method for the potency test was suggested.

狂犬病ウイルス免疫動物における脳乳剤の中和作用について

Horie, et al. reported that the animals intraperitoneally immunized with rabies virus had shown the protection to the intracerebral challenge of the virus, and was not always parallel to the neutralizing activity of the serum (Serum antibody), but was parallel to the neutralizing activity of the perfused brain-emulsion (Brain antibody).In this paper an investigation of the characteristics of Brain antibody formed in mice and guinea pigs which intraperitoneally inoculated with the rabies virus (strain CVS) was presented.The results are summarized as follows:1) The approximate slope rates of neutralization lines of Brain antibody and Serum antibody were 2.0 and 1.0, respectively.2) The slope of neutralization line of Brain antibody heated at 56°C for 30minutes was 2.0 and it was identical with the slope of the original non-heated Brain antibody.3) The slopes of neutralization line of mouse Serum antibody added with the normal mouse brain-emulsion, and of neutralization line of guinea pig Serum antibody added with the guinea pig brain-emulsion immunized with Japanese B Encephalitis virus, and of neutralization line of the mouse brain-emulsion injected intracerebrally with the anti-rabies mouse serum, were identical with the slope of the original Serum antibody.4) The slope of neutralization line of guinea pig Brain antibody added with the immune serum of guinea pigs immunized with Japanese B Encephalitis virus was identical with the slope of the original Brain antibody.5) The Brain antibody blocking test was carried out by using the anti-globulin serum. As a result, it was shown that Brain antibody was blocked by the anti-globulin serum and its neutralizing capacity diminished.6) The neutralizing capacity of Brain antibody was not influenced by the super centrifugation at 100, 000G for 1hour.As stated above, both Brain antibody and Serum antibody had the characteristics as the antibody, but there was the certain difference between two neutralization lines. It was thought that the mechanism of neutralization reaction of both antibodies might not be analogous.