A double-layer mushroom structure is proposed to enhance the interelement isolation of a four-element antenna system, wherein four closely positioned substrate-integrated cavity-backed slot (SICBS) antenna elements are configured for multiple-input multiple-output (MIMO) applications. A wall with a double-layer mushroom structure is positioned in between the four antenna elements. An antenna prototype with a ground plane size of ${\mathbf{0}}.{\mathbf{96}}\;{{\mathbf{\lambda }}_{\mathbf{0}}} \times 0.96\;{{\mathbf{\lambda }}_{\mathbf{0}}}$ ( ${{\mathbf{\lambda }}_{\mathbf{0}}}$ is the free space-wavelength at 2.4 GHz) demonstrates an enhanced interelement isolation of 16 dB for parallel-directed antenna element pairs, while the isolation of the orthogonally directed antenna element pairs remains unchanged over the operating bandwidth ( $\vert {{\mathbf{S}}_{{\mathbf{11}}}}\vert ) of 2.396 –2.45 GHz. With the enhanced isolation larger than 42 dB between each antenna element pair, the envelope correlation coefficient (ECC) is lower than 0.02 across the operating bandwidth. The simulated and measured results validate the good MIMO diversity performance of the proposed antenna system.

Enhanced Isolation of a Closely Spaced Four-Element MIMO Antenna System Using Metamaterial Mushroom

The single- and dual-layer metasurfaces are proposed to miniaturize a low-profile wideband antenna. The single- and dual-layer metasurfaces consist of one and two square patch arrays, respectively, both supported by grounded dielectric substrate to form the waveguided metamaterials. After retrieving the effective refractive index along the propagation direction in the waveguided metamaterial, the effective propagation constant is subsequently derived to initially estimate the resonant frequencies of the dual-mode antenna. With the increased effective refractive index, both the proposed antennas realize the gain greater than 6.5 dBi over the bandwidth of ~30% with a reduced radiating aperture of $0.46\lambda _{0} \times 0.46\lambda _{0}$ and a thickness of $0.06\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength at 5.5 GHz). Moreover, the dual-layer metasurface provides more freedom to increase the effective refractive index with achievable gap widths compared with the single-layer metasurface.

Miniaturized Wideband Metasurface Antennas

A low-profile dual-polarized dipole antenna using wideband artificial magnetic conductor (AMC) reflector with stable radiation pattern for use in 2G/3G/4G base stations operating from 1.7 to 2.7 GHz is presented. The antenna consists of a pair of crossed-dipoles and a wideband AMC reflector which consists of an AMC surface, a metallic ground plane, and the air substrate between them. The AMC is designed to operate with 90° reflection-phase bandwidth of 1.64–2.88 GHz (54.8%). Compared with using perfect electric conductor reflector, the profile height of the dual-polarized dipole antenna using AMC reflector is reduced by half from 36 to 18 mm, resulting in the lowest-profile 2G/3G/4G base station antenna. Six metallic ground walls are used to stabilize the radiation pattern, and the resulted half-power beamwidths are around 68±3° and 81±3° in the H- and V-planes, respectively, across the operating band. More measured results show that wide impedance bandwidths of 1.67–2.98 and 1.64–3.05 GHz for the two input ports, isolation of more than 25 dB, and cross-polarization of less than −20 dB are achieved.

A Low-Profile Dual-Polarized Dipole Antenna Using Wideband AMC Reflector

In this letter, a structure of a small ultra-wideband (UWB) monopole antenna, its design optimization procedure as well as experimental validation are presented. According to our approach, antenna compactness is achieved by means of a meander line for current path enlargement as well as the two parameterized slits providing additional degrees of freedom that help to ensure good impedance matching. For the sake of reliability, the antenna design process (simultaneous adjustment of multiple geometry parameters) is carried out using high-fidelity EM analyses. Surrogate-based optimization involving an auxiliary coarse-discretization EM model it utilized to accomplish the design in practical timeframe. Penalty function approach allows us to reduce the antenna footprint (to only $15.8 \times 22~\hbox{mm}^2$ ) while maintaining acceptable reflection in the UWB frequency range. Experimental validation of the design is also provided.

Structure and Computationally Efficient Simulation-Driven Design of Compact UWB Monopole Antenna

In this paper, an integrated design with a multiple-input multiple-output (MIMO) antenna system for fourth generation (4G) and fifth generation (5G) applications is presented. The proposed design contains a two-element slot-based MIMO antenna system for 4G and a connected antenna array (CAA)-based two-element MIMO antenna system for a potential 5G band. Two rectangular loops are etched on the periphery of the ground plane. The top and bottom portions of the thin loops act as the two 4G MIMO antennas, while parts of their sides are acting as 5G arrays. The antenna system is fabricated on a commercially available Roger 4350 substrate with $\epsilon _{r}$ equal to 3.5, while the dimensions of the board are $100\times 60 \times 0.76$ mm3 representing a typical smart phone back plane size. The integrated antenna system covers multibands at 4G with a combined bandwidth of 1.565 GHz (−6 dB BW) in addition to the band between 16.50 and 17.80 GHz for 5G. The design is planar, low profile, simple, and compact in structure making suitable for wireless handheld devices and mobile terminals. The measured gain at 3.46 GHz was at least 2.22 dBi and at 17 GHz was 8 dBi for the 4G and 5G MIMO antenna systems, respectively. The envelope correlation coefficient was also calculated from the measured 3-D patterns and showed good MIMO performance. This is the first integrated 4G/5G MIMO antenna system with below 6 GHz and above 10-GHz covered bands using CAA.

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A Two Concentric Slot Loop Based Connected Array MIMO Antenna System for 4G/5G Terminals

In this letter, a new broadband circularly polarized (CP) printed-slot antenna fed by a coplanar waveguide (CPW) is designed and fabricated. To achieve a broadband CP wave, an S-shaped slot is employed in the ground to produce orthogonal surface currents for right-hand circular polarization (RHCP). Furthermore, an L-shaped radiator is introduced to obtain a broad impedance bandwidth that can cover the whole CP bandwidth completely. Good agreement is achieved between the simulation and measurement, which shows that the presented antenna covers an impedance bandwidth (S11 <; -10 dB) of 104% from 1.78 to 5.64 GHz, and a 3-dB axial-ratio bandwidth (ARBW) of 58.6% from 2.85 to 5.21 GHz. The surface current analysis and a parametric study of the design are also carried out to explain the mechanism of circular polarization.

CPW-Fed S-Shaped Slot Antenna for Broadband Circular Polarization

In this letter, a new compact ultrawideband (UWB) antenna with band-notched characteristic is proposed for UWB communication applications By using a C-shaped ground, the overall dimension of the proposed antenna is dramatically decreased to 24 × 28 × 1 mm3 To avoid potential interferences, interdigital capacitance loading loop resonator (IDCLLR) is utilized to reject certain bands within the passband of the antenna Due to its high capacitance, the resonator has a smaller size and forms a narrower notched band than many other structures, thus the present design effectively saves many more useful frequencies Good agreement is achieved between the simulation and measurement, which shows that the proposed antenna has an operation frequency band from 3 to 13 GHz with good rejection to the wireless local area network bands (WLANs) (52- and 58-GHz bands)

Compact UWB Band-Notched Antenna Design Using Interdigital Capacitance Loading Loop Resonator

A new compact antenna design with broad bandwidth and quad-sense circular polarization (CP) is presented in this letter. The broadband property is achieved based on a compact monopole structure. Furthermore, the quad-sense CP wave is obtained by a ground plane embedded with a T-shaped slit (TSS) and an annular patch etched by an X-shaped slit (XSS). Good agreement is achieved between the simulation and measurement, which shows that the presented antenna covers the impedance operations from 3.1 to 22.2 GHz ( S11 <; -10 dB), reaching the particularly broad bandwidth of 150%. Moreover, the design achieves good CP waves at Worldwide Interoperability for Microwave Access (WiMAX) (3.626-3.772 GHz) for left-hand CP (LHCP), the wireless local area network band (WLAN) (4.951-5.18 GHz) for right-hand CP (RHCP), X-band (10.9392-11.0456 GHz), and Ku-band (15.14-17.2 GHz) for LHCP. Simulated and measured results show that the CP 3-dB axial-ratio (AR) bandwidths are 4.02%, 4.51%, 1%, and 12.74% with a parasitic notch at the frequency of 17.75 GHz to realize good CP characteristics in quad bands.

A Compact Antenna With Broad Bandwidth and Quad-Sense Circular Polarization

A compact dual-band multiple-input–multiple-output (MIMO) antenna array with eight elements is proposed for the Long Term Evolution (LTE)/Worldwide Interoperability for Microwave Access (WiMAX) mobile applications. The dual-band MIMO array consists of four U-slit etched planar inverse-F antennas (PIFAs) and four L-slit etched PIFAs. The two types of PIFAs are placed orthogonally to reduce mutual coupling between them. With the presented decoupling methods in the design including the disconnection of ground plane, the parasitic resonant strips, and also the modified PIFAs, the excellent element isolation (above 20 dB) and other good MIMO performance are achieved. The overall dimension of the MIMO system is only 140 $\,\times\,$ 70 $\, \times\,$ 9.55 mm $^{3}$ , and good return loss (above 10 dB) is achieved across the operating bands (2.6–2.8 and 3.4–3.6 GHz) for all the PIFA elements. The radiation patterns and envelope correlation coefficient (ECC) of MIMO system are also studied, showing quasi-omnidirectional radiation and accepted envelope correlation coefficient across the dual-band operation for mobile communications.

Isolation-Improved Dual-Band MIMO Antenna Array for LTE/WiMAX Mobile Terminals

A new design of a compact ultra-wideband (UWB) antenna with multiple band-notched characteristic is presented. The proposed antenna utilised a C-shape ground to realise miniaturisation and two mushroom-type electromagnetic-bandgap (EBG) structures to create notched bands. The EBG structure which comprises a slotted patch and an edge-located via can form a narrower notched band than many other structures, thus the presented design effectively saves many more useful frequencies. The antenna achieves an operation frequency band from 3 to 13GHz with good rejection to the Worldwide Interoperability for Microwave Access (WiMAX) and the wireless local area network (WLAN) bands in both simulated and measured results.

Guihong Li

Papers

CPW-Fed S-Shaped Slot Antenna for Broadband Circular Polarization

Compact UWB Band-Notched Antenna Design Using Interdigital Capacitance Loading Loop Resonator

A Compact Antenna With Broad Bandwidth and Quad-Sense Circular Polarization

Isolation-Improved Dual-Band MIMO Antenna Array for LTE/WiMAX Mobile Terminals

Design of compact UWB band-notched antenna by means of electromagnetic-bandgap structures