A broadband dual-polarized planar antenna is proposed for 2G/3G/LTE base stations. The dual-polarized antenna is composed of two perpendicularly crossed bow-tie dipoles. Each bow-tie dipole is excited by a microstrip stub that is directly fed by a coaxial line, making the dual-polarized antenna full planar. Due to the coupling between two crossed bow-tie dipoles, a broad bandwidth is achieved. It is shown that the dual-polarized antenna has a bandwidth of 45% (1.7-2.7 GHz) for return loss >15 dB with an isolation of higher than 30 dB between two polarization input ports. The dual-polarized antenna has a half-power beam width (HPBW) of around 65 ° and an average gain of 8.5 dBi for slant ±45° polarizations. An 8-element dual-polarized planar antenna array is developed for base station applications. A bandwidth of 56% (1.63-2.9 GHz) is obtained for the antenna array. The antenna gain of the array is about 16 dBi and the HPBW is 65±8° for each polarization.

A Broadband Dual-Polarized Planar Antenna for 2G/3G/LTE Base Stations

A compact, high performance, and novel-shaped ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with low mutual coupling is presented in this paper. The proposed antenna consists of two radiating elements with shared ground plane having an area of $50\times 30$ mm2. F-shaped stubs are introduced in the shared ground plane of the proposed antenna to produce high isolation between the MIMO antenna elements. The designed MIMO antenna has very low mutual coupling of (S21 7.4 dB), high multiplexing efficiency ( ${\eta }_{\mathrm {Mux}}> -3.5$ ), and high peak gain over the entire UWB frequencies. The antenna performance is studied in terms of S-Parameters, radiation properties, peak gain, diversity gain, envelop correlation coefficient, and multiplexing efficiency. A good agreement between the simulated and measured results is observed.

Mutual Coupling Reduction Using F-Shaped Stubs in UWB-MIMO Antenna

Nowadays synthetic aperture radar (SAR) and multiple-input-multiple-output (MIMO) antenna systems with the capability to radiate waves in more than one pattern and polarization are playing a key role in modern telecommunication and radar systems. This is possible with the use of antenna arrays as they offer advantages of high gain and beamforming capability, which can be utilized for controlling radiation pattern for electromagnetic (EM) interference immunity in wireless systems. However, with the growing demand for compact array antennas, the physical footprint of the arrays needs to be smaller and the consequent of this is severe degradation in the performance of the array resulting from strong mutual-coupling and crosstalk effects between adjacent radiating elements. This review presents a detailed systematic and theoretical study of various mutual-coupling suppression (decoupling) techniques with a strong focus on metamaterial (MTM) and metasurface (MTS) approaches. While the performance of systems employing antenna arrays can be enhanced by calibrating out the interferences digitally, however it is more efficient to apply decoupling techniques at the antenna itself. Previously various simple and cost-effective approaches have been demonstrated to effectively suppress unwanted mutual-coupling in arrays. Such techniques include the use of defected ground structure (DGS), parasitic or slot element, dielectric resonator antenna (DRA), complementary split-ring resonators (CSRR), decoupling networks, P.I.N or varactor diodes, electromagnetic bandgap (EBG) structures, etc. In this review, it is shown that the mutual-coupling reduction methods inspired By MTM and MTS concepts can provide a higher level of isolation between neighbouring radiating elements using easily realizable and cost-effective decoupling configurations that have negligible consequence on the array’s characteristics such as bandwidth, gain and radiation efficiency, and physical footprint.

/pdf/a-comprehensive-survey-on-various-decoupling-mechanisms-with-8ltuxavmy7.pdf

A Comprehensive Survey on “Various Decoupling Mechanisms With Focus on Metamaterial and Metasurface Principles Applicable to SAR and MIMO Antenna Systems”

The design of a four-band slot antenna for the global positioning system (GPS), worldwide interoperability for microwave access (WiMAX), and wireless area network (WLAN) is presented. The antenna consists of a rectangular slot with an area of ${\mathbf{0}}.{\mathbf{37}}{\lambda _g} \times {\mathbf{0}}.{\mathbf{14}}{\lambda _g} = {\mathbf{48}} \times {\mathbf{18}}\;{\bf m}{{\bf m}^{\mathbf{2}}}$ (where ${\lambda _g}$ is the guide wavelength), a $T$ -shaped feed patch, an inverted $T$ -shaped stub, and two $E$ -shaped stubs to generate four frequency bands. The radiating portion and total size of the antenna are less than those of the tri-band antennas studied in literature. Parametric study on the parameters for setting the four frequency bands is presented and hence the methodology of using the design for other frequency bands is proposed. The multiband slot antenna is studied and designed using computer simulation. For verification of simulation results, the antenna is fabricated and measured. The simulated and measured return losses, radiation patterns, realized peak gains, and efficiencies of the antenna are presented. Measured results show that the antenna can be designed to cover the frequency bands from 1.575 to 1.665 GHz for the GPS system, 2.4–2.545 GHz for the IEEE 802.11b&g WLAN systems, 3.27–3.97 GHz for the WiMAX system, and 5.17–5.93 GHz for the IEEE 802.11a WLAN system. The effects of the feeding cable used in measurement and of the cover are also investigated.

A Multiband Slot Antenna for GPS/WiMAX/WLAN Systems

A very compact ultrawideband (UWB) multiple-input multiple-output (MIMO) antenna with high isolation is presented in this letter. The proposed antenna, consisting of two UWB slot antennas, has a very compact size of $22 \times 26~\hbox{mm}^{2}$ , which is smaller than most of UWB antennas only with single antenna element. A T-shaped slot is etched on the ground to improve the impedance matching characteristic in the low-frequency and reduce the mutual coupling for the frequencies $ \geq 4~\hbox{GHz}$ . By etching a line slot to cancel out original coupling, isolation enhancement at the 3–4 GHz band is achieved. The antenna possesses a low mutual coupling of less than $ - 18~\hbox{dB}$ over the operating band from 3.1–10.6 GHz. The performance of this antenna both by simulation and by experiment indicates that the proposed antenna is a good candidate for UWB applications.

Isolation Enhancement of a Very Compact UWB-MIMO Slot Antenna With Two Defected Ground Structures

A compact multiple-input-multiple-output (MIMO) antenna is presented for ultrawideband (UWB) applications. The antenna consists of two open L-shaped slot (LS) antenna elements and a narrow slot on the ground plane. The antenna elements are placed perpendicularly to each other to obtain high isolation, and the narrow slot is added to reduce the mutual coupling of antenna elements in the low frequency band (3-4.5 GHz). The proposed MIMO antenna has a compact size of 32 ×32 mm
 2 
, and the antenna prototype is fabricated and measured. The measured results show that the proposed antenna design achieves an impedance bandwidth of larger than 3.1-10.6 GHz, low mutual coupling of less than 15 dB, and a low envelope correlation coefficient of better than 0.02 across the frequency band, which are suitable for portable UWB applications.

Compact Printed MIMO Antenna for UWB Applications

In this letter, a modified antipodal Vivaldi antenna is presented. A novel tapered slot edge (TSE) structure is employed in this design. The proposed TSE has the capacity to extend the low-end bandwidth limitation and improve the radiation characteristics in the lower frequencies. A prototype of the modified antenna is fabricated and experimentally studied as well. The measured results show reasonable agreement with the simulated ones that validate the design procedure and confirm the benefits of the modification.

A Miniaturized Antipodal Vivaldi Antenna With Improved Radiation Characteristics

A coax-feed wideband dual-polarized patch antenna with low cross polarization and high port isolation is presented in this letter. The proposed antenna contains two pairs of T-shaped slots on the two bowtie-shaped patches separately. This structure changes the path of the current and keeps the cross polarization under -40 dB. By introducing two short pins, the isolation between the two ports remains more than 38 dB in the whole bandwidth with the front-to-back ratio better than 19 dB. Moreover, the proposed antenna achieving a 10-dB return loss bandwidth of 1.70-2.73 GHz has a compact structure, thus making it easy to be extended to form an array, which can be used as a base station antenna for PCS, UMTS, and WLAN/WiMAX applications.

Wideband Dual-Polarized Patch Antenna With Low Cross Polarization and High Isolation

A novel triband square-slot antenna with symmetrical L-strips is presented for WLAN and WiMAX applications. The proposed antenna is composed of a square slot, a pair of L-strips, and a monopole radiator. By employing these structures, the antenna can yield three different resonances to cover the desired bands while maintaining small size and simple structure. Based on this concept, a prototype of a triband antenna is designed, fabricated, and tested. The experimental results show the antenna has the impedance bandwidths of 480 MHz (2.34-2.82 GHz), 900 MHz (3.16-4.06 GHz), and 680 MHz (4.69-5.37 GHz), which can cover both WLAN in the 2.4/5.2-GHz bands and WiMAX in the 2.5/3.5-GHz bands.

Compact Triband Square-Slot Antenna With Symmetrical L-Strips for WLAN/WiMAX Applications

In this paper, an eight-element MIMO array for 5G smartphone applications in the 3.45-GHz band (3.3–3.6 GHz) is presented. The array consists of two types of four-antenna arrays (U-shaped and L-shaped coupled-fed loop elements), which are symmetrically distributed in the inner of the smartphone frame. The dimension of the system circuit board is $124\,\,\text {mm}\times 74$ mm and the size of two elements is $4.8\,\,\text {mm}\times 9.8$ mm ( $0.055\lambda \times 0.11\lambda $ , $\lambda $ represents the free-space wavelength at 3.45 GHz) and 4.9 $\text {mm}\times 12.5$ mm ( $0.056\lambda \times 0.14\lambda$ ), respectively. The proposed MIMO array is simulated, and a prototype is fabricated and tested. The results show that all the elements can cover the desired band of 3.3–3.6 GHz under the condition of −6-dB impendence bandwidth. The isolations are enhanced to 15 dB by combining the inverted-I ground slots with neutralization line (NL) structure. In addition, the envelope correlation coefficient (ECC) via any two elements is below 0.15 that shows good independence in far-field radiation characteristic. The measured efficiencies of the elements in the operating band are higher than 40%. Moreover, the array ergodic channel capacity is also calculated based on the correlation matrix method to be about 35 bps/Hz with a 20-dB signal-to-noise ratio. In addition, the effects of the user’s hand and the head has been analyzed as well. Based on the above, the proposed eight-element MIMO array is a prospective candidate for future 5G smartphone applications.

/pdf/high-isolation-eight-element-mimo-array-for-5g-smartphone-x49030ee8k.pdf

Wei Hu

Papers

Compact Printed MIMO Antenna for UWB Applications

A Miniaturized Antipodal Vivaldi Antenna With Improved Radiation Characteristics

Wideband Dual-Polarized Patch Antenna With Low Cross Polarization and High Isolation

Compact Triband Square-Slot Antenna With Symmetrical L-Strips for WLAN/WiMAX Applications

High-Isolation Eight-Element MIMO Array for 5G Smartphone Applications