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This paper presents a novel method to design multiple-input multiple-output (MIMO) antennas based on characteristic mode analysis (CMA), which is different from utilizing individual excitation of each characteristic mode for high isolation. The CMA is performed to design a pair of symmetric slots on two connected dipole antennas (a MIMO dipole pair), so that two desired characteristic modes can be generated at the same frequency, one of which is in common mode and the other in differential mode. Hence, when one antenna element is excited, the two characteristic modes combine and cancel each other at the other antenna element, leading to high port isolation. The designed dipole pair is applied for use in 2G/3G/4G MIMO base-station arrays. Simulation and measurement results show that the antenna achieves a wide impedance bandwidth of 1.7-2.7 GHz (45.5%), low coupling below -20 dB, low cross-polarization below -20 dB, high efficiencies over 85%, and stable radiation patterns within the entire band. The results verified the advances of the proposed decoupling method, i.e., simplicity, effectiveness, wide bandwidth, good radiation, etc.

A dual-polarized dual-band antenna with a simple bifunctional metasurface (MS) is proposed. Previous studies often require various elements to design MSs, and most monofunctional MSs are designed to control one intrinsic property of electromagnetic wave. In contrast, the proposed MS uses only one type of element to realize dual functions. In the lower frequency band, the MS helps to excite the TM leaky-wave mode and together with the slot mode to obtain a wide bandwidth of 25.8%. In the higher frequency band, the MS functions as a frequency selective surface to enhance the antenna gain by 6 dB and decreases the distance between the MS and the patch antenna to 0.1 wavelength. By composing the antenna with a pair of stub-loaded slots and a rectangular patch sharing the same ground and diamond-shaped MS, dual bands and dual polarizations are obtained. The MS antenna is first simulated, and then fabricated and measured. The proposed antenna demonstrates the operating bands of 2.12–2.75 GHz (0.63 GHz, 25.8%) for Port 1 and 5.69–5.91 GHz (0.22 GHz, 3.8%) for Port 2, with peak boresight gains of 7.9 dBi at 2.7 GHz and 11.7 dBi at 5.75 GHz.

The performance of a low-profile dielectric resonator (DR) antenna (DRA) is hardly maintained across a wide frequency range due to the multiple higher-order modes. In this letter, a low-profile and broadband DRA is proposed with stable broadside radiation over a wide range of frequencies. A detailed analysis of the excited modes is conducted to identify proper modes for broadband operation. Different air regions are then introduced in the top layer of the proposed DRA. This allows the excitation of the higher-order DR modes with broadside radiation while suppressing the unwanted off-boresight modes. To validate the design, the DRA is developed to cover the frequency range of 3.25–6.1 GHz for potential 5G applications. The fabricated prototype is measured showing a broad bandwidth of ∼64.2%, a peak antenna gain of ∼9 dBi, and a low profile of only ∼0.07λ0.

In this communication, leaky-wave antennas (LWAs) at mm-wave bands are designed on the metal rims of the mobile handsets for mm-wave communications. Two different LWAs, constructed from the rectangular slits and the stepped slits, respectively, are designed at the same frequency band, with their main lobes pointing to different directions. Since the LWAs are narrow, two layers of LWAs can be accommodated along the height of the frame. Hence, the metal frames around the mobile chassis are built by twelve LWAs in total, with four LWAs along each longer edge and two LWAs along each shorter edge of the chassis. Unlike traditional mm-wave antennas in the mobile handset, phased array or feeding networks are not required for the proposed antenna system. The antenna covers a bandwidth from 26.8 to 28.3 GHz. Its coverage efficiency reaches 50% for the gain of above 5.4 dBi, which is better or at least comparable with the phased arrays in the handsets. Due to the distributed arrangement, the antenna system is robust to hand effects and real-life components integrated in the handset. In addition, the LWAs are codesigned with the sub-6 GHz antenna, which reutilizes the shorter frames as the radiator. The whole antenna system has been fabricated, with the measured results agreeing well with the simulated ones.

A simple compact circularly polarized (CP) cross slot antenna with a wide frequency tuning range has been presented in this letter. Four identical varactors are loaded at the ends of the cross slot for varying the operating frequency, and only one voltage is adopted to control the varactors. Distributed inductors and capacitors are employed to realize CP radiation. By varying the value of varactors, a wide tuning frequency range of 41% (1.65–2.5 GHz) is achieved. Stable CP radiation patterns are obtained for all frequencies across the entire operating bandwidth. The proposed antenna is a good radiator that can be used for Internet of Things (IoT) wireless sensing network, WiFi applications, and reconfigurable array developments.

In this communication, a novel dipole configuration with reactive loadings is proposed for the design of low-profile dual-band dual-polarized stacked antenna arrays. For lower band (LB1, 3.3–3.6 GHz) dipole, its inductive loadings are implemented at the end of each dipole arm to suppress the basic resonant mode for band rejection at higher frequencies. For higher band (HB2, 4.8–5.0 GHz) dipole, its LC loadings are implemented at the beginning of each dipole arm, where the inductor and the capacitor, respectively, increase the $Q$ -factor for improving the out-of-band rejection and balance the impedance matching. Hence, LB1 and HB2 dipoles can be closely stacked with high isolation. Moreover, a dual-band artificial magnetic conductor (AMC) reflector is adopted for reducing the distance between the antenna and the ground plane. Consequently, the overall height of the proposed one is only 0.16 $\lambda _{L}$ ( $\lambda _{L}$ being the free-space wavelength at the center frequency of LB1), which is smaller than the previous dual-band stacked designs. The measurement results demonstrate that the array achieves good impedance matching, high isolation, and stable radiation patterns simultaneously, indicating it as a promising candidate for sub-6 GHz base-station services.

A dual-band linearly polarized (LP) and circularly polarized (CP) unidirectional hybrid antenna is proposed in this article. The antenna consists of a cross slot antenna (CSA), a pair of vertical and horizontal metal plates, two side walls, and a cavity reflector, fed by a simple single feeding structure. In the lower frequency band, a loop antenna operating in $1\lambda $ mode is formed by the ground of the CSA, a pair of horizontal plates, and two side walls, to generate the LP radiation. In the higher frequency band, the cross slot works as a magnetic dipole (M-dipole), while the horizontal plates work as an electric dipole (E-dipole). With the appropriate combination, the magnetoelectric (ME) dipole produces an inherent 90° phase difference for the two orthogonal $E$ -fields to achieve CP radiation. The $1\lambda $ modes of the M- and E-dipoles are excited to realize the wideband CP bandwidth. Simulation and measurement are used to study and design the hybrid antenna. The results show that the proposed antenna has an impedance bandwidth (IMBW) of 2.38–2.50 GHz (0.12 GHz, 4.9%) for the LP radiation, and an IMBW of 4.63–7.37 GHz (2.74 GHz, 45.7%) and 3 dB axial ratio bandwidth (ARBW) of 4.10–6.60 GHz (2.5 GHz, 46.7%) for the CP radiation. The radiation patterns at dual bands are stable toward the broadside, having peak gains of 5.75 dBi and 7.53 dBic within the low and high frequency bands.

In this article, a systematic and generally applicable method to synthesize patterns for single antennas is proposed based on characteristic mode analysis (CMA). Both the theoretical analysis and real implementations are taken into consideration. To obtain a desired pattern, we first calculate the weighting coefficient of each mode using the correlation between the characteristic field and the desired pattern. Afterward, the synthesized current and the feeding vector are solved using CMA, providing feeding information, such as feeding numbers, locations, amplitude, and phase. The feeding vector is nonsparse, making practical feeding impossible. In this circumstance, the theory of compressed sensing is applied so that the number of ports can be greatly reduced, and the synthesized pattern is still highly correlated with the desired one. The method is applied to 2-D and 3-D structures, where a mobile handset and a scaled model of the shipboard are utilized as representatives. The prototype of the handset antenna was fabricated and measured, with the desired pattern achieved, having null in the boresight direction and being almost omni-directional on the plane of the chassis. The measured results agree well with the simulated ones. With the synthesized pattern, the handset antenna is robust to the user effects. The method can be generally applied to pattern synthesis for planar and 3-D antennas.

A differentially fed hybrid dipole, slot, and patch antenna with unidirectional radiation patterns is designed in this article. The antenna consists of a metal strip, a patch loaded with a slot, and a simple wideband 180° out-of-phase power splitter (OPS). The OPS can generate two signals with the same amplitude but accurate phase difference of 180° to achieve one-port differential feeding. The hybrid modes of different types of antennas, i.e., dipole, patch, and slot, are excited to obtain five bands. Additionally, the TM01, TM21, and TM03 modes of the patch antenna are excited. By loading the slot and the metal strip, the radiation pattern of TM21 mode is converted from conical to broadside, and the ground walls further concentrate the radiation pattern. The ground walls also enhance the antenna gain, with the increments of 1 dB at 3.5 GHz, 3.4 dB at 4.65 GHz, 4.1 dB at 5.5 GHz, and 1.4 dB at 6.3 GHz. Finally, the antenna is fabricated and measured. The measured results show that the antenna covers five impedance bandwidths (IMBWs) of 1.85–1.91 GHz (3.2%), 3.13–3.66 GHz (15.6%), 4.62–4.98 GHz (7.5%), 5.10–5.82 GHz (13.2%), and 6.10–6.57 GHz (7.4%) for $\vert \,\,{S} _{11}\vert dB. The radiation patterns at each band are toward the broadside, with peak gains of 5.1 dBi at 1.85 GHz, 8.8 dBi at 3.45 GHz, 8.8 dBi at 4.7 GHz, 12.2 dBi at 5.5 GHz, and 9.7 dBi at 6.3 GHz.

A wideband circularly polarized (CP) unidirectional antenna is proposed in this paper. By employing a slot antenna and a pair of horizontal plates as a magnetic dipole and an electric dipole, respectively, the proposed magnetoelectric (ME) dipole antenna is designed for CP radiation. $1-\lambda$ resonant mode of the proposed ME dipole antenna is excited by a single feeding to achieve a wideband characteristic. Simulated results show that the antenna has a wide impedance bandwidth (IMBW) of 4.77-5.5 GHz (0.73 GHz, 14.2%) and 3 dB axial ratio bandwidth (ARBW) of 4.3-5.5 GHz (1.2 GHz, 24.5%). In addition, unidirectional radiation patterns with a peak gain of 5.6 dBi and high radiation efficiency of more than 90% over the operating band are obtained.

In this letter, a low-profile pattern-reconfigurable antenna has been designed. The antenna is modified from a conventional windmill loop antenna, with the radial arms disconnected at the center and a shorting via added between the top and bottom layers. Three different patterns are controlled by three p-i-n diodes, which are located at the center of the bottom layer and operate as switches. A half-wavelength bent dipole with a reflector provides a boresight radiation with directional pattern on the azimuth plane. The second boresight pattern is obtained by a coupled fed half-wavelength dipole together with another one-wavelength dipole. The radiation nulls of the two boresight patterns are complementary to each other on the azimuth plane. A third pattern with omnidirectional radiation on the azimuth plane is obtained when the current is uniformly distributed along the arcs, forming a typical magnetic dipole. The antenna operates at 2.4 GHz wireless local area network (WLAN) band (2.40–2.485 GHz), with the measured average efficiencies of 82%, 82%, and 80% for the three modes, respectively.

Chipless RFID tag is a promising technique for future RFID systems due to its low cost and high reliability. In this paper, three chipless RFID tags are designed based on retro-reflective structures, in order to increase the reading range and enhance the tag's robustness to the direction of the interrogating signals. The three tags include two linearly polarized tags with non-symmetric and symmetric filters and a circularly polarized tag. Before introducing the tag antennas, the design guidelines on how to arrange the filters for higher detection accuracy are provided based on standing wave analysis. Following the rules, retro-radiating tags with filters are designed. Since the E fields from the retro-radiating antennas add constructively in the direction of the incoming signal automatically, the reading distance is greatly increased compared with the conventional tags with orthogonally placed antennas. The tag with symmetric filters and arrangements can further enhance the detection robustness regardless of the reader's positions. Moreover, the circularly polarized tag is insensitive to the polarization of the incoming signals. The experimental results measured in the anechoic chamber show that the retro-radiator based tag can reach a reading distance of 60 cm, which is longer than most of the existing chipless tags. In the measurement, the proposed tag was well detected even when the reader antennas were not at the boresight.

Cardiac hypertrophy is a major pathological process to result in heart failure and sudden death. Rutaecarpine, a pentacyclic indolopyridoquinazolinone alkaloid extracted from Evodia rutaecarpa with multiple pharmacological activities, yet the underlying protective effects and the mechanisms on cardiac hypertrophy remain unclear. This study aimed to evaluate the potential effects of rutaecarpine on pressure overload cardiac hypertrophy. Cardiac hypertrophy in rat was developed by abdominal aortic constriction (AAC) for 4 weeks, which was improved by rutaecarpine supplementation (20 or 40 mg/kg/day, i.g.) for another 4 weeks. The level of angiotensin II was increased; the mRNA expression and the activity of calcineurin in the left ventricular tissue were augmented following cardiac hypertrophy. Rutaecarpine administration decreased angiotensin II content and reduced calcineurin expression and activity. Noteworthily, in angiotensin II-induced cardiomyocytes, rutaecarpine ameliorated the hypertrophic effects in a dose-dependent manner and downregulated the increased mRNA expression and activity of calcineurin. In conclusion, rutaecarpine can improve cardiac hypertrophy in pressure overload rats, which may be related to the inhibition of angiotensin II-calcineurin signal pathway.

A compact dual wideband dual polarized antenna is presented in this paper. The proposed antenna consists of a lower band element, an upper band element, four coaxial cables and a ground reflector. The lower band element is composed of four inductor-ended slots and two 180“ out of phase splitters (OPSs) in a square shape and is excited by Port 1 and Port 2. The upper band element, suspended on the lower band element, embraces two crossed bow-tie dipoles and is excited by Port 3 and Port 4. Simulated results show that the IMBWs of the proposed antenna are 0.65 -1.1 GHz (0.45 GHz, 51.4%) for Ports 1 and 2, and 1.7-2.7 GHz (1.0 GHz, 45.5%) for Ports 3 and 4. The isolation are greater than 34 dB between Port 1 and 2, and greater than 20 dB between Port 3 and 4, respectively. Peak gains of 7.8 dBi within the lower band and 8.8 dBi within the upper band are obtained. The cross polarization suppression are above 55 dB for Port 1 and Port 2 at 0.85 GHz and above 22 dB for Port 3 and Port 4 at 0.85 GHz.

A wideband L-probe fed metasurface (MS) antenna is presented in this paper. The proposed MS antenna is constructed by an MS, an L-probe and a ground plane. The MS is formed with an array of 4 × 4 periodic metal patches and fed by the L-shaped probe for a wideband operation. Simulated results including a wideband impedance bandwidth (IMBW) of 24.6% (2.78-3.56 GHz), a maximum gain of 8.4 dBi, and a high efficiency of more than 92% at 3.15 GHz are achieved. Stable unidirectional radiation patterns are also realized over the whole operating band.

A novel compact wideband circularly polarized (CP) cross-slot antenna (CSA) with flat gain is presented in this paper. The antenna consists of a cross slot with distributed inductor endings, a pair of distributed inductors and a pair of distributed capacitors, and a simple short-ended microstrip feeding line. The two slots are placed in orthogonal positions with the same dimension to generate two orthogonal E-fields, while the 90° phase difference between the two E-fields is achieved by adjusting the distributed capacitors and inductors in the middle, resulting in a wideband CP performance. Simulation results show that the antenna has a wide impedance bandwidth (IMBW) of 2.1-4.0 GHz (63.3%) for S11 < -10 dB and axial ratio bandwidth (ARBW) of 2.3-3.6 GHz (43.3%) for AR < 3 dB. Stable radiation gain is observed across the operating band with a very flat gain at about 2.8 ± 0.2 dBi.

A dual wideband metasurface (MS)-based antenna operating in triple modes is proposed for circularly polarized (CP) operation and these two bands can be controlled independently. The antenna consists of a cross-slot antenna and an MS to generate a dual band at about 3.5 and 5.2 GHz. In the low-frequency band, the large cross-slot radiator (CSR) and the MS are used to generate CP radiation by exciting the degenerate modes of TM10 and TM01. In the high-frequency band, the small CSR and the MS form a cavity, and the small CSR serves as a feeding element to excite two groups of orthogonal degenerate modes, i.e. the first group being TM10 and TM01, and the second being TM12 and TM21, alternately for wideband CP radiation. Simulation and measurement are used to study and design the MS slot antenna. Measured results show that the MS slot antenna has a dual operating band of 3.27–3.87 GHz (0.6 GHz, 16.8%) and 4.41–5.95 GHz (1.54 GHz, 29.7%), peak gains of 6.3 and 7.9 dBic within the low- and high-frequency...

A novel miniaturized dual-band dipole array antenna consisting of two parallel $1 \times 4$ subarrays for use in base stations operating in the digital cellular system (DCS) and wideband code division multiple access (WCDMA) bands is presented. Size miniaturization is realized by utilizing band notch dipoles (BNDs) as array elements and artificial magnetic conductors as reflectors for reductions in width and profile height of the array antenna, respectively. Using the BNDs of high radiation suppression at desired notch frequencies, the radiation from DCS subarray is suppressed in the WCDMA band and vice versa. High isolation between the subarrays, therefore, is achieved while reducing the subarray separation. In addition, a dual four-way unequal power divider is designed for beam pattern synthesis. The measured results show that realized gains of 12.1–12.6 and 12.4–13.1 dBi, respectively, within the DCS and WCDMA bands, as well as the first null depth and sidelobe level, respectively, of lower than −20 and −16 dB, are achieved simultaneously, indicating that the proposed array antenna is suitable for potential base station applications.

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.

This letter presents a wideband cross-slot antenna (CSA) with inductor loadings for dual polarization. The effects of the ground size on the impedance are investigated. To achieve a compact size, a very small ground having the same hypotenuse length as the slot is used. The inductor loadings are used at both ends of the slot to reduce the size further. Simulated results show that the loaded inductors contribute to a more constant impedance to the frequency response at 1- λ mode, and the impedance moves toward the lower frequency with inductors. Based on the constant impedance of the inductor-end slot at 1- λ mode, a dual-polarized CSA using two orthogonal slot radiators is designed. Measured results show that the proposed dual-polarized antenna has wide impedance bandwidths of 56.2% from 1.56 to 2.78 GHz and 60.6% from 1.46 to 2.73 GHz for Ports 1 and 2, respectively, with a high isolation of more than 26 dB over the operating bandwidth. The antenna also has a stable broadside gain of 8.05 ± 0.45 dBi and stable half-power beamwidths of 60.5° ± 1.8° in the E -plane and 76.1° ± 1.5° in the H -plane for Port 1.

In this letter, the high-order mode and ground-edge diffraction of a slot antenna are used to achieve a high gain. To inhibit the multilobes at the high-order mode, ground-edge diffraction is utilized to form a single main lobe by changing the size of the ground plane of the slot radiator. Then, this slot antenna is employed to construct a windmill-shaped array antenna for circular polarization. A four-way sequential-phase feeding network is designed to feed the four slot elements, which are placed in orthogonal positions to form a windmill shape. A reflector is placed under the four slot elements to make the proposed antenna unidirectional. The slot elements are excited in the high-order resonant mode, instead of the fundamental resonant mode, and ground-edge diffraction of the slot elements is used to make the radiation pattern form a single strong lobe with increased gain at the + z -direction. The antenna is studied and designed using simulation and measurement. Measured results show that the proposed antenna has a common bandwidth (overlapping of the impedance bandwidth, the axial-ratio bandwidth, and the 1 dB gain bandwidth) of 4.73–5.53 GHz (0.8 GHz, 15.6%), a realized peak gain of 13.4 dBi, and an efficiency higher than 89.2%.

A low-profile dual-polarized patch antenna with stable radiation pattern for use in base stations operating from 1.7 to 2.7 GHz is presented. The antenna consists of a square patch radiator placed at 20 mm ( $0.14\lambda _{0}$ at the center frequency of 2.2 GHz) above a square ground plane. For bandwidth enhancement, the square patch radiator is dual fed using four probes, each having a U-shape. Two wideband 180° baluns are designed using composite right/left handed transmission lines to generate two signals with same amplitude, but phase shift of 180° for the probes. The radiation pattern is stabilized using four slot groups on the ground plane and a metallic ground wall around the radiating patch. The antenna is studied and designed using computer simulation. Results show that the simulated half-power beamwidths have variations of only 4° and 5° in the elevation (EL) and azimuth (AZ) planes, respectively, across the operating band. Measured results show that the antenna has the impedance bandwidths of 1.68–2.83 GHz and 1.7–2.85 GHz for the two input ports, isolation of more than 38 dB, and cross-polarization of less than −20 dB at the boresight in both the EL and AZ planes. The measured boresight gains are 7.8 ± 0.6 dBi for both two ports, and the radiation efficiencies are 74%–84% and 73%–82% for ports 1 and 2, respectively.

This communication proposes to use the 1- $\lambda $ resonant mode of slot radiator with single feeding for bandwidth enhancement. The impedance of a simple slot radiator is studied using computer simulation. Since operating the slot radiator in the 1- $\lambda $ resonant mode requires a longer slot length, a large square slot is used at both ends of the slot to reduce the required slot length. The results of the study are subsequently used to design a wideband circularly polarized (CP) crossed slot antenna (CSA) with single feeding. The CSA consists of two slot radiators having the same length and placed in a crossed shape, i.e., orthogonal positions. A single microstrip line with a via at the end is used to feed the CSA. By loading reactive elements with appropriate values on each slot near to the feed line, the two slots generate two linearly polarized electric fields with 90°-phase difference for CP operation. The CSA is studied and designed using simulation and measurement. Measured results show that the CSA has a wide impedance bandwidth of 1.52–3.44 GHz (1.92 GHz, 77.4%) and axial-ratio bandwidth of 1.73–3.01 GHz (1.28 GHz, 54%), much wider than the previous directional and bidirectional CSAs using single feeding.

A wideband differentially fed dual-polarized dual-mode antenna is presented in this letter. Four slots are placed a square shape to construct the slot loop antenna, and the outer ground of the slot loop is bended to achieve a compact size. A simple out-of-phase power splitter with a wide bandwidth and accurate 180° phase difference is integrated with the radiator to feed the slot loop. The 1 and 2 λ modes of the slot loop antenna are excited with the differential feeding for a wide impedance bandwidth (IMBW). By loading the distributed inductors at the ends of each slot, a radiator size of 106 × 106 mm2 is obtained to cover LTE700/GSM850/GSM900 bands. Measured results show that the antenna has the IMBWs of 0.63–1.09 GHz (0.46 GHz, 53.5%) and 0.63–1.08 GHz (0.45 GHz, 52.6%) for the two input ports, isolation of more than 31.5 dB, and stable gain of around 7.15 ± 0.35 dBi for Port 1.

A wideband reconfigurable antenna with righthanded circular polarization (RHCP), left-handed circular polarization (LHCP), and linear polarization (LP) is proposed. The antenna consists of a cross slot antenna and a metasurface. Four pin diodes are connected between the slots to achieve the polarization reconfiguration. By loading the metasurface above the slot antenna, the axial ratio bandwidth (ARBW) can be enhanced, and the boresight gain is also increased. The simulated results show that this antenna in RHCP/LHCP has a very wide impedance bandwidth (IMBW) of 4.25~6.52 GHz (42.2 %) and ARBW of 4.79~6.26 GHz (26.6%). The antenna in LP has an IMBW of 5.33~5.84 GHz (9.1%).

An X-band metasurfaced (MS) antenna is proposed for circular polarization (CP) operation. The antenna consists of a patch antenna and a MS, which are printed on a single substrate, resulting in low profile. Results show that, with using the MS, the antenna can achieve an impedance bandwidth (IMBW) of 9.24–10.16 GHz (0.92 GHz, 9.5%) and an axial-ratio bandwidth (ARBW) of 9.54–9.94 GHz (0.4 GHz, 4.1%), and increase the boresight gain by about 2 dB on average within the ARBW.

A compact monopole antenna with a volume of only 8×32×5 mm3 for smartphones applications is presented. The antenna consists of two meander monopoles, having an S-shape and L-shape, on one side of the substrate and a tuning stub on the other side. Simulated and measured results show that the antenna has a dual-band of 824–960 MHz and 1700–3800 MHz which can cover the frequency bands for the GSM850, GSM900, DCS, PCS and UMTS systems and also Band 40, Band 41, Band 42 and Band 43 in the LTE system. The results in gain, efficiency and radiation pattern are also presented.

In this paper, a wideband circularly polarized (CP) slot-antenna array is presented. A feeding network with four output ports is designed using metamaterial transmission line (MM TL) to feed four slot antenna elements, forming a sequential-rotation array (SRA) and resulting in CP operation. The antenna array is studied and designed using computer simulation and measurement. The measured results show that the antenna array has a wide impedance bandwidth (IMBW) of 0.92–3.65 GHz (2.73 GHz, 119.5%) and axial-ratio bandwidth (ARBW) of 1.43–3.59 GHz (2.16 GHz, 86.1%).

A broadband dual-circular polarization (CP) antenna is presented in this paper. The antenna consists of square radiator fed by a feeding network with four outputs. The feeding network is designed using a 3-dB hybrid-coupler chip to obtain a sequential-phase difference of 90° at the four output ports. Simulation shows that the antenna has an impedance bandwidth (IMBW) of 37% (1.1–1.6 GHz) for |S11

A defected ground structure (DGS) with two resonances is proposed to reduce mutual coupling of planar multiple-input-multiple-output (MIMO) antenna. A dual-band MIMO antenna is used for study. The antenna consists of two planar-inverted F-antenna (PIFA) elements printed symmetrically for dual-band operation. The defected ground structure (DGS) is placed between the two PIFA elements to reduce mutual coupling. The antenna is studied and designed using computer simulation, and then fabricated for measurement using the Satimo Starlab system. Results show that the MIMO antenna has the measured bandwidths of 1.56–2.78 GHz (1.22 GHz or 56%) and 4.7–5.82 GHz (1.12 GHz or 21%) in the lower and higher frequency bands, respectively, with mutual coupling of less than −15 dB.

In this paper, a circular polarized electronically-controlled scanning microstrip antenna array is designed, which is based on composite right left-handed transmission line (CRLH TL) and is realized by varactor diodes. Proposed electronically-controlled antenna arrays till now are always linear-polarized as the axial ratio (AR) may be spoiled by the DC feed line, especially in the CRLH TL based case. A more separated CRLH TL integrated with active lumped elements is utilized to solve the problem. The antenna array is composed of the CRLH microstrip transmission line structure and circular polarized microstrip antenna. The direction of the main lobe varies from −1° to −20 ° by continuously modifying the varactor diodes bias voltages from 0 to 20 V with 5 V as a step. The AR remains below 3 dB in the scanning range. The simulation and experimental results show a good consistence.