Compact sub‐6 GHz 5G‐multiple‐input‐multiple‐output antenna system with enhanced isolation

A compact two‐element multiple‐input‐multiple‐output (MIMO) antenna system with improved impedance matching and isolation is presented for future sub‐6 GHz 5G applications. The two identical tapered microstrip line fed modified rhombus‐shaped radiating elements are placed in the same orientation at a compact substrate area of 0.24λ₀ × 0.42λ₀ (where, λ₀ at 3.6 GHz) on a shared rectangular ground. A remodeled T‐shaped ground stub is placed between a pair of radiating element to achieve improved impedance bandwidth and isolation. Further, a split U‐shaped stub connected to center of each radiating element to achieve the desired resonant frequency of 3.6 GHz. The proposed antenna covers a ?10 dB operating band of 3.34 to 3.87 GHz (530 MHz) with more than 20 dB isolation between a pair of elements. MIMO performances are also analyzed and experimentally validated. The measured performances of a prototype are found in good agreement with simulated performances. Further, the simulation study is carried out to see the effect of housing and extended ground plane on two‐element MIMO antenna for practical application. An idea of realization of 12‐element MIMO is also studied using the proposed two‐element MIMO antenna.     

A compact widebeam circularly polarized antenna with wide impedance and axial ratio bandwidths

A compact widebeam circularly polarized antenna with wide impedance and axial ratio (AR) bandwidths is proposed in this study. The antenna is composed of a pair of crossed dipoles, four sequentially rotated parasitic elements, a slotted ground plane with four vertical plates, and four inverted L‐shaped structures. A prototype is fabricated and measured. An impedance bandwidth (S11 < ?10 dB) of 102.4% and a 3‐dB AR bandwidth of 83.5% are measured. And half‐power beamwidth is more than 120° over the whole operating band. Radiation patterns are symmetrical and identical in both principal planes. The compact size of antenna is 0.42λ₀ × 0.42λ₀ × 0.16λ₀.     

Broadband circularly polarized Z‐shaped dipole antenna with parasitic strips

A Z‐shaped dipole antenna with parasitic strips is proposed for wideband and unidirectional circular polarization operation in this article. The dipole arms are bent into L‐shape for circular polarization, and printed balun is used to achieve good impedance matching. To further extend the axial ratio bandwidth, two parasitic strips are employed to introduce an additional band of circularly polarized operation at the high frequency. Measured results demonstrate that the proposed antenna has a 10‐dB impedance bandwidth of 63.3% (1.64‐3.16 GHz) and a 3‐dB axial ratio bandwidth of 51.1% (1.72‐2.9 GHz). Stable radiation patterns with gain around 9 dBic along +z‐axis are also observed.     

A broadband quasi‐Yagi array of rectangular loops on LTCC

In this article, a broadband quasi‐Yagi array of rectangular loops using low‐temperature co‐fired ceramic technology is proposed. The antenna is fed by a simple and compact microstrip‐to‐coplanar strip transition, which serves as balun and impedance transformer simultaneously. Four rectangular loops are used to direct the antenna propagation toward the end‐fire direction. Compared with the planar directors in traditional quasi‐Yagi antenna, they can provide better director effect to improve the radiation performance. Furthermore, they act as good impedance matching elements to broaden the bandwidth. The measured results show that the proposed antenna achieves a wide bandwidth of 42% for S₁₁ < ?10 dB (from 26.1 to 40 GHz), better than 12 dB front‐to‐back ratio, smaller than 14 dB cross polarization and an average gain over 6.5 dBi across the operating bandwidth. The antenna occupies a compact size of 8 × 8 × 1 mm³. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:196–203, 2014.     

A metasurface‐based slit‐loaded wideband circularly polarized crossed dipole antenna

A metasurface‐based low‐profile crossed dipole antenna with wide circularly polarized bandwidth for 2.45 GHz ISM band wireless communications is proposed and fabricated in this article. Consisting of four slit‐loaded rectangular patches, the double‐sided printing crossed dipoles are fed by a pair of vacant‐quarter printed rings which circularly polarized (CP) radiation could be generated. With slits loaded, by properly combining the fundamental mode of the two inverted L‐shaped dipole, the slot mode and extra resonance generated by the AMC surface, a wideband circularly polarized operation can be obtained. After optimization, the final design with an overall size of 0.44λ₀ × 0.44λ₀ × 0.1448λ₀ at 2.4 GHz had measured a 31.6% (2–2.75 GHz) impedance bandwidth and 3 dB axial ratio bandwidths of measured were 23.2% (2.1–2.65 GHz), respectively. In addition, the antenna performed a small gain variation (7.0–7.5 dBic) and a front‐to‐back ratio (FBR) of over 25 dB across the whole CP region.     

Systematic design of 7‐to‐40‐GHz on‐chip mixer based on optimal impedance deviation coefficient

In this article, a 7‐GHz to 40‐GHz ultra‐wideband passive double‐balanced mixer MMIC using compact wideband Marchand balun (CWMB) is presented. The CWMB is analyzed and designed by introducing a novel optimal impedance deviation coefficient. A trade‐off between the needed bandwidth and the acceptable insertion loss in an ultra‐wideband passive‐doubly‐balanced mixer design can be made through introducing the optimal impedance deviation coefficient. Finally, to verify the proposed methodology, a compact wideband passive double‐balanced mixer monolithic microwave integrated circuit (MMIC) was designed and fabricated using a standard gallium arsenide (GaAs) pHEMT technology according to the process characteristics. Experimental results show that an ultra‐wideband mixer MMIC is realized from 7 GHz to 40 GHz (140% fractional bandwidth) with a measured conversion loss between 9.5 dB~12.5 dB (in‐band fluctuation less than 3 dB) and a LO‐to‐RF isolation larger than 34 dB. The measurement results are in good agreement with the simulation results.     

Substrate integrated low‐profile dual‐band magneto‐electric dipole antenna

In this article, a novel substrate integrated low‐profile dual‐band magneto‐electric (ME) dipole antenna is proposed. The entire antenna is constructed by four‐layer printed circuit boards (PCBs). Consequently, the height of the proposed antenna is decreased from 0.25λ₀ to 0.11λ₀ (λ₀ is the free‐space wavelength at 5.5 GHz). By introducing rectangular patches with different sizes as electric dipoles, dual operating bands are achieved. Meanwhile, for the purpose of improving the impedance matching at the lower frequency band, a pair of complementary split‐ring resonators (CSRRs) is etched on the larger rectangular patches. Moreover, the short walls composed of plated through holes operate as a magnetic dipole. The antenna is fed by an equivalent wideband microstrip‐to‐parallel stripline balun. The results show that the antenna obtains dual bandwidths of 4.31‐4.71 GHz (8.8%) and 5.07‐5.89 GHz (14.9%) with VSWR <2, which can be applied for C‐band and 5G WiFi. Over the dual operating bands, stable gain and unidirectional radiation patterns with low polarization and low back lobe are also obtained.     

A low‐profile circularly polarized dielectric patch antenna and array

A square dielectric patch (DP) resonator fusing with the bottom substrate is studied for designing low‐profile circularly polarized (CP) antenna. Based on the theoretical investigation using the constructed analysis model, it can be found that the proposed DP resonator possesses a pair of degenerate dominate modes (TM₁₀₁ and TM₀₁₁), which can be split by introducing perturbations on the DP resonator and then used to design CP antenna fed by a microstrip line directly. To verify the proposed idea, a 2 × 2 array fed by a dual Marchand balun network is designed and implemented. Reasonable agreement between the measured and simulated results is observed. Experimental results show that a measured impedance bandwidth is 380 MHz (5.18‐5.56 GHz) for |S₁₁| < ?10 dB and the 3‐dB axial ratio bandwidth is 90 MHz (5.32‐5.41 GHz). The measured gain is up to 11.77 dBic with a cross polarization of about ?20 dB in the boresight direction.     

A compact dual‐band 2 × 1 metamaterial inspired mimo antenna system with high port isolation for LTE and WiMax applications

This article proposes a compact (43 × 26 × 0.8 mm³) dual‐band two‐element metamaterial‐inspired MIMO antenna system with high port isolation for LTE and WiMAX applications. In this structure, each antenna element consists of a square–ring slot radiator encircling a complementary split ring resonator. A tapered impedance transformer line feeds these radiating apertures and shows good impedance matching. A 2 × 3 array of two‐turn Complementary Spiral Resonator structure between the two antenna elements provides high dual‐band isolation between them. The fabricated prototype system shows two bands 2.34 – 2.47 GHz (suitable for LTE 2300) and 3.35 – 3.64 GHz (suitable for WiMAX). For spacing between two antennas of 10 mm only, the measured isolation between the two antenna elements in the lower band is around ?32 dB while that in the upper band is nearly 18 dB. The system shows a doughnut‐shaped radiation patterns. The peak measured antenna gains for the proposed MIMO system in the lower and higher bands are 3.9 and 4.2 dBi, respectively. The MIMO system figure of merits such as the envelope correlation coefficient, total efficiency are also calculated and shown to provide good diversity performance.     

Ultrawideband circularly polarized antenna with dual band‐notched characteristics

This article presents an ultrawideband (UWB) crossed dipole antenna with circularly polarized (CP) and dual band‐notched characteristics. The proposed design is based on two orthogonal tapered dipoles for UWB CP operation and a square‐shaped cavity for high broadside gain over the entire operating bandwidth (BW). To generate dual band‐notched characteristics, two separated slots are inserted into each dipole's arm. This antenna yields measured impedance BW of 100% (3.2‐9.6 GHz) with dual‐band rejection centered at 5.2 and 5.8 GHz. Correspondingly, dual rejected bands are also observed in the original UWB CP band, which ranges from 3.2 to 8.2 GHz. Additionally, the proposed antenna exhibits high broadside gains better than 6.2 dBic and radiation efficiency greater than 82%.     

Compact dual‐band antenna based on CRLH‐TL for WWAN/LTE terminal applications

In this article, a compact dual‐band antenna based on composite right/left‐handed transmission line (CRLH‐TL) is proposed for WWAN/LTE wireless terminal applications. By using 2 symmetrical CRLH structures, the proposed antenna can easily produce 2 wide separate operating frequency bands with a compact size of 25 × 25 × 6 mm³. Additionally, a pair of matching strips is introduced on both sides of the feeding line to further improve the impedance characteristics of the terminal antenna. The experimental results demonstrate the proposed antenna is capable of working over the frequency ranges of 0.66‐1.06 GHz and 1.68‐2.88 GHz with |S₁₁| < ?6 dB, which can cover the bands of LTE700, GSM850, GSM900, GSM1800, GSM1900, UMTS, LTE2300, and LTE2500 for wireless terminals. Moreover, the multiple input multiple output (MIMO) operating performance of the proposed antenna element is also studied, and an enhanced isolation between the antenna elements is obtained by utilizing the defected ground structures and grounded branches.     

A dual‐polarized cross‐dipole antenna with wide beam and high isolation for base station

In this paper, a dual‐polarized cross‐dipole antenna with wide beam and high isolation is designed and analyzed for base station. The proposed antenna consists of two planar cross dipoles with four square patches, two L‐shaped microstrip lines, two ground plates, four parasitic patches, and a reflector. The square patches are placed between the center of cross dipoles to couple with L‐shaped microstrip lines. By introducing the parasitic patches, the wide beam can be realized. The measured results show that the proposed antenna achieves an impedance bandwidth (|S₁₁| < ?10 dB) of about 18.7% (1.9‐2.35 GHz) and an isolation better than 30 dB. A measured gain of 5.7 dBi and a half‐power beamwidth over 120° at the center frequency are obtained. Furthermore, the size of the proposed antenna is only 0.5λ₀ × 0.5λ₀ × 0.22λ₀ (λ₀ is wavelength at the center frequency).     

A dual‐feed MIMO antenna pair with one shared radiator and two isolated ports for fifth generation mobile communication band

In this article, a pair of unsymmetrical dual‐feed antennas with one shared radiator and two isolated ports is proposed for multiple‐input‐multiple‐output (MIMO) systems. The proposed antenna pair achieves high isolation between the two ports by properly adjusting the distance between the two feeding ports and the position and length of shorting strips on the radiator. The antenna has simple structure and covers the 3.3‐3.7 GHz band, which could meet the demand of future 5G applications. The measured results show that antenna has good impedance matching (better than 10 dB return loss) and high port isolation (better than 20 dB isolation) from 3.35 to 3.65 GHz. The total efficiencies are above 55% and the envelope correlation coefficient is <0.1, which is sufficient for MIMO applications.     

Linearly tapered meander line cross dipole circularly polarized antenna for UHF RFID tag applications

In this article, a circularly polarized antenna for ultra‐high frequency radio frequency identification (RFID) tag is presented. The circular polarization is realized by two orthogonal, unequal length linearly tapered meander line cross dipoles. The meander structure with capacitive tip loading is used for size miniaturization of the antenna. A modified T‐match network is employed to feed the cross dipole structure. The measured 10‐dB return loss bandwidth of the cross dipole antenna is 17 MHz (908‐923 MHz) and the corresponding 3‐dB axial ratio bandwidth is 6 MHz (912‐918 MHz). The overall size of the proposed antenna is 0.17λ₀ × 0.17λ₀ at 915 MHz. The maximum read range between the reader and the tag with the proposed antenna is 4.7 m larger than the analogous linearly polarized tag antenna due to the reduction in polarization loss between the tag and reader antennas. Thus, a maximum read range of 15.66 m with the gain of 1.28 dBic is achieved at 915 MHz.     

Broadband dual‐polarized omnidirectional antenna with simple feeding structure

This paper presents a broadband dual‐polarized omnidirectional antenna with a simple feeding structure. It consists of a monopolar patch element for vertically linear polarization (VP) and a circular printed‐dipole array for horizontally linear polarization (HP). The monopolar patch antenna is loaded with shorting vias and coupled ring in order to broaden the VP bandwidth, nevertheless keeping a low profile. The printed dipoles with integrated balun are arranged on a circular substrate and incorporated with a 1‐to‐4 power divider for achieving the broadband HP omnidirectional radiation. One of the key features is to replace a shorting‐via in the monopolar patch by the coaxial line of the HP element, allowing a simple configuration and not affecting the VP radiation. The final design with a profile of 0.28λ_min has been fabricated and measured. The measurements result in an overlapped impedance bandwidth of 25.4% (2.2‐2.84 GHz) and port‐to‐port isolation of >33 dB. Also, the antenna achieves the peak gain values of 8.0 and 5.6 dBi for the VP and HP radiations, respectively.     

Improved planar Marchand balun using a patterned ground plane

In this article, a novel planar Marchand balun using a patterned ground plane is presented. This new design has a slot under the coupled lines cut on the ground plane so that the even‐mode impedance can be increased substantially. Meanwhile, we propose that two additional separated rectangular conductors be placed under the coupled lines in order to act as two capacitors, so that the odd‐mode impedance will be decreased. The design theory and procedure for optimizing the Marchand balun are presented. As an example, one Marchand balun on a double‐sided PCB is designed, simulated, fabricated, and measured. The measured return loss is found to be better than ?10 dB over the frequency band from 1.2 to 3.3 GHz, or around 100% bandwidth. The measured amplitude and phase imbalance between the two balanced output ports are within 1 dB and 4°, respectively, over the operating frequency band. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

A novel broadband magnetoelectric antenna

A broadband antenna based on magnetoelectric dipole is proposed. The proposed antenna is composed of a bowtie‐shaped electric dipole and an elliptical ring antenna that works as a magnetic dipole. For a broadband performance, a microstrip‐to‐coplanar stripline transition balun is used to excite the antenna. All of them are printed on the same plane perpendicular to the ground. To validate the design, prototypes of the proposed antenna have been fabricated and measured. The measurement results show that the antenna has a wide impedance bandwidth of 66.7% (2.45–4.90 GHz) for voltage standing wave ratio (VSWR) less than 2 and a gain of 6.0–7.3 dBi over the operating frequency band. Meanwhile a high front‐to back ratio better than 16 dB over the operating frequency is achieved. The agreements between the simulation and measurement results indicate that the proposed antenna is suitable for wireless communication systems and phased array systems. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:213–218, 2015.     

A compact balun‐diplexer using interdigital line resonators

A novel compact balun‐diplexer applying new interdigital line resonators (ILRs) is presented in this article. It is found that the proposed ILR can not only reduce circuit size and but also realize high common mode rejection in differential mode operation frequency. By properly converting the symmetric four‐port balanced bandpass filter (BPF) to a three‐port device, a balun BPF with high selectivity and compact size are accomplished using ILRs. Then, the balun‐diplexer can be realized by combining two well‐designed balun filters with two 50 Ω transmission lines. The demonstrated balun‐diplexer with operation at 1.8 and 2.45 GHz have been designed, fabricated, and measured. Excellent performances have been observed. Specifically, 0.4 dB in‐band amplitude error, 1.8 in‐band phase error, more than 50 dB selectivity and 45 dB isolation are obtained. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:485–489, 2015.     

A wideband aperture coupled magneto‐electric dipole with high gain stability

In this article, a wideband aperture coupled magneto‐electric (ME) dipole is proposed. The proposed dipole antenna is based on the traditional ME dipole which consists a pair of horizontal patches and a pair of vertical shorted patches. To achieve a wide impedance bandwidth, a stepped microstrip to slot transition is introduced in the antenna. Then, the vertical part of the dipole is tilted and two metal triangular prisms are employed to enhance the stability of the gain. A prototype antenna is fabricated and tested. Good agreements are found between the simulated and measured results. The measured impedance bandwidth for VSWR ≤2 is more than 125% (2.24‐10.0 GHz). The 1 dB gain bandwidth is about 108% (2.4‐8.0 GHz). Moreover, a stable unidirectional radiation patterns can be found across the 1 dB gain bandwidth.     

High gain flexible liquid crystal polymer based 8‐element printed antenna for millimetric wave applications

In this article, an offset fed printed dipole antenna 2‐element, 4‐element, and 8‐element arrays are developed and analyzed for millimeter wave applications. The 8‐element array antenna is of compact size with dimensions 43.6 × 25.1 × 0.25 mm³. It achieved a broad impedance bandwidth (S₁₁ < ?10 dB) of 15.7 GHz from 24.7 to 40.4 GHz. The mutual coupling between array elements is less than ?35 dB in the operating band. The antenna achieved a gain of 12.62 to 13.1 dB. The 8‐element array antenna is fabricated on liquid crystal polymer material and tested. Impedance matching, far field radiation characteristics, co‐polarized and cross‐polarized patterns and group delay are analyzed in simulation and experimental measurement. The investigated results are in good agreement and hence, the developed array antenna is attractive for wideband millimeter wave applications.