Dual-band Operation Research Articles

A Novel 3-Way Dual-Band Doherty Power Amplifier for Enhanced Concurrent Operation

This article presents the architecture and design methodology for a new type of dual-band Doherty power amplifier (DB-DPA), referred to as 3-Way DB-DPA, which consists of a main amplifier for each band and an auxiliary amplifier handling both bands. The 3-Way DB-DPA improves the average drain efficiency in concurrent dual-band operation compared to the traditional 2-Way DB-DPA, by avoiding early clipping in the main amplifiers, while benefiting from load—pulling from the auxiliary power amplifier (PA). This improvement is verified in theory and simulation at the current-source reference planes and in measurement with a fabricated 1.5- and 2-GHz dual-band PA. A statistical analysis using 2-D continuous-wave (CW) signals with long-term evolution (LTE) probability distribution functions (PDFs) is performed and demonstrated an improvement in the concurrent average efficiency by 15 percentage points compared to the conventional 2-Way DB-DPA. In nonconcurrent operation, the measured CW drain efficiency in the lower band (1.5 GHz) is 82.8% at peak and 66.6% at 9.6-dB backoff, and the measured CW drain efficiency in the upper band (2.0 GHz) is 70.0% at peak and 48.4% at 9.4-dB backoff. The CW concurrent-balanced drain efficiency reaches 66.2/52.0% in the 3-Way DB-DPA at 3-/6-dB backoff. In single-band operation at 1.5/2.0 GHz, the average power and average drain efficiency after linearization by digital predistortion (DPD) are 35.1/37.4 dBm and 65.0/53.7%, respectively, for an LTE signal with 10-MHz bandwidth and 6.1-dB peak-to-average power ratio (PAPR). In concurrent operation, the 3-Way DB-DPA is driven by two 10-MHz LTE uncorrelated signals at 1.5 GHz with 6.86-dB PAPR and at 2.0 GHz with 6.26-dB PAPR, and the average total power and average concurrent drain efficiency after DPD are 37.5 dBm and 54.24%, respectively.

Design and implementation of a dual band bioinspired leaf rectenna for RF energy harvesting applications

In this article, both design and implementation of a novel Omni-directional bioinspired Linden leaf-shaped rectenna are reported. The antenna is designed for the energy harvesting purposes under the operation frequency range between 1.6 and 2.65 GHz with a second harmonic rejection property. At the rectifier stage, voltage doubler circuit is designed and implemented with the help of microstrip transmission lines, which are used for impedance matching procedure between the antenna and the rectifier for the optimum power transfer from the antenna to the load for the operation dual bands of universal mobile telecommunication service and WIFI. In the design, SMS7630Schottky diodes, high frequency capacitors and inductors are used as the main surface mount devices. The FR4 epoxy material is selected as a substrate material for both the antenna and the rectifier circuit due to its low cost and easy—production scheme. The maximum efficiency value realized at the dual band operation is 42% at the 0 dBm input power level. The output voltage value and the harvested power at this point are nearly 960 mV and 0.42 mW with an optimum load RL = 2.2 KOhm. The implemented system can be used efficiently for the RF energy harvesting applications for the proposed frequency bands.

High-Efficiency Triple-Band RF-to-DC Rectifier Primary Design for RF Energy-Harvesting Systems

Radio Frequency (RF) energy harvesting has been emerged as a potentially reliable method to replace the costly and difficult to maintain source of low-power wireless sensor networks. A plethora of dual-band rectifier designs has been proposed in the literature operating in various frequency bands. In this paper, a triple-band RF-to-DC rectifier that operates in the frequency bands of LoRaWAN, GSM-900, and WiFi 2.4 GHz is presented. The system is composed of an impedance-matching circuit, an RF-to-DC rectifier, that converts the ambient RF energy into DC voltage able to feed low-power devices, and an output load. The proposed system resonates at three different frequencies of 866 MHz, 948 MHz and 2423 MHz, which fall within the aforementioned frequency bands of interest. The feasible solution of the proposed system was based on a dual-band rectifier operating in the frequency bands of LoRaWAN and GSM-900. A series of shunt stubs was utilized in the initial design to form the feasible solution of the proposed system. The proposed triple-band rectifier was optimized using a powerful optimization algorithm, i.e., the genetic algorithm. The overall system exhibited improved characteristics compared to the initial design in terms of its resonance. Numerical results demonstrated that the overall system exhibited an efficiency of 81% with 3.23 V of the output voltage, for an input power of 0 dBm and a load of 13 kOhm.

A dual-band circularly polarized antenna using a metallized ferrite disk

We have designed and fabricated a dual-band circularly polarized antenna using a normally magnetized ferrite disk. The disk is metallized on top and is mounted on a grounded dielectric substrate. A hole is then punched at the center of the top metallization. The dual band operation of the antenna is due to two separate unidirectional resonances. The field intensity at the lower resonance is largest close to the outer periphery of the disk whereas at the higher resonance the electromagnetic field is concentrates near the punched hole. A two-section feeding network is used to feed the antenna. Central frequencies of the upper and lower bands are 4.62 GHz and 5.97 GHz, respectively. Experimental impedance bandwidths are 1.5% for the upper band and 3.5% for the lower band with respective axial ratio bandwidths of 17% and 3.3%. Axial ratio beam-width of the antenna is 90–125 degrees in the lower band and 80–130 degrees for the upper band with respect to the bore-sight. Antenna gain at upper and lower frequencies are 5.5 dB and 7.1 dB. Cross polarization of the antenna is 25 dB at both frequency bands.

Coplanar Waveguide-fed Electrically Small via-less Antenna for Dual Band Applications

In this paper, a simple coplanar waveguide fed compact electrically small antenna for dual-band operations without the use of via is presented. The resonances of the structure are obtained by spiraling one of the ground planes of an open-ended CPW transmission line with a short length center feed. The proposed antenna has a geometrical dimension of 0.079λ 01 × 0.079λ 01 mm2 (λ 01 is the free space wavelength of first resonant frequency) with a small electrical size (ka) of 0.35. The experimental studies on the fabricated prototype of the proposed antenna show a 2:1 VSWR bandwidth up to 2.53% and 4.12% for 2.3 and 5.3 GHz, respectively. The simulated antenna reflection and radiation characteristics are demonstrated with physical measurements.

Low-profile dual-band implantable antenna for compact implantable biomedical devices

In this paper, A miniaturized dual-band implantable antenna using meandered line resonator is proposed for bio-telemetry applications. The proposed antenna has dual-band (0.91 GHz and 2.45 GHz) operation, covering the important Industrial, Scientific and Medical (ISM) bands. Miniaturization is achieved using meandered resonator and a square slot etched in the ground plane. The performance of the proposed antenna inside a quasi-implantable biomedical device (IBD) is analysed in a homogeneous skin model, human intestine and human head. The measurements are performed by implanting the quasi-IBD inside a saline solution and minced pork meat. The quasi-IBD consists of the proposed antenna, batteries and printed circuit board (PCB) with electronic components on it. The proposed antenna has compact dimensions of 5.6 ×5.8× 0.25 mm3. The measured peak gains in the minced pork meat are −22.9 dBi and −22.1 dBi at 0.91 GHz and 2.45 GHz, respectively. The low specific absorption rate (SAR) of the proposed antenna allows maximum input power of 3.32 mW at 0.91 GHz and 4.37 mW at 2.45 GHz. To the best of the authors’ knowledge, this is the most compact dual-band implantable antenna reported in the literature for 0.91 GHz and 2.45 GHz ISM bands.

Design of a linear to circular polarization converter integrated into a concrete construction for radome applications

AbstractIn this paper, we present a linear to circular polarization converter integrated in a concrete structure to eliminate signal transmission problem originated from the concrete buildings in microwave regime. Two polarization converter samples and a control specimen made by traditional concrete are designed and their signal transmission responses are compared experimentally. Axial ratio values which can be calculated by the ratio between the co-polar transmission and cross-polar transmission results of the proposed samples are below 3 dB and highly sufficient for linear to circular polarization conversion activity. The operating frequency for the proposed sample 1 is between 6 and 6.5 GHz with 500 MHz of bandwidth. The proposed sample 2 exhibits dual-band operation covering frequency bands, 4.58–5.13 and 6.0–6.4 GHz with bandwidths of 550 and 400 MHz, respectively. Operating frequencies of the samples are in the WIMAX frequency bands. In addition, the liner to circular polarization converter design integrated to concrete has a huge potential to improve reflection and directivity parameters of many antennas if it is considered as a radome.

A novel compact dual‐band circular/linear polarization switchable slot annular antenna with filtering network

A novel compact dual-band circular/linear polarization (CP/LP) switchable slot annular antenna with integrated filtering network is proposed in this paper. The feed network is composed of a couple of stepped impedance resonators (SIR) with favorable dual-band filtering characteristic. The SIR structure loaded with T-shape branches can adjust the center frequency more flexibly especially for dual band operating. A PIN diode is welded on the slot antenna to achieve the transform between the linear polarization and the circular polarization of the filtering antenna. The proposed dual-band CP antenna easily achieves 10 dB impedance bandwidth of 140/180 MHz and 3-dB axial-ratio bandwidth approximating 230/210 MHz at 2.6/4.8 GHz.

Design and Realization of a Frequency Reconfigurable Antenna with Wide, Dual, and Single-Band Operations for Compact Sized Wireless Applications

This paper presents a compact and simple reconfigurable antenna with wide-band, dual-band, and single-band operating modes. Initially, a co-planar waveguide-fed triangular monopole antenna is obtained with a wide operational frequency band ranging from 4.0 GHz to 7.8 GHz. Then, two additional stubs are connected to the triangular monopole through two p-i-n diodes. By electrically switching these p-i-n diodes ON and OFF, different operating frequency bands can be attained. When turning ON only one diode, the antenna offers dual-band operations of 3.3–4.2 GHz and 5.8–7.2 GHz. Meanwhile, the antenna with single-band operation from 3.3 GHz to 4.2 GHz can be realized when both of the p-i-n diodes are switched to ON states. The proposed compact size antenna with dimensions of 0.27λ0 × 0.16λ0 × 0.017λ0 at the lower operating frequency (3.3 GHz) can be used for several wireless applications such as worldwide interoperability for microwave access (WiMAX), wireless access in the vehicular environment (WAVE), and wireless local area network (WLAN). A comparative analysis with state-of-the-art works exhibits that the presented design possesses advantages of compact size and multiple operating modes.

A Low-Profile Dual-Band Patch Antenna With Simultaneous Wide Beamwidth and High Gain by Using Multiresonant Modes

A low-profile aperture-coupled microstrip patch antenna (MPA) under multiresonant modes for wide half-power beamwidth (HPBW), high gain and enhanced-bandwidth is proposed. Firstly, the radiation patterns of the MPA are studied to improve the radiation performance. It demonstrates that the HPBW of the lower TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode could be progressively widened by properly selecting the dielectric constant of the substrate. Meanwhile, by etching a rectangular slot, the high sidelobe in E-plane of the upper TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> mode could be obviously reduced, resulting in enhancing the normal gain. Secondly, the improved feeding network is introduced and studied. The results show that the impedance bandwidth of the antenna is successfully extended over dual operating bands. Finally, the proposed antenna is fabricated and tested. Experimental results show that the antenna has improved-bandwidths (| <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | < –10 dB) with two-minimum poles in the range of 1.42–1.45 GHz for the lower band and 3.95–4.13 GHz for the upper band, respectively, which is about two times wider than that of the traditional counterpart. Besides, the antenna maintains the small thickness of about 0.02 free-space wavelength. Particularly, the wide E-plane HPBW and broadside gain of the MPA are simultaneously enhanced to around 130° and 9.0 dBi at the lower and upper bands, respectively.

Design and experimental verification of compact dual-band SIW power dividers with arbitrary power division

Abstract This paper communicates the design and experimental validation of dual-band SIW power dividers (single-stage and double-stage) with arbitrary power division. The dual-band power dividers are developed for WiMAX (3.5 GHz) and WLAN (5 GHz) applications. The proposed SIW power dividers are realized by a rectangular cavity, two rows of metallic-vias and one pair of unequal complementary split-ring resonators (CSRRs). Two resonating frequencies are produced below the waveguide cut-off frequency due to the unequal CSRRs etched-out on the top-surface of the cavity, which results in size reduction. To realize arbitrary power division, two output-ports are configured asymmetric with respect to input-port. The power division is varied by altering the distance between the two output-ports. Finally, two compact dual-frequency power dividers (single-stage and double-stage) working at 3.5 and 5 GHz are designed and validated through fabrication and measurement. The fabricated prototype exhibits dual-band operation, compact size (0.027 λ g 2 ${\lambda }_{g}^{2}$ ), good magnitude imbalance, return loss and isolation.

Investigation on dual‐band equilateral triangular shaped dielectric resonator antennas for WLAN applications

In this article, two configurations of dual-band equilateral triangular dielectric resonator antennas (ETDRAs) for WLAN applications are proposed namely, configuration-I and configuration-II. The configuration-I uses single ETDRA for dual-band operation; whereas, configuration-II includes two ETDRAs to operate as a dual-band antenna. Both the antenna configurations, which uses 99.7% alumina material having a dielectric constant of εr = 9.9, are excited to operate in the bands of 2.4 to 2.5 GHz and 5.75 to 5.85 GHz. The antennas are excited using a conventional coaxial feed to have a simple feeding mechanism. Prototypes of both the antenna configurations are fabricated and measured. The radiation characteristics of the antennas are discussed. The circuit analysis for the proposed configurations of the dual-band ETDRA is also performed and an appropriate equivalent circuit for each dual-band ETDRA is presented. Further, the performance of the proposed configurations of the dual-band antennas are also compared with other dual-band DRAs reported in the literature.

Low-Pass Filter Based Integrated 5G Smartphone Antenna for Sub-6-GHz and mm-Wave Bands

To maintain the compactness of future 5G smartphones, integration of sub-6 GHz and millimeter-wave (mm-wave) bands is a challenging task due to the large frequency ratio. We, therefore, propose a single-fed triple-band antenna with a large frequency ratio. The proposed antenna is composed of a microstrip patch radiator with an inverted U-shaped slot for dual-band operation in the mm-wave frequencies (28 and 38 GHz). A meandered radiating structure is linked to the microstrip patch radiator through a compact microstrip resonant cell (CMRC) low-pass filter (LPF), which is used for the integration of these structures to be operated at 3.5 GHz. A compact size of 22 mm ×10 mm ×0.508 mm for the proposed antenna was realized by incorporating the radiator slot, an LPF, the truncated ground, and a meandered line structure. Wide, decoupled -10 dB bandwidths of 12.9%, 5.8%, and 2.4% at 3.5, 28, and 38 GHz, respectively, were realized for the proposed MIMO antenna without utilizing an external decoupling structure. A detailed safety study with respect to specific absorption rates and power densities was analyzed in data, reading, and talking modes. Finally, the measurements were performed in an anechoic chamber, and the measured results were in a good correlation with the simulation results.

Quasi-continuous linear phase-gradient metamaterial based on conformal spoof surface plasmon polaritons

In this work, we propose a method of achieving quasi-continuous linear phase gradient for transmitted waves based on conformal spoof surface plasmon polariton (SSPP). To this end, a SSPP structure with high transmission is firstly designed as the unit cell of the metamaterial. To obtain the phase gradient, SSPP structures are arranged delicately in a way that they are conformal to the brachistochrone curve. In this way, quasi-continuous linear Pancharatnam-Berry (PB) phase profile can be realized strictly along one of the two transverse directions. To verify this idea, a dual-band transmissive metamaterial operating in X and Ku band was designed, fabricated and measured. Due to the phase gradient imparted by the conformal SSPP structures, high-efficiency anomalous refraction can be realized within the two bands. Different from the general PGM, the phase gradient of the conformal SSPP structure allows us to achieve the desired anomalous refraction angle without reconstructing the PB phase. Both the simulation and measurement results are well consistent with theoretical predictions. This work provides another strategy of achieving anomalous refraction and may find applications in beam steering, digital beam forming, etc.

Dual-band magneto-electric dipole antenna with high-gain for base-station applications

The paper presents the results of a novel high-gain dual-band magneto-electric dipole (MED) antenna. The antenna comprises two pairs of horizontal metal plates of different heights that are excited by a Γ-shaped feedline structure. The antenna is entirely made of metal plates. Compared to traditional MED antennas, the proposed design exhibits dual-band operation with a higher radiation gain whose frequency ratio can be modified by simply adjusting the heights of the two magneto-electric dipole segments. This feature is necessary for cellular base-station applications. The operation and characteristics of the antenna are validated by the measurements. The measured results confirm the proposed antenna achieving fractional bandwidths of 13.31% (801.9–916.2 MHz) and 19.76% (1710.7–2085.7 MHz) for S11 ≤ −10 dB. It has stable unidirectional radiation patterns and optimum radiation gains of 9.2 dBi and 7.8 dBi at the first and second operating bands, respectively.

A Dual-Band, Polarization-Rotating Reflectarray With Independent Phase Control at Each Band

We present the design and proof-of-concept demonstration of a dual-band reflectarray antenna capable of generating two beams at X- and Ku-bands, whose directions of maximum radiation can be set independently of each other. The reflectarray uses dual-band polarization-rotating (PR) unit cells with 1 bit phase quantization. The proposed unit cell provides independent phase shifts at two frequency bands by controlling a cluster of two orthogonal dipoles to operate as either +90° or -90° reflective polarization rotators. Two dipole clusters are interleaved in a unit cell and used to achieve dual-band operation. Simulation results of a unit cell designed to operate at X- and Ku-bands demonstrate independently controlled, dual-band PR operation over 16.1% and 20% bandwidths for the lower and higher bands, respectively. The dual-band unit cells were used to construct three different static reflectarray prototypes demonstrating the different ways where such independent phase control at the two bands of a dual-band reflectarray antenna may be advantageous. The three static reflectarray prototypes were simulated, fabricated, and experimentally characterized. Simulation and measurement results of these prototypes agree well and demonstrate independent phase shift control at the X- and Ku-bands over a relatively wide field of view without exciting grating lobes.

Fully integrated three-way LDMOS Doherty PAs for 1.8–2.2 GHz dual-band and 2.6 GHz m-MIMO 5G applications

AbstractThis paper presents a fully integrated three-way Doherty architecture to address the challenges of 5G applications using laterally-diffused metal-oxide semiconductor (LDMOS) technology. By using the so-called CDS cancelation method for the Doherty combiner design, a wideband impedance transformation is achieved, that combined with the three-way Doherty power amplifier (DPA) architecture allows for high efficiency in deep back-off, with a reduced load modulation for high bandwidth. Throughout this paper, the design approach and realization are described, while multiple critical design challenges will be addressed such as low frequency drain resonance optimization, impact of in-package coupling effects, and linearity versus efficiency tradeoff. Two state-of-the-art three-way fully integrated LDMOS DPA monolithic microwave integrated circuit (MMICs) are presented to demonstrate how these measures have been successfully applied to different power amplifier (PA) line-up components for 5G base station systems. First, a 60 W 1.8–2.2 GHz multi-stage device for driver application in true dual-band operation is presented. The circuit design pays special attention to extended PA video bandwidth thanks to integrated passive device. After digital pre-distortion (DPD) in dual-band operation, this highly linear device achieves an outstanding adjacent channel leakage ratio (ACLR) of −56 dBc for a 2cLTE 20 MHz 8 dB peak-to-average ratio signal spaced by 345 MHz, thus 385 MHz instantaneous bandwidth (IBW), with 29% efficiency at 35 dBm, 12 dB output back-off (OBO). Second, the simulation and measurement results of a 55 W 2.6 GHz multi-stage DPA for massive-MIMO final stage application are presented, which yields an excellent linearized efficiency of 49% using a 200 MHz 10cLTE signal with an ACLR lower than −47.5 dBc. For 8cLTE 20 MHz (160 MHz IBW), the device yields 50% efficiency with −50.7 dBc ACLR linearized after DPD. The achieved efficiency is well comparable to published GaN DPAs. These results were achieved by improved simulation techniques to minimize frequency dispersion and thus allow high efficiency operation over wide bandwidth. Both devices show that LDMOS is not only a mature technology which allows those PAs to be reliable and low-cost for mass production in very compact packages, but also provide best-in-class RF performance according to the needs of 5G base station systems.

Dual-Band Antenna Pair With Lumped Filters for 5G MIMO Terminals

This article proposes a novel design of the dual-band antenna pair. Starting from the single-band antenna pair composed of T-shaped monopole and T-shaped slot that are intersected with each other, orthogonal T-monopole and odd-symmetrical slot modes are excited. By adding symmetrical low-pass high-stop filters into the horizontal stub of the T-monopole and high-pass low-stop filters into the gap of the T-slot, an extra mode is introduced for each antenna, producing dual-band operation. Impedance bandwidths and radiation efficiencies of both bands can be adjusted flexibly using the filters. A detailed design guideline is given. The dual-band antenna pair operating at partial N78 (p-N78, 3.4~3.6 GHz) and partial N79 (p-N79, 4.8~4.9 GHz) is with a footprint of 15×6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measured results show that the average efficiencies are both -3.4 dB at p-N78/p-N79 for the odd-symmetrical slot and -2.8 dB/-3.7 dB at p-N78/p-N79 for the T-monopole, isolations are better than -16.8 dB at p-N78 and -11.8 dB at p-N79, and ECCs are lower than 0.1 at p-N78 and 0.2 at p-N79. The proposed dual-band antenna pair exhibits great potential to be applied in the fifth-generation (5G) multiple-input multiple-output (MIMO) terminal.

Design and Investigations of Miniaturized Dual-band Quarter Concentric Circular Ring Antenna for LTE and 5G Applications

A miniaturized antenna operating in LTE Band-40 and 5G mid-band is developed and validated in this article. A novel quarter concentric circular ring structure is incorporated in the antenna's radiating patch to achieve dual-band operation. The 5G mid-band operating frequency of 3.60 GHz–3.70 GHz is accomplished by adding a protruded circle and a T-slot pair in the ground plane. Based on the parametric study performed by adjusting the radiating stubs' length and width, the frequency of operation at LTE Band-40 and 5G mid-band is attained with the radiation efficiency of 93.5% and 83.7%, respectively. The optimized dual-band antenna's total size is 32 × 24 × 1.6 mm3. The obtained simulation results and experimental results concur for operating in LTE Band-40 and 5G mid-band applications.

Circularly polarized sequentially rotated antenna array for dual‐band WLAN applications

This article presents a dual-band circularly polarized (CP) 2 × 2 sequentially rotated (SR) antenna array with four slot antennas, a wideband sequential-phase shifter (SPS), and reflected plane for wireless local area network (WLAN) operations. By designing the four slot antennas for dual-band CP operations, the wideband SPS including four outputs with a sequential phase shift of 90° for improving bandwidth, and a conductor-backed reflected plane for enhancing antenna gain, a high-gain and dual-band CP SR antenna array can be realized. The measured impedance bandwidth for return loss of 10 dB is 93.81% (2.36-6.5 GHz). Both measured CP bandwidths for axial ratio of 3 dB are 22.64% (2.35-2.95 GHz) and 49.16% (4.5-6.77 GHz), which can cover all the WLAN bands. Maximum antenna gains are 12.32, 9.91, and 11.66 dBic in the range of 2.4 to 2.484, 5.15 to 5.35, and 5.725 to 5.875 GHz, respectively.