Dual‐band aperture‐coupled rectenna for radio frequency energy harvesting

The article presents a dual‐band aperture‐coupled rectenna for radio frequency (RF) energy harvesting at 2.45 and 5 GHz application. The rectenna consists of a dual‐band π‐shaped slot‐etched aperture‐coupled antenna, designed at the lower substrate of two FR4 substrate layers and a dual‐band rectifier. The proposed antenna design also introduces the harmonic suppression of third‐ and higher order harmonics, ranging from 6 up to 10 GHz from the asymmetrical stubs design at the transmission feedline. The dual‐band rectifier is designed to operate at 2.45 and 5 GHz frequency, successfully achieving high conversion efficiency at 68.83% and 49.90% with the optimum load resistor of value 700 Ω and 1.1 kΩ. The minimum DC voltage of 0.167 and 0.236 V with 0 dBm RF input power can be increased when greater RF power is being applied to it, increasing its flexibility to cater various low‐power applications.     

Multilayer EBG structure for ultra‐wide band SSN mitigation using embedded spiral‐shaped planes

A novel multilayer electromagnetic bandgap (EBG) structure with two spiral‐shaped planes embedded between the power plane and the traditional high‐impedance surface (HIS) is presented. The equivalent capacitance between the power plane and the HIS and the self‐inductance of the patch can be increased significantly, while the self‐inductance of the power plane is decreased. The proposed EBG structure performs excellent ultra‐wide band simultaneous switching noise mitigation and keeps signal integrity in high‐speed digital circuits. The suppression bandgap of the design is from 0.6 to 15 GHz at ?30 dB. Good performance is validated by both simulation and measurement. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Microwave analysis of SiGe heterojunction double‐gate tunneling field‐effect transistor through its small‐signal equivalent circuit

In this study, Si_0.5Ge_0.5 was used as a source junction material in a tunneling field‐effect transistor (TFET), which was analyzed using technology computer‐aided design (TCAD) simulation and a small‐signal non‐quasi static (NQS) equivalent circuit. The NQS equivalent circuit with additional tunneling resistance (R_tunnel) enables more accurate analyses. By using a de‐embedding process, small‐signal parameters in the intrinsic area were obtained. This process was used to analyze the resistance and capacitance in each section, the tendencies of the materials, and the voltage. The error between the NQS equivalent circuit and TCAD device simulation was within 1.9% in the 400‐GHz regime. A cut‐off frequency (f_T) of up to 0.876 GHz and maximum oscillation frequency (f_max) of 146 GHz were obtained.     

A vertex‐fed hexa‐band frequency reconfigurable antenna for wireless applications

Present article embodies the design and analysis of an octagonal shaped split ring resonator based multiband antenna fed at vertex for wireless applications with frequency‐band reconfigurable characteristics. The proposed antenna is printed on FR4 substrate with electrical dimension of 0.4884 λ × 0.4329 λ × 0.0178 λ (44 × 39 × 1.6 mm³), at lower frequency of 3.33 GHz. The antenna consists of SRR based vertex fed octagonal ring as the radiation element and switchable reclined L‐shaped slotted ground plane. Antenna achieves six bands for wireless standards viz: upper WLAN (5.0/5.8 GHz), lower WiMAX (3.3 GHz), super extended C‐band (6.6 GHz), middle X band (9.9 GHz—for space communication), and lower K_U band (15.9 GHz—for satellite communication systems operating band). Stable radiation patterns are observed for the operating bands with low cross polarization. The proposed design achieves hexa band characteristics during switching ON state of PIN diode located at reclined L‐shaped slot in the ground plane. Experimental characteristic of antenna shows close agreement with those obtained by simulation of the proposed antenna.     

Novel compact dual‐narrow/wideband branch‐line couplers using T‐Shaped stepped‐impedance‐stub lines

This article presents a compact model to reduce the physical size and increase the frequency ratio between the second and first resonance frequencies of a dual‐function stepped‐impedance‐stub (SIS) line, which was subsequently employed in the realization of dual‐band branch‐line couplers. The proposed model comprises of a loaded spiral T‐shaped SIS that reduces the size of a conventional SIS line as well as improving its frequency ratio. The proposed model behaves exactly similar to the recently developed dual‐band resonators with the advantage of size reduction of ～35% as well as having a wide range of realizable frequency ratios between 1.4 and 3.7 compared to 1.7–2.7 and 1.8–2.3 for the conventional SIS and T‐shaped transmission‐lines, respectively. Dual‐narrowband and wideband branch‐line couplers were developed based on the spiral T‐shaped SIS lines. The dual‐wideband device's bandwidth was enhanced by 2.7% accompanied by a size reduction of 58.6% in comparison with the conventional dual‐wideband couplers operating at the same frequencies. The theoretical results were verified by measurement. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

A W‐band RF‐MEMS switched LNA in a 70 nm mHEMT process

This work presents a monolithic integrated reconfigurable active circuit consisting of a W‐band RF micro‐electro‐mechanical‐systems (MEMS) Dicke switch network and a wideband low‐noise amplifier (LNA) realized in a 70 nm gallium arsenide (GaAs) metamorphic high electron mobility transistor process technology. The RF‐MEMS LNA has a measured gain of 10.2–15.6 dB and 1.3–8.2 dB at 79–96 GHz when the Dicke switch is switched ON and OFF, respectively. Compared with the three‐stage LNA used in this design the measured in‐band noise figure (NF) of MEMS switched LNA is minimum 1.6 dB higher. To the authors’ knowledge, the experimental results represent a first time demonstration of a W‐band MEMS switched LNA monolithic microwave integrated circuit (MMIC) in a GaAs foundry process with a minimum NF of 5 dB. The proposed novel integration of such MEMS switched MMICs can enable more cost‐effective ways to realize high‐performance single‐chip mm‐wave reconfigurable radiometer front‐ends for space and security applications, for example. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:639–646, 2015.     

Compact meander T‐shaped monopole antenna for dual‐band WLAN applications

A compact coplanar waveguide‐feed monopole antenna with dual‐band characteristics is proposed in this article. The proposed antenna mainly consists of meander T‐shaped monopole and small ground plane embedded with a pair of L‐shaped couple slots and two pairs of I‐shaped notched slots symmetrically. By elongating the meander T‐shaped arms and carefully selecting the positions and lengths of L‐shaped slot and I‐shaped slot, the antenna excites four resonant frequencies at 2.42, 2.52, 4.75, and 5.54 GHz which are formed into two wide bands to cover all the 2.4/5.2/5.8 GHz wireless local area network (WLAN) operating bands, and is with miniaturization structure. Moreover, the antenna can provide nearly dipole‐like radiation patterns and good gains across the dual operating bands. These results prove that the proposed dual‐band antenna is very suitable for WLAN applications. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

A compact printed ultra‐wideband multiple‐input multiple‐output prototype with band‐notch ability for WiMAX,LTEband43, and WLAN systems

A compact ultra‐wideband multiple‐input multiple‐output (UWB‐MIMO) antenna with good isolation and multiple band‐notch abilities is developed in this work. It consists of two quadrant shaped monopole antennas backed by ground stubs. A good isolation is achieved due to the two proposed extended curved ground stubs. The frequency rejection for the WLAN system is realized by loading a capacitive loaded loop resonator adjacent to the feed line. The band rejection for the WiMAX and LTE band43 system is achieved by embedding a quadrant shaped CSRR on each radiator's surface. The measured bandwidth of the antenna is 3.06 GHz‐11 GHz (|S₁₁| < ?10 dB and |S₂₁| < ?18 dB) with a band rejection from 3.5 GHz‐4 GHz to 5.1 GHz‐5.85 GHz, respectively. Time domain performances are investigated in terms of group and phase delay characteristics. Diversity characteristics are evaluated in terms of the envelope correlation coefficient, mean effective gain, and channel capacity loss.     

Dual‐mode resonator with modified dual‐square‐Loop for WLAN and WiMAX quad‐band filter design

We propose the improved configurations with dual‐mode dual‐square‐loop resonators (DMDSLR) for quad‐band bandpass filter (BPF) design. The modified DMDSLR filter employs two sets of the loops. The square loop is designed to operate at the first and third resonated frequencies (2.4/5.22 GHz) and the G‐shaped loop is employed at the second and fourth resonated frequencies (3.59/6.6 GHz). The resonant frequency equations of DMDSLR are introduced for simply designing quad‐band BPF. Resonant frequencies can be controlled by tuning the perimeter ratio of the square loops. A systematic design procedure with the design map is applied for accuracy design. To obtain lower insertion loss, higher out‐of‐band rejection level and wider bandwidth of quad‐band, the miniaturized DMDSLR with meander‐line technique is proposed. The proposed filters are successfully simulated and measured showing frequency responses and current distributions. It can be applied to WLAN and WiMAX quad‐band systems. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:332–340, 2014.     

Poststress RF‐drifts of dual‐band LC VCO in 0.18‐μm CMOS technology

This article studies the RF‐property of a dual‐band voltage‐controlled oscillator (VCO). The designed circuit consists of a dual‐resonance LC resonator and a Colpitts negative resistance cell. The dual‐resonance LC resonator comprises a series‐tuned LC resonator and a parallel resonant resonator. The proposed VCO has been implemented with the TSMC 0.18 μm 1P6M CMOS technology. The VCO can generate differential signals in the frequency range of 3.0–3.37 GHz and 6.95–7.40 GHz with core power consumption of 10.08 and 10.24 mW at the dc drain‐source bias V_DD of 1.4 V, respectively. The die area of the dual‐band VCO is 0.485 × 0.800 mm². The circuit was operated at V_DD = 3 V for 8 h and significant drift in RF parameters was found. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:243–248, 2014.     

Complementary meander‐line‐inspired dielectric resonator multiple‐input‐multiple‐output antenna for dual‐band applications

The communication presents a simple dielectric resonator (DR) multiple‐input‐multiple‐output (MIMO) dual‐band antenna. It utilizes two “I”‐shaped DR elements to construct an “I”‐shaped DR array antenna (IDRAA) for MIMO applications. The ground plane of the antenna is defected by two spiral complementary meander lines and two circular ground slots. In the configuration, two “I”‐shaped DR elements are placed with a separation of 0.098λ. The antenna covers dual‐band frequency spectra from 3.46 to 5.37 GHz (43.26%) and from 5.89 to 6.49 GHz (9.7%). It ensures the C‐band downlink (3.7‐4.2 GHz), uplink (5.925‐6.425 GHz), and WiMAX (5.15‐5.35 GHz) frequency bands. Each DR element is excited with a 50‐Ω microstrip line feed with aperture‐coupling mechanism. The antenna offers very high port isolation of around 18.5 and 20 dB in the lower band and upper band, respectively. The proposed structure is suitable to operate in the MIMO system because of its very nominal envelope correlation coefficient (<0.015) and high diversity gain (>9.8). The MIMO antenna provides very good mean effective gain value (±0.35 dB) and low channel capacity loss (<0.35 bit/s/Hz) throughout the entire operating bands. Simulated and measured results are in good agreement and they approve the suitability of the proposed IDRAA for C‐band uplink and downlink applications and WiMAX band applications.     

Substrate integrated waveguide dual‐frequency dual‐sense circularly polarized cavity‐backed slot antenna

A novel design of dual‐frequency dual‐sense circularly polarized (CP) substrate integrated waveguide (SIW) cavity‐backed slot antenna is presented for dual‐band wireless communication systems. The proposed antenna consists of square SIW cavity, asymmetrical bow‐tie‐shaped cross slot and probe feed. Due to use of asymmetrical bow‐tie‐shaped cross slot, circularly polarized wave radiates at two different frequencies with opposite sense of polarizations. The RHCP radiation occurs at (10.45‐10.54) GHz (Lower band) and LHCP occurs at (11.26‐11.34) GHz (Upper band). Moreover, in each band, sense of polarization can be change by changing the feed position. The front to back radiation ratio (FTBRR) is more than 10.5 dB and cross polarization level is lower than ?20 dB in both the bands.     

Dual‐band dual‐polarized compact planar monopole antenna for wide axial ratio bandwidth application

In this article, a geometrically simple, microstrip line‐fed planar monopole structure with slanting edge ground plane is designed to realize the dual‐band dual‐polarized operation. The proposed antenna consists of a rotated U‐shaped patch and an electromagnetically coupled L‐shaped parasitic radiating element. Owing to the combination of microstrip line‐fed radiating patch and a slanting‐edge rectangular ground plane on the opposite side of the substrate, the proposed dual‐band antenna can generate broad axial ratio bandwidth (ARBW) in the upper frequency band. The overall dimension of the prototype is only 32 × 32 × 1.6 mm³. The measured results validate that the proposed antenna has two operational frequency bands, 29.84% (1.54‐2.08 GHz) for linearly polarized radiation and 71.85% (3.96‐8.4 GHz) for circularly polarized radiation. Measured result shows that 3‐dB ARBW of the proposed antenna is 73.54% (3.80‐8.22 GHz) in the higher frequency band. It shows that the higher frequency band exhibits a left‐hand circularly polarized radiation in the boresight direction.     

Dual‐band rotary standing‐wave voltage‐controlled oscillator

In this article, a dual‐band rotary standing‐wave oscillator (RSWO) is introduced that generates sinusoidal signals by the formation of a standing wave on a ring (closed‐loop)‐distributed composite right/left‐handed (CRL) Inductor‐Capacitor (LC) transmission line network. The LC network consists of four unit cells of CRL LC resonator stacked in series, and two pairs of cross‐coupled transistors are used to compensate for the loss of LC resonator. Varactors are used as the control to switch on/off the high‐ or low‐frequency bands. In the fundamental mode, the RSWO operates at the high‐frequency band. In the harmonic mode, the oscillator provides low‐frequency band outputs. The dual‐band function exploits the multiple oscillation modes of the CRL RSWO. The proposed RSWO has been implemented with the Taiwan Semiconductor Manufacturing Company, Limited (TSMC) 0.18‐μm SiGe BiCMOS technology. It can generate differential signals in the high‐band frequency range of 6.73–8.60 GHz and in the low‐band frequency range of 3.68–3.73 GHz. The die area of the RSWO is 1.123 × 1.123 mm². © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:536–543, 2014.     

A tunable third‐order bandpass filter based on combining dual‐mode square‐shaped substrate integrated waveguide resonator with triangular‐shaped resonator

A frequency reconfigurable third‐order bandpass filter based on two substrate integrated waveguide (SIW) cavities is presented in this article. The purposed filter consists of a dual‐mode square‐shaped resonator and a triangular‐shaped resonator. In the square‐shaped cavity, four lumped capacitors are loaded as electrical tuning elements in the area where the electric fields of diagonal TE₂₀₁ and TE₁₀₂ modes are strongest. And an another capacitor is loaded at the suitable region of the triangular‐shaped cavity. Square‐shaped cavity introduces two transmission zeros and the triangular‐shaped cavity can suppress out‐of‐band spurious modes. The method that combines the resonators with different shapes and multiple modes into an organic whole cannot only achieve synchronous tuning but also have complementary advantages and improve out‐of‐band rejection. To verify its practicality, a SIW reconfigurable bandpass filter is simulated when the capacitance value varies from 0 to 1.4 pF and measured at 0.7, 0.8, and 0.9 pF, respectively. Measured results show that when the center frequency is tuned from 3.42 to 3.52 GHz, the proposed filter exhibits good tuning performance with insertion loss of less than 2.5 dB and return loss of better than 10 dB, which is suitable for fifth‐generation communication system.     

Dual‐feed full‐metal‐case antenna for WWAN/LTE smartphone applications

A dual‐feed small size full‐metal‐case (FMC) antenna for hepta‐band LTE/WWAN operation in smartphone applications is presented. The antenna proposed here is an integrated part of the full metal case located at the top edge of the smartphone, and it only occupies a small volume of 5 mm × 70 mm × 6 mm. It has two feeding ports that are separately connected to an ON/OFF switch (SW1 and SW2) for controlling the lower and higher operation bands, respectively. For the case when SW1 (ON) and SW2 (OFF), Port‐1 is engaged, and a lower operating band that covers the GSM850/900 operation (824–960 MHz) is achieved. In contrast, Port‐2 will be engaged for the case when SW1 (OFF) and SW2 (ON), and with the aid of a wideband matching circuit, the antenna can induce a higher operating band that can cover the DCS/PCS/UMTS2100/LTE2300/LTE2500 operations (1690–2690 MHz). Detailed design considerations of the proposed FMC antenna are described, and both experimental and simulation results are also presented and discussed. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:595–601, 2016.     

Analysis and improvement of PSRR in an envelope‐tracking power amplifier using a common‐drain amplifier topology

A common‐drain power amplifier (PA) for envelope tracking systems is presented. In envelope tracking, the main PA operates mostly in compression and the power supply rejection ratio (PSRR) is not high. Furthermore, the output noise of the supply modulator can be mixed with the RF signal and generates out‐of‐band emissions. In this article, instead of using a common‐source topology, the PSRR of the envelope tracking PA is inherently improved by utilizing a common‐drain topology. A comprehensive analysis shows that the common‐drain topology is less sensitive to the supply noise, as compared to the conventional common‐source topology. The proposed common‐drain PA is implemented using a discrete LDMOS PD20010‐E RF transistor. Measurement results show that the PSRR of the proposed common‐drain PA is improved by up to 7 dB as compared to that of the common‐source PA. For a two‐tone input with 10 MHz bandwidth at the center frequency of 700 MHz, the power added efficiency (PAE) and IM3 of the envelope tracking common‐drain PA are 20% and ? 28 dBc, respectively, at an average output power of 33.4 dBm. The amplifier also shows a 12.4 dB power gain. Moreover, by utilizing the envelope tracking, the PAE is improved by more than 5%.     

A miniaturized planar nonbianisotropic left‐handed metamaterial

In this article, a miniaturized nonbianisotropic left‐handed metamaterial composed of spiral‐S‐shaped resonator and conducting wire is proposed. This symmetrical structure avoids bianisotropy and it shows a controllable low‐loss double negative (DNG) band. Its electrical size is less than half of the well‐known S‐shaped resonator, which makes it to be considered as a good homogenous effective media. Although the structure is not uniplanar, it is not vulnerable to fabrication errors stem from misalignment of both sides. Both the simulation and experiment results demonstrate left‐handed properties. Also, a circuit model is proposed which can accurately predict the magnetic resonant frequency. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Analysis of frequency‐selective impedance loading of transmission lines for dual‐band couplers

This article proposes an analytical design methodology for dual‐band hybrid couplers and baluns structures for any arbitrary frequency ratio using a stub‐loaded transmission line. An analysis of changing the impedance behavior of the stub, is carried out for the two bands of operation, which along with a dispersive analysis, emphasizes certain conditions where the existing methodology is not applicable. In addition, an extra degree of freedom has been included to increase the solutions for a given frequency ratio, thus providing greater flexibility and feasibility of the proposed structure. The design methodology is experimentally validated with the design and fabrication of dual‐band branch‐line and rat‐race couplers for various commercial frequency bands. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2011.