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A compact 2-element antenna for MIMO applications with performance across the WLAN frequency bands is designed and fabricated on paper with a FUJI Film Dimatix 2800 material printer and conductive ink. This antenna is ∼1.1 cm × 3.5 cm and utilizes co-planar feeding techniques and ground design to allow for resonance in the 2.4 and 5 GHz frequency bands with a minimum 800-MHz bandwidth. The design is established using commercially available products for minimal processing. Factors such as ink handling, printing conditions, and paper selection are discussed qualitatively as they relate to antenna fabrication and performance. Successful simulation and fabrication is reported with low correlation, high isolation, and low reflection. [ABSTRACT FROM AUTHOR]

In this paper, a single‐layer filtering antenna based on half‐mode patches is proposed. It consists of a main driven patch and a parasitic patch. A U‐shaped slot is first etched on the main driven patch to generate a new resonant mode and a radiation null simultaneously. Four pairs of shorting pins are introduced on the main driven patch to raise its operating frequency to near that of the U‐shaped slot, thus broadening the impedance bandwidth (IBW). Additionally, a parasitic patch is introduced near the driven patch to introduce an extra half‐TM10 mode and an extra radiation null, significantly enhancing the IBW and the upper‐edge selectivity of the antenna. A prototype was fabricated and tested for validation. It achieves a peak realized gain of 6.55 dBi and −10‐dB IBW of 8.8%, and exhibits good out‐of‐band rejection performance while maintaining a low profile of 0.017 λ0 and a compact transverse size of 0.29 λ02. [ABSTRACT FROM AUTHOR]

An arrayable dual‐polarized antenna is proposed in this paper, which exhibits a low profile and broad bandwidth. A metasurface and a square ring are introduced to realize the broadband operation of the low‐profile dual‐polarized antenna. The total size of the broadband antenna is 0.39λL×0.39λL×0.105λL $0.39{\lambda }_{{\rm{L}}}\times 0.39{\lambda }_{{\rm{L}}}\times 0.105{\lambda }_{{\rm{L}}}$ (where λL ${\lambda }_{{\rm{L}}}$ is the wavelength at the lowest frequency of the operation band [1.31 GHz] in free space), suitable for use as an element of an antenna array. Four elements of the proposed antenna are arrayed to develop an array to demonstrate its application for the base station. The measured impedance bandwidth (return loss >10 dB) of the array is about 70% (1.31–2.74 GHz). Stable radiation patterns are obtained with an average gain of 14 dBi. [ABSTRACT FROM AUTHOR]

This paper presents a small‐sized, planar antenna fabrication for ultra‐wideband (UWB) and vehicle‐to‐everything (V2X) applications. The design is inspired by a hexagonal ring, providing an UWB bandwidth of 16.61 GHz (from 3.33 to 19.94 GHz) and a fractional bandwidth of 142.75%. A suitably placed inverted‐U slot in the feed line helps in achieving the WLAN notch band (from 5.04 to 6.01 GHz). The overall design footprint is 0.17 × 0.23 λ02 in size, provides stable radiation characteristics, and a gain of 4 dBi in the pass‐band with stable time‐domain performance. The proposed antenna also covers both 3.5 GHz (LTE‐42 Band) and 5.9 GHz (DSRC Band), therefore being suitable for modern UWB frontends and V2X communication. [ABSTRACT FROM AUTHOR]

In this paper, a single‐fed broadband circularly polarized (CP) filtering patch antenna based on metasurface is proposed. It consists of a corner‐truncated square patch, a nonuniform metasurface, and a U‐shaped strip. By placing the metasurface above the driven patch antenna, a radiation null is realized at the upper band, and an additional axial ratio (AR) minimum is simultaneously generated to enhance the CP bandwidth. Besides, two more radiation nulls are achieved at each side of the band edges by introducing a U‐shaped strip underneath the patch and embedding a shorting pin into the patch, which further improves the frequency selectivity and suppresses the radiation level. Measured results show that the designed antenna has a wide impedance bandwidth of 19.7% (4.8–5.85 GHz), a CP bandwidth of 19.9% (4.75–5.8 GHz), and an in‐band average gain of 7 dBic with suppression level of more than 18 dB at out of band. [ABSTRACT FROM AUTHOR]

A filtenna (filtering antenna) for the fifth generation (5G) mobile communications in millimeter‐wave (mmWave) band is proposed in this paper. The filtenna is fed by a probe, and two radiation nulls are generated at the upper sideband based on the stacked‐patches structure. Then, two shorting pins loaded on the driven patch are introduced, which then result in the third radiation null. An "X‐character" shape radiation loop is added therefore, the fourth radiation null can be generated. Besides, the fifth radiation null at around 34 GHz is generated by adding four parasitic strips on the top radiation patch. The measured −10 dB impedance bandwidth of the filtenna is from 23.07 to 30.99 GHz. The average gain of the antenna is larger than 5.5 dBi, and the stopband suppression can reach 14 dB with a wide stopband. With the merits of low profile, wide stopband, and stable radiation, the proposed filtenna can be a good candidate for 5G mmWave applications. [ABSTRACT FROM AUTHOR]

This paper proposes a broadband metasurface antenna with size‐varying patches. The metasurface radiator is fed by a microstrip line through a coupling slot on the ground. By varying two parameters of the square patches, great mode controllability can be achieved, resulting in wideband and stable gain. Furthermore, the added slotted metal square ring can effectively improve radiation gain. We designed and tested a C‐band wideband antenna consisting of 4 × $\times $ 4 novel radiator units. The measured impedance bandwidth and 2‐dB gain bandwidth are 59% (4.3–7.9 GHz) and 44.1% (4.6–7.2 GHz), respectively. The designed antenna has a low profile of 0.09 λ $\lambda $. [ABSTRACT FROM AUTHOR]

In this paper, a millimeter‐wave broadband high‐efficiency power amplifier (PA) for Ka‐band (26–32 GHz) using 0.15‐μm GaAs pseudomorphic high‐electron‐mobility transistor process is proposed. The PA utilizes a three‐stage cascade structure and adopts an RC series feedback network, which expands the bandwidth and ensures the circuit stability. To improve the output power and efficiency of the circuit, a tree‐like transistor structure is proposed. The power amplifier, it can provide 23.6 dBm output P1dB with 33.1% power‐added efficiency at 28 GHz with high linearity. The maximum small signal gain can reach 27 dB with 3‐dB bandwidth from 24 to 33 GHz for the measured results. [ABSTRACT FROM AUTHOR]

We discuss high-speed waveguide modulators for optical fiber communications that employ semiconductor quantum wells, with emphasis on electrorefractive devices. The prime advantages of quantum-well material in this application are provided by enhanced electrooptic effects that allow ultracompact devices with low drive voltage requirements. The small size is particularly important for low-cost monolithic integration with other components for guided-wave photonic integrated circuits. In our devices, compactness is also key for obtaining high electrical modulation bandwidth. [ABSTRACT FROM AUTHOR]

This paper presents a high‐power and sharp‐skirt‐selectivity bandpass filter with flexible transmission zero (TZ) and bandwidth. The proposed filter consists of three cascaded dual‐mode resonant cavities and a bandstop resonant structure. The dual‐mode resonant cavity is composed of a substrate‐integrated waveguide structure and a mushroom metal structure, which can implement a controllable bandwidth and generate a TZ for sharp skirt selectivity. Meanwhile, the middle dual‐mode resonant cavity is an oversized waveguide structure to improve power capacity. Moreover, the integrated bandstop resonant structure is used to generate another flexible TZ. The effect of different dimensional mushroom metal structures and bandstop resonant structures are also analyzed in detail. Finally, the proposed structure is fabricated and tested. Simulation results show that the proposed filter has an insertion loss of −1 dB at the passband 8.9–10.7 GHz with two TZs on both sides of the passband. Additionally, the proposed filter can obtain an 11 MW power capacity. Compared with the traditional filters, the proposed filter possesses high‐power and sharp skirt selectivity characteristics, and its position of TZ and bandwidth can be properly adjusted. [ABSTRACT FROM AUTHOR]

In this paper, a novel artificial magnetic conductor (AMC) reflector is proposed for gain stability enhancement of a low‐profile wideband bowtie antenna (operates at C‐band). Two AMC reflectors are investigated: the first one is based on a standard square patch cell while the second one is based on a novel cell geometry called modified cross shape (MCS). The two units' cell geometries are studied and optimized to achieve the desirable performances, namely; low‐profile, wide impedance bandwidth, and gain stability. The proposed antenna structure with 5 × 8 MCS unit cells is fabricated and measured. The results show a significant steady gain compared to similar work in the literature. The fabricated structure presents a low thickness of 0.084 λL (λL is the guided wavelength at the lowest frequency, i.e., 3.94 GHz) with 0.85 dB of gain variation over a wide impedance bandwidth of about 50% (3.94–6.61 GHz). [ABSTRACT FROM AUTHOR]

This paper presents a new wideband waveguide substrate integrated waveguide (SIW) coupler with maximum deviation of ±0.5 dB in a 7.5–12.25 GHz bandwidth (48% fractional bandwidth). Proposed coupler consists of the standard WR90 waveguide and single layer/double clad SIW printed circuit board (PCB) which is placed crosswise on the waveguide. Proposed three port coupler (isolated port was ended with match load) has a two coupling level (average of coupling in 8–12 GHz frequency range) of 43.2 and 58.3 dB, which is correspond with the hole diameter of 3.5 and 3 mm, respectively. The main contribution of this work is based on the hybrid techniques of SIW and RWG for coupler design in the high power microwave application. Validation of the simulation results with measurement one proves that the proposed X‐band waveguide to SIW coupler is a good candidate for use in high power industrial/commercial applications. [ABSTRACT FROM AUTHOR]

In this paper, a novel wideband substrate integrated suspended parallel strip line (SISPSL) to differential shielded grounded coplanar waveguide (GCPW) transition is proposed. By embedding the traditional double‐side parallel‐strip line inside multilayer boards, SISPSL has the advantage of self‐packaging and there is almost no radiation loss. SISPSL has inherent differential transmission properties, and a transition from SISPSL to differential GCPW is designed based on multilayer boards. The measured bandwidth of the back‐to‐back transition is from 0.01 to 40 GHz. [ABSTRACT FROM AUTHOR]

A wideband patch array operating at D‐band for antenna‐in‐package applications is presented in this paper. The array consists of two symmetrically positioned subarray elements and a grounded coplane waveguide feed line. Four E‐shaped patches are loaded in the array to enhance bandwidth. All geometry of the array is manufactured on a single‐layer quartz substrate without via hole, so that the difficulty and cost of fabrication are relieved greatly. Good agreements of reflection coefficient, pattern, and gain between measured and simulated results are achieved. Measurement shows that the array exhibits a −10 dB bandwidth of 19 GHz from 138 to 157 GHz and a 3‐dB gain bandwidth covering 140–159 GHz with a peak gain of 11.8 dBi at 147 GHz. Properties of wideband, moderate gain, low cost, and easy manufacture are achieved in this array. [ABSTRACT FROM AUTHOR]

A compact dual-WLAN-band antenna, in the shape of a paper clip, is presented. The antenna can be easily manufactured by bending few times a single copper wire with a length of about 65 mm, and it operates in the 2.4 and 5.2 GHz bands in the WLAN environment. In addition to the simple configuration, the antenna is easily fed by a 50-Ω mini-coaxial cable which allows it to be flexible in a defined location for installation. An experimental prototype of the proposed antenna with the overall dimensions of about 5 mm × 23.5 mm is constructed, tested, and demonstrated. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2572–2574, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23760 [ABSTRACT FROM AUTHOR]

Presented in this paper is a circularly polarized (CP) wide 45° rotated slot antenna with a broad bandwidth. Characteristic mode analysis is initially carried out to show that, by simply rotating a square slot, CP waves can be radiated if it is properly excited. A simple 50 Ω feedline is then designed to excite the slot for the generation of broadband CP waves. The antenna has a total volume of 30 × 30 × 1.6 mm3. Measurement results indicate a broad S11 ≤ −10 dB impedance bandwidth of 85.7% (3.2–8 GHz), a broadband 3 dB axial ratio bandwidth of 57.1% (3.5–6.3 GHz) and a peak gain of 3.6 dBi are obtained by the antenna. The proposed antenna possesses stable radiation patterns as well as relatively flat gain over its operational bandwidth in addition to being compact. It can thus be used for wireless technologies such as WiMAX 3.5 and 5.5 GHz, WLAN 5.2 and 5.8 GHz in addition to Industrial, Scientific, and Medical 5.8 GHz. [ABSTRACT FROM AUTHOR]

This paper proposes a decoupling technique with bandwidth enhanced by introducing two transmission zeros based on common mode (CM) and differential mode (DM) cancellation. The mutual coupling between antennas can be thoroughly eliminated if the CM and DM impedances are equal. Two transmission zeros with closely spaced frequencies are created by using a neutralization line and a parasitic element. The neutral line and parasitic unit can change the currents of radiation patches in CM and DM to realize an enhancement of decoupling bandwidth. To demonstrate the feasibility of this method, a reference and proposed arrays are fabricated and measured. In measurement, the port isolation of proposed antenna array is enhanced by 10.3–21.56 dB in the desired frequency band. Besides, the efficiency and gain are improved by 0.5–3 dB and 10.4%–18%, respectively. The pattern diversity/envelop correlation coefficient (ECC) is also enhanced. [ABSTRACT FROM AUTHOR]

In this paper, a simple and compact monopole antenna with a high bandwidth ratio (BDR) of around is investigated for super wideband (SWB) applications. Using an F4B substrate with a dielectric constant of 2.65, loss tangent of 0.002, and connecting it to a triangular tapered 50‐Ohm line, the suggested antenna achieves its performance objectives. The proposed antenna has an electrical dimension of 0.14λ × 0.22λ and spans the SWB frequency range of 2.89–60 GHz with a 181.5% fractional bandwidth and reflection coefficient S11 < −10 dB. It has been revealed that the results of both experiments and simulations are remarkably similar to one another in terms of their conclusions. In comparison to other SWB antennas, the suggested antenna has a greater BDR, a larger bandwidth, and a more compact size. Apart from that, the antenna has good gain and good radiation characteristics over the whole operational frequency range. [ABSTRACT FROM AUTHOR]

In this paper, a miniaturized ultra‐wideband filter with ultra‐wide stopband and high selectivity using a capacitive loading stub in a multimode structure is proposed. The second, third, and fourth harmonics of the proposed filter are all suppressed on account of using a capacitive loading stub, which makes it have the characteristic of an ultra‐wide stopband. In addition, there are two transmission zeros located at the upper stopband close to the passband, which improves the selectivity of the proposed filter. The proposed filter is fabricated and measured, and the result shows the filter with the center frequency f0 1.185 GHz has 151% 3‐dB fractional bandwidth. Its upper stopband is extended to 9.18 GHz (7.75 f0) and the 20‐dB roll off rate is 212.5 dB/GHz. What's more, the size of the proposed filter is 0.175 λg × 0.18 λg, where λg is the guided wavelength at the center frequency f0. [ABSTRACT FROM AUTHOR]

Novel broadband circularly polarized (CP) electromagnetic band‐gap (EBG) antenna array was proposed in this paper. The antenna's radiating element is utilized by a microstrip‐fed circular patch, radial slot, and three rectangular notches. The proposed antenna elements are fed by feeding network comprised form four hybrid couplers and microstrip lines with appropriate lengths to support desired phase difference at output ports. Radiating patches are sequentially rotated to enhance CP property and form a 4 × 4 array. Finally, the novel scheme of electromagnetic structure (EBG) was inserted among radiating elements to decrease the mutual coupling. Using these structures results in the improvement of antenna bandwidth to cover the entire C‐band. In addition, CP purity is increased at the implicational band. Measured results indicate that the array has an impedance bandwidth of 4 GHz covering the C‐band totally and 3 dB axial‐ratio bandwidth of 2.6 GHz that is between 4.9 and 7.5 GHz (~42%). The antenna array has a peak gain of 8dBi at 6 GHz. [ABSTRACT FROM AUTHOR]

This paper proposes a novel Class‐F broadband power amplifier design method. A Class‐F power amplifier for 1.3–2.5 GHz is fabricated by step‐matching, combining a harmonic control structure and a parasitic compensation circuit. A bandwidth expansion structure is established based on microstrip lines and capacitor. The proposed structure resolves the low efficiency caused by the coincidence of the fundamental frequency band and second harmonic frequency band, which allows the power amplifier to function properly from 1.1 to 2.5 GHz. A high‐efficiency broadband power amplifier is tested to find that the saturated output power with the proposed device is between 40.1 and 41.7 dBm, the gain is from 9.3 to 14.4 dB, and the drain efficiency is 60.8%–84.2% at 1.1–2.5 GHz frequency. [ABSTRACT FROM AUTHOR]

A novel circularly polarized (CP) planar aperture antenna that is completely self‐designed and manufactured with high gain and wideband is proposed in this paper. The antenna adopts a differential feed network so that the energy is evenly transmitted to the radiation patch. By surface current analysis, the closed loop with linearly polarized (LP) characteristics is changed into two arms of different lengths to generate CP radiation. The uniformity and symmetry of energy improve the wideband and high‐gain performance of the antenna. The fabricated antenna prototype has the characteristics of a wideband of 33.3% (28.1–39.3 GHz) and an average gain of 11.4 dBic, which could achieve 3‐dB axial ratio bandwidth of 12.4% (35.2–39.6 GHz) and a stable left‐handed CP and radiation patterns throughout the operating bandwidth with a peak gain of 15.8 dBic. [ABSTRACT FROM AUTHOR]

This paper proposes a novel decoupling and matching technique to enhance port isolation and broaden their common operating bandwidth for asymmetric antenna arrays. The original antennas have strong mutual coupling and a large inconsistency of bandwidths. After adding the proposed network, the coupling has been suppressed and their operating bandwidths have been equalized. To verify this technique, a reference and proposed antenna arrays with element spacing of 0.1506 λ0 ${\lambda }_{0}$ (λ0 ${\lambda }_{0}$ is the wavelength in free space at the center frequency point) are simulated and fabricated. In the experiment, the port isolation is improved by about 23.7 dB at the center frequency. Their bandwidths with a reflection coefficient of −15 dB are also equalized. The common bandwidth is enhanced by about 110.63%. The proposed antenna array has potential application value in modern wireless communication. [ABSTRACT FROM AUTHOR]

In this paper, a Vivaldi antenna with a grooved, tapered slot loaded with an artificial material lens (AML) is designed and analyzed. The unique feature of the proposed antenna is to provide excellent gain (more than 5.0 dBi) over the entire ultra‐wide bandwidth within the compact area, i.e., 40 × 45 mm2. For improving the gain, symmetrical slot matrices were etched at the flare and AML unit cells were imprinted at the extended dielectric portion. Measured results confirm its operating frequency range from 4.65 to 12.65 GHz, having a peak gain of 9.2 dBi to a minimum of 5 dBi. As compared to conventional antenna, the proposed Vivaldi antenna shows an increase in gain of 2.2 dBi. Furthermore, time‐domain analysis suggests very good isolation (∼35 dB), linear phase response, and negligible group delay (∼1 ns). The compact size, wide bandwidth, good gain, stable radiation, and transient features make it a suitable choice for imaging, and communication applications. [ABSTRACT FROM AUTHOR]

This paper presents a compact multifunctional reconfigurable filter based on double coupled‐line structures with three different filtering modes. Three different working modes of the wideband bandpass filter (BPF), bandstop filter (BSF) and wideband filter with single notch can be switched. One prototype of the reconfigurable filter is constructed and measured. For the wideband BPF mode, the 3‐dB bandwidth is 84.5%with in‐band return loss (RL) higher than 21.5 dB and minimum insertion losses (IL) of 0.9 dB, and rejections for the upper stopband is higher than 22.5 dB. For the wideband filter with single notch mode, the 3‐dB bandwidth is 39.7% and 24.9%, with the minimum in‐band IL of 1.13 dB and 1.5 dB, respectively. The maximum rejections between the two bands are 32 dB, and the upper stop band rejections are higher than 19 dB. For the BSF mode, the 3‐dB bandwidth is 29.6%. [ABSTRACT FROM AUTHOR]

In the paper, a novel type of quadrature coupler with the features of wideband, arbitrary harmonic suppression and small size is proposed, for the first time, by employing susceptance loaded coupled lines. Design equations are derived using the even‐odd mode decomposition analysis. The discussions on arbitrary couplings and harmonic suppressions are also investigated. For demonstration, a prototype with a second harmonic suppression was fabricated and measured. The overall size is 0.19λg × 0.27λg, which is smaller than most of the reported wideband quadrature couplers. Measurement results show that the fractional bandwidth of 40% is obtained under the condition of 15‐dB return loss/isolation, 1‐dB amplitude imbalance, and 90° ± 5° phase difference. The proposed coupler can be a good candidate for wideband applications without using the multi‐cascading and complex miniaturization method. [ABSTRACT FROM AUTHOR]

This paper presents a dual‐band impedance transformer for frequency‐dependent loads with two resizable shunt stubs. The proposed transformer is composed of a single‐band matching network and a dual‐band susceptance stub network (DSSN). The single‐band matching network only consists of a one‐section matching network when the load is within the derived circle areas. The design parameters of the DSSN can be adjusted freely. The bandwidths at the two bands can be enhanced, and the possibility of using transmission lines with extremely high or low impedance is reduced significantly. All the parameters are obtained by solving the analytical design formula. Two examples are presented for illustrating the design process, and a prototype is fabricated and measured for verification. Good agreement between the simulation and the measurement is obtained. Compared with the previous works, the transformer not only has the shortest electrical length but also obtains wide bandwidths. Therefore, the transformer is very applicable for dual‐band systems, especially the dual‐band active device circuits. [ABSTRACT FROM AUTHOR]

A metasurface (MS) antenna for the 5 GHz wireless local area network (WLAN) band is presented in this paper. The antenna is feed by a modified aperture‐coupled structure with an optimized rectangular nonuniform MS to widen the bandwidth and improve the gain. The proposed antenna has a thickness of 4 mm and occupies an area of 50 mm × 50 mm. The operating frequency range of the antenna is 4.72–6.19 GHz, covering the 5.15–5.825 GHz band used by the 5 GHz WLAN. The measured average gain is 7.23 dBi. The simulated specific absorption rate values under 1 g and 10 g standard are lower than the limitation of U.S. and European. Due to its simple structure, wide bandwidth and small size, the proposed MS antenna has great potential in the wearable applications. [ABSTRACT FROM AUTHOR]

This paper presents a bandwidth and center frequency tunable bandpass filter with wide tuning range. The proposed filter employs two cascade cross‐shaped resonators. The cross‐shaped resonator can generate two independent tunable transmission zeros by introducing two microwave varactors. The center frequency and bandwidth can be tuned by adjusting the DC bias voltages applied to the varactors. For demonstration, a filter example was designed, fabricated and measured. The tuning 3‐dB bandwidth from 20% to 30% is achieved when the center frequency is tuned from 3.5 to 5 GHz. Meanwhile the insertion loss is less than 4 dB with a high selectivity. The size of the filter is 0.32λg × 0.36λg where λg is the guided‐wavelength at the center frequency. [ABSTRACT FROM AUTHOR]

In this paper, a near field focusing transmission metasurface (MS) based on polarization sensitivity is developed at microwave frequency. The MS unit cell has only three metal layers, which is less than the published dual‐polarized transmission structure. And the phase shifting range can cover 320° for x‐ and y‐polarized waves. The biggest bright spot of the focusing MS made of the proposed units is its changeable focus point by rotating the horn 0°–90° round its central axis: focusing switching between one and two focusing points. In addition, the developed MS has the following advantages: multifunctional, low sidelobe, high focusing efficiency, small size, wideband, and less layer number. The focusing relative bandwidth is 9.7%, and the maximum focusing efficiency is 30% at center frequency 15.5 GHz. The efficiency is higher than that of published results in transmission orthogonal polarization mode. The proposed MS has potential applications in medical treatment, noncontact sensing system. [ABSTRACT FROM AUTHOR]

A ridge‐waveguide (RW) directly modulated laser (DML) with a coplanar electrode structure is proposed and measured in this paper. Since utilizing the coplanar electrode can significantly reduce parasitic capacitance, the frequency responses of DMLs exhibit a quite low roll‐off. Shortening the cavity length L is attractive to enhance the high‐speed performance of DMLs, but it will increase the mirror loss and the chip resistance at the same time. We analyzed the static and dynamic characteristics of 200‐μm, 250‐μm, and 300‐μm lasers experimentally and theoretically to investigate the impact of L on the coplanar‐electrode DML. Shortening the cavity length can improve the relaxation oscillation frequency fr effectively. The 200‐μm DML achieves a bandwidth of 15.3 GHz. The fr is the most important limiting factor for the laser to obtain a wide bandwidth. Decreasing L and increasing the differential gain are promising for the further improvement of fr. However, shortening L causes a more severe thermal effect and the deterioration of the linearity. This trade‐off must be considered in the future study. [ABSTRACT FROM AUTHOR]

This paper proposes a new feeding topology with internal 180° phase reversal for wideband series‐fed slot array antennas. As a demonstration, a serial fed, half‐wavelength separated, 7‐element array is designed at 5.8 GHz. Comparing with conventional series‐fed arrays, which require one‐wavelength separation, the phase difference between adjacent elements varies less with frequency. Thus, the proposed array has more stable beam pointing and wider 1 dB gain bandwidth. A prototype was fabricated and measured to validate the performance of the feeding topology. A wide operating bandwidth of 22.4% for S11 < −10 dB, a 1 dB gain bandwidth of 14% and bi‐directional peak gain of 10.01 dBi are achieved with the array length of 2.7λ0. The proposed feeding topology shows its potentials in realizing signal coverage on some special occasions, such as coal mines and tunnels. [ABSTRACT FROM AUTHOR]

This paper presents a rigorous theoretical analysis of a thulium doped fiber amplifier (TDFA) operating at around 1900 nm. The performance of the amplifier is analyzed based on the concentration of Tm3+ ions, TDF length, and the pumping power, respectively. A broadband gain of around 41 dB is demonstrated for a Tm3+ doped fiber length of 10 m, and an optimized pump power of 400 mW, while employing an in‐band pumping scheme. The minimum noise figure of 4.15 dB is achieved within a broad bandwidth of around 120 nm. [ABSTRACT FROM AUTHOR]

Abstract: A vertical monopole antenna having a directional radiation pattern is proposed in this paper. The proposed monopole antenna is located vertically on the half‐and‐half finite ground plane of perfect magnetic conductor (PMC) and perfect electric conductor (PEC). The ground dimension is set to be 1λ0. In case of the conventional monopole antenna, the surface currents on a ground plane are cancelled out because of the symmetrical ground with respect to the monopole. However, the surface currents of the presented monopole antenna are not cancelled out due to an asymmetrical ground and flows in one direction, so that the electromagnetic (EM) wave of an antenna does not radiate omni‐directionally but directionally. In this paper, a corrugated soft surface is employed to realize the PMC ground. The measured peak gain and the 10 dB bandwidth are measured to be 4.5 dBi and about 20% at the resonant frequency of 2.4 GHz, respectively. [ABSTRACT FROM AUTHOR]

This paper proposes a 3‐pole wide‐tuning‐range, balanced frequency‐agile bandpass filter (BAL‐FA‐BPF) with constant absolute bandwidth (CABW) and 3 transmission zeros (TZs). Under the differential‐mode (DM) operation, the cascaded trisection coupling topology with source‐load coupling is constructed. Thus, 3 adaptive TZs are generated for the DM responses, which improves the passband selectivity and stopband suppression. Under the common‐mode (CM) operation, the short stubs and lumped elements are added at the symmetric plane which effectively improves the CM suppression. Using the advanced matrix synthesis, a demonstrative BAL‐FA‐BPF is designed with stable CABW and controlled by single‐DC‐bias. The measured frequency tuning range of the DM passband is 2.0 to 3.0 GHz (40%) and 3 dB‐bandwidth is kept at 174 ± 3 MHz (±1.7%). The CM suppression is better than 25 dB. [ABSTRACT FROM AUTHOR]

A dual‐band stub (DBS) in a hybrid lumped and distributed configuration is presented in this paper, which comprises one lumped kernel circuit unit cell (KCUC) centered between two uniform transmission lines. Image parameter theory is imposed to extract the DBS phase and impedance bandwidth properties. An odd‐even mode resonant frequency ratio is defined, capable of determining all the DBS element values as well as regulating the DBS size and its second working bandwidth. By converting the lumped KCUC into a quasi‐lumped microstrip topology, a purely planar DBS is automatically implemented by employing the aggressive space mapping (ASM). Through the customized ASM process, the finalized DBS dimensions can be generated within just a few full‐wave simulations. The relatively high accuracy and efficiency of the ASM are affirmed by comparing its performance to those of the traditional direct optimization algorithms. As an example, a DBS with WLAN dual frequencies and extended bandwidth is designed and fabricated. The measured results agree well with the simulated results, justifying the DBS properties and its ad hoc ASM optimization technique. [ABSTRACT FROM AUTHOR]

In this paper, a miniaturized planar inverted‐F antenna (PIFA) with a volume of 49.5 mm3 is proposed for biomedical implantable devices, operating in Medical Implant Communications Service (MICS, 402‐405 MHz) band and Industrial, Scientific, and Medical (ISM, 2.40‐2.48 GHz) band. It has a wide operating bandwidth in MICS band. The initial PIFA is designed with dual‐band performance, where the lower band is formed by quarter‐guided‐wavelength resonance and the higher band is formed by two‐guided‐wavelength resonance. Furthermore, by etching open‐slots between short and feed on the ground, a new resonance is introduced and moved towards the fundamental one, expanding the bandwidth in MICS band. Also, the introduction of slots lowers the initial resonant frequency in higher band, meeting the frequency demands of ISM band. Finally, the proposed antenna is measured in pork as well as skin‐mimicking gels, showing a bandwidth of 50.7% and 38% in MICS band, and 13.9% and 6.9% in ISM band. [ABSTRACT FROM AUTHOR]

This paper deals with a modified planar inverted F‐antenna designed to operate at 2.3 GHz. The modifications are done with an intention of achieving wide bandwidth. It involves the simulation of a basic PIFA, for which dual U‐Slots are deployed and in order to obtain wider bandwidth the concept of the partial ground is taken into consideration. The main motivation behind this is to achieve an impedance bandwidth over 1 GHz which will prove to be useful in addressing several types of wireless and mobile applications. The simulated findings show that proposed PIFA achieved a bandwidth of 1.35 GHz (55.9%) with a gain close to 4.98 dB. The new antenna's size 20 mm × 10 mm (L1 × L2 mm) was compact and the fabrication cost is also less. The fabricated prototype was tested and measured and a good agreement was observed between the simulated and the measured results. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, a novel design of compact 1 × 4 patch antenna array using electromagnetic band gap (EBG) for wideband operation is introduced. Three unequal arms fed by CPW-to-slotline through a coupling system of 100 Ω T-shaped slotline transitions are utilized for broadening the impedance bandwidth with multiple resonances. By adding two conventional mushroom-type EBG (CMT-EBG) structures on both sides of 100 Ω slotline transitions, dual wideband patch array is obtained. The proposed 1 × 4 patch array with CMT-EBG includes two bands with the measured ranges (S11≤−10 dB) of 6.71-6.97 GHz and 8.60-11.51 GHz. Moreover, more size reduction is achieved by using an edge-shorted mushroom-type EBG (ESM-EBG) for the proposed array. This design with the ESM-EBG indicates almost 37% size reduction compared with the proposed array without EBG. In this paper, an equivalent circuit model of the proposed 1 × 4 array with EBG is also introduced to describe the process of its bandwidth enhancement. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2983-2989, 2016 [ABSTRACT FROM AUTHOR]

In this paper, the effect of coupling between the antenna and ground characteristic mode is investigated by comparing the radiation performance of antennas located inside and outside the ground plane. In general, it is understood that an antenna occupying a larger space has better radiation performance. However, in this paper, it is shown that coupling between the antenna and ground is important for radiation performance, rather than the size occupied by the antenna. The antenna is strongly coupled with the ground characteristic mode when located inside the ground; the −10 dB bandwidth is 130 MHz at 2.45 GHz, and the measured realized efficiency is −0.64 dB in the 2.4‐2.5 GHz band. When the antenna protrudes from the ground plane, the coupling between the antenna and the ground characteristic mode is weak, achieving a narrower −10 dB bandwidth of 50 MHz at 2.45 GHz, and lower measured realized efficiency of −2.20 dB in the 2.4‐2.5 GHz band. In other words, the radiation performance of the same antenna is significantly influenced by the coupling with the ground. [ABSTRACT FROM AUTHOR]

This paper presents the analysis of a T‐stub loaded two element MIMO antenna placed in the vehicular environment at different positions on the vehicle. The MIMO antenna consists of two collinear printed dipoles as the elements. It operates for millimetre wave frequencies from 24.6–42.1 GHz and 50.1–52.5 GHz with a bandwidth of 17.5 GHz and 2.4 GHz respectively. The two elements of the MIMO antenna have the minimum mutual coupling of −89.5dB over the operating band. The envelop correlation coefficient (ECC) of the MIMO antenna is less than 0.01 throughout the band and the diversity gain (DG) is about 10. The MIMO antenna is placed at four different positions on the vehicle in virtual vehicular environment using ANSYS SAVANT. The measured results are matching with the simulation results and the proposed MIMO antenna can be used for future 5G communications for different automotive applications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method to increase the coupling between the ground and the antenna to improve the radiation performance of the mobile antenna. By adjusting the length of the slot antenna located at the center of the 48 mm × 15 mm ground resonating at 2.45 GHz, the coupling between the ground and the antenna can be controlled. When the coupling between the ground and the antenna is sufficiently strong, the ground resonance mode is strongly excited and a better radiation performance can be obtained. As the length of the slot antenna increases from 5 to 10 mm, the coupling between the ground and the antenna becomes stronger and the impedance bandwidth of −10 dB at 2.45 GHz becomes five times wider from 160 MHz (6.5%) to 780 MHz (31.8%). [ABSTRACT FROM AUTHOR]

A 2‐pole fully tunable bandpass filter (BPF) with only two varactors implemented is proposed in this paper. The ultra‐wide center frequency (CF) tuning range is built on short‐ended stepped‐impedance resonators (SIRs). Two varactors are placed at the symmetrical plane of the filter in series and shunt configurations, according to the odd‐even mode analysis the CF and bandwidth (BW) of the passband can be tuned independently without adding any redundant tuning elements. The CF of the proposed filter can be tuned from 0.61 to 2.39 GHz. The 3 dB BW tuning range is 150‐260 MHz at the lower side and 290‐520 MHz at the upper side of the entire passband tuning range. Good agreement is observed between simulated and measured results. [ABSTRACT FROM AUTHOR]

This paper presents the design of a compact dielectric resonator antenna for 2.4 GHz wireless local area network or industrial, scientific and medical (ISM) band applications. The antenna consists of four stacked layers of dielectric resonators along with a rigid structure of coplanar waveguide feed. The complete antenna is placed on a safety helmet conformably to develop a wearable system for rescue workers. The achieved −10 dB bandwidth at 2.4 GHz is 6.6% (2.33–2.49 GHz). The maximum gain achieved with this proposed dielectric resonator antenna is 3.74 dBi. "On head performance" of this proposed helmet antenna is also observed including human head model in the simulation. [ABSTRACT FROM AUTHOR]

This paper presents a dual‐band dual‐sense circularly polarized (CP) antenna for S‐ and C‐band applications. A semicircular patch and a circular slot are first designed to achieve wide operation bandwidth in the C‐band with right‐hand CP (RHCP), and then, a curved slot is properly inserted around the circular slot for S‐band realization with left‐hand CP (LHCP). Final antenna prototype has an overall size of 0.32λL × 0.32λL × 0.01λL, where λL is free‐space wavelength at the lowest CP frequency. Experimental results show that good CP characteristics for both RHCP and LHCP can be achieved. The measured −10 dB impedance bandwidth is from 2.2 to 6.5 GHz, equivalent to about 98.8%. Additionally, the measured 3 dB axial‐ratio bandwidths for lower and upper bands are, respectively, 4.9% (2.4‐2.52 GHz) and 40.8% (4.0‐6.05 GHz). [ABSTRACT FROM AUTHOR]

In this paper, a compact UWB (ultra‐wideband) antenna with three C‐shaped slots for notched band characteristics is presented. The proposed antenna covers a bandwidth between 2.95 GHz and 12 GHz. Three different sizes of C‐shaped slot are integrated in the radiating element to remove three frequency bands at WiMAX (3.2‐3.8 GHz), C‐band (3.7‐4.2 GHz), and WLAN (5.15‐5.85 GHz). The antenna has a compact size (30 × 30 mm2). The simulated results show good and acceptable agreement with measurement results in terms of S‐parameters and radiation patterns. [ABSTRACT FROM AUTHOR]

This paper presents four frequency selective surfaces (FSSs) to be used in an instantaneous frequency measurement (IFM) systems. The FSS based on simple dipoles have a frequency response corresponding to the characteristics of frequency discriminators. An IFM system with 4‐bits is shown with resolution around 300 MHz. The system contains 16 distinct frequency sub‐bands between 3.21 and 8.75 GHz. CST software simulations and measurements of insertion loss are presented and compared with theoretical results to provide the binary codes of the system. [ABSTRACT FROM AUTHOR]

This paper describes the design guidelines for frequency independent 180° phase shifters. The proposed configuration is based on microstrip slot transition technique. The frequency independence feature is due to comparing two quasi‐identical structures and the phase inversion (180°) is related to the chosen inverted orientation of the main line compared to the reference one. Moreover, two different schemes are designed and manufactured and a good simulation to measurement agreement is demonstrated. Thus, interesting results are obtained (more than 10 dB return loss, less than 2.1 dB insertion loss and less than ± 3.6° phase deviation). [ABSTRACT FROM AUTHOR]

In this paper, a slotted circular ultra‐wideband (UWB) microstrip patch antenna is reported. The antenna is designed, simulated, fabricated, and tested experimentally. The antenna operates over a 4.0‐40 GHz (164% fractional bandwidth) range with a return loss of 10 dB and voltage standing wave ratio (VSWR) < 2. The designed monopole antenna is of dimensions 28.1 mm × 17.1 mm with an electrical size of 0.37 λ × 0.23 λ at 4 GHz frequency. The antenna is fabricated on FR‐4 substrate with a dielectric permittivity of 4.4, loss tangent of 0.02, and a thickness of 1.4 mm. The designed antenna exhibits nearly omnidirectional radiation patterns over the entire impedance bandwidth with more than 2.8 dB peak gain for the entire frequency range and 75% of average radiation efficiency. The presented antenna can be used in UWB communications along with C‐band, X‐band, Ku‐band, K‐band, Ka‐band, WLAN, and future wireless applications. [ABSTRACT FROM AUTHOR]

This paper presents a design procedure for a phased array feed network. The procedure is validated by designing and fabricating a set of 28 GHz 8‐element beam steerable antennas. Within the feed, a Taylor n‐bar amplitude taper is implemented using unequal power dividers. At boresight, the taper reduced the sidelobe level by 2.84 dB to −15.2 dB. Beam steering from 0° to 48° is achieved using meanders. An empirical formula for the meander widths is proposed, enabling independent control of amplitude and phase. Empirical formulae for the initial parameters of the unequal dividers are also proposed. The wide transmission lines in this feed network are compatible with low‐cost PCB fabrication techniques. [ABSTRACT FROM AUTHOR]