Showing papers on "Stopband published in 2018"
TL;DR: In this article, the authors provide an overview of basic concepts, types, techniques, and experimental studies of the current state-of-the-art Frequency Selective Surfaces (FSSs).
Abstract: The intent of this paper is to provide an overview of basic concepts, types, techniques, and experimental studies of the current state-of-the-art Frequency Selective Surfaces (FSSs). FSS is a periodic surface with identical two-dimensional arrays of elements arranged on a dielectric substrate. An incoming plane wave will either be transmitted (passband) or reflected back (stopband), completely or partially, depending on the nature of array element. This occurs when the frequency of electromagnetic (EM) wave matches with the resonant frequency of the FSS elements. Therefore, an FSS is capable of passing or blocking the EM waves of certain range of frequencies in the free space; consequently, identified as spatial filters. Nowadays, FSSs have been studied comprehensively and huge growth is perceived in the field of its designing and implementation for different practical applications at frequency ranges of microwave to optical. In this review article, we illustrate the recent researches on different categories of FSSs based on structure design, array element used, and applications. We also focus on theoretical breakthroughs with fabrication techniques, experimental verifications of design examples as well as prospects and challenges, especially in the microwave regime. We emphasize their significant performance parameters, particularly focusing on how advancement in this field could facilitate innovation in advanced electromagnetics.
165 citations
TL;DR: In this paper, a low-profile broadband frequency selective surface (FSS) is presented for wideband shielding, which consists of periodic patterns of circular loops connected among themselves through varactor diodes, which exhibit tunable operation.
Abstract: In this paper, a low-profile broadband frequency selective surface (FSS) is presented for wideband shielding. The FSS consists of periodic patterns of circular loops connected among themselves through varactor diodes, which exhibit tunable operation. The novelty of the proposed design lies in its wideband tuning, where the bandstop response can be varied from 0.54 to 2.50 GHz under the reverse bias voltage, thereby exhibiting a tunable range of 363%. Moreover, the structure exhibits a wide 1.28 GHz stopband (fractional bandwidth of 152%), which is maximum as compared to other wideband FSSs. Additionally, the design is polarization-insensitive and angularly stable for both TE and TM polarizations. A prototype of the proposed structure has been fabricated where the varactor diodes are biased through a novel biasing technique. The sample is measured using parallel-plate waveguide setup as well as the free-space technique, where the measured results show good agreement with the simulated responses.
121 citations
TL;DR: In this paper, a simple technique is presented for the complete suppression of the open stopband in periodic leaky-wave antennas using two similar but non-identical elements per unit cell.
Abstract: A simple technique is presented for the complete suppression of the open stopband in periodic leaky-wave antennas using two similar but nonidentical elements per unit cell. With the technique, one needs only to optimize the distance between the two elements and the dimension of the second element, starting with a quarter of the period and the dimension of the first element. With the simple design procedure, the technique is practical and effective for the open-stopband suppression for various periodic leaky-wave antennas. Two periodic leaky-wave antennas with the technique are demonstrated. The first one is a new developed substrate-integrated waveguide antenna with two nonidentical transverse slots per unit cell. The antenna has a wide scanning range from the backward endfire to the forward direction and does not suffer from blind scanning points at endfires (if it is placed on an infinite ground plane). The antenna is theoretically investigated. The simulation and measured results are consistent with the theoretical results. The second one is a microstrip combline leaky-wave antenna, in which each unit cell contains two nonidentical open-ended stubs. The two examples validate that the technique proposed in this paper can completely eliminate the open stopband in periodic leaky-wave antennas.
116 citations
TL;DR: In this article, a broadband dual-polarized filtering dipole antenna for base station application is presented, which consists of four parts: main radiator, feeding baluns, reflector, and two parasitic loops.
Abstract: This paper presents a broadband dual-polarized filtering dipole antenna for base-station application, which has a compact size of 50 $\text {mm} \times 50\,\,\text {mm} \times 31.8$ mm. The antenna consists of four parts: main radiator, feeding baluns, reflector, and two parasitic loops. Without using complex filtering circuits, the dual-polarized dipole antenna realizes satisfactory filtering performance and enhanced bandwidth by employing only two parasitic loops. Two specific radiation nulls are thus generated and individually controlled by the two parasitic loops. To further improve the upper stopband selectivity and bandwidth, a simple open-ended stub is added to the arms of the dipole. As a result, the bandwidth can be tuned from 7.4% to 47.6%, and the realized gain is decreased dramatically from 8.6 dBi at 2.7 GHz (in-band) to −10 dBi at 2.9 GHz (out-of-band). For demonstration, a broadband dual-polarized dipole antenna is implemented. Measured results show that the proposed antenna has more than 34 dB port isolation over 48.7% (1.66–2.73 GHz) impendence bandwidth (VSWR < 1.5). The measured in-band gain is about 8.15 dBi with stable 3 dB beamwidth 65.4°±2.4° in the horizontal plane, whereas the out-of-band radiation suppression is more than 17 dB.
108 citations
TL;DR: In this article, a broadband bandpass frequency-selective surface (FSS) designed for 5G EMI shielding is proposed, which employs the vertical vias into the 2-D periodic arrays, and such a single 2.5D periodic layer of via-based structure is demonstrated to produce a highly stable angular response up to 60° for both TE and TM polarizations.
Abstract: A novel broadband bandpass frequency-selective surface (FSS) designed for fifth generation (5G) EMI shielding is proposed in this paper. This new design employs the vertical vias into the 2-D periodic arrays, and such a single 2.5-D periodic layer of via-based structure is demonstrated to produce a highly stable angular response up to 60° for both TE and TM polarizations. By cascading two layers of such 2.5-D periodic arrays, the proposed FSS is able to obtain a broad passband as well as the wide out-of-band rejection. Moreover, it has a quite sharp band edge between the passband and the specified stopband. A corresponding equivalent circuit model (ECM) is further developed for better analysis of the operating principle. Finally, a prototype working at the center frequency of around 28 GHz is fabricated and measured. The main novelty of this paper is introducing the 2.5-D concept into designing a wideband FSS, and further reduce the unit size as well as improve the angular stability. Favorable agreement is achieved among the 3-D full-wave simulation, ECM and measurement. All these results demonstrate that the proposed FSS is a good candidate for 5G EMI shielding.
103 citations
TL;DR: In this paper, a wideband omnidirectional dielectric resonator antenna (DRA) with filtering response is investigated, where the DRA is placed on a circular patch and excited by a hybrid feed that consists of a probe and a metallic disk.
Abstract: A wideband omnidirectional dielectric resonator antenna (DRA) with filtering response is investigated. The DRA is placed on a circular patch and excited by a hybrid feed that consists of a probe and a metallic disk. Two omnidirectional DR modes (TM $_{01\delta }$ and TM013 modes) along with a patch mode and a probe mode are simultaneously excited by the hybrid feed, providing a broad bandwidth of 52.8%. The feeding scheme also establishes a cross-coupled structure in the DRA, which introduces a radiation null at the upper edge of the passband. A ring slot and four shorting pins are loaded on the patch to provide another radiation null at the lower edge of the passband. Consequently, a compact wideband filtering DRA (FDRA) with quasi-elliptic bandpass response is obtained without requiring specific filtering circuits. This wideband design is also modified to realize a dual-band FDRA. The metallic disk of the hybrid feed is moved to touch the upper DR face of the cylindrical hole. It divides the wide passband into two separate bands, giving a flat stopband between them. Four additional rectangular ring slots and shorting pins are fabricated on the ground plane to further widen the bandwidth and improve the filtering performance of the second band. As a result, a dual-band FDRA with the bandwidths of 10.1% and 3.73% is achieved. In each design, both the measured and simulated out-of-band suppression levels are about 15 dB.
87 citations
TL;DR: In this paper, a differential dual-polarized filtering dielectric resonator antenna (DRA) is proposed to achieve high isolation for input ports, and the elaborately designed feeding strips ensure controllable input impedances for integration applications.
Abstract: This communication presents a differential dual-polarized filtering dielectric resonator antenna (DRA). In this antenna, a four-leaf-clover-shaped dielectric resonator is excited with two groups of out-of-phase modes. The novel configuration and differential feeding provide the DRA with high isolation for input ports, and the elaborately designed feeding strips ensure controllable input impedances for integration applications. After integrating with a pair of filtering baluns on the opposite side of the reflecting ground, the proposed DRA also exhibits good out-of-band rejection for each port with a wide stopband and two radiation nulls at band edges. A prototype has been designed and implemented, and reasonable agreement between the measured and simulated results can be observed.
80 citations
TL;DR: In this article, a substrate integrated waveguide (SIW)-based LWA is described to overcome the open stopband (OSB) problem and provide beam scanning continuously from the backward to the forward direction from a conventional periodic LWA.
Abstract: For many leaky-wave antennas (LWAs), it is challenging to realize beam scanning through broadside. A problem is the presence of an open stopband (OSB), which restricts radiation in the broadside direction. In this paper, a novel substrate integrated waveguide (SIW)-based LWA is described to overcome the OSB problem and provide beam scanning continuously from the backward to the forward direction from a conventional periodic LWA. It is demonstrated that the $n =-1$ spatial harmonic can be excited efficiently from an SIW LWA and enables broadside radiation. However, it was found in our initial design that when the beam scans through the broadside, the cross-polarization level increases significantly compared to the beam close to the backfire direction. A technique is developed to reduce the cross-polarization level. As a result, a new antenna configuration is created. The antenna design has been realized and measured to validate the concept. The measured beam scanning range of the prototype is from −74° to +45° (119° of beam scanning) when the frequency sweeps from 7.625 to 11 GHz, and the measured cross-polarization level is 20.8 dB low at the main beam direction for the broadside beam.
74 citations
TL;DR: In this article, a set of shorting vias are adopted to load the SIW structure in each unit cell for suppressing the open stopband, and the working principle of the technique is explained, with approximate equivalent circuits.
Abstract: Shorting vias loading in a substrate integrated waveguide (SIW) periodic leaky-wave structure is investigated for suppressing the open stopband. The SIW periodic leaky-wave structure with transverse slots can have the beam scanned in the backward and in the forward directions, but suffers from a large open stopband in which the reflection coefficient is increased and the gain drops drastically. A set of shorting vias are adopted to load the structure in each unit cell for suppressing the open stopband. The working principle of the technique is explained, with approximate equivalent circuits. When the slot and the shorting vias are spaced by a quarter guided wavelength, the series inductance in the slot can be canceled out by the shunt inductance in the shorting vias, and therefore, the open stopband can be suppressed. An antenna based on the via-loaded periodic structure is designed for validation. Simulation and measured results validate that the open stopband is successfully suppressed with the loading of shorting vias.
71 citations
TL;DR: In this article, a new coupling structure implemented on a single-layer substrate and its application to design substrate integrated waveguide (SIW) dual-band and wide-stopband bandpass filters are presented.
Abstract: In this letter, a new coupling structure implemented on a single-layer substrate and its application to design substrate integrated waveguide (SIW) dual-band and wide-stopband bandpass filters are presented. The TE101 and the TE102 modes of SIW cavity are used to design the proposed filters. By adjusting the dimensions of the coupling structure, the coupling coefficients of TE101 and TE102 modes can be controlled that can be used to design wide-stopband and dual-band bandpass filters. In the dual-band filter design, a slotline perturbation is used to lower the resonant frequency of TE102 mode while it has little effect on TE101 mode. To validate the proposed design approach, two SIW bandpass filters (wide-stopband and dual-band) are designed, fabricated, and measured.
71 citations
TL;DR: In this paper, a hybrid spoof surface plasmon polariton (SSPP) and substrate integrated waveguide (SIW) filter was proposed, which has the broadband bandpass and wide out-of-band rejection features.
Abstract: This letter presents a novel hybrid spoof surface plasmon polariton (SSPP) and substrate integrated waveguide (SIW) filter, which has the broadband bandpass and wide out-of-band rejection features. The lower and upper cutoff frequencies of the passband can be independently adjusted by changing the structural parameters of the SSPP and SIW units, respectively. The dispersion curves of the SSPP and SIW units are analyzed and the influences of some structural parameters are investigated. A hybrid SSPP-SIW filter is fabricated based on the proposed method, and the measured passband is at 7.3–11.2 GHz with a relative bandwidth of 44%. The upper stopband rejection level is lower than −40 dB from 11.8 to 19.8 GHz.
TL;DR: In this paper, a dual-beam filtering patch antenna consisting of a slotted patch, a metal strip underneath the patch, two pins, and a ground plane is proposed for wireless communication application.
Abstract: A dual-beam filtering patch antenna consisting of a slotted patch, a metal strip underneath the patch, two pins, and a ground plane is proposed for wireless communication application. A wide operation band with stable symmetrical dual-beam far-field radiation pattern is obtained, and two radiation nulls at the lower and the upper band edges, respectively, are controlled to ensure a sharp rolloff rate at the band edges for both reflection coefficient and realize gain. Undesired higher modes can be suppressed over the stopband by changing the spacing between the patch and ground pane With entire height of $0.058~\lambda _{0}$ , the proposed antenna is implemented to show a −10 dB bandwidth of 3.0–3.8 GHz, a consistent realized gain of about 6.8 dBi within the passband for both two radiation beams directed at ±30°, out-of-band radiation suppression level of higher than 17 dBi, and good band-edge selectivity.
TL;DR: In this paper, a halfmode substrate integrated waveguide (HSIW) filter with coplanar waveguide and co-planar strip (CPS) is proposed.
Abstract: A half-mode substrate integrated waveguide (HSIW) filter incorporated with co-planar waveguide (CPW) and co-planar strip (CPS) is proposed. Quarter-wavelength CPW and half-wavelength CPS resonators etched on the top metal layer are used to realized extended-doublet topology. Meanwhile, wide stopband characteristic is obtained, which is due to different higher order resonant frequencies of HSIW, CPS, and CPW. Finally, an HSIW filter is designed and measured, good agreements are achieved between measured and simulated S-parameters.
TL;DR: The proposed surface Plasmon polariton waveguides are believed to be significantly promising for further developing plasmonic functional devices and integrated 2-D circuits with enhanced confinement of SSPPs in microwave and even terahertz bands.
Abstract: In this paper, a novel planar waveguide based on spoof surface plasmon polaritons (SSPPs) using fish-bone corrugated slot structure is first proposed in the microwave region. Low-dispersion band can be realized by such structure with tight field confinement of SSPPs, resulting in size miniaturization of the proposed waveguide. The high frequency stopband of the proposed ultra-wideband bandpass filter (BPF) is created by using this proposed waveguide, while the low frequency stopband is properly designed through introducing the microstrip-to-slotline transition. The 2-D E-fields distribution, surface current flow, and energy flow patterns are all calculated and illustrated to demonstrate the electromagnetic (EM) characteristics of the proposed ultra-wideband BPF. The BPF tuning characteristics is explored to provide a guideline for facilitating the design process. To validate the predicted performance, the proposed filter is finally designed, fabricated, and measured. Measured results illustrate high performance of the filter, in which the reflection coefficient is better than −10 dB from 2.1 to 8 GHz with the smallest insertion loss of 0.37 dB at 4.9 GHz, showing good agreement with numerical simulations. The proposed surface plasmon polariton waveguides are believed to be significantly promising for further developing plasmonic functional devices and integrated 2-D circuits with enhanced confinement of SSPPs in microwave and even terahertz bands.
TL;DR: This article derives a set of design principles for making photonic crystals with desired photonic stopband properties by taking advantage of spacer group, a design parameter enabled by recent advances in bottom-up assembly processes.
Abstract: Photonic crystals have been widely studied due to their broad technological applications in lasers, sensors, optical telecommunications, and display devices. Typically, photonic crystals are periodic structures of touching dielectric materials with alternating high and low refractive indices, and to date, the variables of interest have focused primarily on crystal symmetry and the refractive indices of the constituent materials, primarily polymers and semiconductors. In contrast, finite difference time domain (FDTD) simulations suggest that plasmonic nanoparticle superlattices with spacer groups offer an alternative route to photonic crystals due to the controllable spacing of the nanoparticles and the high refractive index of the lattices, even far away from the plasmon frequency where losses are low. Herein, the stopband features of 13 Bravais lattices are characterized and compared, resulting in paradigm-shifting design principles for photonic crystals. Based on these design rules, a simple cubic structure with an ∼130-nm lattice parameter is predicted to have a broad photonic stopband, a property confirmed by synthesizing the structure via DNA programmable assembly and characterizing it by reflectance measurements. We show through simulation that a maximum reflectance of more than 0.99 can be achieved in these plasmonic photonic crystals by optimizing the nanoparticle composition and structural parameters.
TL;DR: In this article, the authors proposed a new use of aperture coupling mechanism to combine two bandpass elements for dual/tri-band operation with large frequency ratio but comparable sizes, which can satisfy the simultaneous requirements of future wireless communication systems on short-range high-speed data transmission and long-distance basic coverage.
Abstract: To satisfy the simultaneous requirements of future wireless communication systems on short-range high-speed data transmission and long-distance basic coverage, the coexistence of the millimeter-wave and microwave technologies becomes the inexorable trend. However, it is difficult for the existing dual-/ tri-band filter configurations to achieve a frequency ratio larger than three. In this paper, the new use of aperture coupling mechanism is proposed to combine two bandpass elements for dual-/tri-band operation with large frequency ratio but comparable sizes. For this purpose, a microwave BPF with wide stopband up to millimeter-waveband is implemented based on the complementary frequency response characteristics of the stepped-impedance resonator bandpass filter and low-pass filter. The millimeter-wave BPF can be simply designed using the air-filled substrate-integrated waveguide circular cavities, which exhibit the natural low-frequency cutoff characteristics. Based on the proposed design concept and two BPF elements, the dual-/ tri-band bandpass filters with frequency ratio up to 12.59 and 12.7 were designed, fabricated, and measured. Owing to the independence of the two elements, a diplexer with large frequency ratio can be simply implemented based on the previous dual-band filter. All the simulation and measured results are in good agreement, validating the proposed structures.
TL;DR: In this paper, a half-height pin form for gap waveguides is proposed for reducing the fabrication cost, and its stopband characteristics are investigated and compared with the previous full-height pins at the $V$ -band.
Abstract: Gap waveguide is a promising transmission structure, especially for millimeter-wave (mmW) and terahertz applications. It does not require conductive connection between the upper and the lower plates, which makes this technology gain advantages over conventional rectangular waveguides and substrate integrated waveguides in an mmW and terahertz regime. Different fabrication methods for gap waveguides should be employed for different frequency bands applied, such as molding, milling, die forming, electrical discharge machining, microelectromechanical systems, and 3-D printing. Therefore, different pin forms used in gap waveguides are required to match the applied fabrication methods. In this paper, a new pin form, the half-height-pin form, in gap waveguides is proposed for reducing the fabrication cost, and its stopband characteristics are investigated and compared with the previous full-height pins in gap waveguides at the $V$ -band. A device of a double-ridged gap waveguide with two 90° bends for verifying the stopband characteristic analysis of the new pin form has been designed and manufactured. The measured data confirm our analysis and simulations.
TL;DR: A new kind of highly flexible frequency-agile bandpass filters (FA-BPFs) based on the novel synchronously tuned dual-mode resonator (STDR) with very simple and highly flexible design/control procedures is presented.
Abstract: This paper presents a new kind of highly flexible frequency-agile bandpass filters (FA-BPFs) based on the novel synchronously tuned dual-mode resonator (STDR). The bandwidth (BW), BW variation tendency, passband selectivity (stopband rejection level), and frequency tuning range of the filter can be predefined individually. Benefiting from the unique characteristics of the STDR, the FA-BPF with very simple and highly flexible design/control procedures is achieved. Due to the proposed geometry, two self-adaptive transmission zeros are introduced and move with the passband. The predefined mechanism is investigated in detail, and the simple design and predefined procedures are summarized. Then, three 0.75–1.7 GHz single-band examples with elliptic response are developed to achieve three predefined absolute BWs (ABW). The design techniques and filter superiority are confirmed by the experiments. Moreover, aiming at China 2G/3G/4G cellular wireless/mobile communication system (up to band 40:0.825–2.65 GHz), a novel intrinsically switchable single-/dual-band FA-BPF is presented based on the proposed STDR. An example with a constant ABW1 dB and a fractional bandwidth1 dB (FBW1 dB is designed to validate the theory and analysis. The FA-BPF is able to operate as a highly selective dual-band FA-BPF with 0.76–1.78 GHz/1.61–2.63 GHz tuning ranges, and also can be switched to single-band operation with the continuous tuning range of 0.76–2.63 GHz.
TL;DR: A novel wideband filtering power divider using a three coupled-line structure to provide the equal power division to every outputs and the generalized Chebyshev function is applied to synthesize and analyze the whole structure systematically.
Abstract: This paper presents a novel wideband filtering power divider. Instead of the T-junction in the traditional power divider design, a three coupled-line structure is utilized to provide the equal power division to every outputs. Together with the quarter-wavelength coupled line in each way, a wideband filtering response can be obtained. In order to enhance the frequency selectivity, a pair of half-wavelength open stubs are loaded between the three-line coupled structure and parallel coupled lines to produce a pair of transmission zeros on both sides of the passband. To enhance the upper stopband rejection, two additional open stubs are installed at output ports. A new three-port equivalent network for the three-line coupled structure is proposed, and the circuit model for the filtering power divider can be developed for illustrating the working mechanism and the design process. Furthermore, the generalized Chebyshev function is applied to synthesize and analyze the whole structure systematically. For demonstration, a prototype of the wideband filtering power divider operating at 3 GHz is designed and fabricated. The measured results show a 16-dB bandwidth of 62%, an isolation better than 16.5 dB, and a 29-dB wide stopband from 4.39 to 7.73 GHz ( $1.1f_{0}$ ).
TL;DR: In this paper, a notched-band Vivaldi antenna with high-frequency selectivity is designed and investigated, and the antenna exhibits good impedance match, high radiation gain, and excellent radiation directivity in the passband.
Abstract: In this letter, a notched-band Vivaldi antenna with high-frequency selectivity is designed and investigated. To obtain two notched poles inside the stopband, an open-circuited half-wavelength resonator and a short-circuited stepped impedance resonator are properly introduced into the traditional Vivaldi antenna. By theoretically calculating the resonant frequencies of the two loaded resonators, the frequency locations of the two notched poles can be precisely determined, thus achieving a wideband antenna with a desired notched band. To validate the feasibility of this new approach, a notched band antenna with a fractional bandwidth of 145.8% is fabricated and tested. Results indicate that good frequency selectivity of the notched band from 4.9 to 6.6 GHz is realized, and the antenna exhibits good impedance match, high radiation gain, and excellent radiation directivity in the passband. Both the simulation and measurement results are provided with good agreement.
TL;DR: In this article, a planar power divider with a wide passband/stopband and filtering characteristics is proposed, where the modified parallel-coupled bandpass filter is adopted to increase the slope rate around the passband skirt.
Abstract: The planar power divider with a wide passband/ stopband and filtering characteristics is proposed in this letter. In order to increase the slope rate around the passband skirt, the modified parallel-coupled bandpass filter is adopted. Moreover, utilizing the stub-loaded resonator within the filter, a wide passband can be achieved. Furthermore, the stopband bandwidth and attenuation can be extended with the stepped-impedance coupled lines. An exemplary design of the filtering power divider operated at 2 GHz is presented. In addition, the measured fractional bandwidth at 3 dB and attenuation in the stopband are 57.1% and 40 dB, respectively.
TL;DR: In this article, a wideband decoupling element for mutual coupling reduction in microstrip antenna arrays is proposed, which consists of an asymmetric loop resonator with a coupled microstrip line for wide stopband characteristics.
Abstract: This letter presents the design of a wideband decoupling element for mutual coupling reduction in microstrip antenna arrays. The proposed decoupling unit cell consists of an asymmetric loop resonator with a coupled microstrip line for wide stopband characteristics from 2 to 5 GHz. The bandgap characteristic of the decoupling element is analyzed, and the results are presented. Furthermore, the resonator is deployed in a two-element dual-band microstrip antenna array, and mutual coupling reduction is demonstrated. The decoupling unit cell has a lateral dimension of 2.84 mm and hence enables the packing of antenna elements in very close proximity with reduced mutual coupling. The proposed solution offers additional isolation greater than 15 dB in a V-slot loaded dual-band antenna with edge-to-edge element spacing of ${\text{0.057}}\,\lambda _{o}$ . The prototype dual-band antenna array with decoupling element is fabricated, and the simulation results are validated using experimental measurements.
TL;DR: In this article, the dispersion properties of printed double-sided parallel-strip lines can be controlled by using glide symmetry, which eliminates the stopband between first and second propagating modes and yields to a higher propagation constant, preserving its linearity and the broadband nature of the underlying guiding technology.
Abstract: In this letter, we demonstrate that the dispersion properties of printed double-sided parallel-strip lines can be controlled by using glide symmetry. Glide symmetry is introduced in with corrugations in both strips of a double-sided line. We demonstrate that glide symmetry eliminates the stopband between first and second propagating modes and yields to a higher propagation constant, preserving its linearity, and the broadband nature of the underlying guiding technology. Thus, the glide-symmetric double-sided line can be designed to possess a high equivalent refractive index in an ultrawide range of frequencies. These exceptional properties have been numerically and experimentally validated. Finally, we demonstrate the possibilities of this technology with a specific design, a glide-symmetric double-sided parallel-strip line with filtering properties. Potential applications are low-dispersive leaky-wave antennas and electromechanical tunable phase shifters and filters.
TL;DR: In this article, an integrated optical double notch filter using a cascaded pair of non-identical microring resonators, in conjunction with optical phase modulation, is presented, which results in minimal net phase being introduced by the overall filter at radio frequencies falling outside the region of the notch stopband.
Abstract: A novel-integration-based technique employing a cascaded pair of microring resonators on silicon-on-insulator platform that can achieve a tunable single-passband microwave photonic filter with improved shape factor and extinction ratio is presented. It is based on an integrated optical double notch filter using a cascaded pair of nonidentical microring resonators, in conjunction with optical phase modulation. This results in minimal net phase being introduced by the overall filter at radio frequencies falling outside the region of the notch stopband, thus enabling nearly full antiphase cancellation of the modulation sidebands, which results in the achievement of an improved filter shape factor and extinction ratio. Additionally, it features a bandwidth that is directly determined by the difference between the bandwidths of the two optical notch filters, rather than by their absolute individual bandwidths. Experimental results have verified the concept, and have demonstrated a single-passband filter having tuning range of 6–17 GHz, a shape factor of 1.78, shape-invariant tuning, and a good out-of-band suppression ratio of approximately 20 dB throughout the entire tuning range.
TL;DR: In this article, planar wideband bandpass filters with an extremely wide upper stopband are described. But the filter design differs from conventional approaches in which it is based on the choice of a wide-band bandstop (BS) filter, to which a number of shunt-shorted stubs are connected at specific nodes; the stubs provide transmission zero at the origin.
Abstract: The realization of planar wideband bandpass filters with an extremely wide upper stopband is described. The filter design differs from conventional approaches in which it is based on the choice of a wideband bandstop (BS) filter, to which a number of shunt-shorted stubs are connected at specific nodes; the stubs provide transmission zeros at the origin. Two examples of wideband bandpass filters with extremely wide upper stopbands are presented: filters based on a fifth-order Chebyshev wideband BS filter and a pseudoelliptic function ultra-wideband-BS filter. Relative passbands in excess of 100% are achieved, while the equivalent of at least four harmonic passbands is suppressed.
TL;DR: In this article, a triple-mode bandpass filter using a modified quarter-mode substrate integrated waveguide (QMSIW) cavity is presented, where the dominant mode (TE101) is shifted toward the second resonant mode through the perturbation induced by the metallized via-holes array.
Abstract: A compact triple-mode bandpass filter using a modified quarter-mode substrate integrated waveguide (QMSIW) cavity is presented. It is realized by exploiting the first three resonant modes of the QMSIW cavity. Specifically, the dominant mode (TE101) is shifted toward the second resonant mode (TE202) through the perturbation induced by the metallized via-holes array. The resonant frequency of the third resonant mode (TE303) is lowered toward the TE202 mode owing to the capacitive loading effect of the loaded circular conductive posts array. In this way, by adjusting the via-holes array and the conductive posts array, the resonant frequencies of the first and third resonant modes can be independently tuned while the second resonant mode remains unchanged. As a result, the bandwidth of the resulting filter can be flexibly controlled at a preassigned center frequency. Moreover, to suppress the spurious frequencies generated by the higher order modes, three cascaded defected ground structures were introduced below the feedline to distinctly widen the stopband and increase the out-of-band rejection.
TL;DR: In this article, a microwave filter with a notched frequency of transmission using an epsilon negative unit-cell resonator as a sensor device was proposed for the characterization of life-saving samples such as glucose.
Abstract: This work proposes a microwave filter with a notched frequency of transmission using an epsilon negative (ENG) unit-cell resonator as a sensor device. The device finds important application for the characterization of life-saving samples such as glucose. The ENG structure consists of two complementary geometries in the shape of ring and horn. The structure efficiently inhibits the incoming RF signal and creates a stopband resonance at 2.074 GHz. The printed circuit board of the layout was realized using FR-4 substrate of relative permittivity e r = 4.4, and height of 1.6 mm. It is experimentally seen that in the complementary area of horn and circular ring, the glucose sample perturbs the air–dielectric fringing fields which exist over the complementary area and modifies the frequency of stopband resonance. A change in sensor resonance was recorded and calibrated for different concentrations of glucose sample. The sensor exhibits a linear response for glucose concentration ranging from 20 to 100 mg ml−1 in the sensing area.
TL;DR: It is established that apodized NAA-DBRs are more sensitive to changes in their effective medium than non-apodizedNAA- DBRs, making them more suitable sensing platforms to develop advanced optical sensing systems.
Abstract: This study presents a nanofabrication approach that enables the production of nanoporous anodic alumina distributed Bragg reflectors (NAA-DBRs) with finely engineered light filtering features across the spectral regions. The photonic stopband (PSB) of these NAA-based photonic crystal (PC) structures is precisely tuned by an apodization strategy applied during stepwise pulse anodization with the aim of engineering the effective medium of NAA-DBRs in depth. We systematically assess the effect of different fabrication parameters such as apodization function (i.e. linear positive, linear negative, logarithmic positive and logarithmic negative), amplitude difference (from 0.105 to 0.420 mA cm−2), current density offset (from 0.140 to 0.560 mA cm−2), anodization period (from 1100 to 1700 s), and pore widening time (from 0 to 6 min) on the quality and central wavelength of the PSB of NAA-DBRs. The PSB’s features these PC structures are demonstrated to be highly tunable with the fabrication parameters, where a logarithmic negative apodization is found to be the most effective function to produce NAA-DBRs with high quality PSBs across the UV-visible-NIR spectrum. Our study establishes that apodized NAA-DBRs are more sensitive to changes in their effective medium than non-apodized NAA-DBRs, making them more suitable sensing platforms to develop advanced optical sensing systems.
TL;DR: This LNA is the first concurrent dual-band single-ended-to-differential LNA integrated on-chip operating in ${K}$ - and Ka
Abstract: A concurrent dual-band single-ended input to differential output (single-ended-to-differential) low-noise amplifier (LNA) employing a novel transformer feedback single-ended-to-differential dual-band load is proposed. The developed LNA topology is flexible in controlling the stopband notch frequency by optimizing the transformer’s self-inductance and coupling coefficient. It also has a unique advantage in controlling both the stopband rejection and passband gain balance, simultaneously. The LNA is designed using a 0.18- $\mu \text{m}$ BiCMOS process and exhibits the same single-ended-to-differential peak gains of 19.2 dB at 21.5 and 36 GHz in the low- and high-passband, respectively, with the stopband rejection ratio of 37.1 dB. In the single-ended input to single-ended output (single-ended) mode operation, the designed LNA exhibits the measured peak gains of 15.7/16.6 dB at 21.5 GHz and 15.7/16.7 dB at 36 GHz for the two signal paths. It achieves the best measured single-ended noise figures of 4.3/4.0 and 4.3/4.2 dB for the two signal paths in the respective low and high passbands. The LNA also attains the measured differential gain and phase imbalances of 0.9/1.0 dB and 0.5/10.4 degree in the low/high passband, respectively. This LNA is the first concurrent dual-band single-ended-to-differential LNA integrated on-chip operating in ${K}$ - and Ka -band.
TL;DR: The theory of simple yet unconventional double ladder circuit that exhibits a special degeneracy condition referred to as a degenerate band edge (DBE) is developed, providing insight into the very complex behavior near degeneracy points in periodic circuits.
Abstract: A conventional periodic LC ladder circuit forms a transmission line that has a regular band edge between a passband and a stopband. Here for the first time, we develop the theory of simple yet unconventional double ladder circuit that exhibits a special degeneracy condition referred to as a degenerate band edge (DBE). The degeneracy occurs when four independent eigenstates coalesce into a single eigenstate at the DBE frequency. In addition to possible practical applications, this circuit may provide insight into DBE behavior that is not clear in more complex systems. We show that double ladder resonators exhibit unusual behavior of the loaded quality factor near the DBE, leading to a stable resonance frequency against load variations. These two properties in the proposed circuit are superior to the analogous properties in single ladder circuits. Our proposed analysis leads to analytic expressions for all circuit quantities thus providing insight into the very complex behavior near degeneracy points in periodic circuits. Interestingly, here we show for the first time That a DBE is obtained with unit cells that are symmetric along the propagation direction. The proposed theory of double ladders presented here has potential applications in filters, couplers, oscillators, and pulse shaping networks.