Showing papers on "Stopband published in 2019"

Novel Compact High-Gain Differential-Fed Dual-Polarized Filtering Patch Antenna

Abstract: A novel compact differential-fed dual-polarized filtering patch antenna is proposed. Specific filtering response with radiation nulls is firstly realized for the dual-polarized antenna element by symmetrically loading defected ground structures (DGSs), a cross slot, and eight shorting pins without extra circuits. The DGS with pins can generate a lower edge radiation null for a sharp roll-off rate and simultaneously introduce extra in-band resonance for wide passband. Meanwhile, the cross slot with pins can offer an upper edge null and an in-band resonance. Combining with inherent higher order-mode null of the patch itself, the skirt selectivity and stopband suppression at upper band can be significantly improved. Meanwhile, the $\vert $ Sdd $11\vert $ at the upper and lower stopbands is close to 0 dB to achieve high stopband suppressions. As a result, a compact high-gain dual-polarized filtering patch antenna is readily constructed. Thanks for complete symmetry of above structures, the proposed method is very suitable for dual-polarized antennas, where all the performance for both polarizations are identical. For demonstration, a prototype of the proposed antenna is fabricated and measured. Good agreements between the measured and simulated results are observed, indicating good performance with a large bandwidth of about 23% and a peak gain of up to 8.9 dBi within the passband, as well as out-of-band suppression levels of more than 20 dB. Compared with other reported filtering antennas, the proposed filtering patch antenna not only exhibits good wideband dual-polarization radiation but also features high gain in a compact structure for very high aperture efficiency and ultralow cross-polarization level due to the differential feeding and complete symmetry.

A Wide-Angle Narrowband Leaky-Wave Antenna Based on Substrate Integrated Waveguide-Spoof Surface Plasmon Polariton Structure

Abstract: In this letter, a wide-angle narrowband leaky-wave antenna (LWA) based on substrate integrated waveguide-spoof surface plasmon polariton (SIW-SSPP) structure is proposed. Periodic slots are etched on both the top and bottom surfaces of SIW to introduce an SSPP mode. The periodic slots on the top surface are sinusoidally modulated to realize bidirectional LWA radiation. The problem of open stopband is solved by the asymmetrical design of the top and bottom slots. Thus, a wide bidirectional scanning range from −60° to +63° is achieved. Besides, the relative bandwidth of the fabricated antenna is reduced to only 9% by introducing the slow-wave effect of SSPP. It means the proposed antenna has a large scanning rate, or equivalently beam scanning range/bandwidth ratio.

A Simple, Compact Filtering Patch Antenna Based on Mode Analysis With Wide Out-of-Band Suppression

Abstract: A simple, compact filtering patch antenna with wide out-of-band suppression is presented, where the filtering mechanism is first analyzed and implemented based on mode analysis of a conventional patch antenna. According to the mode analysis, undesired higher-order modes can be effectively suppressed by selecting a proper length ratio of two sides of the patch and the feeding position, thus realizing a wide upper stopband. To further enhance the filtering response, another two simple filtering structures loaded on the patch antenna are also proposed. First, a split-ring-shaped slot is etched on the patch to generate a radiation null at the lower-band edge for improving skirt selectivity. Second, a U-shaped strip is etched underneath the patch and connected with the feeding probe, which can introduce another null at the upper band edge. As a result, a high suppression level of 23 dB in lower and upper stopbands can be realized, respectively, for the proposed filtering antenna, while the upper stopband can extend up to $2.3 f_{0}(f_{0}$ is the center frequency of the antenna). Furthermore, wide passband response can also be achieved by the extra in-band resonances existing in the slot and the strip. A filtering antenna prototype is fabricated and measured for demonstration. Good agreements between the simulated and the measured results are observed, indicating a large impedance bandwidth of 22.6%, high antenna efficiency of 95.6%, and an average gain of about 7.4 dBi. Compared with the reported filtering antennas, the proposed filtering antenna can achieve better wideband filtering response but with a simpler configuration.

SIW-Based Leaky-Wave Antenna Supporting Wide Range of Beam Scanning Through Broadside

Abstract: In this letter, a substrate integrated waveguide-based leaky-wave antenna with wide beam scanning is presented to mitigate open stopband (OSB). The unit cell of this proposed antenna consists of a longitudinal slot and a post placed oppositely offset from the center line. By introducing inductive post along with the longitudinal slot in each unit cell, the OSB is suppressed resulting in continuous beam scanning. An equivalent circuit of the proposed unit cell is developed to explain the impedance matching technique used here to suppress OSB. Dispersion diagram is also used to analyze this seamless scanning. This antenna can scan from –49° to +69° through broadside because of wide impedance matching. Finally, the antenna is prototyped and experimentally verified. Measured results are in accord with simulated results. This antenna provides maximum gain of 14.2 dBi and low level of cross polarization.

Band flips and bound-state transitions in leaky-mode photonic lattices

Abstract: We present analytical and numerical results on the formation and properties of the leaky stop band in one-dimensional photonic lattices. At the second stop band, one band edge mode suffers radiation loss generating guided-mode resonance whereas the other band edge mode becomes a non-leaky bound-state in the continuum. We show that the frequency location of the leaky band edge, and correspondingly the bound-state edge, is determined by superposition of Bragg processes generated by the first two Fourier harmonics of the spatial dielectric constant modulation. At the closed-band state, we discover an analytic condition for the exceptional point where frequency is fully degenerate.

Three-dimensional resonating metamaterials for low-frequency vibration attenuation.

Abstract: Recent advances in additive manufacturing have enabled fabrication of phononic crystals and metamaterials which exhibit spectral gaps, or stopbands, in which the propagation of elastic waves is prohibited by Bragg scattering or local resonance effects. Due to the high level of design freedom available to additive manufacturing, the propagation properties of the elastic waves in metamaterials are tunable through design of the periodic cell. In this paper, we outline a new design approach for metamaterials incorporating internal resonators, and provide numerical and experimental evidence that the stopband exists over the irreducible Brillouin zone of the unit cell of the metamaterial (i.e. is a three-dimensional stopband). The targeted stopband covers a much lower frequency range than what can be realised through Bragg scattering alone. Metamaterials have the ability to provide (a) lower frequency stopbands than Bragg-type phononic crystals within the same design volume, and/or (b) comparable stopband frequencies with reduced unit cell dimensions. We also demonstrate that the stopband frequency range of the metamaterial can be tuned through modification of the metamaterial design. Applications for such metamaterials include aerospace and transport components, as well as precision engineering components such as vibration-suppressing platforms, supports for rotary components, machine tool mounts and metrology frames.

A Wide Stopband Filtering Patch Antenna and its Application in MIMO System

Abstract: This communication presents a wide stopband filtering antenna element and its application in multi-input multi-output (MIMO) system. Microstrip terminated coupled lines and a rectangle patch are utilized to generate the filtering function. By varying the length of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be introduced in the spurious band. Appropriate positioning the location of these transmission zeros enables a wide harmonic suppression. To demonstrate the proposed method, a wide stopband filtering antenna is designed and further applied in a four-element MIMO array. The measured and simulated results agree well. The proposed MIMO antenna obtains an attenuation of 12.6 dB up to $6.6\times $ the center frequency.

A novel neural-based approach for design of microstrip filters

Abstract: This paper presents an intelligent design methodology of microstrip filters in which a dynamic neural network model based on Bayesian Regularization Back-Propagation (BRBP) learning algorithm is used. In this approach, a Low-Pass Filter (LPF) composed of multiple open stubs, and stepped impedance resonators is initially designed for which an Artificial Neural Network (ANN) is trained to improve the performance of the filter. The predicted and measured results of the filter verify the effectiveness of the presented method, suggesting an excellent in and out-of-band performance. According to the measurement, the filter has a very small transition band from 2.087 to 2.399 GHz with 3 and 40 dB attenuation points, respectively, leading to a sharp roll-off rate of 118.6 dB/GHz. In addition the optimized filter has an ultra-wide stopband, extending from 2.399 to 15.01 GHz with attenuation level of 22 dB are The overall size of the fabricated filter is only 0.190 λ g × 0.094 λ g , where λ g is the guided wavelength at 3 dB cut-off frequency (2.087 GHz). A performance comparison with some of the recent published LPFs presented, showing the superiority of the proposed filter.

Mutual Coupling Reduction for Ultra-Dense Multi-Band Plasmonic Nano-Antenna Arrays Using Graphene-Based Frequency Selective Surface

Abstract: Terahertz (THz) band provides huge bandwidth but the molecular absorptions in these frequencies cause high path losses in long-distance communications. Recently, multi-band ultra-massive MIMO (UM-MIMO) systems based on graphene-based plasmonic nano-antennas have been proposed to overcome the distance problem. In the UM MIMO systems, the mutual coupling effect is a challenging problem because of the ultra-dense integration of the multi-band nano-antenna arrays. In this paper, a graphene-based frequency selective surface (FSS) is proposed to reduce the coupling effects in dense plasmonic nano-antenna arrays for multi-band UM MIMO systems. The performance of the proposed structure is evaluated by full-wave simulation for different cases. The results show that the FSS structure has a wide stopband (-15 dB bandwidth, approximately 43%-50%) from 1.1 to 1.7 THz. By inserting the FSS structure between nano-antennas, a high isolation coefficient of -25 dB with a 15 dB fall and an envelope correlation coefficient of less than 0.01 are achieved. The field distributions and the radiation patterns are also presented to confirm that the proposed FSS structure improves the performance of the array with negligible influence on the antenna itself. Moreover, the receiving mode simulation of the array is performed with the FSS structure. It is also asymptotically shown that the mutual coupling experienced by the nano-antenna with the FSS structure is negligible even in the presence of a very large number of closely integrated elements. Finally, the technological issues are discussed for practical implementations.

Reduced Graphene Oxide Membrane Induced Robust Structural Colors toward Personal Thermal Management

Abstract: Angle-independent structural colors are prepared by membrane separation-assisted assembly (MSAA) method with modified reduced graphene oxide (rGO) as the substrate membrane. We show that the wrinkled and crumpled rGO laminates not only ensure uneven morphology of colloidal film but improve color saturation by decreasing coherent scattering. In addition, we study the influence of stopband position on thermal insulation property of the colloidal film for the first time. High absolute temperature difference of 6.9 °C is achieved comparing with control sample. And films with longer stopband positions indicate better thermal insulation performance because of inherent slow photon effect in photonic structure. This general principle of thermal insulation by colloidal films opens the way to a new generation of thermal management materials.

Tunable Substrate Integrated Waveguide Diplexer With High Isolation and Wide Stopband

Abstract: A tunable multilayer diplexer using substrate integrated waveguide (SIW) technology is proposed in this letter. A multilayer design is chosen to easily control the electric and magnetic coupling through circular slots in order to achieve a wide-stopband response. The proposed diplexer works at two unique frequencies (centered at 10.5 and 13.5 GHz) with high isolation (>42dB) and a wide stopband (up to 21 GHz). A varactor diode is used in the proposed diplexer for tuning. The varactor diode is placed in the structure in such a way that both channels can be tuned independently without affecting one another. The results show the flexibility of the diplexer in achieving desired responses and its suitability for integration with any tunable component. Simulated and measured results obtained are in good agreement.

Ultra-Compact TSV-Based L-C Low-Pass Filter With Stopband Up to 40 GHz for Microwave Application

Abstract: In this paper, an ultra-compact low-pass filter (LPF) with wide stopband is proposed based on lumped L-C structure in through-silicon via-based 3-D stacked configuration. The spiral inductor (L), interdigital capacitor (C), and the proposed LPF are theoretically analyzed based on parasitic parameters and equivalent circuit models. To evaluate the characteristics, the proposed LPF is simulated by HFSS, fabricated with CMOS-process-compatible technology, and measured with de-embedding method. Simulation and measured results are in good agreement. Compared with the other literature, the proposed LPF has the most compact size of $0.028\lambda _{g }\times 0.017 \lambda _{g}$ . ( $\lambda _{g}$ is the guide wavelength at $f_{c}$ .) With the cutoff frequency at 10.05 GHz, the filter has an insertion loss of 0.14 dB and reflection loss over 13 dB from dc to 9 GHz in the passband. The suppression levels are better than 20 dB from 20.4 up to 40 GHz in the stopband.

High-Order Input-Reflectionless Bandpass/Bandstop Filters and Multiplexers

Abstract: A coupling-matrix approach for the theoretical design of a type of input-reflectionless RF/microwave bandpass filters (BPFs) and bandstop filters (BSFs) is presented. They are based on diplexer architectures with arbitrary-order bandpass and bandstop filtering channels that feature complementary transfer functions. The transmission behavior of these reflectionless filters is defined by the channel that is not loaded at its output, whereas the input-signal energy that is not transmitted by this branch is completely dissipated by the loading resistor of the other channel. Analytical formulas for the coupling coefficients for the first-to-fourth-order filter designs are provided and validated through several synthesis examples. This theoretical design methodology, along with an optimization step, is also exploited to design input-quasi-reflectionless quasi-elliptic-type BPFs with a transmission-zero-(TZ)-generation cell in their bandpass filtering channel. In addition, the application of the proposed input-reflectionless BPF and BSF networks to input-quasi-reflectionless multiplexer design is approached. It is shown that a single resistively terminated multi-band BSF branch can absorb the input-signal energy not transmitted by the multiplexer channels in their common stopband regions to achieve quasi-reflectionless characteristics at its input. Moreover, experimental microstrip prototypes consisting of 2-GHz third-order BPF and BSF circuits, a 2-GHz sharp-rejection third-order BPF with two close-to-passband TZs, and a second-order diplexer device with channels centered at 1.75 and 2.1 GHz are developed and measured.

Wideband Transmissive Frequency-Selective Absorber

Abstract: In this letter, a new frequency-selective absorber is presented that has wideband transmission/absorption/reflection reduction responses. The presented absorber is completed by lossy cross-dog-bone and lossless second-order frequency-selective surfaces. The modal interaction pole generated by the lossy array is employed to achieve a wideband transmission. Three absorption bands are combined to realize a continuous stopband with high absorptivity. Furthermore, the improved absorber structure is investigated to reduce the strong reflection between the absorption and transmission bands. The 10 dB reflection reduction is obtained with a fractional bandwidth of 126.4%. Meanwhile, the –3 dB fractional passband width is 41.3% with minimum insertion loss of 0.37 dB. The absorption bandwidth of 91.5% is provided with at least 90% absorptivity. The distance between the lossy and lossless layers is only 0.08 $\lambda _{L}$ at the lowest operating frequency. Finally, the proposed design is validated by a good agreement between the numerical simulations and experimental measurements.

Miniaturized microstrip dual-band bandpass filter with wide upper stop-band bandwidth

Abstract: A novel microstrip dual-band bandpass filter (BPF) with bended microstrip lines, rectangular resonators and stepped impedance resonator (SIR) is designed, analyzed and fabricated. This circuit provides two pass-bands with the center frequencies of 3.6 and 5.7 GHz. Moreover, the LC equivalent circuits of the basic and main resonators are meticulously computed so as to present an analytical description. The surface current distributions of the proposed filter are shown to verify the performance of the filter and provide physical insight. The measured data of the proposed filter indicate that the insertion losses are better than 0.53 and 0.67 dB and the return losses are 25 and 24.7 dB in the first and second bands, respectively. One of the most outstanding features of the proposed filter is that the upper band can be tuned between 5.7 and 8.4 GHz without any increment in the circuit size. The compact size, wide upper stop-band bandwidth, low insertion loss, sharp transition bands, and high attenuation level in the stop-bands are the other marked positive points of the designed filter. Finally, a suitable agreement between the simulated and measured S-parameters can be observed.

Polarization-Independent, Narrowband, Near-IR Spectral Filters via Guided Mode Resonances in Ultrathin a-Si Nanopillar Arrays

Abstract: We report the optical properties obtained through experiments, simulation, and theory of ultrathin (<0.1λ), amorphous Si nanopillar arrays embedded in a thin film of SiO_2 designed for narrowband filtering for multi- and hyperspectral imaging in the near-infrared. The fabricated nanopillar arrays are square-packed with subwavelength periodicity, heights of ∼100 nm, and a radius-to-spacing ratio, r/a, of ∼0.2. Specular reflection measurements at normal incidence demonstrate that these arrays behave as narrow stopband filters in the near-infrared (λ = 1300–1700 nm) and attain ∼90% reflectivity in band and a full width at half-maximum as low as 20 nm. Using a combination of full-wave simulations and theory, we demonstrate that these narrowband filtering properties arise from efficient grating coupling of light into guided modes of the array because the nanopillar arrays serve as photonic crystal slabs. This phenomenon is known as a guided mode resonance. We discover that the spectral location of these resonances is passively tunable by modifying array geometry and is most sensitive to nanopillar spacing. Theoretical photonic crystal slab band diagrams accurately predict the spectral locations of the observed resonance and provide physical insights into and support the guided mode resonance formulation. This work demonstrates that these ultrathin all-dielectric nanopillar arrays have advantages over existing hyperspectral filter designs because they are polarization independent, do not suffer from material absorption loss, and have significant implications for minimizing imaging device size.

Integration of Brillouin and passive circuits for enhanced radio-frequency photonic filtering

Abstract: Signal processing using on-chip nonlinear or linear optical effects has shown tremendous potential for RF photonic applications. Combining nonlinear and linear elements on the same photonic chip can further enable advanced functionality and enhanced system performance in a robust and compact form. However, the integration of nonlinear and linear optical signal processing units remains challenging due to the competing and demanding waveguide requirements, specifically the combination of high optical nonlinearity in single-pass waveguides, which is desirable for broadband signal processing with low linear loss and negligible nonlinear distortions required for linear signal processing. Here, we report the first demonstration of integrating Brillouin-active waveguides and passive ring resonators on the same integrated photonic chip, enabling an integrated microwave photonic notch filter with ultradeep stopband suppressions of >40 dB, a low filter passband loss of <-10 dB, flexible center frequency tuning over 15 GHz, and reconfigurable filter shape. This demonstration paves the way for implementing high-performance integrated photonic processing systems that merge complementary linear and nonlinear properties, for advanced functionality, enhanced performance, and compactness.

Dual-Band Filtering Power Divider Using Dual-Resonance Resonators With Ultrawide Stopband and Good Isolation

Abstract: In this letter, a novel compact dual-band filtering power divider (DB-FPD) is proposed. It consists of a U-shaped Wilkinson power divider, two pairs of dual-resonance resonators (DRRs), and a pair of spur lines. With the simultaneous use and appropriate design of the coupled feedlines, mixed electric and magnetic couplings between the DRRs and spur-lines with different lengths, multiple transmission zeros are produced which result in two passbands with desired power division, high-frequency selectivity, good isolation, and an ultrawide stopband. A prototype DB-FPD operating at 2.3 and 3.5 GHz with 3-dB fractional bandwidths of 8% and 6% is designed, fabricated, and measured. The measured responses agree well with the design simulations, exhibiting a stopband up to 13.8 GHz ( $6f_{0}$ ) with 20-dB rejection level.

Ultra-Compact Tuneable Notch Filter Using Silicon Photonic Crystal Ring Resonator

Abstract: A novel ultra-compact photonic tuneable notch filter with large bandwidth, high extinction ratio, fast response, and flat stopband is modeled and designed. It consists of a silicon-based ring resonator with one-dimensional photonic crystal superimposed onto a ring portion. Engineering the defects into the photonic crystal section allows to achieve the equalization of the bottom band of the filter response. Large bandwidth ( B = 10.43 GHz) and high extinction ratio (ER = 41 dB) have been attained with a frequency response of the first-order Butterworth filter type. Continuous and wide range tunability of the central frequency (15 GHz) has been obtained by using the carrier injection technique, together with fast reconfigurability (a1 ns) and power consumption of 47 mW. The device footprint is as very small as about 150 μm2. This performance makes the proposed device suitable for several filtering applications, such as wireless networks (5G) and telecommunication reconfigurable payloads in Telecom and Space scenario, respectively.

A Waveguide Slot Filtering Antenna With an Embedded Metamaterial Structure

Abstract: A novel waveguide slot filtering antenna with an embedded metamaterial is presented. This filtering antenna consists of a common waveguide slot antenna with longitudinal slots cut on the top broad wall of its rectangular waveguide and a metamaterial surface embedded in the bottom broad wall. The metasurface replaces the conventional metal plane in the form of a bed of nails. In the operating frequency band, the metasurface works as a perfect electric conductor, so the antenna radiates as the traditional waveguide slot antennas. While in the stopband, the metasurface performs as a perfect magnetic conductor to suppress the propagation of electromagnetic wave in the waveguide cavity, so the interference signal is rejected and a filter function is achieved. To show the design process and verify its feasibility, a filtering antenna prototype working in the $C$ -band and having a stopband in the $X$ -band is designed, fabricated, and tested. A good agreement between simulation and measurement is obtained, demonstrating efficient radiations in the working band and a strong suppression of more than 35 dB in the stopband.

Compact Microwave and Millimeter-Wave Bandpass Filters Using LTCC-Based Hybrid Lumped and Distributed Resonators

Abstract: A novel class of low-temperature cofired ceramic (LTCC) bandpass filters (BPFs) is proposed in this paper, featuring of compact size and good filtering responses in both microwave and millimeter-wave (mm-wave) bands. By effectively merging the lumped elements and distributed effects, a modified LTCC-based hybrid lumped and distributed resonator (HLDR) is introduced. In detail, the lumped part of a LTCC interdigital capacitor and a high-impedance line is used to reduce circuit size, loss, and cross-talks. The distributed part, saying, the mutual couplings between adjacent HLDRs and to the ground, is used to improve the design flexibility and filtering performance for HLDR filters. With mutual couplings, the coupling matrix method can be applied. Furthermore, the frequency-variant mixed couplings between HLDRs are investigated, and coupling matrix method is improved by introducing a new coupling mechanism. Multiple transmission zeroes (TZs) are firstly realized with second-order in-line topology, but without adding cross-couplings or bandstop structures. To validate above design strategies, one S-band and one Ka-band second-order HLDR BPFs are simulated and measured, respectively. Very compact size, low loss, high-selectivity, and wide upper stopband are observed, especially in mm-wave range.

Design and Analysis of an Ultraminiaturized Frequency Selective Surface With Two Arbitrary Stopbands

Abstract: The paper proposes a new design and its analysis of a 2.5-D ultraminiaturized frequency selective surface (FSS) with two arbitrarily and independently adjustable stopbands. These two stopbands can be adjusted very far away or combined to a single wideband. This new FSS consists of only one dielectric layer printed on both sides with refined meandering-lines connecting vertical via arrays. By applying the proposed approach with an exactly equivalent circuit and closed-form equations, four representative prototypes are demonstrated. The first one has two distant stopbands, which high-to-low resonant frequency ratio can be as large as 6.2. The second one shows that its unit-cell size can be highly reduced to only 2.8% of the free space wavelength at the lower resonant frequency. The third one has a wide stopband, having a fractional bandwidth up to 75.7%. The final one meets the specification of 2.4-GHz and 5-GHz wireless local area network application. The simulated and measured results both validate the FSS performance and demonstrate its excellent versatility never found in literatures before.

Broadside Scanning Asymmetric SIW LWA With Consistent Gain and Reduced Sidelobe

Abstract: In this paper, a backward-to-forward continuous beam scanning leaky wave antenna is presented in substrate integrated waveguide technology. The antenna radiates from a continuous longitudinal slot etched on its broad wall. The slot is excited by using periodic H-plane steps. An impedance matched unit cell structure is used to suppress the open stopband in the broadside direction. Bloch wave analysis is used to obtain the propagation characteristics of the antenna. However, due to radiation being obtained only from the shunt-type radiating element, namely, the longitudinal slot, a gain dip is observed in the broadside direction. Transversal asymmetry is then introduced in the structure to eliminate the gain dip and obtain the consistent gain. A prototype of the antenna is fabricated and measured. Continuous beam scanning is achieved from −29o to +30o about the broadside direction with a gain variation of less than 2 dB over 8.0–12.4 GHz. A measured peak gain of 16.1 dBi is obtained. Key structural design parameters of the antenna are identified for controlling the leakage rate. Next, Taylor tapered aperture illumination is used to obtain low sidelobe level (SLL). The Taylor tapered antenna is also fabricated with the measured SLL below −21 dB.

Design of Dual-Band Bandpass Filter With Multiple Transmission Zeros Using Transversal Signal Interaction Concepts

Abstract: In this letter, a compact dual-band bandpass filter (BPF) based on the transversal signal interaction concepts is presented. The center frequencies of dual-band BPF are centered at 3.8 and 4.8 GHz with 3-dB fraction bandwidths of 11.3% and 10.7%, respectively. Transversal filtering structure is introduced in the proposed dual-band BPF, which provides two signal propagation paths from input to output. Thus, a dozen of transmission zeros are yielded to obtain wide stopband suppression ranging from 5.2 to 16 GHz. To validate the design scheme, a dual-band BPF with high selectivity, compact size, independently controllable bandwidth, and wide stopband suppression is fabricated and measured.

A Compact 3.3–3.5 GHz Filter Based on Modified Composite Right-/Left-Handed Resonator Units

Abstract: In the RF (Radio Frequency) front-end of a communication system, bandpass filters (BPFs) are used to send passband signals and reject stopband signals. Substrate-integrated waveguides (SIW) are widely used in RF filter designs due to their low loss and low cost and the flexibility of their integration properties. However, SIW filters under 6 GHz are still too large to meet the requirement of portable communication devices due to their long wavelength. In this paper, a very compact fully integrated SIW filter is proposed and designed with RT6010 dielectric material to meet the small size requirement of portable devices for next-generation sub-6 G applications. The proposed filter contains two sawtooth-shaped composite right-/left-handed (CRLH) resonator units, instead of traditional rectangular-shaped CRLH resonator units, which makes the filter more compact and cost effective. The filter is designed and fabricated on an RT6010 substrate, with a size of only 10 mm × 7.4 mm. The measurement results illustrated that the proposed BPF shows a passband covering the frequency range of 3.25–3.45 GHz; the minimum passband insertion loss is only 2.4 dB; the stopband rejection is better than −20 dB throughout the frequencies below 3.0 GHz and above 3.8 GHz; S11 is as low as −37 dB at 3.35 GHz; and the group delay variation is only 1.4 ns throughout the operation bandwidth.

High extinction ratio on-chip pump-rejection filter based on cascaded grating-assisted contra-directional couplers in silicon nitride rib waveguides.

Abstract: We present an on-chip filter that is based on the grating-assisted contra-directional coupler (GACDC) implemented on a silicon nitride rib waveguide platform. This filter enjoys the benefit of an unlimited free spectral range (FSR) on the red side of the stop/passband. Unlike a Bragg reflector, the GACDC filter has the advantage of coupling the rejected light contra-directionally into a bus waveguide, instead of reflecting it back to the input. This property makes it an add/drop filter suitable for pump rejection and allows effective cascading to provide an even higher extinction ratio compared to the single-stage version. In this Letter, we experimentally demonstrate that a 16-stage cascaded GACDC filter can provide a stop band with a bandwidth smaller than 3 nm and an extinction ratio as high as 68.5 dB.

Multi-Functional Balanced-to-Unbalanced Filtering Power Dividers With Extended Upper Stopband

Abstract: Two new types of multi-functional RF wide-band differential-mode-to-single-ended filtering power dividers are reported in this brief. Their first configurations exploit half-wavelength ring resonators and coupled-line sections to attain common-mode suppression throughout a broad spectral range. Furthermore, asymmetrical coupled-line stages are incorporated in more-advanced schemes to enlarge upper-stopband bandwidth. Two demonstrative microstrip prototypes for the different structures of this RF tri-functional circuit concept that operate at the 1.7–2.7-GHz 4/5-generation long-term-evolution band are built and tested.