Sharp Passband Research Articles

Correction to ‘Simple wideband FPD with sharp passband selectivity and nice UWB isolation’

Correction to ‘Simple wideband FPD with sharp passband selectivity and nice UWB isolation’

Design of a Novel Balanced-to-Balanced Dual-Band Diplexing Power Divider

In this brief, a balanced-to-balanced (BTB) dual-band diplexing power divider (DBDPD) implemented on a new asymmetric series T-junction MS transition is proposed. Firstly, a four-way BTB power divider (PD) as feed network was designed. The T-junction microstrip-slotline (MS) transitions are employed to realize phase shift and power division within a wide bandwidth. The balanced U-type MS transitions are adopted at each balanced port, which can realize superior common-mode (CM) suppression intrinsically while the differential-mode (DM) responses are independent. Then, the BTB DBDPD is realized by adding four pairs of step impedance resonators (SIRs) asymmetrically to the series T-junction. As a result, an asymmetric series T-junction MS transition with diplexing function is formed, which can flexibly adjust the operating passbands and adapt to the balanced port. Meanwhile, SIRs are employed to realize four sharp passbands. So as to verify the feasibility of the theoretical design, the proposed designs are manufactured. A good agreement can be observed between the simulation and measurement.

Design of a metasurface filtering antenna with tunable radiation nulls

In this article, a low profile wideband metasurface filtering antenna with tunable radiation nulls is proposed. Metasurface structure is used to excite adjacent resonant modes to obtain broadband responses. A U-shaped slot is introduced into the microstrip line to generate a radiation null in the lower stopband. Complementary split-ring resonators (CSRRs) are etched on the metasurface unit to produce another radiation null in the upper stopband edge to improve the filtering effect. The radiation nulls position can be flexibly controlled by changing the size of U-shaped slot and CSRRs. For verification, the corresponding antenna is fabricated and tested. The antenna size is 0.556 λ 0 × 0.556 λ 0 × 0.044 λ 0 (30 × 30 × 2.4 mm3). The measured results agree well with the simulated. The antenna operates from 4.9 to 6 GHz with a flat gain (5.5 dBi), a sharp passband skirt and stable radiation patterns.

Bragg fiber with a doubly defect layer-based tunable multiband optical filter

A Bragg fiber waveguide having double-defect layers in its periodic cladding region is investigated and optimized for inline tunable multi-bandpass filter applications. The proposed waveguide is classified in terms of a symmetric waveguide and an asymmetric waveguide depending upon the refractive index of the defect layers. The required reflectance and confinement loss equations are obtained using the boundary matching technique and the transfer matrix method. Due to the presence of the double-defect layer, two sharp passbands in the bandgap region are observed. The separation of the passbands and their intensities can be controlled by introducing the number of unit cells between the defect layers. Our analysis shows that the passband’s intensity, bandwidth, and central wavelength can also be tuned by changing the refractive index of the core material. In addition, the central wavelength for both defect modes are blue shifted with the increase of the core refractive index. In all of our considered cases, the higher tunability with a core refractive index variation in the right defect mode is 25.38 nm/RIU for the symmetric cases having defect layer refractive indices of 1.45. Similarly, the higher tunability with a core refractive index variation in the left defect mode is 16.9 nm/RIU for the asymmetric cases having a refractive index of 1.45 in the first defect layer and 3.42 in the second defect layer. Hence, our proposed waveguide can work as a tunable multi-bandpass inline filter with a narrow bandwidth.

Capacitive Coupled Wide-Notch Stepped Impedance Narrow-Band Bandpass Filter for WiMax Application

The development of wireless communication standards necessitates optimal filter design for the selection of appropriate bands of frequencies. In this work, a compact in size pair of parallel coupled symmetric stepped impedance-based resonator is designed with supporting to the WiMAX communication standards. The coupled resonator is tuned to allow the frequency band between 3.4 GHz and 3.8 GHz, which is centered at 3.6 GHz. A parasitic effect of capacitively coupled feed structure is used for exciting the two symmetrical stepped impedance resonators. The bandwidth and selectivity of the filter are enhanced with the change of characteristic impedances and controlling the coupling gap between resonators. This design offers single narrow sharp passband selectivity as well as multiple stopband harmonic suppression arising as a result of multiple transmission zeros. The designed filter operates with a fractional bandwidth (FBW) of 11.47%. The proposed single narrowband bandpass filter provides better suppression in either side of the tuned frequency (3.6 GHz) without degrading the passband performance. Also, this novel filter offers an insertion loss of about −0.08 dB and a return loss of greater than −30 dB in passband. This approach is useful for eliminating unwanted spurious harmonics responses that enter the desired response. The suggested bandpass filter has been simulated using Advanced Design System (ADS) tool, and the measurement has been made using a network analyzer, and the results are reported.

Design and Simulation of a Compact Filtenna for 5G Mid-Band Applications

In order to provide an efficient, low cost, and small size radiating structure that passes a certain frequency band with negligible amount of interference, the combination of filters and antennas is proposed to form a single element called filtenna. This paper presents a filtenna element with compact size that can radiates in the 5G mid-band frequency range (3.6-3.8 GHz) and perfectly rejects all the frequencies outside this range. The filtenna is composed of a printed circuit antenna that is terminated with a crescent shaped stub that is coupled electromagnetically with a miniaturized sharp band-pass filter. The simulation results show a filtenna reflection coefficient with a reduced value within the intended 5G band and with high values along the other unwanted frequencies. Moreover, the structure has an omnidirectional pattern with reasonable gain value within the band of interest, and this makes the antenna very suitable for portable 5G devices.

Compact LTCC bandpass SIW filter with high selectivity for 5G exploiting mixed coupling

ABSTRACT A compact LTCC BPF exploiting six SIW cavities with sharp passband skirt for 5 G communication is proposed. The filter has coplanar waveguide (CPW) as input/output structures and six cavities SIW resonators with mixed coupling, and the size of the filter has been reduced because of 3D integration. The size of this filter is compact with 7.0 × 3.8 × 1.2 mm3, which is miniaturized enough to be integrated in the subsystem. The simulation and measurement results demonstrate the proposed BPF passband centers at the frequency of 28.0 GHz with a 3 dB bandwidth of 6.5% and the filter has wide application in 5 G wireless communication.

Filtering dual‐patch antenna with flat gain response using F‐shaped feeding structure

AbstractA novel wideband filtering dual‐patch antenna with a flat gain response is presented in this letter. This filtering antenna mainly consists of two parts: two patches and an F‐shaped feeding structure. The upper and lower patches are fed by two different horizontally placed narrow strips from the F‐shaped structure. Two patch modes are simultaneously excited within the passband, yielding a 29.3% bandwidth with a very flat gain response and a stable radiation pattern. Furthermore, a pair of radiation nulls are generated symmetrically at the two sides of the passband owing to the mutual coupling between two patches. As a result, a filtering antenna without any extra filtering circuit is obtained which achieves a realized gain of 10 dBi within the passband and an out‐of‐band suppression level of 15 dB in the lower stopband and 20 dB in the upper stopband. Compared to the traditional patch antennas, this proposed filtering antenna demonstrates a very flat gain response, a sharp passband skirt, and a good selectivity, which is well designed and very suitable for high band cellular communication (2.0‐2.7 GHz).

Temperature sensing scheme based on fiber ring microwave photonic filter with erbium doped fiber amplification

AbstractThe temperature sensing scheme based on fiber ring microwave photonic filter (MPF) with erbium doped fiber amplification (EDFA) is proposed and experimentally demonstrated. The fiber ring is used as the time delay element, as well as a sensing element, and by introducing an EDFA to compensate the loss in the fiber ring, the number of the effective sampling taps and thus the suppression ratio are increased. When the EDFA power is set at 0.74 mW, the 3 dB bandwidth of the passband and suppression ratio of the MPF are estimated to be 82.5 kHz, and 15 dB, respectively. The superior sharp passband characteristics make the fiber ring MPF with an EDFA very advantageous for sensing. In our experiment, temperature sensing by using the fiber ring MPF with an EDFA has been carried out for demonstration. The temperature variations induce refractive index changes of the fiber, which will change the time delay of each tap of the fiber ring MPF, and as a result, the FSR of the MPF will be changed. By tracing the peak point shift of the MPF's passband, the temperature variations can be monitored. Our experimental results show that there is a good linear relationship between temperature change and frequency shift, and by measuring passbands with different frequencies, different sensitivity can be obtained. In our experiment, the sensitivity is estimated to be −5.89, −11.74, and − 17.7 kHz/°C, respectively, when the passbands at 0.8, 1.6, and 2.4 GHz are adopted for temperature monitoring.

Novel terahertz metasurfaces based on complementary coupled split ring resonators

In this paper, we propose a terahertz metasurface unit cell based on an efficient coupling between two completely symmetric complementary split-ring resonators via a coupling slot. This coupling allows the excitation of a dark eigenmode resonance that is otherwise forbidden. In turn, the radiation losses are highly suppressed and the excited eigenmode features a quite large quality factor. Interestingly, this kind of coupling leads to the restoration of the symmetry of the unit cell of the coupled resonators with respect to the terahertz field illumination. More importantly, we show that the quality factor of this dark mode resonance can be tuned by modifying the coupling slot length and reach a high value of 67.4. Furthermore, a laser beam machining technique can be easily exploited during the fabrication process of this design. Besides using this design as a sharp bandpass filter, it can be utilized as an efficient biosensor. We show that a sensitivity level of 6.3 × 104 nm/RIU is indeed doable using the proposed structure. This design may emerge as a potential candidate for future biosensors and hence utilized during the development of new cancer biomarkers.

Design of a very compact and sharp bandpass diplexer with bended lines for GSM and LTE applications

In this paper a new miniaturized bandpass-bandpass diplexer with sharp pass-band is designed and fabricated. The proposed diplexer includes two bandpass filters with sharp pass-bands. Coupling lines and stepped impedance resonators are used to form each bandpass filter. In this paper, two filters are designed in the schematic circuit mode, and then they are combined to form the final diplexer layout. After combining these bandpass filters, the transmission lines are bended to reduce the overall size of the designed filter. The operating frequencies of the designed diplexer could be selected at the desired frequencies by changing the design parameters. Proposed diplexer shows good isolation which is better than 20 dB in entire operating frequency band. Also, insertion losses in the passbands are better than 0.7 dB in output ports. The final size of the fabricated diplexer is 19.8 mm × 51.3 mm or 0.08 λ g × 0.22 λ g which shows good reduction, compared to the recent designed diplexers. The designed diplexer operates at 900 MHz and 2.6 GHz, corresponding to GSM and LTE frequencies.

Planar In-Phase Filtering Power Divider With Tunable Power Division and Controllable Band for Wireless Communication Systems

A wideband in-phase power divider with tunable power division ratio (PDR) and filtering response is presented. The proposed design is quite compact and consists of a three-line coupled structure and loaded with a pair of varactor-loaded short-ended stubs at two output terminations. A variable power division is realized by tuning the coupling factors between the centerline and sidelines of the three-line coupled structure using a pair of varactors. A varactor at the center of the loaded short-ended stub and another one connecting the end of the stub to the ground is used to control the center frequency and band of operation. A prototype is modeled using the microstrip technique and then simulated and tested. The experimental result indicates a tunability of PDR from 0.5:1 to 2:1 across wideband range of 60% and a controllable band from 35% to 63.2%, with 13% center frequency tunability, sharp passband cutoff selectivity, as well as harmonic suppression to more than 6 GHz (4 times the center frequency). Moreover, the overall loss is around 1–1.2 dB; the isolation is more than 14 dB, whereas the differential phase is less than 7° in all the investigated cases.

Design of a compact microstrip power‐divider diplexer with simple layout

A new design of microstrip power-divider (PD) diplexer with simple layout is presented. The proposed design is directly formed up by two independently designed dual-mode filtering PDs without any additional matching network at the common port, thus bringing significant design flexibility and size reduction to the design process. For validation, a prototype PD diplexer working at 2.45 and 2.98 GHz is finally implemented and measured. Measured results agree well with the simulated ones. Results indicate that the PD diplexer exhibits sharp passband selectivity, good port-to-port isolation and high channel isolation, which is very attractive for applying to the multi-standard wireless communication systems.

Design and Analysis of a Programmable Receiver Front End Based on Baseband Analog-FIR Filtering Using an LPTV Resistor

This paper presents a programmable receiver frontend that uses periodically time-varying components. A sharp programmable filtering response was achieved at RF using a linear periodically time-varying (LPTV) resistor in conjunction with a passive mixer and an integrate-and-dump circuit. The LPTV resistor along with the integrate-and-dump circuit is shown to achieve a programmable finite-impulse response (FIR) baseband filter. The baseband filter is then upconverted with the passive mixer to achieve sharp bandpass filtering at the desired RF center frequency. Further, it is shown that an additional S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> constraint can be imposed on the FIR filter design to allow for impedance matching to the antenna impedance. The implemented receiver achieved high close-in linearity with 17 dBm of IIP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> at only 1.2× bandwidth frequency offset, while achieving a wideband impedance match with S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> better than -10 dB throughout the local oscillator range of 0.1-1 GHz.

A dual notched band UWB-BPF based on microstrip-to-short circuited CPW transition

AbstractThis paper proposes a dual notched band ultra-wideband (UWB) bandpass filter (BPF) based on hybrid transition of microstrip and coplanar waveguide (CPW). The CPW in ground plane houses a stepped impedance resonator shorted at ends, and is designed to place its resonant modes within the UWB passband. The microstrips on the top plane are placed some distance apart in a back-to-back manner. The transition of microstrip on top and shorted CPW in the ground is coupled through the dielectric in a broadside manner. The optimized design of the transition develops the basic UWB spectrum with good return/insertion loss and extended stopband. Later, defected ground structure, embedded in CPW, and split ring resonators, coupled to feeding lines are utilized to develop dual sharp passband notches. The simulated data are verified against the experimentally developed prototype. The proposed dual notched UWB-BPF structure measures only 14.6 × 7.3 mm2, thereby justifying its compactness.

Reconfigurable RF Multiband Filter With Widely Tunable Passbands Based on Cascaded Optical Interferometric Filters

Despite the increasing importance and critical needs, reconfigurable radio frequency (RF) multiband filters are currently underdeveloped even both RF electronics and photonics technologies are being explored. Although RF multiband filters with large numbers of simultaneous passbands and wide frequency tuning range are extremely desired, achieving such functionality is extremely challenging. In this paper, a photonics-based highly tunable and reconfigurable RF multiband filter is proposed through the combination of a special designed tunable Mach–Zehnder interferometer and a reconfigurable Lyot loop filter. Both the passband frequencies and the number of simultaneous passbands are adjustable, that one or multiple passbands are continuously tuned over a 20 GHz frequency range, and the number of simultaneous passbands is reconfigurable from zero to seven. As a result, the proposed RF multiband filter can be configured with various passband combinations through the same setup, providing exceptional operation flexibility. Furthermore, broadband operation and excellent filter selectivity are obtained, with sharp passband profiles and over 35-dB sidelobe suppression.

Simple wideband FPD with sharp passband selectivity and nice UWB isolation

A simple wideband filtering-response power divider (FPD) with sharp passband selectivity and good UWB isolation is presented. By ingeniously integrating multimode resonators and stub attached coupled-line isolation network, the FPD is initially built. Compared to those in the literatures, the presented wideband FPD features its simple structure and good wideband performance. For demonstration, a prototype FPD with a central frequency of 2.46 GHz and 3 dB fractional bandwidth of 22.8% is implemented. Final results indicate that this FPD possesses not only sharp frequency selectivity and wide stopband attributing to six created transmission zeros, but also an isolation better than 16 dB over an UW isolated frequency band (from DC to 2.67f 0).

Design of Miniaturized Dual-Band Low-Pass–Bandpass and Bandpass Filters

In this paper, a lumped-element structure with four potential transmission zeros (TZs), one zero-value transmission pole (TP), and three nonzero TPs is first proposed to design dual-band low-pass-bandpass filter (DB-LBF). Then, a pair of capacitors to block zero-value TP and an inductor to generate another nonzero TP are introduced in the DB-LBF structure to transform the low-pass passband into bandpass passband, so that a dual-band bandpass filter (DB-BPF) is constituted. Closed formulas and guidelines are given for two types of filter design. As examples, a 0.9/2.4-GHz DB-LBF with compact size of $0.05\lambda _{g\_{}{\mathrm{ lb}}}\times 0.079\lambda _{g\_{}{\mathrm{ lb}}}$ and a 0.395/1.575-GHz DB-BPF with compact size of $0.032\lambda _{g\_{}{\mathrm{ bb}}}\times 0.027\lambda _{g\_{}{\mathrm{ bb}}}$ are designed and fabricated. Both DB-LBF and DB-BPF have two independently controlled passband frequencies and also exhibit wide passband, low insertion loss, good return loss, and sharp passband selectivity. Moreover, they are also compatible with integrated circuit process.

Integrated SOI High-Order Phase-Shifted Bragg Grating for Microwave Photonics Signal Processing

An integrated high-order phase-shifted Bragg grating, comprising six quarter-wave sections between Bragg grating mirrors in a laterally-corrugated strip waveguide has been realized in silicon-on-insulator technology. A box-like transmission window is created within the 10-nm-wide grating reflection band, realizing a sharp bandpass optical filter with out-of-band rejection exceeding 40 dB and a steep roll-off of ∼300 dB/nm in the transition band. The sharp optical filter has been experimentally tested in microwave photonics (MWP) signal processing applications, namely spectral separation of an optical sideband comprising 1.25 Gb/s data from a 15-GHz-spaced carrier, and sideband suppression for dispersion compensation in a radio-over-fiber link. The results of the characterizations indicate negligible power penalty in terms of bit-error rate for the sideband separation and robust mitigation of dispersion-induced transmission impairment. The device has an ultrasmall footprint of ∼450 × 0.5 μm2, and can be monolithically integrated with germanium photodiodes or silicon modulators as well as other passive subsystems to implement advanced on-chip MWP signal processing functionalities.

Optically Controlled Fast Reconfigurable Microwave Photonic Dual-Band Filter Based on Nonlinear Polarization Rotation

A high-speed optically controlled microwave photonic (MWP) reconfigurable dual-band filter is presented, which is achieved using a Lyot loop filter for spectrum slicing and ultrafast nonlinear polarization rotation (NPR) effect in a semiconductor optical amplifier for high-speed tuning. Through the control of optical pump power, the MWP filter is switchable between four different operation states-all-block state, dual-band state, and single-band state with two different passband frequencies. The use of NPR greatly increases the tuning speed of the MWP filter to gigahertz range, making it capable for high-speed tuning in dynamic multiband applications. The four operation states and high-speed adjustment significantly improve operation flexibility of the filter. Furthermore, good passband quality is also obtained that the sidelobe suppressions of both passbands are over 40 dB with clean and sharp passband profiles, providing good filter selectivity.