Good In-band Research Articles

Wideband n-Way filtering power dividers with good isolation and arbitrary power ratios

This paper presents a n-way filtering power divider (FPD) with arbitrary power ratios and good in-band isolation using modified Luzzato power dividers. Three-line coupled lines are introduced at the output ports to improve the impedance matching and out-of-band rejection. And half-wavelength stepped-impedance transmission lines and resistors are used to form the entire isolation network. To explore the mechanism of the topology, the even–odd mode method is applied. To obtain a wide isolation bandwidth, two transmission zeros are introduced to widen the isolation by changing the values of resistors of the isolation networks. Finally, three FPDs with different splitting ways and power ratios are designed and fabricated. And the simulated and measured results agree well with each other.

Design of Multiband Bandpass Inline Topology Filters Using Compact Multicoupled Line Structures

This paper presents the synthesis and design of multiband bandpass filters (MBPFs) with in-line topology. The coupled-line coupling structures are employed to achieve multi-channel responses and compact footprint. Two different approaches are developed in this research to implement coupled-line MBPFs based on frequency transformation methods. The first synthesis method is based on the direct mapping technique. According to this method, a quad-band bandpass filter is theoretically synthesized and designed. The second proposed method is based on generlized ladder-type network analysis with frequency-invariant reactance elements (FIRs). It enables designing MBPFs with arbitrary number of passbands. To validate this method, a sext-band MBPFs is theoretically investigated, synthesized and designed in microstrip technology as well. Very good in-band filter performance and very good band-to-band isolation are observed for the proposed MBPFs. These results show that the proposed synthesis methods and structures are attractive solutions to design MBPFs with coupled line technology.

A Distortion-Free All-Digital Transmitter Based on Noise-Shaped PWM

A novel pulse-width modulation (PWM) architecture for all-digital transmitters (ADT) that achieves good in-band and out-band performance with a very low ratio between the modulated signal frequency and the carrier frequency is presented in this paper. The proposed scheme reduces the harmonics leaving only those corresponding to multiples of the carrier frequency, overcoming the spectral limitations of other PWM implementations and relaxing the filter requirements. The binary signal is obtained using a table-based approach with very low computational complexity, mapping the complex I/Q baseband signal to duty cycles of a square wave with low distortion. In addition, a new parallelized noise shaping circuit to reduce the distortion caused by the discretization of the duty-time intervals is presented. The digital radio frequency signal is generated using a high-speed serializer and a standard pulse former. The ADT is simulated under different scenarios to evaluate the influence of time resolution in terms of Adjacent Channel Power Ratio (ACPR) and Error Vector Magnitude (EVM). The transmitter performance is verified by an FPGA implementation using 64-QAM modulated signals, achieving values of ACPR1, ACPR2, and EVM better than −47 dBc, −53 dBc, and −35 dB, respectively, using 64 quantization levels for the PWM signal.

Low-Profile Single-Layer Half-Mode SIW Filtering Antenna With Shorted Parasitic Patch and Defected Ground Structure

A low-profile single-layer half-mode substrate integrated waveguide (HMSIW) filtering antenna with compact circuit size is presented in this brief. The antenna features simple structure and consists of a half-mode substrate integrated waveguide cavity (HMSIWC), a shorted parasitic patch, and a folded defected ground structure (DGS) etched into the metallized ground plane. The half-mode technology is employed to reduce the overall dimension in the design. The shorted parasitic patch and the HMSIWC, both operating at half-mode states, are coupled with each other to form a second-order filtering response. And also a radiation null at higher stopband is introduced owing to the effects of the cross coupling. Furtherly, by etching a folded DGS into the metallized ground plane, an additional resonance in the passband and a controllable radiation null at lower stopband are simultaneously generated to broaden the impedance bandwidth and improve the selectivity of lower stopband respectively. For verification, a prototype of the developed HMSIW filtering antenna is designed, fabricated, and measured. The measured and simulated results are in good agreement, showing a wide impedance bandwidth of 9.2% at center frequency of 2.84 GHz, a flat in-band gain response with two controllable radiation nulls at both edges of the operating band, and a maximum boresight realized gain of 5.75 dBi. The proposed HMSIW filtering antenna demonstrates good in-band and out-of-band performance even with a very low profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.015~\mathbf {\mathrm {\lambda }} _{0}$ </tex-math></inline-formula> .

Circular monopole filtering antenna with improved sideband selectivity and in-band impedance using circular-stub-load resonator

Abstract In the design of the filter antenna, the filter unit with the same structure as the radiation patch not only improves the selectivity of the band edge, but also helps to improve the in-band impedance. In this design, a compact circular monopole filtering antenna with improved sideband selectivity and in-band impedance using a circular-stub-load resonator is proposed. To obtain better sideband selection characteristics and in-band impedance characteristics, and reduce the mismatch problem caused by the introduction of the filter, a branch-loaded filter with the same resonance mode as the antenna radiation patch is designed. In addition, different shape branch loading structures of the bandpass filter are also studied. The experimental results show that when the loading unit of the filter and the radiation structure of the antenna have the same structure, both good in-band impedance characteristics and sideband selectivity characteristics can be obtained from the filter antenna. The antenna reflection coefficient bandwidth is from 3 to 11 GHz (114%), and the maximum reflection coefficient is only −15 dB, showing good in-band impedance characteristics and sideband selection characteristics. The filter antenna realizes the integration of antenna filtering without increasing the size, and the final size of the antenna is 30 × 25 mm2.

Ultra‐miniaturized filtering power divider chip on integrated passive device technology using complex isolation network

In this letter, an ultra-miniaturized filtering power divider (FPD) chip based on integrated passive device (IPD) technology using a complex isolation network is proposed. Three lumped L represents inductor, C represents capacitor (LC) tanks and two electromagnetic hybrid coupling units are used to realize the third-order quasi-elliptical filtering response with high-frequency selectivity and wide stopband, which are designed and realized by using the IPD process to achieve ultra-miniaturized size. In addition, the complex impedance is utilized to form the isolation network, so good in-band isolation can be easily achieved. Moreover, the working principle and design method of this proposed FPD is well illustrated, a prototype with 3-dB fractional bandwidth of 19.3% at 2.6 GHz (f0) is in final designed and fabricated. The isolation is higher than 16 dB within the passband, and upper-stopband attenuation higher than 20 dB is extended to 40 GHz (15.4f0). It occupies only 2.76 mm × 2.0 mm, that 0.023λ0 × 0.017λ0, where λ0 is the free-space wavelength at f0.

Multi-Band Transmission Using Reconfigurable Complex Multi-Band Delta Sigma Polar Modulator

This brief presents a new reconfigurable complex multi-band delta sigma polar modulator (CMB-DSPM) architecture for multi-band transmission. In this brief, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6^{\mathrm{ th}}$ </tex-math></inline-formula> order band-pass delta sigma modulator (DSM) is designed and implemented for reconfigurable triple-band transmission. The proposed DSM architecture utilizes the advantage of a complex DSM structure to reduce the required processing block and polar quantizer to reduce the quantization noise. The proposed CMB-DSPM architecture improves the in-band and out-of-band performance in terms of signal-to-noise distortion ratio (SNDR) and coding efficiency (CE), respectively. The proposed scheme is validated in MATLAB/SIMULINK-based digital signal processing platform using three 5 MHz long-term evolution (LTE) signals. The results show up to 12.4 dB improvement in SNDR and 12.3% improvement in CE compared to the standard cartesian DSM architecture. The measured EVM is below 3%, which shows the good in-band performance of the proposed scheme.

Design of compact microstrip bandpass filter with two switchable operating passbands

A new bandpass filter (BPF) with two switchable operating passbands has been proposed. The BPF topology is formed by switchable resonators and stepped-impedance resonators. The two operating bands can be switched on and off independently. For verification, a switchable BPF with a third-order Chebyshev bandpass response was designed and fabricated using microstrip technology. The developed BPF was measured to verify the predicted and simulated results. A close agreement was observed between them. The proposed switchable BPF has good in-band and out-of-band performances. Besides, the attenuation is > 30 dB as the passband is switched off.

Theory and Design of a Flexible Two-Stage Wideband Wilkinson Power Divider

This article presents the design scheme of a wideband Wilkinson Power Divider (WPD) with two-stage architecture utilizing quarter-wave transmission lines and short-circuit stubs. The bandwidth of the proposed WPD is flexible and can be controlled using the design parameters. The proposed design achieves excellent isolation between output ports in addition good in-band performance. The analysis of the proposed circuit results in a simplified transfer function which is then equated with a standard band-pass transfer function to determine the parameters of transmission lines, stub’s impedances, and the value of the isolation resistors. Furthermore, it is also demonstrated that a simple alteration in the proposed circuit enables the design of a wideband DC isolated WPD that maintains a good in-band and isolation performance. A number of case studies have been included to highlight the flexibility of the proposed design. Two distinct prototypes are developed on different boards to demonstrate the wideband performance of the proposed design. An excellent agreement between the experimental and measured results for both the designs over a wide band including very good isolation between ports validate the proposed design.

Coding Efficiency Enhancement Using Time Interleaved Level Splitting and Optimized Multi-Level Delta Sigma Modulation in Digital Transmitter

This paper proposes a novel scheme for energy-efficient transmitter design using optimized multi-level DSM (OML-DSM) along with time-interleaved level splitting technique. This scheme significantly improves the overall transmitter efficiency by providing high coding efficiency (CE) at the DSM stage and high drain efficiency (DE) at the amplification stage. The position of quantization level and quantization level selection window range is optimized in OML-DSM to achieve better CE compared to conventional multi-level DSM. These optimized multi-level signals are further split into bi-level signal streams using time-interleaved level splitting technique to improve the DE at the amplification stage. A 10 MHz LTE signal with 12 dB PAPR is used for simulation and measurement purposes. For hardware validation, 6-level OML-DSM is applied, which converts the 10 MHz LTE signal into six quantization levels and level splitter split these multi-levels into three bi-level signal streams with different magnitude and power levels. These bi-level signal streams are amplified using class-E SMPAs. The output of SMPAs is combined with Gysel unequal power combiner. Hardware results show that the CE and channel efficiency is improved by 18.7%, and 11.4%, respectively, compared to conventional 6-level DSM. The measured EVM is 2.2%, which shows good in-band performance.

Compact Square Substrate Integrated Waveguide Filtering Power Divider With Wideband Isolation

In this letter, a new compact filtering power divider (FPD) on the square substrate integrated waveguide (SIW) with wideband isolation is proposed. As the isolation network is embedded in a square SIW cavity, good in-band isolation, compact structure, and low insertion loss can be simultaneously attained. The proposed FPD consists of the coplanar waveguide feeding line of Port 1, the capacitor, a resistor, and the square SIW cavity. TE101, TE201, and slot-line modes can realize third-order filtering response. Center frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) and bandwidth of the filtering response can be independently adjusted. In order to achieve out-of-band isolation, Port 2/3 is placed in the specific position to suppress the high-order modes according to the electric-field distributions of these modes. Finally, a prototype with in-band return loss of 20 dB across 5.59-6.4 GHz is designed at 5.99 GHz. The bandwidths of isolation higher than 21 dB and upper stopband attenuation higher than 20 dB are extended to 2.79f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and 2.83f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , respectively.

A self‐packaged wideband filtering power divider based on substrate‐integrated suspended line

In this study, a filtering power divider (FPD) is proposed by utilizing one T-shaped tri-mode stepped-impedance resonator with input/output coupling structures based on substrate-integrated suspended line (SISL). The circuit topology and SISL technology are combined together to reach balance in performances such as compact size, wideband, high frequency selectivity, low loss, good in-band isolation, wide stopband, and self-packaging so that there are no obvious flaws. Wide bandwidth and two near-band transmission zeros are contributed by the proposed circuit topology. Good isolation can be obtained by comparing different coupling schemes with one resistor. An additional transmission zero for extending the upper stopband can be achieved by the two closely placed stubs without increasing the size of the design. Low loss and self-packaging can be realized by SISL technology. For demonstration, a prototype is implemented with the size of 0.5λg × 0.28λg, which exhibits the 1-dB fractional bandwidth of 26.3%, the frequency selectivity of 0.25/0.37 at the lower/upper edges of the passband, and the insertion loss of 1.1 dB (including transition) at the center frequency (f0) of 3.34 GHz, while the in-band isolation is higher than 20 dB and the 15-dB stopband is achieved up to 3.74 f0.

Microstrip switchable diplexer based on dual‐mode stub‐loaded stepped‐impedance resonators with three operating states

A new three-state switchable diplexer based on dual-mode stub-loaded stepped-impedance resonators (SL-SIRs) has been proposed. The three-state diplexer comprised six SL-SIRs with a distributed coupling structure. By appropriately adjusting the structural parameters of the SL-SIRs, a two-pole filtering response can be implemented at each channel passband. In addition, three p-i-n diodes, which were connected to the T-junction of the input coupled-line, were used to control the switching between the three operating states. Moreover, each operating state can be switched independently. For the purpose of demonstration, a three-state switchable diplexer was designed and fabricated using microstrip technology. The simulated results were consistent with the measured results, which indicate that the proposed switchable diplexer not only has a good in-band performance but also provides good isolation of better than 25 dB between output channels.

Design of multi‐standard single/tri/quint‐wideband asymmetric stepped‐impedance resonator filters with adjustable TZs

This study presents an original asymmetric stepped-impedance resonator filter combined with meander coupled-line structures and enabling the realisation of finite transmission zeros (TZs) and the implementation of multi-band bandpass filters. The meander coupled sections (MCSs) tune the TZs and resonant frequencies: with higher-order spurious frequencies cancelled by the TZs, a single wideband with wide stopband from 1.18 to 1.84 GHz is possible. Furthermore, by positioning the finite TZs between the high-order spurious frequencies and adjusting the coupling strength between resonators, a quint-wideband filter can be realised, with centre frequencies of 1.19, 4.29, 5.43, 6.97, 9.9 GHz and fractional bandwidths of 31.9, 15.4, 15.8, 4.3, 39.2%, respectively. More importantly, two filters with single/quad-wideband performance can be realised by tuning the parameters of the MCS, and therefore they can be designed separately by using only one original structure. The triple-wideband filter is realised with the help of the asymmetric parallel uncoupled microstrip section. These filter structures enjoy the advantage of single/multi-band versatility, structure reusability and simplicity. The good in-band and out-of-band performance, low loss and simple structure of the proposed single/tri/quint-wideband filters make them very promising for applications in future multi-standard wireless communication.

Design of a wideband filtering power divider with good in‐band and out‐of‐band isolations

In this article, a wideband filtering power divider with good in-band and out-of-band isolations is designed based on a hybrid Wilkinson and Gysel structure. To achieve a good in-band response, two additional in-band transmission poles can be introduced by installing the coupled-line structures at each port. By mounting a stepped impedance open stub at the input port, two transmission zeros are generated near the passband to improve the passband skirt. Furthermore, the out-of-band rejection and isolation are achieved by the other two transmission zeros, which are produced by the open stub and the three coupled-line sections mentioned above. Additionally, a good in-band isolation is realized by the isolation resistor between output ports. For the demonstration, a wideband filtering power divider centered at 1.5 GHz with a 56% fractional bandwidth and 20-dB isolation is designed and fabricated. The simulated and measured results are in good agreement with each other.

Coupling-Matrix-Based Systematic Design of Single-DC-Bias-Controlled Microstrip Higher Order Tunable Bandpass Filters With Constant Absolute Bandwidth and Transmission Zeros

This paper presents a systematic design procedure of microstrip higher order tunable bandpass filters (BPFs) that can realize a constant absolute frequency bandwidth (ABW) and transmission zeros (TZs) with the minimum number of varactors and a single controlled dc-bias voltage. To this end, intrinsic frequency dependence of interresonator couplings is employed instead of external controls, but the design has faced a difficulty of realizing ideal frequency curves of coupling coefficients at all the coupling regions, including nonadjacent couplings. To overcome such a difficulty, this paper introduces a frequency-curve shape design approach considering upward- or downward-curved convex that is dependent on the types of interresonator coupling. As illustrative examples, fourth- and sixth-order tunable BPFs are proposed and designed, starting from a coupling-matrix synthesis. Their structural parameters can be efficiently designed with the proposed design method. The frequency agility with keeping a constant ABW, acceptable low insertion loss, a good in-band return loss level, and TZs is numerically and experimentally demonstrated for both fourth- and sixth-order tunable BPFs.

A New Balanced-to-Unbalanced Filtering Power Divider With Dual Controllable Passbands and Enhanced In-Band Common-Mode Suppression

A new microstrip balanced-to-unbalanced power divider with dual bandpass filtering response is presented in this paper. The generalized mixed-mode scattering matrix for the filtering balanced-to-unbalanced power divider is derived to guide the design. Differential-mode (DM) dual-band filtering response is analyzed under the odd-mode excitation to show that the frequency ratio (k = f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) and bandwidth of these two passbands could be flexibly controlled. For the even-mode excitation, two intrinsic transmission zeros generated by additional open-ended stub are introduced, aiming to achieve the enhancement of in-band common-mode (CM) suppression. In addition, good in-band isolation and port matching are realized by introducing a grounded resistor. To validate the design concept, two prototypes centering at 1 and 2.5 GHz (k = 2.5), as well as 0.76 and 2.75 GHz (k = 3.62) are implemented following the given design procedure. Tested results of the two fabricated circuits, well agreeing with the simulated ones, exhibit high performances in terms of DM response, in-band CM suppression, port-to-port isolation, and port matching.

Millimeter-Wave Dual-Mode Filters Realized in Microstrip-Ridge Gap Waveguide Technology

In this paper, we propose novel microstrip-ridge gap waveguide (MS-RGW) millimeter-wave bandpass filters based on a dual-mode resonator. The resonator represents a rectangular patch grounded by a set of vias, whose pair of fundamental degenerate modes are separated in the spectrum using the via position perturbation. MS-RGW feeding lines are realized as periodically grounded microstrip lines inserted into a perfect magnetic conductor (PMC) structure, which are fed via the 2.92-mm connector through the specifically designed transition. A detailed analysis of the filters is provided together with the analysis of their building blocks—mushroom-based PMC surface, MS-RGW with periodically grounded microstrip line, and dual-mode resonator. The proposed filters are fabricated using standard PCB technology and the measured results show that the filters exhibit low losses, good in-band and out-of-band characteristics, and good selectivity. As such, the proposed filters represent excellent candidates for millimeter-wave filtering applications since they reconcile the requirements for high performance, low loss, and low cost.

Compact low-loss microstrip diplexer using novel engraved semi-patch cells for GSM and WLAN applications

This paper presents a novel microstrip diplexer constructed by integrating the engraved semi-patch cells. It operates at 1.8 GHz for global system for mobile communication (GSM) and 2.4 GHz for wireless local area network (WLAN). The introduced structure is well miniaturized so that it has a compact size of 0.022 λg2. The others advantages of the proposed diplexer are the low insertion losses less than 0.16 dB, good in-band channel isolation higher than 34 dB and two wide fractional bandwidths. Moreover, 1st, 2nd and 3rd harmonics are attenuated with the maximum level of −20 dB. A harmonic attenuation method is presented based on analyzing the resonance modes. In order to verify the simulation results, the designed diplexer is fabricated and measured. The simulation and measurement results are in a good agreement.

A High-Performance Dual-Mode Filtering Power Divider With Simple Layout

This letter presents a simple microstrip dual-mode filtering power divider (FPD) with sharp frequency selectivity and good in-band isolation. A new topology is proposed to integrate only a single resonator and a resistor to realize the dual functions of the power division and filtering. In order to further improve its frequency selectivity and obtain wide upper stopband, three open-ended stubs are integrated into the input and outputs of the FPD, respectively. The presented FPD stands out from those in the literature, by both improved performance and simple design layout. For validation, a prototype FPD operating at 2.2 GHz with 3-dB fractional bandwidth of 18.2% is designed and fabricated. The experimental results agree well with the simulated ones. The results indicate that the new FPD exhibits better than 32-dB in-band isolation along with 24-dB harmonic suppression up to 6.28 GHz ( $2.85~f_{0}$ ).