Passband Edges Research Articles

Compact Microstrip NWB/DWB BPFs With Controllable Isolation Bandwidth for Interference Rejection

In this paper, a novel and planar topology, which can be used to design notched-/dual-wideband bandpass filters (NWB/DWB BPFs) with controllable isolation bandwidth, is presented for interference rejection. Here, the isolation band is referred to notch band for NWB BPFs, while stopband between two passbands for DWB BPFs. The proposed topology is started from a novel T-shaped resonator with two poles and three zeros. Then, a pair of parallel-coupled lines and two open-ended stubs is added. With the help of the added parts, the extra four poles are introduced, and another two zeros are suppressed or excited according to whether it is required to realize a notched- or dual-band response. Due to the existence of multiple transmission poles and zeros, the excellent filtering responses, i.e., high isolation level, sharp selectivity, and good passband flatness, can be achieved. Besides, it is found that the isolation bandwidth of BPFs based on the proposed topology can be continuously varied from a narrow notch band to a wide stopband while the outer two passband edges are maintained unchanged by using suitable para-meters. To validate this, two prototypes are designed and measured, including a six-mode NWB BPF with 3-dB passband fractional bandwidth (FBW) of 94.1% and 20-dB notch FBW of 2.39%, and a three-mode DWB BPF with 3-dB passband FBWs of 36.2% and 22.6% and 20-dB stopband FBW of 14.5%.

Transition between flat magnitude and flat group delay low pass recursive digital filters

Many a paper has been written on the characteristics of the continuous-time and discrete-time low-pass filters which are designed to have either maximally flat magnitude characteristics or maximally flat group delay responses. The polynomial (all pole) low pass recursive digital filters which are characterised by characterise the transition between a flat magnitude and flat group delay characteristics, named Transitional Butterworth Thiran (TBTh) recursive digital filters, is considered. The characteristics of the resulting filter change gradually from the characteristics of the well known Butterwort's filter to the characteristics of the Thiran's filter with the maximally flat group delay characteristic. Poles of the TBTh filter are obtained by interpolating between poles Butterworth and Thiran's filters by varying a parametar which controls the pole positions that enables a tradeoff between the steepness magnitude characteristic at passband edge and group delay deviation.

Design of Dual-Band Bandpass Filter With Simultaneous Narrow- and Wide-Bandwidth and a Wide Stopband

This paper presents a novel dual-band bandpass filter with narrow and wide passband simultaneously and a wide stopband. The dual-band bandpass filter is implemented using a stepped-impedance ring loaded resonator (SIRLR). The properties of the SIRLR are analyzed in detail based on the even- and odd-mode equivalent circuits. Resonant modes, excited by SIRLR, can be controlled and used to form a narrow passband at 2.4 GHz with bandwidth ratio of 8% and a wide passband from 3 to 5 GHz, with insertion losses less than 1.5 dB for both two passbands. Three transmission zeros are created near the passband edge to improve the passband selectivity and achieve a sharp cutoff skirt (over 60 dB/GHz). In addition, for wide stopband consideration, rectangular stub loaded resonators (RSLRs) are tapped on the input and output ports of above dual-band filter without destroying the dual-band performances. Thus, the proposed dual-band filter with a wide stopband region from 5 to 20 GHz with a rejection level of 25 dB is also achieved. The measured results show a good agreement with the simulated results.

A high‐selectivity dual‐polarization filtering antenna with metamaterial for 5G application

AbstractA high‐selectivity dual‐polarization filtering antenna with metamaterial is presented in this letter. The multilayer coupled radiation structure of the antenna determines a filtering function. With the metamaterial layer designed above the antenna, a sharp roll‐off rate at high pass band edge and a better out‐of‐band rejection occurs, thus a better high selective filtering characteristic can be achieved. Simulating and measuring the antenna, the impedance bandwidth (VSWR <2) of the antenna is from 3.25 GHz to 3.85 GHz; meanwhile, the maximum gain can reach 9dBi. The gain of antenna can quickly decrease 43dBi at the high pass band edge from 3.85 GHz to 4.05 GHz and the antenna has an out‐of‐band rejection level of 27dBi from 4.05 GHz to 5 GHz. The tested results verify our designs and the antenna could be a good candidate for the 5G anti‐interference wireless terminal communication system.

New low-loss tunable microstrip band-pass filter with two transmission zeros

In this paper, a low-loss tunable microstrip band-pass filter with two transmission zeros (TZs) around the pass-band edge is proposed. Making use of exactly same structure, three different fractional-bandwidth variations (i.e. constant fractional bandwidth, decreasing fractional bandwidth and increasing fractional bandwidth) can be realize by adjusting the amount of coupling between microstrip pairs. A prototype filter with constant fractional bandwidth is fabricated on a er = 3.38, 32 mil Rogers substrate. The center frequency of the fabricated filter is tuned from 770 to 1300 MHz by two varactor diodes. The constant relative bandwidth and insertion loss of the filter are 11 ± 0.2% and less than − 2.2 dB respectively. S-parameters and performance of the proposed filter are measured by Agilent VNA which show a good agreement with simulation results.

Design of tri‐band bandpass filter using symmetrical open stub loaded step impedance resonator

A tri-band bandpass filter design by using conventional stub loaded step impedance resonator (SLSIR) is presented. The proposed SLSIR consists of three tri-loaded open-circuited stubs parallel attached to a short and open-circuited stub. A tri-band bandpass filter is designed using two proposed symmetrical SLSIR's separated by a short-circuited stub. In this configuration, the filter produces three bands of frequencies at 0.9, 2.4 and 5.5 GHz, respectively. It is shown that the resonating frequencies can be independently controlled by loaded stubs. For better out of band rejection and increased selectivity, four finite frequency transmission zeros around three passband edges are achieved. The obtained fractional bandwidths are 23, 10 and 17% centred at 0.9, 2.4 and 5.5 GHz, respectively. The proposed design topology is fabricated on a substrate RT/Duroid 5880. The simulated and measured results show good accordance. The fabricated prototype has a compact size of ( 0.13 × 0.16 ) λ g at 0.9 GHz.

Compact Frequency and Bandwidth Tunable Bandpass–Bandstop Microstrip Filter

This letter presents the design and implementation of a compact microstrip filter with frequency and bandwidth (BW) reconfiguration. The proposed filter consists of a transmission line coupled with a U-shaped microstrip line resonator. Varactor diodes are deployed at specific locations and are tuned to achieve BW and frequency reconfiguration from 0.8 to 1.5 GHz. The transition from the bandpass mode to the bandstop mode is achieved by reconfiguring the transmission zeros simultaneously. The filter percentage lower passband edge tuning and 17.33% higher passband edge tuning. The proposed filter has simple geometry, low profile, and offers a higher level of operational flexibility in the designed frequency range. The filter is tuned with the help of simple actuators requiring simple bias circuitry. The prototype filter is fabricated, and the simulation results are validated using the experimental measurements.

Implementing Quasi-Elliptic Microstrip Filters Using Terminating Half Sections

This letter presents a technique for the introduction of transmission zeros (TZs) using half section matched terminations for implementing high selectivity filters in planar technology. The proposed technique does not require any cross coupling between nonadjacent resonators or multiple signal paths, and it can be easily incorporated on any planar filter using lumped, quasi-lumped, and/or distributed elements depending on the desired response. Two different bandpass filter topologies are employed for applying the proposed technique. Both prototypes are designed, manufactured, and measured. The measured results show that the TZs can be independently located very close to the passband edges, without degrading the original filter response.

Wideband filtering Yagi antenna array

ABSTRACTA novel wideband high-gain antenna array with filtering response is presented. The proposed array consists of four Yagi antenna elements and one feeding network, which could realize signal filtering, power splitting as well as impedance transforming characteristics simultaneously. The operating mechanism is analysed and the detailed design procedure is presented. For demonstration, a 2×2 array is designed at the center frequency of 3.0 GHz with the measured fractional bandwidth of 73.3%. Measured in-band maximum gain is 13.2 dB, whereas the out-of-band suppression level is better than 23.2 dB. Compared with the conventional array, the proposed filtering array shows high suppression in the stopband, good selectivity at passband edges and flat antenna gain in the passband. The simulated and measured results provide a good verification for the theoretical concepts.

Wideband filtering Yagi antenna array

ABSTRACTA novel wideband high-gain antenna array with filtering response is presented. The proposed array consists of four Yagi antenna elements and one feeding network, which could realize signal filtering, power splitting as well as impedance transforming characteristics simultaneously. The operating mechanism is analyzed and the detailed design procedure is presented. For demonstration, a 2 × 2 array is designed at the center frequency of 3.0 GHz with the measured fractional bandwidth of 73.3%. Measured in-band maximum gain is 13.2 dB, whereas the out-of-band suppression level is better than 23.2 dB. Compared with the conventional array, the proposed filtering array shows high suppression in the stopband, good selectivity at passband edges and flat antenna gain in the passband. Simulated and measured results provide a good verification for the theoretical concepts.

Broadband Pattern-Reconfigurable Filtering Microstrip Antenna With Quasi-Yagi Structure

In this letter, a compact pattern-reconfigurable filtering microstrip antenna is presented with broad bandwidth, good selectivity at the passband edge, and flat gain-frequency response. The pattern-reconfigurable filtering antenna has four resonant modes that can be adjusted independently: Three of them are created by multimode resonator (MMR), and the other one is by radiator. The four resonant modes are well distributed in desired band, and the resonant mode of radiator is located between the first two resonant modes of MMR. By the incorporation of two p-i-n diodes and metal strips, the radiation patterns can be reconfigured. When the resonant mode of radiator shifts slightly, the bandwidth and in-band characteristic of the filtering antenna are basically unaffected. Finally, a pattern-reconfigurable filtering antenna prototype with a fractional bandwidth of 25% at 5.2 GHz is designed and manufactured. The measured results are well-followed designed ones.

A compact UWB‐BPF based on microstrip‐to‐CPW transition with multiple transmission zeros

AbstractA hybrid microstrip‐to‐coplanar waveguide (CPW) based broadside coupled ultra‐wideband (UWB) bandpass filter (BPF) of compact nature with multiple transmission zeros (TZ) is proposed. The CPW in ground consists of a short circuited multiple mode resonator (MMR), which is in conjugation with two microstrip lines on the top, arranged in back‐to‐back manner. Initially, the impedance ratio of the MMR is adjusted to place its resonant modes quasi‐equally within the UWB passband and later the dimensions of microstrip lines are optimized to enhance the broadside coupling. The setup generates a passband with reduced insertion loss, small group delay and multiple TZ. The presence of TZs provide sharp roll‐offs at either passband edges and a wide stopband. The experimental BPF is fabricated and its measured data validated against simulation results. The proposed structure measures 14.6 × 9.6 mm2.

Miniaturized impedance inverter 2.4 GHz filter with optimal transmission zeroes

AbstractA compact bandpass microstrip filter with high selectivity capability is fully investigated in this article. The basic characteristics, circuit models, and design formulas are explained completely. This technique provides more freedoms for putting the transmission zeroes with negative coupling structures in appropriate frequencies and leads to highly selective, low profile and compact filters. To validate the procedure, 3 design examples based on impedance inverter (K), admittance inverter (J) and λ/4 resonators are presented. All of the filters operate at 2.4 GHz with the fractional bandwidth more than 10% but different values in source–resonator–load couplings. The latter is obtained by tilting the middle J‐inverter toward the main line. For tilt‐angle equal to 90°, more than 50 dB null‐depth has been achieved in filters stop‐band near 8% of passband edges showing the appropriate figure of merit for this symmetrical filter. Simulated results performed by CST Microwave Studio and measured results are in good agreement with the theoretical peers.

Wideband multi-stage CROW filters with relaxed fabrication tolerances.

We present wideband and large free spectral range optical filters with steep passband edges for the selection of adjacent WDM communication channels that can be reliably fabricated with mainstream silicon photonics technology. The devices are based on three cascaded stages of coupled resonator optical waveguides loaded on a common bus waveguide. These stages differ in the number of resonators but are implemented with exactly identical unit cells, comprised of a matched racetrack resonator layout and a uniform spacing between cells. The different number of resonators in each stage allows a high rejection in the through port response enabled by the interleaved distribution of zeros. Furthermore, the exact replication of a unique cell avoids the passband ripple and high lobes in the stopband that typically arise in apodized coupled resonator optical waveguide based filters due to fabrication and coupling induced variations in the effective path length of each resonator. Silicon photonics filters designed for the selection of 9 adjacent optical carriers generated by a 100 GHz free spectral range comb laser have been successfully fabricated with 248 nm DUV lithography, achieving an out-of-band rejection above 11 dB and an insertion loss of less than 0.5 dB for the worst channels.

Compact and high selectivity dual‐mode microstrip BPF with frequency‐dependent source–load coupling

In this letter, a dual-mode microstrip bandpass filter (BPF) with compact size and high selectivity is designed with a short-stub centred loaded resonator. Owing to the frequency-dependent source–load coupling and the intrinsic characteristics of the short-stub loaded resonator, three transmission zeros that are located near the passband edges and in the upper-stopband can be generated to improve the selectivity. The compact BPF with fractional bandwidth of 3.5% located at 2.4 GHz for WLAN application has been designed and fabricated, and good agreement between simulation and measurement verifies the validity of this design methodology.

A High-Selective Frequency Selective Surface With Hybrid Unit Cells

In this paper, a novel frequency selective surface (FSS) is proposed. It has two metal layers and the configurations of the unit cells of these two layers are different, so-called hybrid unit cells. The designed FSS has three transmission zeros and steep roll-offs at the edges of the passband. In our design process, the top layer is used to achieve two transmission zeros at the edges of passband and the bottom layer is used to achieve wideband performance and transmission zero at the right side of the passband. The effects of the geometrical parameters on the frequencies of transmission poles and zeros are analyzed. By establishing an equivalent circuit, the matching impedance network is obtained quickly by Microwave Office and the flatness and insertion loss of the passband are improved after introducing the matching impedance network. The prototype of the proposed FSS is manufactured and tested. The measured −1.5-dB passband is from 13.2 to 19 GHz, and its relative bandwidth can achieve 36%. The measured results verify the design. This FSS is a good candidate to strengthen the performances of $Ku$ -band satellite and $Ku$ -band active radar.

Compact Tunable Bandpass Filter With Wide Tuning Range of Centre Frequency and Bandwidth Using Short Coupled Lines

A new compact microstrip tunable bandpass filter with continuous control of center frequency and bandwidth is proposed in the paper. The proposed design is based on short parallel-coupled lines, which are tuned by properly loading varactors. The structure exhibits a pair of transmission poles and one-side passband edge transmission zero that can be flexibly adjusted for required positions. A thorough theoretical analysis is derived to estimate the performance of the proposed filter and verify the initial values of design parameters. To verify the design concept, a prototype is fabricated and measured. The fabricated circuit has an extreme compact size (smaller than $0.03\lambda _{g}\times 0.1\lambda _{g}$ ). The simulated and measured results agree well with the derived theory, and indicate wide tunable center frequencies (0.56–1.15 GHz) and 1-dB bandwidth (65–180 MHz).

Wideband Filtering Power Divider With Embedded Transversal Signal-Interference Sections

By exploring embedding transversal signal-interference sections in a Wilkinson power divider, this letter proposes a novel methodology for the filter and power divider co-design. The structure realizes simultaneous power division and filtering in a single uniplanar circuit. In this letter, the equations as well as the detailed design methodology are given. In the last section, simulations and experiments are carried out, the results of which show a filtering power-division performance with 90% bandwidth (15-dB return loss) and two transmission zeros at the passband edges.

Wideband reconfigurable bandpass filter using coupled lines loaded with varactor loaded stubs

In this article, a novel reconfigurable bandpass filter with tunable passband edge and bandwidth is proposed. The bandpass filter enables the two band edges independently adjustable to meet the needs of different systems. The wide tuning range of the bandwidth is achieved by controlling the tuning mechanism to altering not only the coupling strength of the coupled lines but also the transmission zeroes positions of the resonator. The lower passband edge can shifts from 760 to 840 MHz with the upper passband edge keeping still and the upper edge of the passbands from 981 to 1107 MHz with the lower edge keeping still. The overall tuning range of 3 dB fractional bandwidth is from 15.5% to 36%. The upper stopband attenuation of the fabricated structure can reach to 40 dB within a wide frequency range.

Low windage resistance frequency‐selective rasorber based on windmill‐shape coupling line arrays

In this Letter, the authors report on the analysis, design, fabrication and measurement of a low windage resistance frequency selective rasorber (FSR) based on windmill-shape coupling slot line arrays. A lossy structure is added to the traditional frequency selective surface structure to make up a FSR with the characteristics of small insertion loss within the passband and weak reflection at frequencies below and above the passband meanwhile. In addition, the hollow structure can reduce windage resistance effectively. The measurements show that an insertion loss of 1.01 dB can be obtained at 7.71 GHz, while both lower and upper passband edges have at least 10 dB reflection reduction under the normal incidence. Both simulation and experiment results exhibit that the proposed FSR is insensitive to both transverse-electric (TE) and transverse-magnetic (TM) polarisation. The proposed FSR can be applied in the field of radome, cloaking and other microwave applications.