Wide-Stopband Bandpass Filter Based on Signal Interference Feedback

In this work, it is shown that complementary spiral resonators (CSRs) etched in the ground plane of a microstrip line are useful for the implementation of band pass filters with very small dimensions and wide stop bands. By combining the CSRs with two series capacitive gaps and inductive vias, two transmission zeros arise. By properly allocating such transmission zeros at both sides of the pass band of interest, the out-of band rejection and frequency selectivity of the filters can be controlled. A prototype device example is reported to illustrate the performance and size of these CSR-based filters. This is an order-three Chebyshev band pass filter centered at ƒ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> =1.1GHz with 10% fractional bandwidth. Measured in-band losses (optimum value) are IL=−4.42dB, in-band return losses are better than 9dB, and stop band rejection is better than 55dB up to 2.57GHz. Filter area is as small as 23.2 mm × 8.9 mm, that is 0.22 λ × 0.08 λ, where λ is the wavelength (at the central filter frequency) of a 50Ω microstrip line in the considered substrate. The key novel and advantageous aspect of the reported filters is their small size, which is related to the small electrical size of CSRs. Another advantage is frequency selectivity, which is due to the presence of a transmission zero at both edges of the pass band. The limitative aspect is their relatively small unloaded quality factor (Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</inf> ), this being attributed to the small dimensions of the considered resonators. These CSR-based devices can be of interest in those applications where size and frequency selectivity are the most severe requirements.

In this article, a novel miniaturised dual-wideband bandpass filter (DWB-BPF) based on two different resonators including a quasi-spiral loaded multiple-mode resonator (QSL-MMR) and L-shaped transmission line (LS-TL) is presented. At the first step, in order to design a single wideband BPF filter with controllable transmission zeros near the centre frequency, the open circuit impedance parameter of quasi-spiral loaded resonator Z21 is determined in terms of ABCD matrix. Then an equivalent circuit model of the proposed structure is derived and the impedance characteristic and electrical length of LS-TLs to achieve a DWB-BPF with excellent selectivity are calculated through even- and odd-mode analysis. The proposed filter possesses both compact and simple structure as well as two wide passbands with fractional bandwidth (FBW) of 70% and 22.8% for its first and second passbands, respectively. The proposed technique creates two transmission zeros at the lower and upper stopbands of each passband resulting in a very sharp roll-off accompanied by a wide stopband. Notably, the circuit size is reduced and the bandwidth is enhanced in comparison with its conventional counterparts. The theoretical performance of the filter is verified by the experimental one where a good agreement is reported between them.

This paper presents a narrow-band band-pass filter with high selectivity and low insertion loss. The filter has a good characteristics of narrow-band filtering and harmonic suppression. Its harmonic suppression ability is realized by Transmission zeros which result from loading open stub coupling line. The center frequency and bandwidth is determined by the length of coupling line. Based on even-odd mode analysis and transmission line theory, the filter is analyzed and the formula is deduced. The central frequency of the filter is 6.63GHz, and its 3dB bandwidth is 290MHz. The minimum insertion loss in the pass-band is 0.44dB. The proposed filter has a suppression of -31dB in the two harmonic frequency points. In order to verify the theory and confirm the simulation results, the filter is fabricated and tested. And the measured results are in good agreement with the simulation results.

A new class of high-quality-factor (Q) and hybridly-integrated quasi-elliptic-type bandpass filters (BPFs) with symmetrical quasi-reflectionless characteristics is reported. Its circuit architecture is based on loading the input and output ports of a quasi-elliptic-type BPF-it exhibits two transmission poles and four transmission zeros (TZs)-with resistively-terminated bandstop-filter (BSF) branches to absorb the reflected RF power. The quasi-elliptic-type power transmission response is obtained by incorporating multi-resonant cells that exhibit one pole and two TZs and allow for quasi-elliptic-type responses to be realized without the need for cross couplings. A hybrid integration scheme using capacitively-loaded high-Q ceramic coaxial resonators and microstrip-type impedance inverters is proposed for size compactness and low passband insertion loss. The concept is experimentally validated at 3 GHz through the manufacturing and testing of a filter prototype that exhibits a passband with in-band insertion loss (IL) <0.9 dB (corresponds to an effective quality factor of 430) and wide quasi-reflectionless characteristics. Keywords-Absorptive filter, bandpass filter (BPF), ceramic resonator, microstrip filter, reflectionless filter.

In this paper, a bandpass filter (BPF) with wide upper stopband and low radiation loss based on the substrate integrated defected ground structure (SIDGS) is presented. The BPF is composed of two sets of stepped-impedance SIDGS resonant cells with two microstrip feed-lines. Such slow-wave SIDGS cells can introduce the passband resonances with a wide upper stopband. Besides, the SIDGS surrounded by the bottom ground layer with metal-vias can not only suppress the radiation loss but also can be flexible for integration. To verify the mechanisms mentioned above, a wide upper stopband BPF with a passband centered at 2.4 GHz (i.e., fo) is implemented and fabricated. The measured stopband is up to 19.3 GHz (i.e., 8fo) with a rejection level of 29 dB, while the total loss (i.e., including radiation, metal, and substrate loss) is less than 30% up to 19 GHz. The core size of the BPF is about 0.16 λ $g$ X 0.16 λg, where λ $g$ is the microstrip guided wavelength at the center frequency.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter presents a novel compact lowpass filter with two transmission zeros. By tap-connecting the stepped-impedance hairpin unit, two transmission zeros can be generated when an interdigital structure is introduced between the two low-impedance sections. Further, the two transmission zeros can be adjusted easily to obtain a larger zero separation without the need to change the stepped-impedance unit. Therefore, a sharp transition, an expanded stopband, a low insertion loss, and a compact size can be obtained simultaneously. Two filters with single and two asymmetric units are designed, fabricated, and tested. The measured results demonstrate good performance: compact size, low passband insertion loss, broad stopband, and sharp skirt characteristic. </para>

This paper presents a novel connecting-line coupling technique for the design of compact and low-loss bandpass filters (BPFs) with multiple controllable transmission zeros (TZs). Traditional gap-coupling methods are highly sensitive to fabrication errors and have limited design flexibility. By contrast, the proposed approach enables precise control of coupling strength without modifying resonator geometry. Such control is achieved through independent adjustments of the lengths, widths, and positions of connecting lines. Furthermore, the proposed approach facilitates the generation of up to n TZs for an nth-order BPF, thus considerably improving the BPF’s frequency selectivity and stopband attenuation. To validate the effectiveness of this method, four filters are designed and fabricated: a second-order stripline BPF, a fourth-order microstrip BPF, a fifth-order stripline BPF, and a sixth-order wideband microstrip BPF. The second-order BPF is based on asymmetric connecting-line coupling, whereas the fourth-, fifth-, and sixth-order BPFs are based on symmetric connecting-line coupling. Excellent agreement between simulation and measurement results is achieved for these designs, with low insertion loss, high roll-off rates, and high tolerance to fabrication variations being noted. The proposed technique is suitable for filters ranging from narrowband to ultra-wideband filters and across low to millimeter-wave frequency bands, making it a highly versatile and practical solution for modern RF and microwave communication systems.

An original architecture of a fully-reconfigurable bandpass filter (BPF) is presented. It consists of two series-cascaded—through inter-stage connecting lines—spectrally-overlapped second-order BPFs and a filtering cell that generates two out-of-band transmission zeros (TZs) for selectivity enhancement. The three inter-cascaded filtering blocks comprise six frequency-tunable resonators that interact by means of static impedance inverters. By controlling the natural frequencies of the resonators in all filtering units through variable-reactance elements, an overall frequency-agile bandpass transfer function in terms of center frequency, bandwidth, and TZs is attained. Furthermore, since the passband-width is controlled without altering the inter-resonator couplings, benefits are obtained in terms of lower in-band insertion loss and larger bandwidth tuning ratio that can be practically reduced to zero (i.e., intrinsic switching-off state). The operating principles of the devised filter-cascade concept are expounded. Also, an evanescent-mode cavity-resonator prototype with tunable response in the range 2.9–3.5 GHz is built and tested for experimental verification. To the best of the authors' knowledge, the developed BPF circuit demonstrates one of the highest electronic-reconfiguration capabilities reported up to date for 3-D BPFs.

In this paper, a design of compact LTCC bandpass filter with three layers and three Transmission Zeros (TZs) is proposed, which obtain a high skirt selectivity with narrow passband and wide stopband. The mixed Electric and Magnetic (EM) coupling and Source-Load (S-L) coupling are utilized to create TZs in this design. And the simulated results of the proposed filter are presented to validate, which show that the passband is 2.2GHz-2.6GHz with center frequency 2.4GHz. Due to the LTCC multilayer structures, the filter's size is 2.9 mm × 2.8 mm × 0.4 mm (0.064λ g × 0.062λ g × 0.009λ g ).

A design methodology using quasi-lumped elements for compact millimeter-wave on-chip bandpass filter (BPF) is presented in this work. To implement BPF using this approach, a novel inductor cell is presented first and then using this cell along with metal-insulator-metal (MIM) capacitors, two BPFs are designed. For the purpose of proof-of-concept, all three designs are implemented and fabricated in a standard 0.13-μm (Bi)-CMOS technology. The measurements show that the inductor cell generates a notch at 47 GHz with a chip size of 0.096 × 0.294 mm2 without pads. Moreover, the 1st BPF has the center frequency at 27 GHz with an insertion loss of 2.5 dB and it has one transmission zero at 58 GHz with a peak attenuation of 23 dB. Unlike the 1st design, the 2nd design has two transmission zeros. The center frequency of this BPF is located at 29 GHz with a minimum insertion loss of 3.5 dB. Without the measurement pads, the chip sizes of the two BPFs are 0.076 × 0.296 mm2 and 0.096 × 0.296 mm2, respectively.

A novel dual‐wideband bandpass filter (BPF) using shorted stepped‐impedance stub‐loaded lowpass filter is proposed. The stub introduces two transmission zeros (TZs) to divide the low passband into dual‐passband. By tuning the stub dimension parameters to control the TZs, the centre frequency and bandwidth (BW) for each passband can be tuned flexibly, and wide upper stopband can be realised. For demonstration, a dual‐wideband BPF operating at 1.08 and 3.05 GHz is designed, fabricated, and measured, and its 3 dB fractional BWs are 103.2 and 48.5%, respectively. The measured results are in good agreement with the simulated ones.

A new sharp-rejection dual-bandstop filter is proposed in this paper. Two wide stopbands are realized by Path 1 composed of a T-type structure. Three transmission poles in each stop-band and nine transmission zeros out of band within 2f0 are achieved by the signal interaction of Path 1 and Path 2, guaranteeing sharp rejection and high filtering performance. In addition, the extraction process of the transmission poles and zeros is presented based on S-parameters theory. The 3-dB fractional bandwidths of 67.8% and 33.0% with the center frequency 0.575 and 1.425 GHz are obtained. The measured results agrees well with those of simulation.

High selective bandpass filter with mixed electromagnetic coupling and source–load coupling

A novel concise sine substrate integrated waveguide (SSIW), with both sides metallized via holes periodic undulation, is firstly proposed for developing bandpass filter (BPF) at millimeter frequency range. It has advantages of remarkable simplicity, compact size and low insertion loss. Simultaneously, a broadband microstrip to SSIW transition is proposed. Transition experimental results show less than 2 dB insertion loss at nearly whole Ka passband. Then, several Ka band SSIW BPFs with different passband widths and center frequencies are designed and fabricated. The experimental results demonstrated that the SSIW BPF passband width and center frequency could be designed by using different undulate amplitudes and periods of the SSIW.

A compact substrate integrated waveguide (SIW) bandpass filter with wide stopband, high selectivity and tunable transmission zero with open ended stub is proposed. The complementary split ring resonator (CSRR) is etched on the top layer and defected ground structure (DGS) is carved on the bottom layer to enhance the skirt selectivity of the band pass filter and suppress the higher order modes to exhibit wide stopband. A pair of open-ended stubs are inserted at port 2 to improve the upper stopband selectivity. Tuning the stub length enhances electric coupling and shifts the transmission zero thereby improving the out- of- band rejection on the upper sideband. The measured passband center-frequency, minimum insertion loss, return loss, 3 dB bandwidth and fractional bandwidth are 10.1 GHz, 1.52 dB, 15 dB, 2.71 GHz (8.75–11.46 GHz) and 23.8% respectively. To validate the design, the prototype was fabricated and measured, and the measured results are in good agreement with the simulated responses.