Compact spiral band pass filter with low group delay

This paper presents a design of compact wideband bandpass filter (BPF). The BPF is based on the traditional highpass filter formed by three short-circuited stubs separated by uniform impedance lines. Since the uniform impedance line sections of the traditional filter are replaced by the stepped impedance lines, the size of the filter can be miniaturized. For a demonstration, a compact BPF with center frequency of 1.3 GHz and fractional bandwidth of 85% has been designed and implemented in microstrip technology. The size of the fabricated BPF is only about $\mathbf{0.45} \lambda_{\pmb{g}}$ by $\mathbf{0.8} \lambda_{\pmb{g}}$. Moreover, the experimental results are in good agreement with the simulation predictions.

The main objective of this work is the study, design and simulation of a narrow-band compact band pass filter using the technique of a rectangular-shaped linear resonator closed on a capacitive load and based on magnetic coupling. This filter is intended for wireless communication systems (Wi-Fi, Bluetooth, RFID, and ISM). It is attractive considering the substrate and tracks used and also in terms of size (7.485 × 8.18) mm2. It also has good selectivity (300 MHz bandwidth) and low insertion loss (−0.01 dB).

In this letter, two quarter wavelength microstrip stubs with a shorted slot line resonator etched in the ground plane is used to design a compact wideband bandpass filter (BPF). Wideband characteristics are obtained using broadside-coupling between the stubs and the slot line. 3-dB fractional bandwidth (FBW) is varied by changing coupled line widths. The filter has the advantages of compactness, wide bandwidth, low passband insertion loss (IL), low group delay variation and ease of fabrication. One prototype fabricated filter has a FBW of 60.0% with a maximum passband IL of 0.9 dB and group delay variation of 0.40 nS. BPF occupying area is less than 0.19lambdagtimes0.20lambdag, where lambdag is the guided wavelength at midband frequency 2.5 GHz. Good agreement between measurements and simulations are obtained.

In this research, a novel compact tri-band microstrip bandpass Filter is design using Asymmetric SIRs and DGS to achieved the characteristic of low insertion loss, high selectivity, wider range of bandwidth, low group delay for WiMAX (2.5GHz), WiMAX (3.4GHz) and UWB applications. The novel filter is design intentionally selecting the impedance ration(R) and length of the microstrip of the asymmetric SIRs and DGS is used to improve the coupling strength of the last band. The measurement entities of the novel filter for WiMAX (2.5GHz), WiMAX (3.4GHz) and UWB (4.12–5.32GHz) are insertion losses (S21) are −0.26dB, −0.07dB, −0.05dB, and return losses (S11) are −11.29dB, −19.25dB and −22.64dB respectively. The response of the filter was simulated using Ansoft HFSS Simulator.

Design of a miniaturized symmetrical band pass filter (BPF) using parallel-coupled half-wavelength micro strip resonators with improved stop band characteristics and 2nd harmonic suppression is presented. The proposed filter is designed at a center frequency of 5.25 GHz with a stop band insertion loss greater than-10dB at 5.15 GHz and fractional bandwidth of 20% (4.74–5.80GHz). The conventional parallel-coupled line band pass filter structure has been folded symmetrically about the horizontal plane and consecutive saw tooth periodic grooves are introduced to the parallel lines. Thus there has been a significant improvement in 2ndharmonic suppression to almost-34.51dB. Size reduction of 46.73% is accomplished with respect to the conventional filter.

A compact wideband bandpass filter (BPF) with broad stopband using hybrid half‐mode substrate integrated waveguide (HMSIW) resonator and open‐circuit tri‐section SIRs (OTSIRs) is proposed. A BPF with 3 transmission poles (TPs) and 3 transmission zeros is obtained by cascading the HMSIW resonator and OTSIRs using J and K inverters. A demonstrated wideband BPF with the stopband up to 4.4 times the designed center frequency for a 20 dB rejection level is designed, fabricated and measured. The measured results verify the predicted attractive features.

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 novel compact microstrip bandpass filter which is realized by combining new slow-wave effect with hairpin microstrip folded lines configuration, is proposed. The filter is not only compact in size due to the slow-wave effect, but also has multi-transmission zeros on both sides of the passband, and low insertion loss in bandpass. The filter has, for the first time, been optimally designed and fabricated. The results of the theory and experiment are demonstrated. The agreement between the predicted and measured results is excellent.

A compact stub-coupled microstrip square open-loop resonator-based bandpass filter (BPF) is proposed.In this work, a back-to-back fork-shaped open stub and two attached stubs are internally accommodated inside the square loops using open gaps. Significantly, large coupling coefficient value can be obtained in the square open-loop resonator using those loaded stubs. In this design structure, the inserted stubs enhance to couple the two loops electromagnetically to each other. The proposed filter has strong electric coupling, because the open sides of the two coupled loops are proximately placed face-to-face in parallel. Similarly, the rectangular stubs attached with the internal wall of loops help to connect magnetic couplings between the two loops, as a result, the mixed coupling generates strong electromagnetic coupling in the BPF with an adequate input reflection coefficient and broader bandwidth in required frequency band. The open-loop BPF at 14.4 GHz is realized by an embedded open-stub combined with attach-stubs. The designed filter shows the simple topology, low insertion losses, and sharp rejections. The S-parameter response of the fabricated filter closely matches with the simulation results and, therefore, the feasibility of the proposed filter is confirmed. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2412–2416, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27054

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.

In this paper, an ultra-wideband (UWB) band-pass filter (BPF) with a sharp notch band is presented. The UWB BPF consists of modified elliptical-ring and multi-mode stub-loaded resonator (MM-SLR). By adding the asymmetric tight coupled lines resonator via input/output (I/O) lines, it can be achieved UWB band-pass response. With adding two bends to the middle resonator, a notch band at 6.86 GHz is created, so that it can be controlled using the mathematical formulas (MF). In the meantime, the equivalent circuit of the middle resonator is obtained using L–C analysis. Measured results of fabricated filter have the advantage such as ultra-wide pass band (flandfHof the defined UWB pass band are 3.776 and 10.42 GHz, which satisfy the requirements of FCC-specified UWB limits), compact size, low insertion loss <0.65 dB and the stop band of the proposed filter is from 11.1 to 16.32 GHz with attenuation of −39.8 to −42.14 dB, respectively. The proposed UWB filter is realized using the substrate with dielectric constant of 2.2 and substrate height of 0.787 mm. Experimental verification is provided and good agreement has been found between simulation and measurement results.

A compact wide band reconfigurable bandpass filter (BPF) which utilises a hemi-circular flower shaped multimode resonator (MMR) is presented. The proposed MMR provides three resonant modes which fall within the broad frequency spectra. Among these, two modes are even and one is odd. These modes are optimised by varying the dimensions so as to obtain the desired frequency response. The fractional bandwidth is more than 96 per cent. The filter can be operated as multi-band BPF. In OFF condition of ‘Pin’ diode, the centre frequencies are 2.43 GHz, 3.5 GHz, and 5.9 GHz in ON condition of ‘Pin’ diode centre frequencies are 2.43 GHz, 3.5 GHz, 5.9 GHz, 6.5 GHz, and 8.8 GHz which are used for vehicular, WiMAX, intelligent transportation systems and satellite communication respectively. Microstrip filter structures are integrated with ‘Pin’ diodes. Appropriate biasing has been provided by choosing lumped components with precise values. The insertion loss in OFF condition are 0.5 dB, 0.67 dB, and 0.8 dB and in ON condition 0.5 dB, 0.7 dB, 1.2 dB, and 1.9 dB. The measured results agree well with the full-wave simulated results.

A compact high-temperature superconducting wideband bandpass filter (BPF) based on a triple-mode resonator is developed in this paper. The triple-mode resonator is constructed by connecting a folded end-coupled open-loop resonator (FEOR) with two asymmetric stepped-impedance resonators (SIRs). The FEOR and asymmetric SIRs have the characteristics of harmonic frequencies suppression. A meander three parallel-coupled lines structure (MTPLS) is proposed to implement sufficient external coupling strength. Simulated results show that the filter is centered at 1GHz (fc) with 100% 3-dB fractional bandwidth (FBW) and has an upper stopband to 3.5 fc. The measured results show the return loss is larger than 20dB and the insertion loss is less than 0.06dB.

Planar microwave bandpass filters (BPFs) are an essential component in many communication systems. Traditional BPF design focuses on the application of frequency-invariant K-/J-inverters inserted between the two resonant modes or served as the external coupling to feed the resonators. This design method is most suitable for narrow bandwidth BPFs, but for wideband cases it is difficult for a direct application. To solve this problem, a synthesis method based on a modified general Chebyshev function and the Richard’s transformation has been proposed to characterize the frequency response over the whole frequency range for the wideband BPF designs. As for the corresponding circuit structure, short-circuited stepped-impedance multi-mode resonators (MMRs) serve as the foundation to the designs in this dissertation. By parallel-connecting or folding the MMRs, a class of dual-wideband BPFs has been developed. Based on the above discussion, this dissertation presents the wideband BPF designs in two aspects, the proposed filter synthesis procedure and a new class of circuit structures to realize the target filtering responses. As the foundation of this research work, short-circuited MMRs have been researched in the first place for a single-wideband BPF design. n sections of cascaded commensurate lines are used to group the resonances, and short-ended stubs are shunt on its two sides to inductively feed the MMR. For the filter design, a Chebyshev filtering function is used to characterize the frequency response of the circuit. By equating the filtering function to the transfer function of the circuit, the design parameters are obtained. The first set of dual-wideband BPFs is formed by parallel-connecting two dissimilar single-wideband BPFs, both formed by stepped-impedance MMRs. The two transmitting paths of 180o phase difference are used to generate up to two pairs of transmission zeroes (TZs) with symmetry to the dual-wide passbands. By appropriately choosing the characteristic impedances of the two paralleled MMRs, one pair of TZs is located in real frequencies contributing to the attenuation between the two passbands, whereas the second pair of TZs is located in imaginary frequencies adjusting the group delay within the passbands. The short-circuited stubs, in shunt connection on the two sides of the MMR, act as the inductive loading element to feed the MMR and to flatten the passband. In the meanwhile, they introduce TZs at multiple of π to suppress the DC-component. Following a similar design principle, the second set of dual-wideband BPF has been proposed as an improved design in terms of realizing a more compact size, the greater flexibility in terms of reflection zeros in the passband and an extra degree of freedom in choosing characteristic impedances. The generic structure of the proposed filters is formed by folding a MMR along its symmetrical plane and by coupling a pair of short-circuited stubs on the two ends of the MMR. Thus, two signal transmitting paths, one from the folded MMR and another from the loaded stubs, are used to generate additional TZs between the two passbands. By increasing sections of the loaded MMR, the reflection zeros in the passband is enlarged. Under fully-coupled structure, the merit of compact size and extra design freedom is obtained. For these two sets of dual-wideband BPFs mentioned above, the even-/odd-mode analysis method has been used to derive the transfer function to characterize their frequency responses. Given the properties of the proposed filters, the commonly used generalized Chebyshev filtering function as well as its transferred dual-band function is not appropriately used herein. Instead, a generalized Chebyshev filtering function, originally developed for a single-wideband BPF design, is readily applied. By directly formulating a filtering function with mirror to the origin, it has dual passbands respectively located at positive and negative frequency ranges. To accurately account for the wideband response, a TZ is assigned at the origin. Next, the Richard’s transformation is applied to transfer the normalized frequency response to its dual-band counterpart. With this proposed synthesis procedure, the targeted filtering function is characterized by a ratio of two polynomials. By equating these two aforementioned functions, which are the ideal filtering function from the specifications and the transfer function from the circuits, all the circuit design parameters are obtained. Finally, the proposed single-/dual-wideband bandpass filters have been synthesized and designed for practical implementation. The experimental results of the fabricated filter circuits have strongly verified these new filter structures and their corresponding synthesis method proposed.

This paper presents a design of a new compact bandpass filter in coplanar waveguide implementation composed of serpentine shape shunt-stubs. The serpentine shape shunt-stubs allow to increase the inductive loading and thus to reduce the size of the filter. The proposed filter has two transmission zeros on the both sides of the passband. The equivalent circuit model has been proposed to describe the filter behavior. The measured center frequency, bandwidth and insertion loss are 5 GHz, 50 % and 0.5 dB, respectively. The geometrical size of the proposed filter is 20times13.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Good agreements between both measured and simulated results have been observed.