Passband Return Loss Research Articles

Performance analysis of optimum Chebyshev filters at microwave frequencies

The paper suggests that optimum Chebyshev filters present an excellent choice for microwave filter design, as this approximation offers minimum return loss in the half-power passband, provides a maximum cutoff slope, and maintains low sensitivity in the passband. A comparative analysis is conducted with the chained-function filters to demonstrate the efficacy of this approximation, since chained-function filters also utilize Chebyshev polynomials to shape the filter’s characteristic function. The optimum Chebyshev filter, along with two chained-function filters, each of the sixth-degree, are realized, simulated, and compared as lowpass stepped impedance filters with a half-power passband of 1 GHz. After a detailed comparison, it is concluded that the optimum Chebyshev filter outperforms, or at least matches, the performance of the chained-function filters. This suggests that the optimum Chebyshev filter can effectively replace chained-function filters in all applications, offering a superior solution.

Parametric Synthesis of Single-Stage Lattice-Type Acoustic Wave Filters and Extended Multi-Stage Design.

This study proposes a single-stage lattice-type acoustic filter using an analytical solution method for either a narrow passband filter or a wider passband filter using two kinds of parameter assignments in the Butterworth-Van Dyke (BVD) model. To achieve the goal of a large bandwidth or high return loss, two first-order all-pass conditions are used. For multi-stage lattice-type filters, the cost function is defined and design parameters are extracted by using pattern search, while the initial values are provided through single-stage design to shorten optimization time and allow convergence to a better solution. This method provides the S-parameter frequency response for the filter on the YX 42° cut angle of lithium tantalate (electromechanical coupling coefficient of about 6%) that can meet the system specifications as much as possible. Finally, the three-stage lattice-type was applied to various 5G bands with a fractional bandwidth of 2-5%, resulting in a passband return loss of 10 dB and an out-of-band rejection of 40 dB or more.

Synthesis design of quad‐band bandpass filter with mixed frequency transformation method

AbstractThis paper presents an analysis method to design quad‐band bandpass filters (BPFs) based on the mixed frequency transformation method. The frequency mapping technique is employed to obtain the design parameters by defining the frequency ranges of each passband. By using the proposed approach, the resonant angular frequencies and susceptance slope parameters can be obtained analytically. To validate our theory, a third‐order Chebyshev BPF and a fourth‐order elliptic BPF with different bandwidths are successfully synthesized. Moreover, a second‐order test BPF with a Chebyshev approximation and 20 dB passband return loss is synthesized, designed, fabricated, and measured. The measured insertion losses are 1.82, 2.01, 3.12, and 2.51 dB for each passband and measured return losses are better than 15.2 dB for all passbands. The measured results verify the designed BPF and also confirm the theoretical prediction.

Design of Modified Jacobi Microstrip Lowpass Filter for L-Band Application

In this brief, a design of microstrip lowpass filter with the 1 GHz cutoff frequency is revisited, where a class of modified Jacobi polynomials is used for the filter design. The optimization procedure for these filters includes the passband return loss minimization and the roll-off factor enhancement using the magnitude correction of the transmission coefficient. Mentioned correction is performed by introducing the multiple transmission zeros such that LC ladder prototype filter can be realized symmetrically. Three seventh degree filters for L-band applications are realized and simulated: allpole, with a single and double transmission zeros. It is shown that, among these three stepped impedance lowpass filters realizations, the filter with simple transmission zeros offers the best performance.

An Inter digital- Poison Ivy Leaf Shaped Filtenna with Multiple Defects in Ground for S-Band bandwidth Applications

The proposed work, a filtenna for s band application is implemented. It is designed by embedding an Interdigital band pass filter (IDBPF) and leaf shaped antenna which are operated in S band. The IDFBPF is having seven resonators with one end shorted through dual vias. It offers a bandwidth of 1.3GHz from 1.65GHz to 2.95GHz. A Dumbbell shaped DGS (Defected Ground Structure) provided in ground to improve the filter characteristics. Measured pass (BRL) band return loss (S11) & insertion loss (S12) are -18dB & -4.6dB correspondingly. Further, leaf shaped antenna is designed based on modified polar transformation equation; it has 2.7 GHz bandwidth from 1.3 GH to 3 GHz and has a gain of -5.45dBi, and return loss (S11) of -19.5 dB. The filtenna is obtained by integrating the IDBBPF in the fodder line of the leaf designed antenna. The final model has 1.2 GHz operating bandwidth from 02.30 GHz to 03.50 GHz with peak arrival damages at 2.4GHz and 3.1GHz with -20dB and-24dB respectively. The designed filtenna has a pass band gain of -5.3dBi. The shift in operating band is due to combining the filter with antenna. The proposed model is invented on FR4 substrate having a wideness of 01.60 mm and having a dimension of 0.25 0.58 ?02. In this final model two complementary slip ring resonators (CSRR) are used in addition with four dumbbell structures as defects in the ground plane to avoid ripples in return loss (S11) graph. A high degree of concordance exists between empirically measured and simulated outcomes. The radiation band is showing its application in S band wireless mobile communications, Wi-Fi and ISM 2.4GHz band.

A novel cross‐coupled filter with triangular resonators

In this article, a novel isosceles right triangle resonators filter is presented based on cross-coupling technology. The whole filter is a square structure and it consists of four isosceles right triangle resonators. By introducing negative cross-coupling between two resonators, a fourth-order cross-coupling dielectric waveguide filter with two out-of-band transmission zeros (TZs) is implemented. By changing the sign of the coupling coefficient, the TZ can be changed around the passband. Positive coupling is achieved through a coupling partition and shallow coupling blind holes, and negative coupling is achieved through symmetrical upper and lower blind holes. The new resonator structure is introduced and the design, simulation, and physical measurement of the filter are discussed. The results show that the center frequency of the filter is 3.5 GHz and the relative bandwidth is 5.7%. The passband return loss is more than 14 dB, the insertion loss is less than 0.1 dB.

3-D Printing Quantization Predistortion Applied to Sub-THz Chained-Function Filters

This paper investigates physical dimension limits associated with the low-cost, polymer-based masked stereolithography apparatus (MSLA) 3-D printer, with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50 ~\mu \text{m}$ </tex-math></inline-formula> pixels defining the minimum print feature size. Based on the discretization properties of our MSLA 3-D printer, multi-step quantization predistortion is introduced to correct for registration errors between the CAD drawing and slicing software. This methodology is applied to G-band <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5^{th}$ </tex-math></inline-formula> order metal-pipe rectangular waveguide filters, where the pixel pitch has an equivalent electrical length of 8.5° at center frequency. When compared to the reference Chebyshev filter, our chained-function filter exhibits superior S-parameter measurements, with a low insertion loss of only 0.6 dB at its center frequency of 182 GHz, having a 0.9% frequency shift, and an acceptable worst-case passband return loss of 13 dB. Moreover, with measured dimensions after the 3-D printed parts have been commercially electroplated with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50 ~\mu \text{m}$ </tex-math></inline-formula> thick layer of copper, the re-simulations are in good agreement with the S-parameter measurements. For the first time, systematic (quantization) errors associated with a pixel-based 3-D printer have been characterized and our robust predistortion methodology has been successfully demonstrated with an upper-millimeter-wave circuit. Indeed, we report the first polymer-based 3-D printed filters that operate above W-band. As pixel sizes continue to shrink, more resilient (sub-)THz filters with ever-higher frequencies of operation and more demanding specifications can be 3-D printed. Moreover, our work opens-up new opportunities for any pixel-based technology, which exhibits registration errors, with its application critically dependent on its minimum feature size.

SLM Printed Waveguide Dual-Mode Filters With Reduced Sensitivity to Fabrication Imperfections

This letter presents an eighth-order dual-mode waveguide filter, fabricated using the selective laser melting (SLM) technique. The filter employs four dimpled ellipsoid dual-mode resonators, operating at the fundamental TM₁₀₁ mode. During printing, the filter can be mechanically self-supported without any internal supports. Compared to the filters employing tuning posts, the proposed filter is less sensitive to fabrication errors in terms of their impacts on passband return loss (RL), frequency shift, and bandwidth. The filter was demonstrated at WR-112 band (7&#x2013;10 GHz), with a measured insertion loss of 0.25&#x2013;0.4 dB and an RL &#x003E;15 dB across the passband of 8&#x2013;8.46 GHz.

A compact multilayer substrate integrated waveguide quasi‐elliptic bandpass filter for millimeter‐wave applications

AbstractA multilayer substrate integrated waveguide (SIW) quasi‐elliptic bandpass filter based on the printed circuit board (PCB) process is presented for millimeter‐wave applications in this article. The proposed filter consists of four SIW cavities, in which the upper and lower cavities form the vertical couplings, and the two lower cavities form a mixed coupling by a short‐ended conducting strip and metallized vias. The four‐order filter can form the cross‐coupling and mixed‐coupling mechanism to introduce transmission zeros (TZs). Moreover, the filter can achieve miniaturization by vertical couplings with a size of about 0.77 × 0.49 λ02, where λ0 is the wavelength of the center frequency (25.75 GHz). Measured results show that the filter has a 3 dB bandwidth of 15.1%, the insertion loss of 1.29 dB at the center frequency (25.75 GHz) and the passband return loss better than 17 dB. Three TZs (23.1, 29.0 and 31.6 GHz) are obtained to improve the filter selectivity.

A half‐mode substrate integrated waveguide filtering power divider with Fourier‐varying via holes

AbstractIn this article, a novel design methodology of a half‐mode substrate integrated waveguide (HM‐SIW) filtering Wilkinson power divider is proposed. The width between the two metallic rows of vias in the conventional HM‐SIW divider is governed by a truncated Fourier series expansion to obtain specific passband/stopband performance. The optimized varying width is obtained using the even‐mode analysis, whereas the odd‐mode analysis is used to find the optimum values of three isolation resistors that achieve acceptable isolation and output ports matching over specific frequency range. For validation, a HM‐SIW divider with a center frequency of 12.3 GHz and 3.7% 10‐dB fractional bandwidth is designed, simulated, and measured. Simulated and measured results show a good agreement with passband return loss and transmission losses better than −15 and −3.0 dB, respectively.

Wideband Band-Pass Filter Design Using Coupled Line Cross-Shaped Resonator

In this paper, a wideband bandpass filter with a coupled line cross-shaped resonator (CLCSR) is proposed. The proposed bandpass filter is composed of two open-end parallel coupled lines, one short-end parallel coupled line, one branch microstrip line, and the parallel coupled line feed structure. With the use of the even and odd mode approach, the transmission zeros and transmission poles of the proposed bandpass filter are analyzed. The coupling coefficient of the parallel coupled line feed structure is big, so the distance between the parallel coupled line is too small to be processed. A three microstirp lines coupled structure is used to realize strong coupling and cross coupling. This structure also can reduce the return loss in passband and increase the out-of-band rejection. The transmission zeros can be adjusted easily by varying the lengths of the open-end parallel coupled line or the short-end parallel coupled line. The proposed bandpass filter is fabricated and measured. The simulated results agree well with the measured ones, which shows that the design method is valid.

Multi‐layered substrate integrated waveguide waffle‐iron filters

This study presents the implementation of a waffle-iron filter in multi-layered substrate integrated waveguide technology, together with an approximate technique for measuring the stop-band scattering parameters of such a multi-mode waveguide filter. Two filters are designed for different stop-band widths, and tested. Two measurement techniques are presented – one utilising a set of measurements with different probe positions, and one using a radiating horn. Measured results for the two prototypes, show better than 12 dB pass-band return loss over 8.5–10.5 GHz for both, with stop-band attenuation in excess of 70 dB over the harmonic bands 15–43 GHz for one and 15–48 GHz for the other.

Compact four‐pole wideband bandpass filter with mixed electric and magnetic coupling

AbstractA wideband bandpass filter (BPF) based on two dual‐mode stub‐loaded stepped‐impedance resonators (SLSIRs) with mixed electric and magnetic coupling (MEMC) is proposed. Magnetic coupling is realized by using a transmission line, open end‐coupling and inter‐digital‐coupling provide a weak and a strong electric coupling, respectively. Due to the canceling effect of MEMCs, together with its harmonic effect, four transmission zeros (TZs) aside the passband are created and the selectivity of the filter is therefore highly improved. To verify the proposed design, a four‐pole wideband BPF operating at 3.35 GHz with 3 dB fractional bandwidth (FBW) of 32.96% is designed, fabricated, and measured. The measured minimum insertion loss is 0.95 dB, and the passband return loss is better than 11 dB.

A 3-D Printed Bandpass Filter Using TM₂₁₁-Mode Slotted Spherical Resonators With Enhanced Spurious Suppression

This article presents a Ka -band fourth-order slotted spherical resonator waveguide bandpass filter (BPF) with a wide spurious suppression stopband. It uses the first higher-order TM211 mode rather than the fundamental TM101 mode of the spherical resonator in order to obtain a higher unload quality factor ( $Q_{\mathrm {u}}$ ) for smaller in-band insertion loss, as well as a larger filter volume that gives better tolerance to fabrication errors in high frequency applications. By introducing slots that interrupt surface currents, the fundamental TM101 and two higher spurious modes (TE101 and TM311) can be suppressed without compromising the unloaded quality factor of the TM211 mode. In addition, the filter topology is optimized to further enhance the suppression level of the spurious passbands. A Z-shaped topology has been found effective in decreasing the coupling strength of the spurious TM311 mode. An analysis is performed to demonstrate the better tolerance of the Z-shaped filter over the conventional TM101-mode spherical resonator filter. For verification, a fourth-order slotted spherical resonator waveguide BPF with a center frequency of 31 GHz and bandwidth of 880 MHz is designed and manufactured using a selective laser melting (SLM) 3-D printing process. The measured results show an average in-band insertion loss of 1.53 dB, and a passband return loss better than 13.6 dB. The stopband of the filter is extended up to 40.9 GHz with a rejection level greater than 20 dB.

CMOS Millimeter-Wave Ultra-Wideband Bandpass Filter With Three Reflection-Zeros Using Compact Single TFMS Coupled-Line Hairpin Unit

In this brief, a modified coupled-line (CL) hairpin unit topology with short-circuited ends is proposed to design a compact millimeter-wave ultra-wideband (UWB) bandpass filter (BPF). Thin film microstrip configuration is used for the implementation of CL hairpin unit. The passband return loss bandwidth is enhanced by three attenuation poles achieved by appropriately selecting a single set of CL impedances. Explicit design equations along with graphs are provided by using even-and-odd mode analysis. A prototype filter is fabricated using 0.35- ${\mu }\text{m}$ BiCMOS technology. The fabricated UWB BPF achieves an extended passband from 25 GHz to 95 GHz around 60 GHz with more than 115% fractional bandwidth along with a wide return loss bandwidth. The filter size is very small with the overall width comparable to the width of a 50 ${\Omega }$ line. The measured results are in good agreement with those of predicted ones up to 110 GHz.

3-D Printed Slotted Spherical Resonator Bandpass Filters With Spurious Suppression

In this paper, a third-order waveguide bandpass filter (BPF) based on slotted spherical resonators with a wide spurious-free stopband is presented. The resonator consists of a spherical cavity with slots opened at the top and bottom. Compared with a non-slotted spherical resonator, the slotted resonator suppresses the two spurious modes (TM211 and TE101) whilst maintaining the fundamental TM101 mode. The unloaded quality factor of the TM101 mode is not significantly degraded. This is achieved by interrupting surface current and radiating the unwanted spurious modes with the slots. The BPF is designed at a center frequency of 10 GHz with a fractional bandwidth of 1%. Two filter prototypes are fabricated, one using metal-based selective laser melting (SLM) and the other by polymer-based stereolithography apparatus (SLA) techniques. The slots also facilitate the copper electroplating process for the SLA-printed filter. The measured results show that the average passband insertion losses of the SLM- and SLA-printed filters are 0.33 and 0.2 dB, respectively. The corresponding passband return losses are better than 22 and 20 dB. The filters demonstrate excellent passband performance and wide spurious-free stopbands up to 16 GHz with stopband rejections of over 20 dB.

Wideband Bandstop Filter With Extreme Sharp Skirt Selectivity

A novel and simple wideband bandstop filter with extreme sharp skirt selectivity is proposed. The wideband bandstop response with multi-transmission zeros and large skirt-band attenuation rate is realized based on the modified coupled-line sections with open-/short-circuited termination and two quarter-wavelength transmission lines. In order to simultaneously improve stopband rejection (SR) and passband return loss, the gray boxes with different circuit structures are introduced. For demonstration, a designed prototype operating at 1 GHz with 64% relative bandwidth of 17-dB SR is simulated, fabricated, and measured.

Miniaturized 38GHz Circular Substrate Integrated Waveguide Band Pass Filter using Low Temperature Co-Fired Ceramic Technology

This study presents design approach for realizing miniaturized Substrate Integrated Waveguide (SIW) Band Pass Filter (BPF) using Low Temperature Co-fired Ceramic (LTCC) technology at TMRND's LTCC Lab. Design method for the SIW BPF is based on the circular cavity structure with four pole Chebyshev and operating at center frequency of 38 GHz. This SIW BPF is an important part of the Remote Antenna Unit (RAU) transceiver for the Radio over Fiber (RoF) system. Two types of circular SIW BPF have been designed and investigated in term of performance and structure size which are planar SIW BPF and compact SIW BPF. Both SIW BPF were developed using LTCC Ferro A6M materials with dielectric constant of 5.8, loss tangent of 0.002 and metallization of gold. The insertion loss for planar SIW BPF and compact SIW BPF were measured at 6.2 dB and 6.3 dB, respectively. The passband return losses for both types of the SIW BPF were measured at more than 10 dB. The size of the compact SIW BPF is 6.94×6.94 mm² meanwhile size for planar SIW BPF is 12.15×4.145 mm². The size of the compact SIW BPF is reduced to nearly 10% compared to a planar SIW BPF structure.

Sixteenth‐mode substrate integrated waveguide bandpass filter loaded with complementary split‐ring resonator

A novel sixteenth-mode substrate integrated waveguide (SMSIW) bandpass filter loaded with complementary split-ring resonator (CSRR) is proposed. The filter size is reduced by introducing the SMSIW circular cavity loaded with CSRR. The SMSIW occupies only 6.25% of the conventional substrate integrated waveguide with same resonant frequency. Further miniaturisation is achieved by loading the SMSIW circular cavities with CSRRs. The designed filter is centred at 2.45 GHz with a bandwidth of 8.2%. The measured minimum insertion loss is 0.9 dB and passband return loss is below 10 dB. Good agreement is achieved between simulated and measured results.

3D printed bandpass filters using compact high‐ Q hemispherical resonators with improved out‐of‐band rejection

RF design and implementation of ceramic-filled resin-based 3D printed millimetre-wave bandpass filters (BPFs) using a new class of compact high-quality-factor hemispherical cavity resonators are addressed. Design concept of the hemispherical resonator is discussed for BPF applications in both X and Ka bands. For validation purpose, the Ka-band fourth-order BPF is fabricated with a high-temperature-resistant ceramic-filled resin using a fast and low-cost stereolithography-based 3D printing technique, and its surface metallisation is realised by employing electroless copper/silver plating. The proposed BPF's geometrical configuration contributes to a significantly improved out-of-band rejection. The RF-measured results demonstrate the Ka-band BPF an insertion loss of 0.43−0.9 dB from 31.52 to 32.42 GHz, a passband return loss mostly better than 15 dB, and a small frequency shift of about 0.06%.