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By using integrated lumped elements based on through-silicon via (TSV) technology, a 3-D low-pass filter (LPF) with ultracompact size and ultrawide stopband is proposed. The 3-D magnetic coupling is enhanced between microsize spiral inductors to increase the mutual inductance and improve the high-frequency performance. A coaxial TSV with enhanced capacitance in high resistivity silicon (HRS) is utilized both as capacitor and as a vertical interconnection without any overhead in area and routing. The 3-D nature of the proposed filter yields a miniaturized size of 0.2 x 0.10 mm². The LPF is analyzed with equivalent circuit model and validated with the well-matched S-parameters obtained by finite element method simulation and measurement. With -3-dB cutoff frequency at 2.6 GHz, the LPF exhibits an insertion loss below 1 dB, a reflection loss over 17 dB in the passband, and a suppression level over 20 dB from 5.28 up to 40 GHz in the stopband.

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 (7–10 GHz), with a measured insertion loss of 0.25–0.4 dB and an RL >15 dB across the passband of 8–8.46 GHz.

This letter presents our study on a compact and low-loss E-band bandpass filter (BPF) based on multilayer groove gap waveguide (GGW). Different from other reported planar GGW filters and vertically stacked substrate integrated waveguide (SIW) filters, the proposed filter realizes a cross-coupled quadruplet topology by introducing a pair of unique circular capacitive holes across layers, innovative ridges (capacitive iris), and conventional inductive irises on the same layer, which reduces the insertion loss (IL) while having a smaller size. By tuning the dimensions of the coupling structures and cavities, the filter is optimized to exhibit a superior performance in simulation. The designed filter is fabricated using CNC machining and verified in experiment. The measured results agree with the simulated ones quite well, showing an average IL of 0.45 dB and an 8% relative 3-dB bandwidth at a center frequency of 73.65 GHz. Therefore, the proposed multilayer GGW structure opens a new avenue in designing high-performance filters in millimeter-wave bands.

In this letter, a combined approach based on circuit equivalent and field analysis is employed to design a waveguide low-pass filter. According to the field analysis and out-of-band transmission poles responses, the transmission pole spacing distribution method is proposed to obtain a wide stopband. The simulation indicates that this method can provide a well-performed harmonic suppression. Different from the large-scale parameter optimization method for the wide stopband, this technique has the advantage of consuming relatively small computation resources. Finally, the X-band waveguide low-pass filter is fabricated and tested. Measurements show that the stopband suppression can exceed the fourth-order harmonic of the fundamental mode with more than 56-dB suppression levels.

In this letter, we present a general design method for tunable matching networks that have a prescribed filter characteristic over a range of complex port impedances. The approach enables prediction of the achievable tunable impedance range, given a filter topology and tuning element values. As experimental validation, a 2.5-GHz second-order Chebyshev filter is designed using Skyworks SMV2205-040LF varactor diodes to tune the filter resonator and inverter. It is shown that the filter can match port impedances in a region that spans a range of real and imaginary parts of the impedance between 10 and $150~\Omega $ with an insertion loss of 1.5 dB.

This letter presents a second-order and a third-order $W$ -band bandpass filter (BPF) based on rectangular microcoaxial structures. Rectangular microcoaxial line has the advantages of low dielectric and radiation loss, small size, and easy integration, which is conducive to the design of passive devices. The resonant unit based on rectangular microcoaxial structure consists of a metal cavity, a rectangular metal block suspended inside, and a grounded cylinder. It is used to design two Chebyshev filters. In order to facilitate the interconnection with other devices, ports of the filter are added with rectangular coaxial line to coplanar waveguide (CPW) transitions. The center frequencies of two filters are 93.3 and 94.3 GHz, respectively. Finally, the two filters are fabricated and measured to verify the design method. The minimum insertion loss in passband is 1.3 and 1.5 dB. Good agreements between the simulated and measured results are achieved.

This letter suggests a design methodology for triple-band wireless power transfer (TB-WPT) filters. The proposed triple-bandpass filter (TB-PF) is designed using two complementary split-ring resonators CSRR-DGSs coupled in a back-to-back configuration, and operates at 0.6, 2.4, and 2.7 GHz. Each of the transmitter and the receiver has a size of 25 mm $\times25$ mm. The measured power transfer efficiencies were 96% for 0.6 GHz, 74% at 2.4 GHz, and 70% at 2.7 GHz, respectively, at a separation distance between the transmitter and receiver of 10 mm.

In this letter, novel miniaturized bandpass filters with wide stopband performance are proposed on the basis of the half-mode T-septum substrate integrated waveguide (HMTSSIW) resonator. The resonant TE n 00 and TE n 0 m modes of the HMTSSIW resonator are analyzed precisely using the Ritz–Galerkin method, and their resonant frequencies can be controlled flexibly by adjusting the sizes of resonator. A three-order HMTSSIW filter is fabricated using MEMS technology on the benzocyclobutene dielectric. Simulated and measured results show the advantages of compact size and wide stopband. Then, an electric coupling structure is introduced, which allows the further suppression of the spurious TE300 mode by the controllable mixed coupling. Finally, a miniaturized HMTSSIW filter with 20-dB suppression beyond $10.37f_{0}$ is simulated and measured.

Based on the hybrid microstrip and substrate-integrated waveguide (SIW) technologies, a compact filter with wide-stopband characteristics is presented in this letter. Two microstrip-based uniform impedance resonators (UIRs) are etched between two SIW cavities, which not only resonate to generate transmission poles, but also constitute coupling-null structures to prevent the propagation of TE102 mode. In addition, the staggered higher mode frequencies of the UIRs and SIW cavities also contribute to harmonics rejection of the two resonant structures. The suppression method of higher order modes is carefully illustrated. For validation, a prototype operated at 10 GHz is designed, fabricated, and measured. The experimental results show good agreement with simulation. Besides suppressing the TE102 and TE201 modes, the proposed filter also has the capability to suppress other harmonics, presenting an ultrawide stopband compared with the conventional SIW filters.

An intrinsically switchable ferroelectric barium strontium titanate (Ba( x )Sr(1– x )TiO3, BST)-based film bulk acoustic resonator (FBAR) quad channel filter bank is presented for the first time. The design incorporates a matching network free of tunable elements and provides a high isolation >30 dB across all four filter paths when the resonators are switched off. The measured insertion loss for the four 2.5 stage BST FBAR filters range from 6 to 7 dB with an out-of-band rejection >30 dB, which is an improvement over previously reported BST ladder-type structure. The filter bank, realized through T-networks, occupies an area of 840 $\mu \text {m} \times 340\,\,\mu \text{m}$ and operates across four different bands solely through the BST-based acoustic resonators.

This letter presents a novel configuration high- $Q$ coaxial tunable filter that employs a single rotational mechanism to tune the filter while using fixed $\lambda $ /4 resonators. A prototype filter is designed for the proof of concept, which has a tuning range of 11.6% from 685 to 770 MHz, over which bandwidth (BW) variation is within 10.5 MHz ± 0.7 MHz. In addition, the proposed design methodology can be scaled to realize higher order filters. The proposed filter promises to be useful in a wide range of telecommunication applications, including flexible payload in aerospace applications.

Today’s phones have as many as 60 front-end radios covering multiple frequency bands. For each frequency band, acoustic filters offer high- ${Q}$ , good power handling, and linearity in a very small package. These properties are crucial when addressing the “explosion” in the number of radios and the filters needed by today’s Smart Phones. Moving forward, filter integration will become essential for cost and size. A novel lithium tantalate (LT) bonded to silicon hybrid substrate silicon SAW (SiSAW) was developed that provides temperature compensation, good power handling properties, while mostly eliminating spurious modes created between the LT/Si interface. One of several advantages of this technique is that one can integrate as many filters as needed onto one die. This provides for cost savings as well as area savings while reproducing the inherent performance of high-quality temperature compensated (TC)-surface acoustic waves (TC-SAWs).

A novel dual-mode (DM) dielectric waveguide (DW) filter with controllable transmission zeros (TZs) is presented. The DM filter is based on a cascaded implementation, utilizing individual DM DW cavities. The filter is practically realized by embedding three circular blind holes at different positions in the surface of a dielectric silver-coated square cavity. By changing the relative position of the blind holes or rotating the direction of the proposed DW cavity, the filter’s TZs’ frequency locations can be flexibly adjusted. The zero points can be set in frequency at the low end of the passband, at the high end of the passband, or they can be generated at both the low and high ends of the passband in order to improve the selectivity of the filter. In this study, the two-cavity fourth-order filter is taken as an example, and the experimental results validate the feasibility of the presented theoretical design.

This letter presents a novel class of compact dual-mode bandpass filters based on half-mode substrate-integrated waveguide (HMSIW) cavities. By using both TE102 and TE301 modes of the HMSIW rectangular cavity as resonant modes and TE101 mode as nonresonating mode, a novel HMSIW doublet with two poles and two transmission zeros (TZs) is implemented. The TZs can be located at one side or both sides of the passband. Therefore, flexible responses can be obtained. A two-pole HMSIW filter with asymmetric response and a four-pole HMSIW filter with quasi-elliptic response have been designed, fabricated, and measured, to demonstrate and verify the proposed structure. Compared with substrate-integrated waveguide (SIW) counterparts, the dual-mode HMSIW filters have the advantage of smaller size.

We propose a second-order $RC$ -only voltage-mode active all-pass filter (APF) as an analog time-delay cell. The core circuit of the proposed APF is canonical and consists of only one transistor, one resistor, and two capacitors. Therefore, this design is area efficient, and it is suitable for low-gigahertz frequency applications, where conventional $LC$ designs are not practical, due to large inductor sizes. The APF design equations are derived and the circuit noise and sources of nonideality are discussed. The proposed 65-nm CMOS APF is experimentally verified to demonstrate a wideband range of 0.4–2 GHz and a continuously tunable delay in the range of 30–57 ps with an rms delay variation error $1870~\mu \text {m}^{2}$ while drawing 2.47 mA from a 1-V supply.

In this letter, we present an innovative filter configuration employing transversal coupled triple-mode spherical resonators while capable of realizing transmission zeros (TZs). Transversal coupling involves simultaneous source and load-controlled couplings to all the three modes of the spherical resonator. Spherical resonators inherently have very large quality factor (Qu) and exhibit a farther spurious response thus yielding bandpass filters (BPFs) with lower insertion loss and wider spurious-free window. The design methodology for transversal coupling is explained and is employed for designing a third-order bandpass filter with TZs. In addition, a sixth-order bandpass filter using cascaded trisection is also presented. A third-order BPF with symmetric TZs is fabricated for verifying proof of the concept. The filter designed at 6.545 GHz with a bandwidth of 120 MHz has an insertion loss better than 0.1 dB and a spurious-free window better than 1.7 GHz. The proposed filter promises to be useful in aerospace applications that demand high Qu, low volume, and wider spurious-free window.

This letter presents, for the first time, a new filter-enhanced linearity measurement technique using a dual-band and dual-mode filter. While traditional two-tone linearity tests are simple and effective, their ultimate performance is determined by the quality (dynamic range and noise floor) and cost of the employed equipment. On the other hand, the proposed method consists of a simple conventional single-tone test facilitated by a low-cost appropriately designed bandstop filter (BSF). In particular, the employed dual-band/dual-mode absorptive BSF suppresses the fundamental frequency by over 35 dB (absorptive notch) and the second harmonic by over 25 dB (reflective notch), allowing for accurate measurement of the third harmonic, and hence, IP3. The proof-of-concept system is demonstrated at 2 GHz. The filter absorbs with better than 20 dB of reflection the excitation signal at $f_{0}=2$ GHz and reflects the signal at $2f_{0}=4$ GHz. With just the insertion of the presented filter and without improving the measurement equipment, we demonstrate an improvement of over 12.7 dB in the IP3 characterization to a maximum of 81 dBm. We also demonstrate the ability to conduct this test with just a low-cost power detector in lieu of a spectrum analyzer leading to a simple scalable measurement technique.

In this letter, a cross-coupled dual-bandpass filter (BPF) with separate electric and magnetic coupling paths (SEMCPs) for 5G sub-6 GHz applications is proposed. Source-to-load couplings are also introduced in this structure for the flexibility of heterogeneous feed lines. Five controllable transmission zeros (TZs) in total are produced in the dual-band filter. The filter achieves good overall performance by adopting two pairs of quarter-wavelength stepped-impedance resonators (SIRs). To minimize the size of the filter and enlarge the controllable range of the second passband, the SIRs forming the second passband are separated and folded onto two different layers. The measured dual band filter achieves fractional bandwidths of 7.82% and 4.08%, centered at frequencies of 3.45 and 4.9 GHz with insertion losses of 1.15 and 1.42 dB, respectively.

This letter presents a new filter to suppress radio frequency interference (RFI) in microwave remote sensing instruments, particularly a wideband autocorrelation radiometer (WiBAR). RFI increases the noise floor and results in a decreased signal-to-noise ratio (SNR) of the WiBAR delay peak. The proposed filter operates like a Fabry–Perot interferometer (FPI) in optics and has the frequency response of a comb filter with many evenly spaced alternating pass and stop bands. The frequencies of these bands are varied with an electrically adjustable phase shifter. The design of a comb filter with an airy finesse value of 20 has been verified by simulation and measurement.

In this letter, a class of rectangular waveguide filters with central-post resonators is introduced. By introducing a central post in an oversized rectangular cavity, the resonant frequency of TE301-mode can be brought close to that of TE201-mode. The two resonant modes are coupled to adjacent fundamental mode resonators by inductive irises. A doublet coupling topology can be used to model the physical configuration, and flexible filter responses with finite-position transmission zeros (TZs) can be realized. Four 4-pole filters with different TZ positions are designed and simulated. A seven-pole filter with two cascaded central-post resonators is fabricated and measured. In the seven-pole filter, each central-post resonator independently controls one TZ on the lower side and very close to the passband. The measurement results of the seven-pole filter agree with the simulated counterparts very well, thus validating this filter design technique.

This letter presents a novel tri-band filter design using an ultraminiaturized substrate-integrated waveguide (SIW) cavity operated at evanescent mode. Two miniaturized SIW cavities in a face-to-face form are vertically stacked to build the proposed tri-band filter. The top and bottom metal layers form the cavity’s broadside walls, and the middle layer possesses three identical patches which are formed by evenly trisecting a circular patch. These patches are shorted to the cavity’s bottom wall through one, two, or four via-holes. The patches together with the host cavity exhibit three frequency-distinct resonances that create the filter’s triple passbands. The resonance frequencies are independently controlled, and six passband-edge transmission zeros are created for good selectivity. The filter size is only $0.22\,\,\lambda _{d} \times 0.22\,\,\lambda _{d}$ , and the measured in-band minimum insertion losses are 2.31, 2.25, and 3.01 dB for the first, second, and third bands, respectively. It is believed that the proposed tri-band filter has obtained the best circuit area efficiency in the SIW tri-band filter category.

In this letter a new type of singlet is introduced, called stopband singlet . The new singlet is implemented in rectangular waveguide, exploiting TE301 as resonating mode and TE10 mode as nonresonating bypass coupling. Unlike the previously introduced singlets [which produce one transmission zero (TZ) and one reflection zero (RZ)], the stopband singlet generates one TZ alone (the RZ is pushed to infinity). The novel structure allows designing filters with resonating couplings introducing TZs very close to the passband (difficult to implement with other resonating waveguide discontinuities). A prototype two-pole filter with one TZ has been designed and fabricated to validate experimentally the novel singlet configuration.

This letter proposes a novel trisection filter by stacking three substrate-integrated waveguide (SIW) cavities vertically. The trisection topology can be divided into two cascaded second-order topologies in the vertical direction, which can make the filter structure more compact. Moreover, two transmission zeros can be controlled independently by changing the signs of coupling coefficients between the adjacent stacked SIW cavities. Finally, a third-order filter sample is fabricated using printed circuit board (PCB) technology, and the measured S-parameters have good agreement with the simulated ones.

In this letter, a novel folded ridge substrate-integrated waveguide (FRSIW) is proposed by folding a classic ridge substrate-integrated waveguide (RSIW). The FRSIW demonstrates a size nearly half of its RSIW counterpart while keeping the main propagation properties of the RSIW. A prototype of the wideband FRSIW filter with compact size has been designed and tested. The measurements show that the proposed wideband FRSIW filter has the advantages of low loss, compact size, and easy fabrication and integration with other electronic systems.

In this letter, a new differential dielectric strip resonator (DSR) filter with dual passbands is proposed. By loading a pair of ground bars underneath the traditional half- wavelength ( $\lambda /2$ ) DSR with high permittivity (supported by a low-permittivity substrate with the bottom ground plane), the TM10 and TM30 modes can be controlled to be in a close spacing. Meanwhile, both of them can be differentially excited for the design of the differential dual-band bandpass filter (BPF). The external quality factors and coupling coefficients for both bands can be independently controlled through proper layout; meanwhile, the common-mode (CM) suppression in the two differential-mode (DM) passbands is more than 25 dB. Finally, a differential DSR BPF with dual-band response operating at 8.13 and 11.13 GHz is given to verify the proposed idea.

In this letter, new patterns of symmetric trisection bandpass filter (BPF) with reflection-type half-wave resonators, mixed cross-coupling, and different paths for signal propagation are discussed. The various coordinates of the conductive connection of loads to the end half-wave resonators are used in the filter. This leads to different signal paths from input to output of the filter. Due to the various connections of loads and mixed cross-coupling, satisfying condition $K_{13} = 0$ , the same filter has different frequency responses. When we use one port position, two transmission zeros, located on the $\sigma \! $ -axis of the complex plane $s = \sigma + j\Omega $ , are generated, and we obtain a flat group delay. If another port position is used, two transmission zeros are generated on the $j\Omega $ -axis, $\Omega = (\omega /\omega _{0} - \omega _{0}/\omega)$ /fractional bandwidth (FBW), and a quasi-elliptic response is presented. In both cases, two transmission zeroes are equidistant relative to $s =0$ and they are controlled by a mixed coupling coefficient. The results of the measurements and simulation are presented.

This letter presents the design and fabrication of a 287-GHz resonator and a bandpass filter. The fabrication is conducted using an additive microfabrication process, based on successive photolithography and metal electroplating steps. This process has allowed the fabrication of a single-cavity resonator and a 3.5% relative bandwidth two-pole bandpass filter. The cavity has a measured unloaded $Q$ of 137, and the filter has a measured loss of 4.6 dB and matching better than 20 dB in very good agreement with E-M simulation results.

In this letter, a new method for rectangular waveguides bandpass filters with improved stopband performance is presented. By setting the position of the coupling window, the coupling of the high-order mode can be attenuated, which makes it difficult to form parasitic passbands. It can significantly improve the stopband rejection of the filter without introducing additional elements. Furthermore, the whole structure can be fabricated using the conventional computer numerical control (CNC) milling technology. A Ka -band waveguide filter is designed and tested. The stopband rejection of the design is increased from 1.4 times to 1.94 times the center frequency of the filter with the insertion loss of 0.5 dB. Finally, the measurement results validated the proposed design.

In this letter, new patterns of symmetric trisection bandpass filters (BPFs) of two types with all mixed couplings are discussed. The condition under which the first-type filter with a central reflection-type resonator transforms into a delay line filter is considered. A second-type filter with a central through-type resonator becomes a quasi-elliptic filter under the same condition. As a result, the two transmission zeros are located equidistant regarding $s= 0$ on the complex plane $s= \sigma + j \Omega $ , $\Omega = \omega /\omega _{0} - \omega _{0}/\omega $ )/FBW, mymargin for both types of filters, when this condition is fulfilled. A position of these transmission zeros with respect to $s= 0$ is expressed in terms of the mixed coupling coefficients. Two compact microstrip trisection BPFs of different types with all mixed couplings were proposed, fabricated, and measured.

In this letter, a compact self-packaged folded substrate-integrated waveguide filter with loaded stubs is presented. Transmission zeros (TZs) at the same number of filter order are designed to improve out-of-band performance. The position of each TZ is controlled independently. The first spurious resonance increases by up to 3.8 times the fundamental frequency by suppressing the original first parasitic resonance. A Ka -band filter with a benzocyclobutene (BCB) polymer as a dielectric is fabricated and measured to verify the design concept.

This letter presents the first substrate integrated waveguide (SIW) ${k}$ -band filters tuned with contactless printed circuit board (PCB) tuners. Unlike previous efforts, the presented filters exhibit two key advantages that make them particularly attractive with respect to manufacturing, performance, and reliability: 1) they are based on low-cost PCB technology and 2) they employ contactless tuners that exhibit no hard contacts with the evanescent-mode (EVA) cavities they control. A proof-of-concept two-pole prototype with 3.2–3.4 dB loss is experimentally demonstrated in the 20–26.5 GHz band. The fabricated resonators employ a unique contactless tuner geometry that minimizes insertion loss (IL) by utilizing extended cavity sidewalls. This design improves IL by an average of 10 dB in the demonstrated band. This letter also discusses fabrication imperfections and their impact on filter performance.

This letter demonstrates the first successful realization of a monolithic wafer-level integrated air-filled waveguide resonator in the millimeter-wave W-band. The fabrication of the proposed design builds upon previously published processes by spin-coating two layers of thick positive resist to construct the waveguide channel. The fabricated design achieves an insertion loss of 2.12 dB, unloaded quality factor of 97.6, and 3-dB fractional bandwidth of 3.0% at the center frequency of 76.6 GHz. The proposed concept illustrates a new technique for integrated filter realization at such frequencies.

A new class of multiband acoustic-wave resonator-based RF filters with reconfigurable bandpass-to-bandstop (BP-to-BS) transfer function characteristics is reported. They are based on a hybrid integration scheme in which multiresonant acoustic-wave-lumped-element-resonators (AWLRs) are combined with five static and one switched impedance inverters. Each multiresonant AWLR controls the number of bands and their center frequencies. Switching between the bandpass and bandstop modes of operation is achieved by changing the coupling path between its input/output ports through an RF-switched impedance inverter. For practical validation purposes, two prototypes were designed, manufactured, and tested. They include a single-band BP-to-BS filter at 418 MHz and a dual-band BP-to-BS filter with bands centered at 418 and 433.9 MHz.

A compact reconfigurable bandpass-to-bandstop filter with wide tuning range is presented. The bandpass-to-bandstop transformation is achieved by a p-i-n diode. In the bandstop mode, the two-pole bandstop response is obtained by introducing the inductive coupling between the two resonators of the notch filter. In the bandpass mode, the center frequency and an external quality factor are controlled by two pairs of varactors. A pair of transmission zeros is generated by two transmission paths, which improves the selectivity. The fabricated filter demonstrates a wide frequency tuning range with a miniaturized circuit size of $0.16\lambda _{\mathbf {g}}\times 0.11\lambda _{\mathbf {g}}$ . The simulated and experimental results are presented with good agreement.

© 2001-2012 IEEE. Terahertz (THz) tunable filter plays a significant role for miniaturization and multifunction in application systems. The frequency of existing schemes for tunable waveguide filter can only reach up to the W-band. The selection of tuning and assembly solution for THz band is significant and challenging. In this letter, we investigate the design of bimorph microactuator which uses microelectromechanical system (MEMS) technology. Based on this microactuator, we propose a THz tunable waveguide bandpass filter, whose center frequency can be tuned from 247 to 260 GHz. It is the first time to extend the center frequency of tunable waveguide bandpass filter to over 220 GHz while using MEMS bimorph microactuators to tune. The tuning ratio of the filter is 5.26%, and the measured insertion loss is better than 6 dB in the passband.

A series code selective filter (CSF) for full-duplex communication is presented. The CSF passes a desired signal in a frequency band only when the signal is tagged with a pseudonoise (PN) code that matches the code at the filter. This approach is shown to reject a transmit signal in the same band as a desired receive signal. The coded transmitter signal is orthogonal through appropriate code selection from a codebook and the PN sequence spreads the signal energy outside the filter bandwidth (BW). The CSF achieves a self-interference rejection of 23.2 dB over a 10-MHz BW using on-chip generated Walsh codes. The CSF operates from 300 to 675 MHz and consumes 28.2 mA from a 1-V supply at 500 MHz. The CSF achieves an IIP3 of 15.7 dBm. The CSF was implemented in a 45-nm CMOS silicon on insulator process and occupies an area of 0.9 mm2.

Package-integrated and ultra-thin low-pass filter (LPF) and bandpass filter (BPF) with footprint smaller than $0.5\lambda _{0}\times 0.5\lambda _{0}\times 0.025\lambda _{0}$ at the operating frequencies of 28- and 39-GHz bands are presented for 5G and mm-wave small-cell application. Such package integration of 5G filters with ultrashort 3-D interconnects allows for low interconnect losses that are similar to that of on-chip filters, but low component insertion loss of off-chip discrete filters. These thin-film filters exhibit a cross-sectional height of $188.5~\mu \text{m}$ and can be utilized either as embedded components or integrated passive devices in module packages. Three topologies of LPF and BPF in total are modeled, designed, and fabricated on precision thin-film buildup layers on glass substrate as a core. Large-area panel-compatible semiadditive patterning (SAP) process is utilized to form high-precision topologies to aid the low-cost fabrication of ultraminiaturized filters. SAP also enables the realization of ultra-thin traces to precisely model high-impedance inductive lines compared to conventional subtractive etching and printing techniques. This results in filters with low insertion loss, low VSWR, and high selectivity. The simulated and measured results of filters show an excellent correlation.

Single-layer capacitively coupled structure integrated with substrate-integrated waveguide (SIW) is developed to design evanescent-mode bandpass filters. The planar gap-coupled structure is proposed as an alternative for the conventional inductive aperture-coupled one for filter excitation below the cutoff frequency of the SIW. The proposed planar capacitive excitation enables considerable miniaturization and resonates at a small fraction of a 3-D structure’s cutoff frequency. The proposed integration is analytically discussed using lumped-element equivalent circuit accompanied with experimental verification. Measured scattering parameters are compared to those of simulations, which demonstrate good agreement.

Split-type multiband bandpass filters (BPFs) and bandstop filters (BSFs) with input-reflectionless capabilities are reported in this letter. In the multiband BPF case, they consist of a duplexing network with a split-type multiband BPF channel—main channel—and its complementary resistively terminated multiband BSF channel—auxiliary channel—that absorbs the input-signal energy that is not transmitted by the overall filter. The multiband BSF counterpart is obtained from the latter by interchanging the roles of the main and auxiliary channels. The operational foundations, theoretical design rules, and synthesis examples of the devised split-type input-reflectionless multiband filters under a coupling-matrix-based formulation are described. Furthermore, for practical validation purposes, two microstrip prototypes corresponding to 3.85-/4.55-GHz second-order dual-band BPF and BSF circuits are constructed and measured.

This letter presents a novel hybrid spoof surface plasmon polariton (SSPP) and substrate integrated waveguide (SIW) filter, which has the broadband bandpass and wide out-of-band rejection features. The lower and upper cutoff frequencies of the passband can be independently adjusted by changing the structural parameters of the SSPP and SIW units, respectively. The dispersion curves of the SSPP and SIW units are analyzed and the influences of some structural parameters are investigated. A hybrid SSPP-SIW filter is fabricated based on the proposed method, and the measured passband is at 7.3–11.2 GHz with a relative bandwidth of 44%. The upper stopband rejection level is lower than −40 dB from 11.8 to 19.8 GHz.

[EN] A new topology of microwave filter based on sub- strate integrated waveguide (SIW) with alternating dielectric line sections is presented in this letter. The two alternating sections are waveguides without and with a dielectric material acting, respectively, as the inverters and the resonant sections of the pro- posed filter. This topology allows to easily design and manufacture compact filters with lower losses and higher rejection band than other available SIW realizations. For validation purposes, a prototype of a four-pole bandpass filter, based on alternating dielectric line sections, has been designed and manufactured, including successful experimental results., This work was supported in part by the Generalitat Valenciana Research Project under Grant PROMETEOII/2015/005, in part by the Ministerio de Educacion, Cultura y Deporte (Spain) through the Fellowship Program for Training University Professors under Grant FPU14/00150, and in part by the Ministerio de Economia y Competitividad (Spain) through the Research and Development Project under Grant TEC2016-75934-C4-1-R.

This letter demonstrates a design of a compact balanced bandpass filter (BPF) with stopband extension and common-mode (CM) suppression using asymmetric stepped-impedance resonator (SIR) pairs and a spoof surface plasmon polariton (SPP) feeding structure. The configuration of balanced SIR pairs is analyzed theoretically to obtain a wide stopband response and intrinsic CM suppression within differential-mode passband. Moreover, a novel SPP feeding structure is adopted as a low-pass filter and impedance matching section for enhancing filter transmission responses. Finally, a balanced BPF operating at 0.85 GHz with the SPP feeding structure is designed and fabricated to verify the design method.

This letter proposed a resistor-free absorptive common-mode filter (A-CMF). Also, a novel methodology of CM noise absorption is introduced. By making use of the dielectric loss of printed circuit board (PCB), CM noise is absorbed in the proposed A-CMF at 2.45 GHz without using surface-mount resistors. In this letter, an equivalent circuit model is built, analyzed, implemented, and fabricated on a four-layer PCB. Finally, the measured results are compared with the simulated ones, where a very good agreement can be found.

In this letter, a miniaturized differential substrate-integrated waveguide (SIW) bandpass filter with dual-band response has been illustrated. Two complementary split-ring resonators are etched on the top metal layer. According to the theory of evanescent-mode propagation, a differential-mode (DM) passband below the waveguide cutoff can be obtained. Next, the fundamental frequency of the SIW cavity can be tuned closely to the second harmonic by partially removing the dielectric material inside the SIW cavity which constructs another DM passband. With the proper positions of the feeding lines, the third harmonic can also be well suppressed. Moreover, good common-mode suppression has been achieved for the employment of the proposed balanced structure and the center frequencies of the two DM passbands can be flexibly controlled. A differential filter operating at 6.22 and 8.24 GHz has been realized and fabricated to validate the design idea.

Microwave planar balanced single-/dual-band bandpass filters (BPFs) with symmetrical quasi-reflectionless differential-mode behavior are presented in this letter. They are made up of a direct single-/dual-band BPF branch with virtually short-ended stubs in differential-mode operation, whose input and output accesses are loaded with stub-loaded-type single-/dual-band bandstop filter (BSF) branches that are terminated with a resistor. These BSF branches exhibit a quasi-complementary transfer function with regard to the one of the BPF branch and absorb the differential-mode input-signal energy not transmitted by the filter to achieve quasi-reflectionless capabilities. The theoretical foundations of the proposed balanced quasi-absorptive single-/dual-band BPFs and synthesis examples are given. Furthermore, for experimental-demonstration purposes, microstrip prototypes of 3-GHz second-order single-band and 2.85/3.15-GHz first-order dual-band BPFs are manufactured and characterized.

[EN] 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., This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness under Grant TEC2013-48036-C3-3-R and Grant TEC2016-75934-C4-1-R.

This letter proposes a new optimization technique for wiggly parallel-coupled line (PCL) structure design. Compared with other existing wiggly PCL design approach, our proposed technique does not require complicated math formula derivation and is able to consider several performance indexes simultaneously. We use our technique to design a compact ultra-wideband (UWB) microstrip bandpass filter (BPF) at 3.1–10.6 GHz for achieving low passband insertion loss and good linearity, and satisfying out-of-band rejection. This filter can be used in indoor and hand-held UWB systems.

A novel compact high-temperature superconducting low-pass filter (LPF) with an ultrawide stopband, excellent out-of-band rejection, and a low insertion loss is presented. This filter consists of a four-order LPF constructed by four interdigital hairpin stepped-impedance resonators (IHSIRs) and two pairs of radial stubs (RSs) in the input and output ports of the filter. The four-order IHSIR LPF brings transmission zeros for a high selectivity, and the RSs exhibit a characteristic of extending the LPF’s stopband effectively. The proposed LPF with cutoff frequency $f_{c}$ at 3 GHz is implemented on a 0.5-mm-thick MgO wafer with double-sided YBCO films. The measured results show a 30-dB harmonic suppression from $1.08f_{c}$ to $7f_{c}$ , a steep roll-off of 197.1 dB/GHz, and an in-band insertion loss less than 0.13 dB. Moreover, the LPF possesses a miniaturized size of $0.21\lambda _{\text {gc}} \times 0.03\lambda _{\text {gc}}$ .

A novel but very simple bandpass filter using just three pairs of coupled lines with multiple transmission zeros (TZs) and transmission poles is proposed in this letter. The filter structure can be seen as the two one-wavelength ring resonators coupled each other with $\lambda _{g}/4$ coupled length and sandwiched between the $3\lambda _{g}/4$ input and output feedlines. Good out-of-band suppression and sharp roll-off skirts can be realized by multiple fixed and tunable TZs without complicated coupling scheme. For further demonstration, a filter example with center frequency at $f_{0}= 2.1$ GHz is implemented with generation of eight TZs at the frequency range from 0 to $2f_{0}$ for theoretically calculated certification. Good agreement between simulation and measured results validates the design method.

A high-temperature superconducting wideband bandpass filter based on a triple-mode resonator is developed in this letter. A novel triple-mode resonator, which can not only generate a wide passband at low frequency but also suppress the harmonic responses and obtain a wide stopband, is proposed. To further improve the selectivity, we load two stubs at the input and output ports to generate one transmission zero at the low passband. The simulation results show that the filter is centered at 1 GHz ( $f_{c}$ ) with 111% 3-dB fractional bandwidth and has an upper stopband to 3.5 $f_{c}$ . The measured results show that the return loss is larger than 15 dB, and the insertion loss is less than 0.26 dB.