Passband Insertion Loss Research Articles

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.

Micromachined Filters at 450 GHz With 1% Fractional Bandwidth and Unloaded <italic>Q</italic> Beyond 700

This letter presents two silicon-micromachined narrowband fourth-order waveguide filter concepts with center frequency of 450 GHz, which are the first narrowband submillimeter-wave filters implemented in any technology with a fractional bandwidth as low as 1%. Both filters designs are highly compact and have axial port arrangements, so that they can be mounted directly between two standard waveguide flanges without needing any split-block interposers. The first filter concept contains two TM110 dual-mode cavities of circular shape with coupling slots and perturbations arranged in two vertically stacked layers, while the second filter concept is composed of four TE101 series resonators arranged in a folded, two-level topology without crosscouplings. Prototype devices are fabricated in a multilayer chip platform by high-precision, low-surface roughness deep-silicon etching on silicon-on-insulator wafers. The measured passband insertion loss of two prototype devices of the dual-mode circular-cavity filters is 2.3 dB, and 2.6 dB for three prototypes of the folded filter design. The corresponding extracted unloaded quality factors of the resonators are 786 ± 7 and 703 ± 13, respectively, which are the best so far reported for submillimeter-wave filters in any technology. The presented filters are extremely compact in terms of size; their footprints have areas of only 0.53 and 0.55 mm2, respectively, and the thickness between the waveguide flanges is 0.9 mm.

Microstrip Compact Twin-Interdigital Steped Impedance Resonator-Based Bandpass Filter for C-Band Applications

This research focuses a new microstrip twin-interdigital type bandpass filter based on stepped impedance resonator (SIR) structure. The proposed structure consists of two slightly different interdigital capacitances within a single SIR resonator that behaves as a bandpass filter (BPF) of center frequency 4.3 GHz with 700 MHz bandwidth at 3 dB pass band. This design is not only subjected to size reduction, but also low pass-band insertion loss and high return loss as well. The Sonnet software tool has been used to design and simulate the microstrip BPF. The fabricated BPF was measured using the Agilent 8510C vector network analyzer (VNA) and achieved the insertion loss of 0.5 dB and the return loss of 26 dB. The measured results were compared with those simulated results which were very close to each other. The fabricated BPF can be used for Cband Applications.

A compact planar diplexer based on via-free CRLH TL for WiMAX and WLAN applications

AbstractIn this paper, design and development of a via-free composite right/left handed transmission line (CRLH TL)-based diplexer for WiMAX and WLAN bands is reported. The diplexer is having two channels, where each channel consists of a separate bandpass filter (BPF). The BPF of both channels are designed on via-free CRLH TLs based on a newly proposed right-angled corner-modified split ring resonator (RAC-MSRR) structure. The RAC-MSRR incorporates meander paths because of which working scope of frequencies is focused for measured center frequencies (f1) 3.5 GHz with −3 dB fractional bandwidth (FBW) of 21.21% (BPF1 channel) and (f2) 5.6 GHz with −3 dB FBW of 13.29% (BPF2 channel). For diplexer design, T-section is used for joining two BPFs which results in very good isolation of more than 32.5 dB over the frequency band of 2.5–8.0 GHz. The designed diplexer has passband insertion loss of −0.87 dB at f1 and −1.25 dB at f2. Overall size of the fabricated diplexer including 50 Ω feed line is 18 × 15 mm2. Equivalent lumped circuit model parameters of the diplexer are obtained from the pseudo-inverse matrix technique. Measured results show good concurrence with simulated results and subsequently approve the proposed model design.

Compact D-CRLH resonator for low-pass filter with wide rejection band, high roll-off, and transmission zeros

AbstractA compact low-pass filter (LPF) with wide rejection band based on T-type circuit of an enhanced dual composite right-/left-handed (D-CRLH) resonator is presented in this paper. The resonator has only one cell with series and parallel tank circuit. The parallel LC tank circuit has been realized by an interdigital capacitor and one shorted finger, whereas its series LC tank circuit is realized by an air gap capacitance and a short circuit stub. The filter has wide rejection band bandwidth with three transmission zeros (TZs). The filter bandwidth and TZs frequencies are controlled by the D-CRLH element values. The results of the proposed filter demonstrate minimum insertion loss in passband, high roll-off rate, and good figure of merit. The measured results are in good agreement with the simulated results. The detailed filter design is discussed in terms of circuit modeling, dispersion analysis, and full-wave simulation. Finally, the filter size is compact (0.10 λg × 0.15 λg) at cut-off frequency.

A Compact and High-Isolated Multiresonator-Coupled Diplexer

A compact and high-isolated microstrip diplexer by using multiple-coupled resonators with separated electric and magnetic coupling paths and dual-mode characteristic has been presented. Multiple transmission zeros have been obtained, and some of them can be controlled by the electric and the magnetic couplings. The diplexer has been fabricated and measured, and the design has been demonstrated. The developed diplexer has a measured passband insertion loss of not more than 2.15 dB, a measured isolation of more than 38 dB, and a compact circuit size of $0.66\lambda _{\mathrm{g}} \times 0.15\lambda _{\mathrm{g}}$ at the lower frequency band.

A compact dual-band bandpass SIW filter using uniplanar combination of the CRLH and resonant type metamaterials

ABSTRACTA new manner of obtaining dual bandpass behaviour in substrate-integrated waveguide (SIW) using a uniplanar combination of composite right/left-handed (CRLH) transmission line and complimentary double split single ring resonator (CDSSRR) is presented and analysed in this paper. The proposed dual band structure has the advantage of miniaturisation due to the presence of both the passbands below the characteristic cutoff frequency of the SIW.A high passband transmission zero overcomes the poor frequency selectivity, and the two resonant frequencies are independently controllable. There are very low insertion losses in both passbands as compared to DGS structures and fabrication simplicity is ensured due to an intact ground. The potential for application of the proposed structure to the design of completely planar miniaturised dual band bandpass metamaterial filters has been verified by fabricating a two-stage filter based on the proposed combination. The measured results are in good agreement with the simulation results.

Continuous frequency and bandwidth tunable combline cavity bandpass filters with internally mounted motors

Novel design methods for implementing continuous centre-frequency and bandwidth tunability are reported. Coupling bandwidths are tuned through the mechanical rotation of a metallic plate suspended between resonators. Centre-frequency tuning is achieved via the vertical actuation of a moving part mounted within each resonator. In addition, each resonator and transformer is designed so that motors can be housed within them – adding tunability without compromising the overall filter volume. A second-order filter, based on combline cavity structures, capable of bandwidth tunability of 49–67 MHz for all centre frequencies in the range of 1.751–1.998 GHz is presented. Passband insertion loss is kept below 1.2 dB for all tuning states with return loss above 10 dB. A five-pole filter is also fabricated with centre-frequency tunability of 14% from 1.764 to 2.015 GHz and 15 dB bandwidth tunability of 107% from 41 to 85 MHz. Midband insertion loss is kept below 1.4 dB in all tuning states. The five-pole filter is compared to other tunable filters in the UHF range and is shown to reduce midband insertion loss by 36% from the next best filter (2.2–1.4 dB).

Compact Microstrip IF Lossy Filter With Ultra-Wide Stopband

A novel compact six-pole intermediate frequency lossy filter based on double-layer microstrip coupled microstrip resonators is proposed in this paper. A detailed theoretical analysis for the performance operation mechanism is illustrated. Significant advantages of the proposed structure over existing lossy filters include its low passband insertion loss variation, compact footprint, and ultra-wide stopband bandwidth. Excellent experimental results are provided to confirm these improvements, by using LCP bonded PCB multilayer technology. In general, the fabricated prototype filter operates at 0.97 GHz, with 0.19-dB insertion loss variation in the passband. In addition, it obtains a sharp selectivity with a pair of transmission zeros, as well as the 10th harmonic suppression with better than the 32-dB rejection level. Good agreement between the measured and simulated results can be observed finally.

Wiggly Parallel-Coupled Line Design by Using Multiobjective Evolutionay Algorithm

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.

Reduction of Passband Insertion Loss for a Dual Band Bandstop Filter

Reduction of Passband Insertion Loss for a Dual Band Bandstop Filter

Design and characterisation of dual‐mode suspended‐substrate stripline filter

A new design technique of a dual-mode ring-resonator suspended-substrate stripline filter is reported here to achieve low passband insertion loss, high quality factor, and good spurious response. A fourth-order bandpass filter was designed and fabricated at the operational frequency of 2.07 GHz with two ring resonators packaged in a metallic cavity where each ring resonator is one wavelength long. The transmission zeros of the dual-mode filter are generated due to the phase cancellation between the two paths in a ring, thus a sharp-skirt selectivity filter response was achieved. Perturbation notch structure was implemented on each ring resonator to provide the electromagnetic coupling of two degenerate modes, thus a dual-mode response of the filter can be synthesised. Measurement results of the first dual-mode filter prototype showed a return loss and an insertion loss of better than 16.42 and 0.926 dB, respectively, while an out-of-band rejection of up to 55 dB was achieved. The novel filter design technique proved that no cross-coupling is required to obtain the transmission zeros of the filter, thus the sharp-skirt response was achievable.

A New Compact and Wide-band Band-stop Filter Using Rectangular SRR

This paper proposes a novel compact band-stop filter based on Rectangular SRR unit cell. The BSF structure consists of modified microstrip line connected to 50 Ω feed line on both sides and Rectangular-SRR which has been added and located in the center of the proposed design. The R-SRR dimensions are chosen and optimized in order to achieve a resonant frequency in the undesired band. This filter is designed, simulated and optimized using two electromagnetic solvers. The circuit performances have been investigated and found to have an excellent BSF characterized by high power rejection level in the stop-band, low insertion loss in the both pass-bands and compact size. The experimental results illustrate that the proposed BSF achieves a wide fractional bandwidth of 72 % at 2.2GHz.

Design of a Suspended Stripline Narrow Bandpass Filter with Ultrawideband Harmonic Suppression

A design method of narrow bandpass filters (NBPFs) of 4–6% bandwidth with ultrawideband suppression of harmonic passbands, utilizing two cascaded step impedance resonators (SIRs) in a suspended stripline, is proposed in this paper. The proposed design utilized the characteristics of a suspended stripline, which provides a much higher characteristic impedance ratio as compared with that of the microstripline, enabling ultrawideband harmonic suppression. As an example of the NBPF, a filter with a passband center frequency f0 of 0.75 GHz and bandwidth of 5% was implemented and proved to suppress the harmonic passbands up to 13.5 f0. Since the proposed filter was implemented on the suspended stripline, the passband insertion loss was only −0.9 dB, which is low as compared with other previous designs. The proposed filter is a compact high-performance low-loss NBPF, which can be applicable to various wireless systems.

WR-3 Waveguide Bandpass Filters Fabricated Using High Precision CNC Machining and SU-8 Photoresist Technology

This paper presents two WR-3 band (220–325 GHz) filters, one fabricated in metal using high precision computer numerically controlled milling and the other made with metallized SU-8 photoresist technology. Both are based on three coupled resonators, and are designed for a 287.3–295.9-GHz passband, and a 30-dB rejection between 317.7 and 325.9 GHz. The first filter is an extracted pole filter coupled by irises, and is precision milled using the split-block approach. The second filter is composed of three silver-coated SU-8 layers, each 432 μm thick. The filter structures are specially chosen to take advantage of the fabrication processes. When fabrication tolerances are accounted for, very good agreement between measurements and simulations are obtained, with median passband insertion losses of 0.41 and 0.45 dB for the metal and SU-8 devices, respectively. These two filters are potential replacements of frequency selective surface filters used in heterodyne radiometers for unwanted sideband rejection.

Unequal termination impedance parallel-coupled lines band-pass filter with arbitrary image impedance

This paper presents an analytical design for a microstrip parallel-coupled line bandpass filter (BPF) with arbitrary termination and image impedances. Using the proposed design formulas, multistage arbitrary termination impedance BPFs can be designed with a very high impedance transforming ratio (r). The fractional bandwidth and return losses are maintained even though the r and image impedance are varied. To validate the design formulas, two- and three-stage BPFs are fabricated and measure at the center frequency (f0) of 2.6 GHz. The filter 1 and filter 2 are designed with termination impedances of 50–300 Ω and 20–50 Ω, respectively. The measured results of both filters show a good agreement with the simulations. The measured passband insertion and return losses of filter 1 are better than 0.8 and 19.6 dB, respectively. Similarly, the measured passband insertion and return losses of filter 2 are better than 1.5 and 19 dB, respectively.

Novel Differential Dielectric Waveguide Filter Using Spatial Coupling Mechanism

This letter presents a novel differential dielectric waveguide (DW) filter using a spatial coupling mechanism. The DW resonator operating in TE $_{20\delta }$ -mode is reasonably cut and applied to the design of compact differential filter. Different from the traditional DW filter, the coupling between the DW resonators can be fulfilled by placing the cut planes of the DW resonators face-to-face in an open space. Meanwhile, the proposed differential filter can work well whether the employed DW resonators have the common ground plane or not, leading to a high flexibility. For demonstration, two kinds of differential DW filters with and without the common ground plane are designed and measured, and their simulation and measured results are presented. Both of them showcase high performance, such as low insertion loss of the differential-mode passband and good common-mode suppression.

Multistage second-order microring-resonator filters with box-like spectral responses and relaxed fabrication tolerances * * Project supported by the National High Technology Research and Development Program of China (Nos. 2015AA017001, 2015AA010103) and the Natural National Science Foundation of China (NSFC) (Nos. 61235001, 61575187, 61535002, 61204061, 6157031748, 61377067).

We demonstrate an optical filter based on multistage second-order microring resonators (MRs) with box-like spectral responses. Compared with single-stage high-order optical filters with the same number of MRs, the demonstrated structure has comparable performances in the aspects of passband flatness, rolling-off slope and insertion loss. Moreover, the architecture relaxes the fabrication tolerance, electrical wiring and tuning difficulty since there are only two MRs in each stage. We experimentally demonstrate this kind of optical filter with five stages, which shows a 3-dB bandwidth of ~17 GHz, a rolling-off slope of ~5 dB/GHz and an on-chip insertion loss of ~6 dB.

A Compact Tri-Band Bandpass Filter with High Out-of-Band Rejection

This paper presents a planar tri-band bandpass filter with high out-of-band rejection over a wide band. The filter is based on two pairs of λ/4 resonators embedded inside an open loop ring resonator without any size increase, where each pair of resonators are electromagnetically coupled to each other and the feedlines. This results in the excitations of passbands, where the first passband is generated by the open loop resonators. The second and the third passbands are excited by λ/4 resonators. The proposed technique provides sufficient degrees of freedom to control the center frequency and bandwidth of the three passbands independently. In addition, the six transmission zeros created around the passbands results in a tri-band filter with high selectivity, sharp 3 dB cut-off frequency, high isolation, low passband insertion-loss and high out-of-band harmonic rejection across an ultra-broadband frequency range up to 17 GHz. The proposed technique has the ability to switch from triple to dual band by removing one pair of the inner resonators. Design methodology and simulation results of the filter are provided.

Two-Layered Substrate Integrated Waveguide Filter for UWB Applications

In this letter, an ultra-wideband (UWB) substrate integrated waveguide (SIW) filter using ridge resonator is presented. The filter relies on designing SIW ridge resonator. The comb-shaped resonator makes the filter to be realizable for UWB characteristics. The upper edge of the passband can easily be adjusted by the width of small rod in the ridge resonator. A parametric study is done to show how bandwidths can be adjusted. The measurement results show that a reflection coefficient of better than −14 dB has been obtained over the frequency band of 3.1–10.6 GHz. The maximum insertion loss in passband is almost 1 dB. Moreover, a stopband from 11.4 to 17.4 GHz with a suppression magnitude better than 47 dB has been achieved.