Suppression Of Spurious Responses Research Articles

Suppression of microstrip filter spurious responses using frequency-selective resistive elements

The spurious responses of microstrip filters were suppressed to extend the stop band. Even-order spurious resonances are suppressed using resistive loads at the voltage nodes of the fundamental resonance, which are the antinodes at the spurious frequency. Odd orders are removed using additional resonators which are deliberately lossy, and whose fundamental resonant frequency is equal to the spurious resonance of the main resonators. Equations for initial estimates for losses and required coupling coefficients are given. Of three filters designed and measured, two show 30 dB stop band attenuation, at the cost of only a small increase in pass-band loss and a small increase in substrate area.

Suppression of transverse-mode spurious responses for saw resonators on SiO2/Al/LiNbO3 structure by selective removal of SiO2

A SiO(2)/Al/LiNbO(3) structure has a large electromechanical coupling factor (K(2)) and good temperature coefficient of frequency (TCF) for applications as a SAW duplexer of the Universal Mobile Telecommunications System (UMTS) Band I. However, the SiO(2)/Al/LiNbO(3) structure also supports two unwanted spurious responses; one is caused by the Rayleigh mode and the other by the transverse mode. As the authors have previously discussed, the Rayleigh-mode spurious response can be suppressed by controlling the cross-sectional shape of a SiO(2) overlay deposited on resonator electrodes. In this paper, a new technique to suppress the transverse-mode spurious responses is proposed. In the technique, the SiO(2) overlay is selectively removed from the dummy electrode region. The spurious responses are analyzed by the laser probe system. The results indicate that the spurious responses in question were hybrid modes caused by the coupling between the main (SH) SAW and another (Rayleigh) SAW with different velocities. The hybrid-mode spurious behavior was dependent on the velocities in the IDT and the dummy regions (v(i) and v(d)). The hybrid-mode spurious responses could be suppressed by selectively removing SiO(2). Furthermore, the SAW energy confinement could be enhanced in the IDT electrode region when v(i) < v(d). The transverse-mode spurious responses were successfully suppressed without degrading the SAW resonator performances.

Spurious-response suppression of substrate integrated waveguide filters using multishape resonators and slotted plane structures

This article introduces effective techniques to improve the stopband frequency response of substrate integrated waveguide filters. First, a filter is constructed by using different cavity resonators which resonate at the same fundamental mode but at different high-order modes. A cascade connection of circular and rectangular cavities is used to separate high-order modes, because the second resonant mode of the circular cavities is more than rectangular ones. Second, inserting transverse radiating slots at the proper positions of cavities, their second longitudinal resonant modes are shifted down and effectively rejected. Third, four cells of slotted plane structure (SPS) are adopted to the top plane of the both input and output feed lines of the filter to reject the undesired passbands or improve steepness of the filter. Also, a combination of the radiation slots with SPS is used to reject the spurious responses accompanied by sharp steepness of the filter. Comparing between the measurement values and simulation results verifies the effectiveness of the proposed configurations and the hybrid technique. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.

Zero Temperature Coefficient of Frequency Surface Acoustic Wave Resonator for Narrow-Duplex-Gap Application on SiO2/Al/LiNbO3 Structure

In this paper, we describe a zero temperature coefficient of frequency (TCF) surface acoustic wave (SAW) resonator on a SiO2/Al/LiNbO3 structure. We studied the dependence of TCF and electromechanical coupling factor (K2) of shear-horizontal (SH) SAW on SiO2 thickness, where the SiO2 shape control technique is applied to suppress spurious responses caused by the Rayleigh mode. As a result, we could realize a high performance SAW resonator having moderate K2 (8%) and zero TCF with complete suppression of the Rayleigh-mode spurious response. We demonstrated that the SiO2 shape control technique is effective for suppression of the Rayleigh-mode spurious response in the SAW resonator using the SiO2/Al/LiNbO3 structure for a wide range of SiO2 thicknesses. We also revealed the applicability of the SiO2/Al/LiNbO3 structure to SAW duplexers with a narrow duplex gap.

Impedance matching and spurious-response suppression in stepped-impedance low pass filters

In this article, the method of least squares is used to design a stepped-impedance low pass filter with arbitrary specifications on the pass, transition, and stop bands, having different input and output impedances.The equivalent circuits of the line sections and step discontinuities are used (with appropriate dispersion relations) to determine the filter transmission matrix and the scattering parameters, which are then used to construct an error function. Its minimization is performed by the combination of particle swarm optimization and conjugate gradient methods. The conversion of lumped filter designs, by Butterworth, Chebyshev, and elliptic methods to the equivalent microstrip filters (namely conversion of L and C components to strip lines) may be difficult to realize. The proposed method of least squares procedure leads to the design characteristics having sharper transition bands and a wider pass band. The rectangular split ring resonators, as patterned ground plane, will remove the spurious responses in the stop band and actually increase the stop bandwidth. The results obtained by full-wave simulation softwares, fabrication, and measurements verify the proposed method for low pass stepped-impedance filter design. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26184

A Compact Microstrip Square-Loop Dual-Mode Balun-Bandpass Filter With Simultaneous Spurious Response Suppression and Differential Performance Improvement

A microstrip balun-bandpass filter (BPF) using capacitively loaded square-loop dual-mode resonator is proposed; it realizes not only simultaneous size reduction and spurious response suppression in filtering but also overall good differential performance of the balun. The phase and amplitude imbalance improvements due to the loaded resonator are also studied and verified by a prototype balun-BPF operated at 2.55 GHz with 3.5% fractional bandwidth. The experimental results reveal that size reduction of 47% and spurious suppressions of 30 dB beyond <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$1.5 f _{0}$</tex></formula> are achieved as compared to that of the conventional structure. The loading effect of the prototype balun-BPF reports 180.8 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex></formula> and 0.97 dB as phase and amplitude imbalances at the operating frequency respectively.

Spurious-response suppression in microstrip Parallel-Coupled bandpass filters by using Defected Microstrip Structures

This paper presents a novel Parallel-Coupled Microstrip Line (PCML) bandpass filter by etching of some slot resonators on the strip for suppressing the first spurious response. These slots perform a serious LC resonance property in certain frequency and suppress the spurious signals. Slot on the strip that is called Defected Microstrip Structure (DMS). The DMS interconnection disturbs the current distribution only across the strip, thereby giving a modified microstrip line with certain stop band and slow-wave characteristics. The measured results show a satisfactory rejection level more than 30dB at first spurious passband without affecting the passband response.

Analysis of Rayleigh-Mode Spurious Response Using Finite Element Method/Spectrum Domain Analysis for Surface Acoustic Wave Resonator on Nonflat SiO2/Al/LiNbO3 Structure

Because of their low insertion loss, high out-of-band rejection, and high power durability, miniature surface acoustic wave (SAW) duplexers are widely used in mobile phones. Substrate materials substantially limit and determine the performance of SAW duplexers; for their applications to Band I and Band IV systems with large pass-band widths and wide frequency separations between the transmitting and receiving frequency bands, a larger coupling coefficient (K2) is of primary importance. We have developed a shape-controlled SiO2 film/Al electrode/LiNbO3 substrate structure for their applications. It could lead to a large K2 and suppression of Rayleigh-mode spurious response. In this paper, we report the analysis using finite element method/spectrum domain analysis (FEM/SDA) for the SAW resonator on a nonflat SiO2 film/Al electrode/LiNbO3 structure. It was clarified that the shape-controlled SiO2 was effective in terms of achieving a large K2 for the SAW resonator with suppressed Rayleigh-mode spurious responses and bulk wave radiation. Furthermore, the experiment results showed a good agreement with the analysis results.

Design of Dual-Passband Microstrip Bandpass Filters With Multi-Spurious Suppression

A systematic design method for microstrip bandpass filters with both dual-passband response and multi-spurious suppression is proposed in this letter. The filter is composed of stepped impedance resonators (SIRs). A novel asymmetric SIR structure is proposed to effectively increase the degree of freedom in the dual-passband bandwidth design. As a consequence, the transmission zero of the coupling stage could be used to suppress the unwanted higher order spurious responses. A complete design procedure considering both the synthesis of passband responses and the suppression of spurious responses is also depicted in detail. A fifth order filter is designed and fabricated to demonstrate this idea. The measured results show that the upper stopband can have an attenuation level near 30 dB up to more than 20 GHz (8.16 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ).

A semi-lumped microstrip UWB bandpass filter

In this paper, a miniaturized bandpass filter for ultra-wide-band applications is proposed. It is based on the embedding of high-pass structures in a low-pass filter. A semi-lumped technology combining surface-mounted capacitors and transmission lines has been used. The filter design rules have been carried out. Furthermore, two filters having a 3-dB fractional bandwidth of 142 and 150%, centered at 0.77 and 1 GHz, respectively, have been realized for a proof of concept. Measured characteristics, in good agreement with simulations, show attractive properties of return loss (|S11| &lt;−18 dB), insertion loss (&lt;0.3 dB), and a maximum group delay and group delay variation of 2 and 1.3 ns, respectively. A distributed filter based on the same low-pass/high-pass approach has been also realized and measured for comparison. The size reduction reaches 85% for the semi-lumped filter, and its selectivity is improved with a shape factor of 1.3:1 instead of 1.5:1. The semi-lumped filter's drawback is related to a smaller rejection bandwidth compared to the distributed one. To improve the high-frequency stopband, an original technique for spurious responses suppression based on capacitively loaded stubs has been proposed. Even if the performances do not reach that obtained for the distributed approach, with this technique spurious responses are pushed until eight times the center frequency. A sensitivity study vs. critical parameters has also been carried out, showing the robustness of the design.

Compact Ultra-Wideband Bandpass Filter Using Dual-Line Coupling Structure

This letter presents a novel compact ultra-wideband (UWB) microstrip bandpass filter with spurious response suppression. A dual-mode ring resonator is constituted to allocate its first two resonant frequencies in the UWB band, and the dual-line parallel-coupled structure is used in this compact UWB filter, which is expected to achieve much tighter coupling degree. Simulated and measured results are found in good agreement with each other, showing a wide passband from 4.9 to 10.9 GHz, 15 dB return loss bandwidth of about 5 GHz, minimum insertion loss of 0.49 dB at 7.3 GHz, and wide upper stopband with more than 20 dB attenuation up to 20 GHz.

Spurious-Response Suppression in Microstrip Parallel-Coupled Bandpass Filters by Grooved Substrates

Application of the grooved substrate is presented to suppress the first spurious response of microstrip parallel coupled-line filters. The grooves are oriented parallel to all coupled lines and just next to them. It is shown that the grooves equalize the even- and odd-mode phase velocities in microstrip coupled lines and, therefore, suppress the spurious response. Sets of design graphs are derived for various depths of the grooves and the curves of equal even/odd-mode phase velocities are shown. Design equations based on well-known arbitrary image impedances are reviewed and the image impedances are optimized according to the design graphs. This eventually makes it possible to select the even/odd-mode characteristic impedances for each section of the filter as close as possible to the phase velocity equalization curve. Finally, an equal ripple filter of order 3 is designed using the proposed method. The grooves were simply machined and the measurement shows a rejection of more than 35 dB in the first spurious response, as predicted in simulated results.

The Design of Coupled Resonator Bandpass Filter With Wide Stop-Band

A compact four-pole bandpass filter with multi-order spurious response suppression is proposed. The combination of dissimilar resonator structures with the same fundamental frequency but with different spurious frequencies may improve the stop-band rejection by the mutual cancellation of spurious responses. The measured results show that better than -20 dB rejection levels in the stop-band up to 4.5 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> have been obtained. Moreover, an embedded-resonator topology is used, which makes the structure of filter to be more compact.

Performance improvement and size reduction of microstrip dual-mode bandpass filter

A novel miniaturised dual-mode bandpass filter with multi-arc resonators is proposed. The size of the dual-mode filter can be reduced significantly by using the microstrip dual-mode resonator consisting of multi-arcs; meanwhile insertion loss and spurious response suppression are improved. A prototype filter is designed and implemented at 3.6 GHz with 2.8% fractional bandwidth, which shows a low passband insertion loss of 1.02 dB and a wide stopband with rejection better than 20 dB up to about 8.5 GHz.

NOVEL MICROSTRIP HAIRPINLINE NARROWBAND BANDPASS FILTER USING VIA GROUND HOLES

In this paper, we present a novel improved hairpinline microstrip narrowband bandpass filter with via ground holes. The new filter design methodology is derived from conventional hairpinline filter design. This design methodology incorporates use of λ/8 resonators, thereby reducing the size of the filter by 35% as compared to the conventional design. An analysis is presented to show the effects of tap point height and microstrip width on fundamental parameters of filter and subsequent relationships are developed. Through use of via ground holes and a wider microstrip line for resonators, 3 dB Fractional Bandwidth (FBW) less than 2%, Insertion Loss (IL) less than 1.6 dB and Return Loss (RL) better than 40 dB is achieved with midband center frequency 1 GHz. Spurious response suppression is achieved till 3f0. Robustness of this design approach is demonstrated by designing filters on two more substrates having er 2.17 and 9.2. As low as 0.48% FBW was achieved by using different substrates. The design approach is successfully tested for center frequency upto 2 GHz beyond which folding the resonator becomes practically difficult. Finally, a bandpass filter is designed with this design methodology and fabricated using FR4 substrate. S-parameter measurements show a good agreement with the simulated results.

A novel compact CPW bandpass filter with spurious response suppression

AbstractIt is an important issue to suppress the spurious response of the coplanar‐waveguide (CPW) bandpass filter (BPF). In this letter, a novel CPW BPF at 1.57 GHz with spurious responses suppression for application in Global Positioning System is presented. By adjusting the filter structure, the wide stopband rejection greater than 20 dB from 1.8 to 4.5 GHz could be obtained away from the designed central frequency without increasing the circuit dimension. The designed CPW‐BPF is investigated numerically and experimentally. Measured results show a good agreement with the simulated analysis. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2941–2944, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22898

Novel bandpass filter with size reduction and harmonic suppression

AbstractA novel microstrip bandpass filter with size reduction and harmonic suppression is proposed in this article. The filter is based on microstrip open loop resonators with coupled open stubs. By adding coupled open stubs to open loop resonator, extra controllable transmission zero can be obtained. The extra transmission zero can be tuned at the second harmonic frequency to suppress spurious response. When compared with the conventional microstrip open‐loop bandpass filter, this filter could achieve size reduction and spurious responses suppression simultaneously. A demonstration filter was designed, fabricated, and measured. Theoretical and experimental results are presented and show good agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 914–916, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22323

Dual‐mode microstrip bandpass filter with spurious response suppression

AbstractA dual‐mode bandpass filter (BPF) using microstrip patch resonator is proposed. Open‐stubs are added on the feed‐lines to suppress the spurious response and improve the stopband rejection effectively with little increase in circuit size. Furthermore, a reduced‐size dual‐mode BPF with spurious response suppression using microstrip slotted‐patch resonator is successfully designed. The simulated and measured results are presented and both are in good agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 556–558, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22190

Spurious responses suppression of parallel coupled-lines microstrip bandpass filters: Comparison and improvements of planar approaches

In this paper, three methods to reject the first spurious harmonic in parallel-coupled microstrip filters are investigated. The authors proposed an extension of these approaches to also suppress the second unwanted passbands while keeping the initial passband practically unchanged. Then, two of these techniques are combined to achieve a wider upper stopband. Indeed, the sinusoidal perturbation technique is well combined with overcoupled end sections to reject the first three spurious passbands of an order three filter. A comparison of simulations and experimental results is made, with a discussion on each method efficiency and possible applications to higher order filters. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2007.

A novel microstrip square-loop dual-mode bandpass filter with simultaneous size reduction and spurious response suppression

In this paper, a new capacitively stepped-impedance resonator(CSIR) is proposed to develop the microstrip square-loop dual-mode bandpass filter. Using this new design, simultaneous size reduction and spurious response suppression for the dual-mode bandpass filter can be achieved. An analytical formulation of this novel resonator is given in order to elucidate the spurious frequencies relocation design. Together with this formulation, a generalized dual-mode bandpass filter model is developed so as to ease the analysis of transmission zero and insertion loss. A prototype filter is designed at 900MHz with 1.5% fractional bandwidth. Significant spurious suppressions up to 33 and 35 dB are measured at 1.8 and at 2.7 GHz, respectively. A circuitry size reduction of 54% is achieved when compared with that of the conventional structure. Moreover, the CSIR allows frequency tuning and, thus, a varactor-tuned filter is designed and a measured tunable center frequency between 1.5-1.62GHz is demonstrated. Utilizing the proposed structure, not only size reduction,as well as spurious response suppression, but also center frequency tuning can be achieved.