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This paper presents a direct synthesis procedure for efficient design of a class of ultra-wideband bandpass filters with composite series and shunt transmission-line stubs. The proposed single-stage bandpass prototype is formed by cascading two sets of series open-ended and shunt short-ended stubs through a multisection nonuniform transmission line. All the stubs are set with an identical electrical length, i.e., [[theta].sub.c], at lower cutoff frequency [f.sub.c] and the middle connecting line is composed of stepped-impedance transmission line with i sections, and each section has an electrical length [[theta].sub.c]. The proposed filter topology aims to construct an ultra-wide bandpass filter with Chebyshev equal-ripple responses and (i + 3) in-band transmission poles. Based on the derivation of the transfer function, a synthesis approach is established and systematically described to design this type of filters according to the specifications such as lower/upper cutoff frequencies. Next, a multistage bandpass filter prototype is proposed and the synthesis design procedure is also presented. The implementation is achieved by using hybrid microstrip line and slotline sections. Compared with traditional stub filters, the proposed filters achieve higher order transmission zeros and thus provide higher selectivity. As design examples, two single-stage and one three-stage bandpass filters are designed and fabricated to confirm the theoretical predictions. Index Terms--Bandpass filter, equal-ripple response, multistage, series/shunt stubs, single stage, synthesis design, ultra-wideband.

In this paper, a new concept for a dual-mode dielectric resonator is presented, which is based on TM-mode operation in dielectric rods. By arranging the dielectric rods in Y-shape configuration, new fundamental eigenmode resonances are found to be present. The eigenmodes are coupled parallel to the input and output of the filter to result in a doublet coupling scheme. The filter was laid out by the global eigenmode approach. For filter configurations showing E-plane/H-plane mirror symmetry, the required parameters are determined and optimized by an eigenmode solver. A nonplanar Y-shape monoblock ceramic was constructed to achieve bandpass operation at 2 GHz. Measurement results of the constructed dual-mode filters are presented for the first time. The setup is suitable to demonstrate the zero-shifting property of the doublet by slightly adjusting the position of the ceramic inside the cavity. An unloaded quality factor of 4000 was extracted from the measurements. Good agreement between measured and computed results is obtained. Index Terms--Bandpass filters, dielectric resonator filters, dual-mode filters, transmission zeros.

This paper proposes a circuit topology which reduces the chip size of single-pole-double-throw (SPDT) quarter-wavelength bandpass filter-integrated switches (FIS). A 40-GHz mHEMT MMIC SPDT switch has been implemented and demonstrates a measured insertion loss lower than 1 dB and an isolation better than 30 dB. Another 50-GHz pHEMT MMIC SPDT achieves 1.5 dB insertion loss and 22 dB isolation. The low insertion loss and high isolation shows that the circuit performance is improved along with the reduction of the size. The systematic design approach of the reduced-size FIS is described, together with the analysis of the insertion loss and isolation. Index Terms--Filters, reduced-size, single-pole-double-throw (SPDT), switches.

A simple dual-bandpass filtering structure is proposed. The filter is implemented by means of a new hybrid waveguide-microstrip technology. The novelty of the structure is that it combines two standard printed microstrip coupled fine resonators, with a resonance of the base waveguide cavity, to implement a dual-band operation. Important aspects about the filter design, useful for practical applications are treated. This includes a study on the maximum coupling that can be achieved to the cavity resonance, and guidelines to control the positions of the two passbands and the transmission zeros. Besides, an example has been designed, manufactured and tested. The measurements on the fabricated prototype have confirmed the validity of the new structure to perform dual-band operation. Index Terms--Dual-band filter synthesis, dual-band filters, hybrid waveguide-microstrip technology, microstrip resonators, microwave filter.

A new coupling scheme for microstrip bandpass filters with quarter-wavelength ([lambda]/4) stepped-impedance resonators is proposed. In the proposed coupling scheme, two adjacent [lambda]/4 stepped-impedance resonators are coupled by directly connecting an admittance inverter between them. By properly designing the connecting position, one may adjust the coupling coefficient between two resonators so that narrow to broad bandwidth filters may easily be fabricated without coupling gaps. Here, the admittance inverter is realized by a [lambda]/4 stepped-impedance fine. Based on the proposed coupling scheme and the conventional magnetic coupling structure, the filters with narrow or wide bandwidth may be designed and implemented. In addition, folded fines are adopted to make the filter size compact. In this study, a two-pole filter with a 3-dB bandwidth of 5.1% and two four-pole filters with 3-dB bandwidths of 33% and 51% are successfully fabricated. Good agreement between measured and simulated results is observed. Index Terms--Microstrip bandpass filter, quarter-wavelength ([lambda]/4) resonator, stepped-impedance resonator.

Miniature, light weight and low-loss filters are important components for wireless and mm-wave applications. Here, we present a novel implementation of integrated cavities on a thin-film technology with through-substrate vias on 100/[micro]m thick high-resistivity wafers. A 60 GHz horizontally integrated cavity bandpass filter is demonstrated. The filter has an insertion loss of 1.5 dB, a relative bandwidth of 6% and excellent agreement between simulations and measurements is obtained, even in terms of insertion loss. The measured unloaded quality factor is used to demonstrate that the losses in high-resistivity silicon are mainly due to dielectric damping rather than bulk conductivity at millimeter wave frequencies. A feeding point is presented for the excitation of rectangular cavities that greatly increases the attenuation of the filter at the higher frequency band by preventing the second order mode to be excited within the cavities. Finally, a size and performance comparison is made between this filter and a microstrip coupled lines filter in the same technology. The thin-film technology also integrates high-Q inductors, high-density capacitors and resistors. Active circuits can also be included by means of flip chip and therefore, the technology allows the implementation of a novel architecture for millimeter wave transceivers. Index Terms--Bandpass filter, high-resistivity silicon (HRSi), integrated cavities, system in a package (SIP), thin film.

The long-tail transient responses of a bandpass network to pulsed and switched-tone stimuli are examined and a time-domain closed-form expression of the envelope response is developed. It is shown that the long-tail response leads to interference in frequency-hopping communication systems. Interference, and in particular co-site interference, can result in any radar, communication, or RF sensor system becoming exposed to unintentional pulsed RF signals. In the experimental study, 900-MHz Chebyshev bandpass filters are considered. Index Terms--Bandpass filters, communication system performance, filter distortion, frequency hop communication, time-frequency analysis, transient response.

A yttrium iron garnet/gadolinium gallium garnet-gallium arsenide (YIG/GGG-GaAs)-based magnetically-tunable wideband microwave band-pass filter with large tuning ranges for the center frequency (5.90-17.80 GHz) and the bandwidth (1.27-2.08 GHz) in the pass-band using a pair of cascaded band-stop filters is reported. The design and numerical simulation of the band-pass filter that incorporates multisegment microstrip meander-lines and 2-D nonuniform bias magnetic fields were first carried out using Ansoft High Frequency Structure Simulator (HFSS) software suite. The measured transmission characteristics of the band-pass filter at center frequency of 8.28 GHz, using 2-D nonuniform bias magnetic fields centered at 2,750 Oe and 4,150 Oe facilitated by Nd-Fe-B permanent magnets, shows a -3-dB bandwidth of 1.73 GHz, an out-of-band rejection of -33.5 dB, and an insertion loss of -4.2 dB. A good agreement between the simulation and experimental results for the band-pass filter in the center frequency and the bandwidths of the pass-band and the two guarding stop-bands has been accomplished. Index Terms--Bandpass filters, bandstop filters, ferromagnetic resonance (FMR), tunable filters, yttrium iron garnet (YIG) filters.

In this paper, several mathematical models that are more realistic representations of mechanical bandpass filters are studied. Such filters can be used in energy scavengers to convert energy from vibration sources into small amount of electricity. A mechanical bandpass filter is an ensemble of cantilever beams where at the tip of each beam a mass, known as the proof mass, is mounted. A beam with a proof mass at its tip is called a beam-mass system. By studying a variety of models representing the filter dynamics, it will be unraveled to what extent fabrication errors in beam-mass systems of a filter and/or the coupling of such systems can alter the bandpass behavior of a fabricated filter. [DOI: 10.1115/1.2950056] Keywords: bandpass behavior, coupling of filter components, energy scavenging, fabrication errors, mechanical bandpass filters

We demonstrate a new class of bandpass frequency selective surface (FSS), the building block of which, unlike the traditional FSSs, makes use of resonant dipole and slot structures that have dimensions much smaller than the operating wavelength. This design allows localization of bandpass characteristics to within a small area on the surface which in turn facilitates flexible spatial filtering for an arbitrary wave phasefront. The proposed FSS is made up of periodic array of metallic patches separated by thin air-gaps backed by a wire mesh having the same periodicity (<< [lambda]). The array of metallic patches constitute a capacitive surface and the wire mesh a coupled inductive surface, which together act as a resonant structure in the path of an incident plane wave. Like traditional FSSs, the capacitive and inductive surfaces of the proposed FSS can easily be fabricated using printed circuit technology on both sides of microwave substrates. It is shown that by cascading such bandpass surfaces in a proper fashion, any arbitrary multipole filter or non-commensurate multiband response can be obtained. The frequency response of the proposed miniaturized-element frequency selective surface (MEFSS) is demonstrated for various incident angles and it is shown that one-pole designs are less sensitive than two-pole designs to the angle of incidence. Dual band designs are also possible based on two-pole designs, but are more sensitive to incident angle than single band designs because of their larger (in terms of wavelengths) spacing. Prototypes of single-pole and dual-pole MEFSSs are fabricated and tested in a waveguide environment at X-band frequencies and excellent agreements between the measured and simulated results are demonstrated. Index Terms--Bandpass radome, frequency selective surfaces (FSSs), spatial filter.

A state-space approach to estimating intermodulation distortion in bandpass [G.sub.m]-C filters with fully balanced, weakly nonlinear transconductors is introduced. It results in compact analytic expressions applicable to [G.sub.m]-C filters of any order. For verifying the theory, two [G.sub.m]-C filters with fully balanced weakly nonlinear transconductors have been designed using Cadence. They have been simulated in SpectreS as well as modeled and simulated in Simulink. Theory and simulation results are found in good agreement. Index Terms--Bandpass, circuit analysis, continuous-time filter, distortion model, fast algorithm, fully balanced, fully differential, [G.sub.m]-C filter, intermodulation distortion (IMD), perturbation, state-space model, weak nonlinearity.

This paper presents a scheme to accurately tune the quality factor of second-order LC bandpass filters. The information of the magnitude response at the center and one of the cutoff frequencies is used to tune both the amplitude and the quality factor of the filter using two independent yet interacting loops. Furthermore, the synergic interaction between the loops makes the proposed scheme stable and insensitive to the mismatch between the input amplitudes. A chip prototype was implemented in a 0.35-[micro]m CMOS process and consumes 4.3 mA from a single 1.3-V supply. Measurement results show that at 1.97 GHz the quality factor is tunable from 60 to 220 while the amplitude is tunable between -15 and 0 dBm with worst case quality factor and amplitude tuning accuracies of 10% and 7%, respectively. Index Terms--Automatic Q-tuning, CMOS circuits, LC bandpass filter, Q-enhancement. Digital Object Identifier 10.1109/TCSI.2006.888783

Continuous-time bandpass (BP) sigma-delta modulators ([summation][DELTA]Ms) employing surface acoustic wave (SAW) resonators as loop filters are presented. Compared with the loop filters realized with [G.sub.m]-C and LC resonators, the SAW resonator has the advantage of high-Q factor, wide resonant frequency range and accurate resonant frequency without the need for automatic tuning. With the proposed anti-resonance cancellation and loop filter phase compensation techniques, a second- and a fourth-order BP [summation][DELTA]Ms are demonstrated in a 0.35-[micro]m CMOS technology. Both modulators are tested with 47.3-MHz off-chip SAW resonators. The second-order modulator attains a dynamic range of 57 dB and peak signal-to-noise distortion ratio (SNDR) of 54 dB and the fourth-order one achieves a dynamic range of 69 dB and peak SNDR of 66 dB, both in a 200-kHz signal bandwidth. The fourth-order modulator is also measured in a 3.84-MHz signal bandwidth and achieves a dynamic range of 52.5 dB and peak SNDR of 50 dB, an effective 8-bit resolution. Index Terms--Analog-to-digital converter (ADC), sigma-delta modulator ([summation][DELTA]M), bandpass (BP), surface acoustic wave (SAW) resonator. Digital Object Identifier 10.1109/TCSI.2007.890615

Coplanar-waveguide (CPW)-fed microstrip bandpass filters are proposed with capacitive couplings suitably introduced at the input/output (I/O) ports, as well as between the resonators for spurious suppression. By adopting these capacitive couplings, several open stubs are established so that adjustable multiple transmission zeros may independently be created to suppress several unwanted spurious passbands, thereby extending the stopband and improving the rejection level. In this study, the capacitive couplings required at the I/O ports, as well as across the resonators, are realized by the broadside-coupled transition structures between the top microstrip layer and the bottom CPW layer so that the I/O ports may properly be matched and the spurious responses may effectively be suppressed. Specifically, a fifth-order bandpass filter, centered at [f.sub.0] = 1.33 GHz with a stopband extended up to 8.67 GHz (6.52 [f.sub.0]) and a rejection level better than 30 dB, is implemented and carefully examined. Index Terms--Bandpass filter, coplanar waveguide (CPW), dual metal-layer structure, microstrip, spurious suppression.

An ultra-selective high-temperature superconducting bandpass filter was designed and fabricated to satisfy the demands of the third-generation wireless communications. This filter was designed to have 12-pole quasi-elliptic response with 4.68-MHz bandwidth in the third-generation communications band (a fractional bandwidth of 0.0023). Full-wave simulations were conducted by using Sonnet software. A novel, compact, and low radiation resonator with a high-quality (Q) factor value was developed to reduce the parasitical coupling. In order to satisfy the demand of high band-edge steepness, three pairs of transmission zeros at finite frequencies were introduced in the cascaded quadruplet coupling structure. The filter was fabricated on a 2-in-diameter 0.43-mm-thick sapphire wafer with double-sided YBCO films. The measurements showed that the passband center frequency ([f.sub.0]) of the filter is 2.038 GHz at 67 K with a midband insertion loss of 0.67 dB and the return loss better than 15 dB. The measured response of the filter also exhibited ultra-high band-edge steepness of 140-220 dB/MHz. Better than 60 dB of out-of-band rejections for frequencies very close to the band edge (|f - [f.sub.0] | > 2.7 MHz), better than 90 dB at frequencies 7.5 MHz away from the center frequency and up to 100 dB of wideband rejections were achieved. Index Terms--High-temperature superconducting (HTS), microwave filter, third-generation wireless communications.

This paper presents a novel compact meta-structure, which is characterized by left-handed properties. In the novel structure, two linear arrays of metallic vias and short-stub inductors are used to generate shunt inductors besides the series interdigital capacitors. Compared with conventional composite right/left-handed transmission-line structures, the new structure has weaker coupling to other components and is easily controlled by adjusting the shunt inductance and series capacitance to produce different left-handed properties. Due to the isolation of two via arrays, the proposed structure can also be transplanted directly from the microstrip system to the coplanar-waveguide system. We have proposed an efficient procedure to retrieve the equivalent propagating modes for both forward and backward waves based on the matrix pencil method, which provides an easy way to study the propagation characteristics. Using such a meta-structure, a series of super-wide bandpass filters are designed and fabricated at different frequency bands. Good agreements between simulation and experiment results have been achieved, and good performance in passbands and stopbands has been observed with a relative 3-dB bandwidth larger than 70%. For easy design of such super-wide bandpass filters, an experienced formula is given between the physical size and the center frequency of the 3-dB passband, which can be used to redesign any filters at other frequency bands. Index Terms--Composite right/left-handed (CRLH) transmission line (TL), matrix pencil method, meta-structure, propagating mode, super-wide bandpass filter.

This paper proposes a novel video denoising method based on nondecimated wavelet band filtering. In the proposed method, motion estimation and adaptive recursive temporal filtering are performed in a closed loop, followed by an intra-frame spatially adaptive filter. All processing occurs in the wavelet domain. The paper introduces new wavelet-based motion reliability measures. We make a difference between motion reliability per orientation and reliability per wavelet band. These two reliability measures are employed in different stages of the proposed denoising scheme. The reliability per orientation (horizontal and vertical) measure is used in the proposed motion estimation scheme while the reliability of the estimated motion vectors (MVs) per wavelet band is utilized for subsequent adaptive temporal and spatial filtering. We propose a novel cost function for motion estimation which takes into account the spatial orientation of image structures and their motion matching values. Our motion estimation approach is a novel wavelet-domain three-step scheme, where the refinement of MVs in each step is determined based on the proposed motion reliabilities per orientation. The temporal filtering is performed separately in each wavelet band along the estimated motion trajectory and the parameters of the temporal filter depend on the motion reliabilities per wavelet band. The final spatial filtering step employs an adaptive smoothing of wavelet coefficients that yields a stronger filtering at the positions where the temporal filter was less effective. The results on various grayscale sequences demonstrate that the proposed filter outperforms several state-of-the-art filters visually (as judged by a small test panel) as well as in terms of peak signal-to-noise ratio. Index Terms--Motion estimation, video denoising, wavelets.

A new filtering paradigm is introduced, called synchronous filtering, which notably includes complex or polyphase filters as a subset. The theory introduced demonstrates how a given time invariant filter can be implemented using a combination of modulators and a core filter, which itself could be time varying. That the equivalent synchronous filter processes the identical time-domain complete response as the original is also proven. Sub- and superheterodyne, as well as higher order, filters are discussed. Finally, a companding polyphase filter is introduced for the first time as another instance of a synchronous filter. Index Terms--Bandpass filters, complex filters, modulators, polyphase filters, synchronous filtering.

A sixth-order 10.7-MHz bandpass switched-capacitor filter based on a double terminated ladder filter is presented. The filter uses a multipath operational transconductance amplifier (OTA) that presents both better accuracy and higher slew rate than previously reported Class-A OTA topologies. Design techniques based on charge cancellation and slower clocks are used to reduce the overall capacitance from 782 down to 219 unity capacitors. The filter's center frequency and bandwidth are 10.7 MHz and 400 kHz, respectively, and a passband ripple of 1 dB in the entire passband. The quality factor of the resonators used as filter terminations is around 32. The measured (filter + buffer) third-intermodulation (IM3) distortion is less than -40 dB for a two-tone input signal of +3-dBm power level each. The signal-to-noise ratio is roughly 58 dB while the IM3 is -45 dB; the power consumption for the standalone filter is 42 mW. The chip was fabricated in a 0.35-[micro]m CMOS process; filter's area is 0.84 [mm.sup.2]. Index Terms--Capacitive reduction techniques, fast operational transconductance amplifiers (OTAs), high-Q switched-capacitor (SC) filters, SC filters.

A CMOS fully integrated 12th-order bandpass filter for low interemdiate frequency Bluetooth receivers is presented. The design is optimized to meet the selectivity and dynamic range requirements of Bluetooth while consuming relatively low power. The filter is based on unity gain cells and utilizes linearized MOSFET resistors for tuning. It exhibits a bandwidth of 1 MHz and a programmable center frequency range of 2 to 4 MHz. Experimental results obtained from a standard 0.5-[micro]m CMOS chip show that the filter exhibits an in-band dynamic range of 53.3 dB at gain of 0 dB, and 52 dB at gain of 15 dB, while consuming a total current of 1.32 mA. Attenuations of more than 10, 38, and 55 dB, are achieved for blockers one, two, and three, respectively. Index Terms--Bluetooth (BT) receivers, CMOS analog integrated circuits (ICs), current mode circuits, intermediate-frequency (IF) bandpass filters.

In this paper, we propose a compact planar bandpass filter design with wide stopband. The double split-end quarter-wave-length ([lambda]/4) resonator is introduced to reduce the resonator size while providing additional transmission zeros. Optimal split-end length is determined to provide transmission zeros that attenuate the two lowest spurious resonance frequencies. The singly loaded quality factor ([Q.sub.si]) of the optimal-length [lambda]/4 s tepped-impedance resonator (SIR) is also analytically derived. Using the proposed technique to design an Nth-order filter, N + 1 controllable transmission zeros are generated and used to suppress spurious frequency responses. The experimental design shows that the sixth-order filter can provide a very broad stopband of 8.5 times the fundamental frequency with at least 37.8 dB of attenuation using the SIRs with a stepped-impedance ratio (R) of 0.528. Index Terms--Microstrip, microwave filter, spurious response, stepped-impedance resonator (SIR), transmission zero.

Different approaches for designing bandpass filters with transmission zeroes are investigated by using the transmission-line theory and the finite-difference time-domain method. The filters are composed of capacitively coupled uniform impedance microstrip resonators, stepped-impedance microstrip resonators, and tapped feed lines. Different design modifications are discussed and, as a result, a design with double-coupled resonators is proposed. Based on this structure, a miniaturized filter capacitively loaded by high-permittivity dielectric inclusions and fabricated by using low-temperature co-fired ceramic (LTCC) technology is presented. The measured and simulated S-parameter spectra of the LTCC-filter are in good agreement. Index Terms--Finite-difference time-domain method (FDTD), low-temperature co-fired ceramic (LTCC), microstrip filters, resonance, transmission zeroes.

Highly miniaturized RF bandpass filter using a thin-film bulk acoustic wave resonator (TFBAR) is designed and fabricated for 5-GHz-band application. The topology of the fabricated filter is based on a ladder-type configuration that has a common trimming inductor connected concurrently with two shunt TFBARs and the trimming inductor is directly connected to the ground. The role of unit the TFBAR's physical characteristics such as the size and thickness of the TFBAR determine the performance of the TFBAR filter, including the effect of the electrical impedance-matching characteristics of the TFBAR filter. The shape of the fabricated TFBARs are tetragons with unparallel sides and the sizes of resonator are smaller than 70 x 70 [micro][m.sup.2] to ensure the ranges of impedance-matched filter performance. The insertion loss and bandwidth of fabricated TFBAR filters are less than 2.8 dB and 160 MHz at 3 dB. The out-of-band rejection is over 30 dB. The actual size of filter is smaller than 700 x 600 [micro][m.sup.2], including signal and ground pad sizes. Index Terms--Effective electromechanical coupling factor, finite-element method (FEM), ladder-type configuration, microelectromechanical system (MEMS), thin-film bulk acoustic resonator (TFBAR), wireless local area network (WLAN).

The experimental 6-8.6-GHz five-pole bandpass filter being presented is composed of ridge-waveguide resonator segments, evanescent-mode inter-resonator coupling sections, and planar-circuit impedance-matching port networks. To reduce overall filter size, cavities are filled with a low-loss moldable dielectric material that does not shrink during curing. Good agreement is observed between measured and predicted filter response characteristics. Two additional bandpass filter designs with different fractional bandwidths further highlight the versatility of the design methodology that relies entirely on the use of commercially available general-purpose design software. Index Terms--Bandpass filter, evanescent-mode waveguide, high power, injection molding, moldable dielectric, ridge waveguide, waveguide filter.

This paper presents the characteristics of a miniaturized microstrip filter, which has two separate coupling paths: electric coupling path and magnetic coupling path between two resonators. Either magnetic coupling or electric coupling in two paths can be dominant in the total coupling coefficient of the inter-stage resonators with the similar configuration, but different positions of transmission zero points (ZPs). Based on the proposed filter topology, second- and fourth-order filters have been designed and fabricated for the first time. Advantages of using this type of filter are not only its low insertion loss and much more compact size, but also its controllable transmission ZPs. Index Terms--Bandpass filter (BPF), odd and even mode, separate electric and magnetic coupling paths (SEMCPs), zero point (ZP).

A periodic stepped-impedance ring resonator (PSIRR) is proposed to design dual-mode bandpass filters with a miniaturized area and desirable upper stopband characteristics. Design parameters of a PSIRR include impedance ratio R of the hi-Z to low-Z sections, their lengths, and number of impedance steps 2N. The resonant characteristics of PSIRRs with various N and R values are investigated by both the transmission-line theory and electromagnetic simulation. Proper choice of the above parameters leads to an optimal reduction of circuit area and extension of upper rejection bandwidth. Two extra transmission zeros exist in the upper stopband and are tunable via changing the arm lengths of the line-to-ring coupling structure. Realized by the standard microstrip technology, the dual-mode PSIRR bandpass filter has not only the first spurious response at higher than 3.7 x the passband frequency, but also an area reduction of better than 60% against a conventional ring filter. Experimental results of several fabricated circuits validate the analysis and theoretical prediction. Index Terms--Bandpass filter, dual mode, miniaturization, periodic structure, ring resonator, stepped-impedance resonator.

We report several types of coplanar waveguide tri-section stepped-impedance resonator (SIR) structures that offer further size reduction compared to the conventional two-section SIRs. In addition, the tri-section SIRs provide flexibility of introducing effective capacitive coupling to the ground lines for realizing slow-wave structures. The slow-wave effect can be used to implement more compact bandpass filters. The principles of achieving size reductions using tri-section SIRs are described and confirmed by simulation results. To demonstrate the effectiveness of the proposed tri-section SIRs in size reduction, the tri-section SIRs with slow-wave effects were implemented in a two-pole directly coupled bandpass filter and a fourth-order quasi-elliptic bandpass filter with reduced size. The measured results matched well with the theoretical prediction. Index Terms--Bandpass filters, cascaded quadruplet (CQ) filter, coplanar waveguide (CPW), fractional bandwidth (FBW), stepped-impedance resonator (SIR).

Wide-stopband and compact microstrip bandpass filters (BPFs) are proposed using various dissimilar quarter-wavelength ([lambda]/4) stepped-impedance resonators (SIRs) for multiple spurious suppression. The use of [lambda]/4 SIRs is essential in widening the filter stopband and reducing the circuit size. By properly arranging the individual [lambda]/4 SIR, which has the same fundamental resonance frequency [f.sub.0], but has different spurious (harmonic) resonance frequencies, and also carefully misaligning the maximum current density nodes, several higher order spurious resonances may be suppressed so that a BPF with wide stopband may be realized. In this study, the basic concept of multiple spurious suppression is demonstrated by thoroughly investigating the spurious characteristics of the fourth-order interdigital BPFs, which consist of two different types of [lambda]/4 SIRs. To widen the rejection bandwidth, the fourth-order coupled-resonator BPFs based on three and four different types of [lambda]/4 SIRs are implemented and carefully examined. Specifically, a very wide-stopband microstrip BPF composed of four dissimilar [lambda]/4 SIRs is realized and its stopband is extended even up to 11.4 [f.sub.0] with a rejection level better than 27.5 dB. Index Terms--Bandpass filter (BPF), coupled resonator, microstrip, quarter-wavelength stepped-impedance resonator, spurious suppression.

This paper presents an analysis of the sensitivity of coupled resonator filters in which some direct couplings are missing. The effect of changes in the coupling coefficients and resonant frequencies of the resonators is investigated by directly computing the gradient of the scattering parameters. It is shown that structures that are modular in the input-to-output direction are much less sensitive than those with modularity in the orthogonal direction for the same frequency response. Index Terms--Bandpass filters, elliptic function filters, filter synthesis, sensitivity.

An analytical technique for extracting phase, visibility, and amplitude information as needed for interferometric astrometry for the Space Interferometry Mission (SIM) is presented. This model accounts for a number of physical and instrumental effects and is valid for the general case of a bandpass filter. I was able to obtain a general solution for polychromatic phasors and to address the properties of unbiased fringe estimators in the presence of noise. For demonstration purposes I studied a rectangular bandpass filter with two different methods of optical path difference (OPD) modulation: stepping and ramping OPD modulation. A number of areas for further studies relevant to instrument design and simulations are outlined and discussed. OCIS codes: 120.2440, 120.2650, 120.3180, 120.5050, 120.5060.

This paper proposes a new class of slow-wave bandpass filters that uses a microstrip line periodically loaded with microstrip ring or stepped-impedance hairpin resonators. The new slow-wave periodic structures utilize the parallel and series resonance characteristics of the resonators to construct a bandpass filter. Unlike conventional slow-wave filters, the proposed bandpass filters are designed to produce a narrow passband at the fundamental mode of the resonators. The new filters provide lower insertion loss than that of parallel- or cross-coupled ring and stepped-impedance hairpin bandpass filters. The calculated frequency responses of the filters agree well with experiments. Index Terms--Bandpass filter, hairpin resonator, ring resonator, slow-wave periodic structure.

Zolotarev rational functions may be used in certain bandpass filter applications for which two narrower passbands are required. Coupled-resonator low-pass prototypes for narrow bandpass filters based on even- and odd-degree Zolotarev functions are synthesized using a transformed variable. Compared to other filters, those with Zolotarev responses have sharper skirt selectivity, resulting in lower passband distortion. Index Terms--Bandpass filters, Chebyshev filters, circuit synthesis, elliptic filters, passive filters, resonator filters.

An analytical study compared a high temperature superconducting microstrip filter and its gold counterpart with respect to insertion loss, transmission characteristics, bandwidth and other attributes. It was found that the high temperature superconducting filter used in the experiment holds a lot of promise for high efficiency communications systems. Design technique, filter fabrication, experimental arrangements, findings and conclusions are presented.

A fast and efficient radial mode-matching technique (RMMT) is applied to the analysis and design of components in circular ridge waveguide technology. Five different structures are investigated with respect to their performance as filters and polarizers. For fast computation, pie-shaped metal ridges and septa are assumed to better fit the cylindrical coordinate system. In practice, the pie-shaped structures are approximated by rectangular cross-section metal inserts. The validity of this approximation is investigated by comparing with measurements and finite-element analysis. It is found that for thin etchable inserts, the measured filter response is in excellent agreement with the theoretical prediction and that for polarizers, the axial ratio response is not particularly sensitive to the ridge shape. Differences between computed and measured results occur only at return loss and isolation levels beyond 25 dB. A central processing unit time comparison with HFSS (4.0) results in a 10-min versus 3-h advantage in favor of the RMMT. Index Terms - Bandpass filters, mode-matching methods, polarization, ridge waveguides.

It is known that a continuous time signal [Chi](t) with Fourier transform X([Nu]) band-limited to [absolute value of [Nu]] [less than] [Theta]/2 can be reconstructed from its samples [Chi]([T.sub.o] n) with [T.sub.o] = 2[Pi]/[Theta]. In the case that x([Nu]) consists of two bands and is band-limited to [[Nu].sub.o] [less than] [absolute value of [Nu]] [less than] [[Nu].sub.o] + [Theta] 2, successful reconstruction of [Pi](t) from [Pi]([T.sub.o] n) requires an additional condition on the band positions. When the two bands are not located properly, Kohlenberg showed that we can use two sets of uniform samples, [Pi]([2T.sub.o]n) and [Pi]([2T.sub.o] n+[d.sub.1]), with average sampling period [T.sub.o], to recover [Pi](t). Because two sets of uniform samples are employed, this sampling scheme is called Periodically Nonuniform Sampling of second order [PNS(2)]. In this paper, we show that PNS(2) can be generalized and applied to a wider class. Also, Periodically Nonuniform Sampling of Lth-order [PNS(L)] will be developed and used to recover a broader class of band-limited signals. Further generalizations will be made to the two-dimensional case and discrete time case.

The constrained set for good critical frequencies in linear-phase FIR Mth-band filters where the center frequency is an integer multiple of phi/M are derived to obtain good passband and stopband characteristics. In this, the results of lowpass filters constraints are applied to multiband filters. The linear combination of good lowpass and bandpass Mth-band filters results in good Mth-band multiband filters. A distance of 2 phi/M from another critical frequency is desired for critical frequencies of good linear-phase FIR Mth-band multiband filters.

Low loss bandpass filters consisting of Fabry-Perot resonators excited by waveguide fed slots coupling to higher order resonator modes are demonstrated. For close reflector spacings, the waveguide couples efficiently through the slots to the TEM(sub 400) and TEM(sub 300) modes. The characteristics of both rectangular and circular waveguide feeds with various slot lengths and widths are presented. At X-band the filters have unloaded Q values which range from 1000 to 7000 with insertion losses less than 1 dB. The filters which have the rectangular waveguide feeds are mechanically tunable over a 20% bandwidth.