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This letter presents a novel microstrip tri-band filter in which a shunt-stub bandpass filter and a dual-band bandstop filter are integrated into a single structure of short length. The two stopbands of the bandstop filter are allocated within the wideband passband of the bandpass filter, resulting in a filter having three passbands. Good return loss is obtained using an optimization routine. This technique has high flexibility on setting the bandwidths and center frequencies of passbands. A prototype filter is designed and fabricated. Good agreements between simulation and measurement in respect of low insertion loss and high isolation are demonstrated.

This paper presents an ultra-wideband bandpass filter (UWB BPF) using quarter-wavelength inverter-lines at both sides of a three-pole interdigital filter. The relations between the impedances of the inverter-line with the load and those of the interdigital filter connected to the inverter-line were studied. From these, the design procedures for the impedance matching at the UWB passband edges were shown. Then the designed BPF from the above results showed that the bandwidth was 24% wider than that of the sole interdigital filter by additional two conjugate matching poles. The fabricated BPF achieved the performances of the required passband by the five matching poles.

In this paper, we utilize low temperature co-fired ceramic technology (LTCC) to realize a modified short-circuited stub bandpass filter suitable for ultra-wideband (UWB) applications. By modifying the conventional short-circuited stub bandpass filter structure with stubs and connecting lines of lower characteristic impedances, the number of stubs has been reduced from 5 to 2 on a high dielectric constant substrate (er=40). A wireless local area network (WLAN) stopband in the frequency range of 5.15 to 5.825GHz has been inserted into the filter characteristic using three short-circuited coupled lines. The filter is fabricated and measurement results show that it has an insertion loss less than 1.0dB and return loss better than 10dB in the pass bands. A bandwidth ratio of 109.49% has been achieved. Measurement results agree well with simulation results. The dimensions of the filter are 4×8×0.57mm3.

In this paper, a simple method to obtain a notch in the ultra-wideband (UWB) bandpass filter is presented. UWB bandpass filter is designed using ground plane aperture technique. To reject the undesired wireless local area network (WLAN) signals, a complementary single split ring resonator (CSSRR) is placed under the coupled lines of the bandpass filter. The CSSRR has flat insertion loss and good roll off rate than the conventional complementary split ring resonator (CSRR). The proposed filter offers an ultra wide bandwidth bandpass filter characteristics with a steep notch function around 5.5GHz. Hence the interference from the devices operated in the IEEE 802.11a spectrum can be avoided properly. IE3D simulation results of the notched UWB bandpass filter is in good agreement with the measurement results.

A novel compact wide bandpass filter is proposed by cascading two square-ring resonators, a quarter wave length short-stub and a quarter wavelength open-stub. This filter offers wide passband, with high out-of-band rejection and suppression of second spurious harmonic. Design procedure of a filter at 1GHz with 50% fractional bandwidth is presented showing good agreement between simulation and experimental results.

A novel versatile single FDCCII-based voltage-mode universal biquadratic filter with three inputs and four outputs is presented. The proposed circuit can act as a multifunction voltage-mode filter with two inputs and four outputs and can perform simultaneous realization of voltage-mode bandreject, highpass, bandpass and lowpass filter signals from the four output terminals, respectively. On the other hand, it also can act as a universal voltage-mode filter with three inputs and a single output and can realize five generic voltage-mode filter signals without requiring any inverting input voltage signals and component-matching conditions. The proposed circuit employing single FDCCII, two grounded capacitors and two resistors, which are the minimum components necessary for realizing a second-order voltage-mode universal filtering response from the same topology. Both its active and passive sensitivities are low.

This paper presents a novel microstrip dual-band filter in which a shunt-stub bandpass filter and an open-stub bandstop filter are integrated into a single structure of short length. The bandstop filter is centered within the passband of the bandpass filter, resulting in a filter having dual passbands. Good return loss is obtained using an optimization routine. This method is suitable for designing dual-band filters having wide bandwidths. Good agreement between theory and measurements in respect of low insertion loss and high isolation is demonstrated.

To realize the compact ultra-wideband (UWB) bandpass filters, a novel filter prototype with two short-circuited stubs loaded at both sides of a stepped-impedance resonator (SIR) via the parallel coupled lines is proposed based on a distributed filter synthesis theory. The equivalent circuit of this filter is established, while the corresponding 7-pole Chebyshev-type transfer function is derived for filter synthesis. Then, a distributed-circuit-based technique was presented to synthesize the elements' values of this filter. As an example, a FCC UWB filter with the fractional bandwidth (FWB) @ -10 dB up to 110% was designed using the proposed prototype and then re-modeled by commercial microwave circuit simulator to verify the correctness and accuracy of the synthesis theory. Furthermore, in terms of EM simulator, the filter was further-optimized and experimentally-realized by using microstrip line. Good agreements between the measurement results and theoretical ones validate the effectiveness of our technique. In addition, compared with the conventional SIR-type UWB filter without short-circuited stubs, the new one significantly improves the selectivity and out-of-band characteristics (especially in lower one -45 dB@1-2 GHz) to satisfy the FCC's spectrum mask. The designed filter also exhibits very compact size, quite low insertion loss, steep skirts, flat group delay and the easily-fabricatable structure (the coupling gap dimension in this filter is 0.15 mm) as well. Moreover, it should be noted that, in terms of the presented design technique, the proposed filter prototype can be also used to easily realize the UWB filters with other FBW even greater than 110%.

A novel electronically tunable high input impedance voltage-mode multifunction filter with single inputs and three outputs employing two single-output-operational transconductance amplifiers, one differential difference current conveyor and two capacitors is proposed. The presented filter can be realized the highpass, bandpass and lowpass functions, simultaneously. The input of the filter exhibits high input impedance so that the synthesized filter can be cascaded without additional buffers. The circuit needs no any external resistors and employs two grounded capacitors, which is suitable for integrated circuit implementation.

This paper presents the ultrawideband filters for UWB fullband (range of 3.1-10.6 GHz) applications. This filter consists of ring filter for wide-bandwidth and coupled line structure for suppressing unwanted passband in upper and lower stopbands. Especially, the filter structure was realized on silicon substrate using thin film technology, adequate for wafer level packaging, which can be integrated with CMOS UWB chipset that is currently on development. To minimize the dimension of the filter, the Hilbert structure was applied in ring filter and the meander shaped broadside coupled structure was also adopted in the coupled line structure. The size of the fully realized filter structure is 4.4 x 3.6 mm 2 . The insertion loss in passband is 1.5 dB and the return loss is larger than 15 dB, respectively. The group delay in center frequency is 0.2ns and the group delay variation is less than 0.15 ns.

This paper presents an ultra-wideband (UWB) bandpass filter using a combination of broadside-coupled structure and lumped-capacitor-loaded shunt stub resonator. The broadside-coupled microstrip-to-coplanar waveguide structure provides an ultra-wide bandpass filtering operation and keeps a good stopband at lower frequencies from DC at the same time. The lumped-capacitor-loaded shunt stub resonator creates two transmission zeros (attenuation poles which can be located at the outsides of the two bandedges of the UWB bandpass filter to improve the out-band performance by selecting a suitable combination of the length of the shunt stubs and the capacitance of the loaded chip capacitors. The filter was designed based on electromagnetic simulation for broadside-coupled structure, microwave circuit simulation and experiments for determining the transmission zeros. The filter was fabricated on a one-layer dielectric substrate. The measured results demonstrated that the developed UWB bandpass filter has good performance: low insertion loss about 0.46 dB and low group delay about 0.26 ns at the center of the passband and very flat over the whole passband, and less than -10 dB reflection over the passband. The implemented transmission zeros, particularly at the low frequency end, dramatically improved the out-band performance, leading the filter satisfy the FCC's spectrum mask not only for indoor but also for outdoor applications. These poles improved also the skirt performance at both bandedges of the filter. A lowpass filter has been also introduced and integrated with the proposed bandpass filter to have a further improvement of the out-band performance at the high frequency end. The filters integrated with lowpass section exhibit excellent filter performance: almost satisfying the FCC's spectrum mask from DC to 18 GHz. The developed UWB bandpass filter has a compact size of 4 cm x 1.5 cm, or 4.8 cm x 1.5 cm with lowpass section implemented.

A rectangular waveguide compatible NRD guide E-plane bandpass filter is proposed for 55 GHz band OFDM applications. The NRD guide E-plane bandpass filter is constructed by inserting a metal foil array in the E-plane of NRD guide. Simulation, fabrication, and handling of the filter are not difficult because each resonator is constructed by a couple of metal foils of a simple shape. A Chebyshev response 5-pole bandpass filter with a very narrow bandwidth of 550 MHz is designed and fabricated at 55 GHz band. Simulated and measured filter performances agree well with the design specifications. Insertion loss of the fabricated filter is found to be around 2.0 dB. Although temperature stability of the fabricated filter are found to be within manageable level, the adoption of cyclo olefin polymer can be one of solution for the temperature stability improvement.

This paper proposes a Mel-Wiener filter to enhance Mel-LPC spectra in the presence of additive noise. The transfer function of the proposed filter is defined by using a first-order all-pass filter instead of unit delay. The filter coefficients are estimated based on minimization of the sum of the square error on the linear frequency scale without applying the bilinear transformation and efficiently implemented in the autocorrelation domain. The proposed filter does not require any time-frequency conversion, which saves a large amount of computational load. The performance of the proposed system is comparable to that of ETSI AFE. The optimum filter order is found to be 3, and thus filtering is computationally inexpensive. The computational cost of the proposed system except VAD is 53% of ETSI AFE.

A novel structure of bandpass filter using NRD guide E-plane resonators is proposed. The NRD guide E-plane resonator is constructed by inserting metal foils in the E-plane of NRD guide. Simulation, fabrication and handling of the filter are very easy because each resonator is separated by simple metal foils. Chebyshev response bandpass filters are designed based on the theory of direct-coupled resonator filters and fabricated at 60 GHz. Simulated and measured filter performances agreed well with the design specifications. Insertion losses of the fabricated filters were found to be around 0.3 dB for 3-pole filter and 0.5 dB for 5-pole bandpass filter, respectively.

A novel wideband bandpass filter with improved stopband characteristics is presented in this paper. Dual-mode square ring resonator is used in the proposed filter. New formulas based on the even- and odd-mode analysis are derived to facilitate the design of transmission zeros of the square ring resonator. A short-circuited stub and a piece of aperture-enhanced parallel-coupled lines are introduced to the input and output of the resonator to lower the passband return loss and widen the stopband of the filter significantly. The filter has a 50% fractional bandwidth, is compact in configuration, and shows remarkably improved performance compared with previously reported filters of the same kind. The measured filtering response shows a good agreement with the simulated result.

In this paper a new method for the design and optimization of microstrip parallel coupled-line bandpass filters is presented which allows for the specification of frequency bandwidths and arbitrary source and load impedance transformation. The even- and odd- mode theory and the relationships between impedance, transmission and scattering matrices and their properties are used to construct a positive definite error function using the insertion losses at discrete frequencies in the pass, transition and stop bands. The dispersion relations for the coupled line are also taken into account. The minimization of the error function determines the widths, gap spacings and lengths of the coupled-line filter, for the optimum design and realization of filter specifications. The proposed filter design and optimization method is coded by computer programs and the results of simulation, fabrication and testing of sample filters together with comparisons with available full-wave analysis softwares, indicate the efficacy of the proposed method. Filter design with up to 50% bandwidth and the design of shorter lengths of coupled line sections are achievable by the proposed method in part due to the incorporation of impedance matching.

This paper presents a design procedure of multilayer single-input/single-output dual-band filters of small size fabricated in high-permittivity LTCC (Low Temperature Co-fired Ceramic) substrates. The present dual-band filter, with pass bands of 950 MHz and 1.9 GHz, consists of two single-band filters each one of which has a matching circuit for controlling the input impedance in the pass band of the counterpart. Discussed first in this paper is a dual-band filter that has the matching circuit connected to the single-band filters externally. Then, a dual-band filter with the matching circuit embedded in its body is investigated together with metallization patterns of the matching elements. Presented finally is a very small single-input/single-output dual-band filter suitable for dual-band wireless communication systems.

Based on the periodical-loaded principle, a new wider stop-band filter is presented. The design equations are provided, the validity of which is proved by the measured results. Compared with loaded stub of length 1/4λ g , the improved T-shape stub can change admittance paralleled with microstrip line and widen the band width of the band-stop filter. The size of the filter loaded by one side can be reduced by 2/3. The stop-band filter loaded by one side and two sides are simulated and realized. The filter loaded by two sides can achieve very wide stop-band. In addition, the stop-band of the new type of filter is deep and steep.

It is noticed that drain reactance of a MESFET is significantly changed by laser irradiation, and a novel optically tunable filter is proposed. One MESFET works not only as a negative resistance, but as a tuning element. Tuning range of 104MHz is obtained in X-band by optical tuning.

A novel low insertion-loss and wideband microstrip band-pass filter has been designed and tested. The basic configuration of this novel dual-mode filter is a square ring resonator with direct-connected orthogonal feed lines, and dual-perturbation elements are introduced within the resonator at symmetrical location. The effects of the size of the perturbation element are studied. A new filter having wider bandwidth and transmission zeros are presented. The proposed filter responses are in good agreement with the simulations and experiments.