Microwave Bandpass Filters Using Re-Entrant Resonators
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Abstract:
Design techniques for microwave bandpass filters using re-entrant resonators are presented. The key feature is that each re-entrant resonator in the filter generates a passband resonance and a finite frequency transmission zero above the passband. Thus, an N th degree filter can have N finite frequency transmission zeros with a simple physical realization. A physically symmetrical five-pole re-entrant bandpass filter prototype with five transmission zeros above the passband was designed and fabricated. Measured results showed good correspondence with theories.Keywords:
Passband
Realization (probability)
Distributed element filter
Elliptic filter
Four new classes of microwave bandpass filters are defined herein. They are realized in triplate stripline and are exceedingly small devices as a result of using transmission line elements which are a quarter-wavelength well above the frequency of the passband. Each filter corresponds to a bandpass S-plane prototype which is derived using exact synthesis procedures from a specification of transmission zero locations. Passband and stopband widths may be independently specified and an extremely high degree of selectivity can be achieved when necessary. The slope of a filter skirt can he chosen to be such that 60 dB of attenuation is reached at a frequency < 3 percent from the comer of the passband.
Passband
Stopband
Elliptic filter
Transition band
Stripline
Distributed element filter
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A multilayer broadside-coupled microstrip-slot-microstrip structure is used to design a bandstop filter with a wide passband for ultra wideband (UWB) applications. The design procedure for the proposed filter is based on the conformal mapping technique and the even- and odd-mode analysis. The theoretical analysis indicates that value of the coupling factor between the top and bottom layers of the structure can be used to control the width of the stopband, whereas centre of that band can be controlled by the length of the coupled structure. To limit the passband of the proposed bandstop filter to 3.1–10.6 GHz, which is the specified bandwidth for UWB systems, a broadside-coupled bandpass filter is integrated with the proposed device. The simulated and measured results show that the proposed device achieve <0.5 dB insertion loss across most of the passband and >20 dB insertion loss at the stopband. The device also shows a flat group delay across the passband with <0.15 ns peak-to-peak variation. Hence, it is a suitable choice for the UWB systems that require a distortionless operation.
Wideband
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Given how important multiband filters are in the current era, little work seems to have come up with methods that can produce multiband filters of more than two passbands with flexibility in inner-band frequency selection, as well as specific bandwidths for each passband.In this paper, a novel method called the chained-response method is proposed.This method can produce multiband filters with the flexibility to specify accurately the bandwidths for each passband as well as its inner-band frequency selection.This paper describes the design procedure for this method.In order to validate the design procedure, a symmetrical dualpassband filter with bandwidths of 0.2 GHz for both passbands is designed.In order to show the novelty of this method, which is the flexibility of inner-band frequency selection and the specific bandwidths, an asymmetrical dual-passband filter with bandwidths of 0.2 GHz and 0.4 GHz is designed.Both the symmetrical and asymmetrical dual-passband filters are fabricated with a waveguide structure and the measurement results for both show good agreement with the theoretical ones.Finally, the mathematical modelling for a symmetric triple-passband filter and a symmetric quad-passband filter are briefly discussed to show how the proposed method can be expanded for designing filters with more than two passbands.
Passband
Elliptic filter
Transition band
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This paper describes a synthesis method for quadruple-passband microwave filters. A frequency transformation method is developed for finding the locations of poles and zeros of the filter response. An eight-pole microstrip quadruple-passband filter is synthesized for validation, with designed pass bands at 1.85-1.88, 1.943-1.97, 2.03-2.057, and 2.12-2.15 GHz. The filter is realized in microstrip and the measured results show good agreement with the theoretical ones.
Passband
Elliptic filter
Transition band
Distributed element filter
Network synthesis filters
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The design and synthesis of various types of microwave elliptic function filters has been accomplished by a number of authors. However, one problem in this field which remains is the realization of compact narrow-band bandpass elliptic function filters. In this paper, a procedure is presented which enables this class of filters to be constricted in a compact digital form. Since the physical realization is in the form of an n-wire line, one-quarter of a wavelength Iong at the center frequency of the passband, where the impedance levels are stepped along the center of the coupled lines, the filter has been termed the stepped digital elliptic filter. The absence of awkward interconnections in the filter due to the stepped digital structure inherently implies that reasonable insertion loss characteristics may be achieved in the X-band region and above, and also simplifies the mechanical construction. It is shown that the resonant elements in the filter, due to the design procedure adopted, are relatively insensitive to the absolute bandwidth of the filter, and consequently fractional bandwidths of approximately 30 percent and below may be readily achieved while the normalized impedance values of the elements in the network remain of the order of unity. This latter result is similar to that obtainable from conventional interdigital filters but in the case of narrow bandwidths the stepped digital filter is considerably smaller in physical size. A systematic procedure is also formulated for the inclusion of the parasitic lumped end effect capacitances into the overall design procedure in order to maintain the equiripple passband and stopband responses. Experimental results are presented for a five-element, 11 percent bandwidth filter and are shown to be in good agreement with theoretical predictions.
Passband
Elliptic filter
Waveguide filter
Constant k filter
Center frequency
Butterworth filter
Distributed element filter
Network synthesis filters
Mechanical filter
Electronic filter topology
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This letter presents a compact planar tri-band bandpass filter with high selectivity. The proposed filter employs two sets of resonators, i.e., stub-loaded resonators and half-wavelength resonators. The former is designed to operate at the first and third passbands and the latter at the second passband. The passband frequencies can be conveniently tuned to desired values. One set of resonators is embedded in the other and thus the filter is compact in size. On each side of each passband, there is at least one transmission zero, resulting in high skirt selectivity. For validation, a demonstration filter is implemented. The design methodology and the experimental results are presented.
Passband
Elliptic filter
Transition band
Stub (electronics)
Butterworth filter
Electronic filter topology
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This paper describes a synthesis method for symmetric dual-passband microwave filters. The proposed method employs frequency transformation techniques for finding the locations of poles and zeros of a desired filter. This method can be used to design dual-passband filters with prescribed passbands and attenuation at stopbands directly without the need for any optimization processes. To validate the procedure a dual-passband stripline filter is designed and fabricated. The stripline dual-passband filter is designed with passbands at 3.90-3.95 and 4.05-4.10 GHz, and 30-dB attenuation at the stopband. This measured results show a good agreement with the theoretical ones. The frequency transformation for symmetric dual-passband filters is also extended to include asymmetric dual-passband responses. This flexible frequency transformation preserves the attenuation characteristics of the low-pass filter prototype. Examples are shown to discuss the flexibility of this transformation.
Passband
Elliptic filter
Stopband
Stripline
Butterworth filter
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Citations (148)
This chapter describes novel concepts, methodologies, and designs for compact filters and filter miniaturization. The new types of filters discussed include ladder line filters, pseudointerdigital line filters, compact open-loop and hairpin resonator filters, slow-wave resonator filters, miniaturized dual-mode filters, multilayer filters, lumped-element filters, and filters using high dielectric constant substrates.
Distributed element filter
Waveguide filter
Constant k filter
Network synthesis filters
Electronic filter topology
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A class of digital filters with variable cut-off based on EMQF filter sections and sharpening method
A new filter class with variable cut-off frequency is designed based on elliptic filter sharpening technique. A higher order IIR filter with a sharp transition band is constructed by using several identical low-order EMQF (elliptic minimal Q-factors) filters and an additional compensating section. The stopband attenuation is achieved by cascading EMQF subfilters, and the compensation section is designed to minimize the overall passband ripple. For the tuning of the cut-off frequency we propose a simple version of the spectral parameter approximation technique. Low-degree approximating polynomials are developed to represent coefficients of the EMQF subfilters and coefficients of the compensating section in terms of the passband cut-off frequency. In the tuning procedure, the new coefficient values are obtained by the polynomial evaluation consisting of several multiplications and additions. The analytical methods are derived for the filter design and for the tuning procedure. Design and implementation of sharp variable filters is illustrated by means of examples.
Elliptic filter
Passband
Network synthesis filters
Stopband
Transition band
Sharpening
Butterworth filter
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Techniques are presented for obtaining an optimum filter response for narrow-band requirements of a single passband and a single stopband. For certain transformed equiripple passband responses, including Chebyshev and elliptic function responses and a new "double n/2 poles" response, the minimum number of resonators can be easily determined, resulting in reduced size and weight relative to more conventional frequency-symmetric bandpass or bandstop filters.
Passband
Stopband
Elliptic filter
Transition band
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Citations (10)