Sharp Rejection Characteristics Research Articles

A Frequency Transformation for Co-Designed Multi-Passband/Multi-Embedded-Notch RF Filters

A class of multi-resonant RF filtering stage that exhibits a multi-band bandpass filtering transfer function with embedded in-band notches is presented. It is derived from the application of a composed lowpass-to-multi-passband/multi-stopband frequency transformation that converts the normalized lowpass prototype into the proposed multi-passband/multi-embedded-notch filtering cell. Thus, when employed in higher-order filtering networks, high-selectivity multi-band bandpass-filter (BPF) counterparts with embedded in-band stopbands are synthesized. Furthermore, two different approaches for out-of-band transmission-zero (TZ) generation in these type of filters to achieve sharp-rejection characteristics into them are detailed. The operational foundations of the engineered multi-passband/multi-embedded-notch filtering stage are described, along with several illustrative first-to-multi-order theoretical design examples with/without stopband TZs. Moreover, for experimental-demonstration purposes, a proof-of-concept microstrip prototype of a third-order dual-band BPF with two and one embedded notches in its lower and upper transmission bands, respectively, is manufactured and characterized.

Using adaptive filter as a notch filter to cancel adjacent channel interference in cellular systems

Since the interference/noise signal characteristics such as amplitude, frequency and phase are variable over time and sometimes unknown, therefore, most wireless systems, especially cellular systems, have difficulty extracting the useful signal and its frequency from the distorted signal. So, an adaptive filter is used for this purpose, where its transmission function is adjusted according to an optimization algorithm and this enables it to adapt along with the change in the signal characteristics in order to reach the ideal filter coefficients that permit to reduce the error to the minimum. However, adaptive filter algorithms have evolved to allow the adaptive filter to function as a notch filter by tracking the unknown frequency of the interference signal from adjacent channels in an environment where there is no full knowledge of the signal characteristics. Thus, these algorithms initially estimate the sinusoidal frequency of the interference signal quickly and accurately and then update the filter coefficients using this estimation, and this contributes to remove the noise and the single/multiple narrowband interference from the broadband signal where the frequency response of the adaptive notch filter has sharp rejection characteristics at the notch frequency corresponding to the interference frequency to be removed.

CPW-Fed UWB antenna with sharp and high rejection multiple notched bands using stub loaded meander line resonator

This paper presents a CPW-fed UWB filter-antenna with sharp and high rejection multiple band notches for band-notched UWB communication applications. The band notch operation is achieved by employing a sharp bandstop filter (BSF) with multiple reject bands using only one element meander line resonator at the bottom layer through theoretical calculations and parametric studies. The adjustment of the notched bands is successfully accomplished by loading the meander line with open ended stubs to modify the harmonic frequencies to the desired bands. The structure of the proposed BSF is simple and compact so that the proposed filter-antenna is achieved with the same size of the reference UWB antenna without an extra area. Measurement results show that the proposed filter-antenna has two notches at the WiMAX systems operating in the 5.8GHz (5.725–5.85GHz) and at the international telecommunication union (ITU) operating in the 8.2GHz (8.025–8.4GHz). Also, it has sharp rejection characteristics at the edges of the federal communication commission (FCC) band for UWB communications. The experimental measurements are in good agreement with theoretical and simulation results for the BSF and the filter-antenna. Moreover, the filter-antenna exhibits stable omnidirectional radiation patterns except at the notched bands.

Design of Compact UWB Bandpass Filter with Sharp Rejection Characteristics

This study presents an Ultra-Wideband (UWB) filter with sharp rejection characteristics at the upper Wireless Local Area Network (WLAN) band. The filter adopts the modified Composite Right/Left-Handed (CRLH) Transmission Lines (TLs), the unit cell of which is theoretically analyzed to derive the design formulas. Subsequently, a UWB bandpass filter is designed using these formulas. The measurement results show that the fabricated UWB bandpass filter has an insertion loss of less than 1.1 dB, bandwidth of 3.1~4.9 GHz and a rejection of more than 50 dB at 5.8 GHz.

A Metamaterial-Based Terahertz Low-Pass Filter With Low Insertion Loss and Sharp Rejection

In this paper, we present an efficient low-pass terahertz (THz) filter design based on MEMS technology. With a cascaded arrangement of two functional meta-layers, we demonstrate a nearly loss-free response at the lower frequency passband and sharp rejection characteristics at the higher frequency stopband, with a steep roll-off of 296 dB/THz. The bandwidth of the low-pass filter is easily tuned by scaling the structural parameters of the metamaterial unit cell. The low-pass filter works efficiently even at oblique angles of incidence, making it attractive for practical applications in THz signal processing.

Low insertion loss wideband bandpass filter with six transmission zeros

A modified wideband bandpass filter based on a bandstop filter is realised using half-wavelength and one-wavelength open-circuited resonators. Six transmission zeros are utilised to obtain the sharp rejection characteristics over a broad stopband. The passband bandwidth can be varied by changing the impedance of the configuration. A compact prototype filter with 27% bandwidth is demonstrated. Without coupling gaps between resonators, the new filter shows low insertion loss and is easy for fabrication. To illustrate the concept, a bandpass filter is designed, fabricated and measured. Simulated and measured results are found in good agreement with each other.

A NOVEL WIDE-STOPBAND BANDSTOP FILTER WITH SHARP-REJECTION CHARACTERISTIC AND ANALYTICAL THEORY

A novel bandstop fllter with wide-stopband performance is proposed and discussed in this paper. This circuit conflguration includes two-section coupled lines and three open-circuit transmission- line stubs. Due to the symmetry of this proposed structure, closed-form equations for scattering parameters are investigated. Transmission zeros and poles location for difierent circuit parameters are discussed, and the corresponding design curves are given. In order to verify this new fllter circuit structure and its corresponding design theory, several typical numerical examples are designed, calculated and illustrated. Furthermore, a practical wideband bandstop fllter with i20dB fractional bandwidth of 94% centered at 3GHz with sharp rejection characteristics is fabricated to validate the theoretical prediction. The measured frequency response of the fllter agrees excellently with the predicted result.

Design of a compact and sharp-rejection low-pass filter with a wide stopband

In this paper, a compact and sharp-rejection low-pass filter is proposed and analyzed. By combining a stepped-impedance shunt open stub and two additional shunt open stubs, a compact low-pass filter with wide upper stopband and very high passband selectivity is realized. Wide stopband and sharp rejection characteristics are achieved by realizing three transmission zeros near the passband edges. This filter demonstrated very good measured characteristics at cut-off frequency ( of 2.49 GHz, including a low insertion loss of dB, a wide stopband from 2.8 to 7 GHz and an attenuation slope of 49 dB/GHz. Experimental results also show a good agreement with the predicted results.

A COMPACT BANDSTOP FILTER BASED ON TWO MEANDERED PARALLEL-COUPLED LINES

In this paper, a compact wideband high-rejection microstrip bandstop fllter using two meandered parallel-coupled lines of difierent electrical lengths and characteristic impedances in shunt is presented. The transmission and re∞ection zeros of the fllter can be controlled through analytical equations and rulers given. Using this signal interferences technology, this fllter obtains a low insertion loss and sharp rejection. Bandwidth and rejection level of the fllters of this bandstop fllter can be designed by choosing difierent even- and odd- mode characteristic impedances values of the coupled lines. According to the transmission zeros number, two types of fllters are shown in the paper. To validated this topology, a wideband bandstop fllter with a 3dB cutofi frequency bandwidth of 92% centered at 2.6GHz with sharp rejection characteristics is built to verify the theoretical prediction. The measured frequency response of the fllter agrees excellently with the predicted result.

Compact Wideband Bandstop Filter With Four Transmission Zeros

This work presents a new type of compact wideband bandstop filter (BSF) with four transmission zeros in the stopband. The proposed filter topology consists of a coupled line directional coupler connected in parallel to an interference transmission line. The filter characteristics can be easily controlled by the coupling factor of the coupled line coupler and the characteristic admittances of both the coupler and the transmission line. Design equations and curves are provided for the filter design. To validate the proposed topology, a compact microstrip BSF centered at 2.0 GHz with a measured 20 dB rejection bandwidth of 100% and sharp rejection characteristics is designed and built.

Sharp-rejection microstrip bandpass filters with multiple transmission zeros

A simple design of a sharp-rejection microstrip bandpass (BPF) filter is presented. By creating multiple transmission zeros in the lower and upper stopbands, sharp rejection characteristics are obtained. The basic filter unit consists of a single parallel coupled-line section and an open-ended stub. A lossless transmission line model approach is used to derive the design equations for frequency responses and transmission zero positions. The bandwidths are controllable by the zero locations that in turn are controlled by varying the impedances of the configuration. To validate theoretical predictions, two prototype BPFs operating at lower band 2.4 GHz of WLAN are fabricated in microstrip form.

Low insertion loss, wideband bandpass filters with sharp rejection characteristics

A general circuit configuration using two transmission-line sections is presented to design a sharp-rejection bandpass filter. Sharp rejection characteristic is obtained by creating two transmission zeros across the filter passband by interfering signals propagating through the transmission lines. A simple lossless transmission-line model is used for filter analysis. If an impedance variation of 20-130 ? is considered, the present method is most suitable for 10-50% 3-dB fractional bandwidth variation. Two prototype bandpass filters having approximately 29% fractional bandwidth at the midband frequency 2.9 GHz are fabricated in microstrip line. The filter structures are simple and easy to fabricate. Theoretical, simulated and measured results are in good agreement.

Sharp-Rejection Ultra-Wide Bandstop Filters

In this letter, a modified optimum bandstop filter (BSF) design is presented. Broad stopband and sharp rejection characteristics are achieved by realizing three transmission zeros near the passband edges. Stopband rejection depth and bandwidth can be controlled by the impedances of the configuration. A lossless transmission line model analysis is used to derive design equations. Further, a compact geometry is chosen by replacing the low impedance section with its equivalent dual-high impedance lines, which facilitates convenient folding. To validate the theoretical prediction, a single unit sharp-rejecting prototype BSF having a 20 dB rejection bandwidth of 126% at 1.5 GHz has been fabricated.

Compact tapped stepped impedance open stub dual‐band bandstop filters with sharp rejection characteristics

AbstractIn this article, a novel transmission line (TL) shunt stepped impedance open stub configuration has been presented to design a dual‐band bandstop filter with impedance controlled center frequencies and bandwidths. Design guidelines are derived using lossless TL model. The high‐impedance lines required for TL sections facilitate convenient meandering that makes the geometry compact. To validate theoretical predictions, a prototype filter operating at two bands 1.5 and 3.4 GHz has been fabricated. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2274–2277, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24635

Design of 50–70 GHz Planar Wideband Bandpass Filter on Liquid Crystal Polymer Substrate

In this paper, the authors propose a novel and compact 50-70 GHz planar microstrip bandpass filter, possessing sharp-rejection, low insertion-loss and wide-band characteristics, based on Liquid Crystal Polymer (LCP) substrates. The filter is fabricated on LCP substrates by using standard processing technologies. The proposed filter exhibits a return loss level better than 10 dB, an insertion loss of 5 dB and a 3-dB bandwidth of 30%.The measured and simulated results show good agreement, proving that LCPs are potential and very promising materials for flexible millimeter-wave substrate applications.

Design of ultra‐wideband bandstop filter with three transmission zeros

AbstractIn this article, a compact microstrip coupled‐line configuration has been presented to design a wideband bandstop filter with three transmission zeros. These transmission zeros are utilized to obtain sharp rejection characteristics. A loss‐less transmission line model is used to obtain the filter design parameters. To validate the theoretical prediction, a single section sharp‐rejecting, compact, bandstop filter having a 20‐dB rejection bandwidth of ∼100% at 1.5 GHz has been fabricated. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2955–2957, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23819