Stopband Characteristics Research Articles

Miniaturized defected ground structure using lumped capacitor

AbstractIn this letter, the miniaturized bandstop filter with lumped capacitor element is presented. The resonator is based on a stopband characteristic of U‐shaped defected ground structure (DGS) section. Lumped capacitor element is embedded into DGS section without altering the geometry. The resonant frequency of DGS section is significantly lowered in accordance with increase of capacitor value. The DGS section with different capacitance values is designed and fabricated. From the measured results, size reduction over 60% is achieved by this method. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 802–804, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24152

COMPACT SLOT ANTENNA WITH EBG FEEDING LINE FOR WLAN APPLICATIONS

A compact CPW-fed slot antenna is proposed for dual- band wireless local area network (WLAN) operations. In this paper, electromagnetic band gap (EBG) structures with square-shaped lattices have been incorporated into the feed network for harmonic suppression. Experimental results show that EBG structures not only exhibit well-behaved band stop characteristics, but also enhance the bandwidth of the proposed antennas. For the proposed antenna with square-shaped lattices, the i10dB return loss bandwidth could reach about 38.4% for the 2.4GHz band and 23.8% for the 5GHz band, which meet the required bandwidth speciflcation of 2.4/5GHz WLAN standard.

Wideband Simultaneous Switching Noise Suppression in Mobile Phones Using Miniaturized Electromagnetic Bandgap Structures

A via stitching (VS)-electromagnetic bandgap (EBG) is analyzed with the compact circuit modeling method. From this analysis, a compact EBG structure is proposed to mitigate wideband simultaneous switching noise (SSN) in mobile phones. This EBG structure is compact enough to be used in mobile phones. Simulations and measurements show that the proposed EBG structure meets the requirements of stopband characteristics, having a stopband range from 750 MHz to 3.25 GHz with –60 dB suppression.

Tunable Combline Bandpass Filter Using Cross-Coupled Stepped-Impedance Resonators with Enhanced Characteristics

This paper proposes a tunable combline bandpass filter with high selectivity, constant bandwidth, and good stopband performances. A filter with these characteristics is obtained by applying cross-coupling to the conventional combline bandpass filter using stepped-impedance resonators(SIRs). For high selectivity and constant bandwidth, cross-coupling is utilized and the SIR configuration is used for enhanced stopband performances. The proposed combline tunable bandpass filter with 5% of fractional bandwidth at 1.6 GHz was fabricated and tested. The measured results showed 11.6% tunability with constant bandwidth, high selectivity and enhanced stopband characteristics.

Synthesis of ultra-wideband bandpass filter employing parallel-coupled stepped-impedance resonators

To design an ultra-wideband (UWB) bandpass filter with the fractional bandwidth (FBW) up to 110% (3.1%10.6%GHz), a new filter prototype consisting of multi-stage parallel-coupled stepped-impedance resonators (SIRs) is synthesised based on the transmission-line theory rather than the conventional multi-mode property. Asymmetrical SIRs are employed instead of the conventional symmetrical/quasi-symmetrical ones, so that an extra degree of freedom is introduced in circuit parameter selection. As a result, the minimum dimension of the coupling gaps between the adjacent SIRs is successfully enlarged to be more than 0.1%mm, which alleviates the requirement on fabrication precision. A simple equivalent circuit for this filter prototype is represented in the form of distributed parameters and the corresponding Chebyshev filtering function is derived as well. The relation between the number of poles in passband, N p , and the stage of the filter, n , is summarised to be N p =3 n +2. To validate the newly derived synthesis theory, a one-stage UWB filter is first synthesised to compare with the previously published results obtained by the electromagnetic (EM) simulator. Furthermore, a two-stage filter is synthesised to successfully meet the Federal Communications Commission (FCC)+s indoor/outdoor spectrum specifications. The fabricated UWB filter exhibits a compact size of 26.58+mm in total length, low insertion loss (0.9+dB at 6.85+GHz), flat group delay (0.5+0.1+ns), good stopband characteristics (+S21+++40+dB at 1+2+GHz) and steep skirt property (+28+dB/GHz) as well. It should be noted that the proposed filter prototype can be also used to realise aUWB filter with an FBW even greater than 110+.

A 24-/60-GHz CMOS On-Chip Dual-Band Bandpass Filter Using Trisection Dual-Behavior Resonators

This letter presents the design and implementation of a 24-/60-GHz millimeter-wave dual-band on-chip bandpass filter using a 0.18-mum standard CMOS process. The concept of quarter-wavelength stepped-impedance resonator (lambda/4 SIR) is utilized to realize stopband characteristics at desired frequencies and reduce the chip size. The structure of the open-circuited dual-behavior resonators (OC-DBRs) produces one passband with two transmission zeros on either side. The size of the designed filter is 1.030 times 0.590 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Novel microstrip lowpass filter using stepped impedance resonator and spurline resonator

AbstractA novel low‐pass filter (LPF) is introduced in this article. The filter consists of a pair of feed lines with spurline resonators and a compact step impedance hairpin resonator. Because of the use of spurline resonators, the LPF exhibits better stopband characteristics and improved ripples performances. The proposed microstrip filter was examined, simulated, and measured. Measurements are given and a good agreement is achieved between simulated and measured results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 196–197, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23993

A novel 2.4 GHz and 6.8 GHz dual‐band transmitter using defected ground structure

AbstractA novel dual‐band module transmitter is presented in this article. It works as a power amplifier at 2.4 GHz that satisfies the 802.11b/g wireless LAN standard and performs as an active frequency doubler at 6.8 GHz with the stop band characteristics of defected ground structure (DGS). The equivalent circuit unit and the stop band characteristics of the microstrip DGS are analyzed and simulated. For the proposed transmitter, second harmonic suppression is below −52.6 dBc in the amplifier mode, and fundamental suppression is below −41 dBc in the frequency doubler mode. It achieves 13.7 dBm of P1 dB and its gain is 16.5 dB at amplifier mode, and its maximum output is 7.8 dBm at 6.8 GHz in frequency double mode. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3225–3228, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23935

High-Resolution Tunable Microwave Filter Using Hybrid Analog-Digital Controls via an Acoustooptic Tunable Filter and Digital Micromirror Device

A programmable broadband Radio Frequency (RF) filter is designed using a Digital Micromirror Device (DMD), an Acoustooptic Tunable Filter (AOTF), and a Chirped Fiber Bragg grating (CFBG). This hybrid analog-digital optical design enables implementation of RF filters with higher number of taps in comparison with an AOTF-only RF filter design and improved RF tunability in comparison with a DMD-only design. A 3-tap RF filter is theoretically analyzed and experimentally demonstrated using a combination of analog and digital optical tap selection. Filter nulls recorded at 6.90, 6.945, and 6.99 GHz show the tunability improvement with the hybrid design. Implementation of higher tap count filters can lead to similar improvements in filter tunability and pass-band and stop-band characteristics.

Multiple band-stop bow-tie slot antennas for multiband wireless systems

A novel and simple design of wideband coplanar waveguide (CPW)-fed bow-tie slot antennas with multiple band-stop characteristics featuring multi-network applications is presented. A frequency stop band can be created by embedding the slot with a pair of stubs, which causes the resultant magnetic fields almost counterbalance in the slot and to be non-responsive at the desire stop band. The effects of the dimensions of the stub on the stop band are also analysed. Dual band-stop characteristic is also accomplished by embedding two pairs of stubs in the slot. Details of the proposed designs and experimental results of the constructed prototypes are presented.

Super-Resolution Focusing Using Volumetric, Broadband NRI Media

We describe the design, fabrication and testing of broadband negative permeability and broadband negative-refractive-index (NRI) metamaterials. The NRI metamaterial is designed to address two major limitations of current NRI media: high loss and narrow bandwidth of operation. The proposed NRI design has a backward-wave bandwidth of 44.3%. This large bandwidth allows the structure to operate away from resonant frequencies, where the loss is significantly lower. The stopband characteristics of a lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /3 slab of the negative permeability medium were measured. In addition, the focusing characteristics of the NRI medium were tested and resolution beyond the diffraction limit was experimentally observed. The slab measured in this paper achieved a resolution enhancement of 2.0 over a bandwidth of 0.33%.

Angle and polarization‐independent bandstop frequency selective surface for indoor wireless systems

AbstractA novel bandstop frequency selective surface (FSS) is presented. It has good frequency stability for horizontally, vertically, and circularly polarized waves, incident normally or at oblique angles. This bandstop characteristic can provide physical security to WLAN and other indoor wireless systems, whereas passing mobile/cellular phone and personal communication signals. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2315–2317, 2008; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.23654

Improved EBG‐loaded waveguide low‐pass filter

AbstractA new design of electromagnetic band gap (EBG) waveguide low‐pass filter (LPF) loaded with double‐array is described to improve the stopband characteristics. Broader gapband width, about 2‐GHz broader than the traditional filters, greater stopband attenuation, and moderate passband insert loss (0.5 dB) can be obtained. Theoretical and measured results are in good agreement. The filter can be employed for the out‐of‐passband clutter rejection of traditional filters. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2090–2093, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23608

Broadband bandpass filters using slotted resonators fed by interdigital coupled lines for improved upper stopband performances

This paper proposes new broadband microstrip bandpass filters based on slotted linear tapered-line resonator (SLTR) and slotted step impedance resonator (SSIR) structures for size reduction and improved stopband performances. A comprehensive treatment of slotted resonators and both ends of the resonator with interdigital coupled lines is described. The design concept is demonstrated by two filter examples including one with an SLTR and another one with an SSIR. These filters have not only compact size but also a wider upper stopband resulting from resonator bandstop characteristics. The simulated and experimental results of stopband performances are better than 15 dB for a frequency range up to 25 GHz.

Analysis of the ${\rm TE}$-Pass or ${\rm TM}$-Pass Metal-Clad Polarizer With a Resonant Buffer Layer

A metal-clad optical polarizer with a resonant buffer layer has been investigated by the finite-element method in this paper. Important waveguide design parameters, such as the refractive index, thickness, interaction length, fabrication tolerance, and band-stop characteristics, have been analyzed in detail. Mode coupling within the polarizer and the losses due to coupling between the polarizer and the input and output waveguides are considered using the normal mode analysis. The loss behaviors of and modes are explained and the roles of the resonant buffer layer are interpreted. By using ultralow index layers, resonance, as well as its phase-matching conditions and excellent performance, has also been presented and discussed for this structure for the first time. Simulations show that high performance can be achieved in a wide range of the cladding thicknesses (ges 2 mum) and interaction length for both TE-pass and TM-pass polarizers. With optimized parameters under 3-mm length, it is possible to obtain a broadband TE-pass polarizer with an extinction ratio of more than 40 dB and insertion loss below 0.2 dB over 200 nm, and a TM-pass polarizer with an extinction ratio of more than 30 dB and insertion loss below 0.4 dB over 28 nm.

Microstrip microwave band gap structures

Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are formed by removing the substrate material in a periodic manner. This paper also demonstrates that these structures can serve as a non-destructive characterization tool for materials, a duplexor and frequency selective coupler. The paper presents both experimental results and theoretical simulation based on a commercially available finite element methodology for comparison.

A coupled‐defected ground structure lowpass filter using inductive coupling for improved attenuation

AbstractA coupled‐defected ground structure (C‐DGS) with closely located DGS cells is proposed for the application of high‐performance lowpass filters (LPFs). The closely located DGS cells create the coupling of ground currents between adjacent DGS cells, and the coupling effect greatly improves the stopband characteristics because of an additional attenuation pole without structural modification. A LPF that uses the C‐DGS has an attenuation slope of 110.8 dB/GHz and a −20‐dB rejection band that ranges from 3.8 to 15.6 GHz. The C‐DGS improves the DGS circuit performance and extends the scope of DGS applications. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1541–1543, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23419

Compact ultra-wideband antenna with dual bandstop characteristic

A simple and compact ultra-wideband microstrip-fed planar antenna with dual bandstop characteristic is presented. By using a U-slot defected ground structure (DGS) in the feedline, a stopband of 600 MHz (from 5.45 to 6.05 GHz) for band rejection of WLAN is achieved. To obtain another stopband, an arched slot is etched on the radiating patch. Experimental results show that the designed antenna, with a compact size of 30 times 24.5 mm, has an impedance bandwidth of 2.8-11 GHz for voltage standing wave ratio (VSWR) less than 2, except two frequency stop-bands of 3.5-4.25 GHz and 5.45- 6.05 GHz. Moreover, the antenna has good omnidirectional radiation patterns in the H-plane.

A microstrip dual‐band bandpass filter with reduced size and improved stopband characteristics

AbstractA novel compact microstrip dual‐band bandpass filter (BPF) is developed with remarkably improved stopband characteristics. Two‐square open‐loop resonators are embedded in a U‐shaped resonator to achieve a significant size reduction of the filter. Meanwhile, a cross‐coupling between nonadjacent resonators is exploited to produce multiple transmission zeros in the stopbands of the filter. As a consequence, wide stopbands with sharp and large attenuations are obtained. Theoretical and measured frequency responses of the designed filter show a good agreement.© 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 618–620, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23154

Elastic Wave Transmission and Stop Band Characteristics in Unidirectional Composites

Elastic wave transmission characteristics in unidirectional fiber-reinforced composites are studied based on the two-dimensional finite element analysis. The composite is assumed to be a lay-up of a finite number of monolayers, each of which contains a single row of fibers spaced at equal distance. Influences of the stacking number and misalignment of monolayers as well as the presence of coating layer around the fibers on the wave transmission spectra are demonstrated for unidirectional SiC-fiber-reinforced Ti-alloy composites. It is shown that the transmission coefficients fall to low values in certain bands of frequency, i.e., stop bands in terminology analogous to perfectly periodic structures. This feature is found to appear more clearly for the transverse wave incidence, irrespective of the misalignment of monolayers. The stiffness reduction of the coating layer is shown to shift the stop bands to lower frequencies, which can be a useful feature for the monitoring of the fiber/matrix interfacial damage.