Design Equations for a Class of Wide-Band Bandpass Filters (Short Papers)

Design equations and experimental data for a class of bandpass filters having up to two attenuation poles at finite frequencies in the stopband are presented. The new designs are obtained by a relatively simple modification of only the end sections of conventional interdigital and half-wave parallel coupled-line filters. Practical realizability constraints generally limit the design technique to wide-band flters.     

Miniaturized microstrip lowpass filter with wide stopband using double equilateral U-shaped defected ground structure

A compact double equilateral U-shaped defected ground structure (DGS) unit is proposed. In contrast to a single finite attenuation pole characteristic offered by the conventional dumbbell DGS, the proposed DGS unit provides dual finite attenuation poles that can be independently controlled by the DGS lengths. A 2.4-GHz microstrip lowpass filter using five cascaded double U-shaped DGS units is designed and compared with conventional DGS lowpass filters. This low pass filter achieves a wide stopband with overall 30-dB attenuation up-to10 GHz and more than 42% size diminution.     

Characteristic function for quasielliptic filters

The characteristic function of a new class of sharp-cutoff filters is derived in closed form. The magnitude response of these filters has the same transition bandwidth as the elliptic filters, and its attenuation poles can easily be adjusted to produce either equal-ripple or general stopband attenuation.     

Compact and Harmonic Suppression Wilkinson Power Divider With Short Circuit Anti-Coupled Line

A compact Wilkinson power divider using a short circuit anti-coupled line for harmonic suppression is presented in this letter. The structure consists of a pair of anti-coupled line short circuited by a capacitive load realized by a low impedance line. It can offer three finite attenuation poles in the stopband, while arbitrary phase shift can be obtained in the passband. Design procedures have been clearly presented. A 1.8-GHz power divider is designed, fabricated and measured for demonstration. It agreed well with the simulated results. The circuit area of the proposed divider is only 40% of that of the conventional one. Furthermore, the proposed divider has spurious pass-band suppression as high as 20dB.     

Decoupled solutions for design of filters having TEM resonatorswith attenuation poles in upper stopband

The equivalent circuits together with decoupled equations are provided as a solution to the problem of designing the filters having TEM resonators with an attenuation pole in the upper stopband. The proposed method simplifies the design of inserting attenuation poles and gives us much flexibility. The presented design example verifies the exactness of the solutions and shows the usefulness of the approach     

Wide Stopband Parallel-Coupled Stacked SIRs Bandpass Filters With Open-Stub Lines

In this letter, spurious passband suppression in parallel-coupled stacked stepped-impedance-resonators (SIRs) bandpass filters (BPFs) by means of open-stub lines is proposed and implemented. These filters are composed of parallel-coupled stacked SIRs and open stubs. Moreover, the structure with tapped feeding is employed to create transmission zeros near both sides of the passband skirt. The proposed structure can improve the harmonic suppression so that a wide upper stopband with a satisfactory attenuation level would appear in this BPF. Measured results of the fabricated circuits show that the idea works very well     

Parallel coupled microstrip filters with suppression of harmonic response

Corrugated coupled microstrip lines are proposed to design planar microwave filters with suppression of spurious response at twice the center frequency (2f/sub o/). The corrugated structure is designed to equalize the phase velocities of the two eigenmodes in the propagation direction. The designed bandpass filters have a wide upper stopband with satisfactory attenuation levels. In addition, the symmetry of the passband response is improved. Measured results of two fabricated circuits show that the idea works very well.     

A modified Chebyshev bandpass filter with attenuation poles in thestopband

This paper describes a design method of a modified Chebyshev bandpass filter with attenuation poles in the stopband. The insertion of attenuation poles into resonators in the authors' bandpass-filter design is accomplished by connecting a lumped inductor or capacitor in series with a shunt-type coaxial transmission-line resonator. The inserted poles which are distributed over the stopband can be chosen such that the insertion loss of the filter has equiripple characteristic and maximum attenuation in the stopband with the given number of attenuation poles. The modified Chebyshev bandpass filter designed by this method can be effectively used in diplexer design     

Photonic bandpass filters with high skirt selectivity and stopband attenuation

A new photonic signal processor topology that simultaneously achieves both a high-Q and a high skirt selectivity and stopband attenuation filter response is presented. It is based on a novel dual-cavity bandpass optical structure in which two pairs of active fiber Bragg grating cavities are used with an optical gain offset to control the poles and stopband attenuation characteristics of the filter. This concept enables a large improvement in the filter stopband attenuation, rejection bandwidth, and skirt selectivity to be realized. Measured results demonstrate both a narrow bandpass bandwidth of 0.4% of center frequency and a skirt selectivity factor of 16.6 for 40 dB rejection, which corresponds to a 6.5-fold improvement in comparison to conventional single cavity high-Q structures. To our knowledge, this is the best skirt selectivity reported for a photonic bandpass filter to date. The new photonic filter structure has been experimentally verified and excellent agreement between measured and predicted responses is shown.     

E-Plane Integrated Circuit Filters with Improved Stopband Attenuation (Short Papers)

Improved stopband attenuation is achieved by thick strips, by reduced waveguide sidewall dimensions, and by double planar integrated circuits. In contrast to thick strips which may cause high passband insertion losses and filters with reduced waveguide dimensions which require additional tapers, double planar E-plane integrated circuit filters combine the advantages of low costs, high stopband, and low passband insertion losses. Computer-aided design of a four-resonator Ka -band double metal insert filter achieves a calculated stopband attenuation between 40 and 60 GHz of more than 50 dB, the calculated minimum passband insertion loss is 0.43 dB (measured 1.8 dB). Higher order mode excitation and finite thicknesses of the inserts are included in the calculations.     

Transmission Characteristics and a Design Method of Transmission-Line Low-Pass Filters with Multiple Pairs of Coincident Zeros and Multiple Pairs of Coincident Poles

The transmission characteristics and a design method are presented for a transmission-line Iow-pass filter with multiple pairs of coincident zeros in the finite frequency of the passband and multiple pairs of coincident poles in the finite frequency of the stopband and for a transmision-line low-pass filter with Butterworth characteristic in the passband and multiple pairs of coincident poles in the finite frequeney of the stopband. The former transmission-line low-pass filter shows an improved skirt attenuation performance and delay characteristic than a Chebyshev transmission-line low-pass filter in the same network degree. The latter type of transmission-line low-pass filter shows an improved skirt attenuation performance in comparison to a Butterworth transmission-line low-pass filter in the same network degree, it is positioned about in the middle between a Butterworth type and a Chebyshev type, the delay characteristic is improved considerably in comparison to the Chebyshev type, and the characteristic is close to that of the Butterworth type. With this design method, the connecting unit elements in addition to the stubs contribute to the attenuation response. The design example is shown on the basis of a concrete specification, and it is shown that the obtained attenuation strictly fulfills the specification.     

Least-squares monotonic lowpass filters with sharp cutoff

A new class of lowpass-filter functions with no finite zeros and a monotonic magnitude response is first derived by using a least-squares norm to minimise the passband attenuation, and these filter functions are then augmented by adding one pair or multiple pairs of j?-axis zeros. The magnitude characteristics of these filters are compared with those of the generalised inverse Cheby?shev filters and are found to be superior, both in the passband and in the stopband.     

Substrate Integrated Waveguide Filter With Improved Stopband Performance for Satellite Ground Terminal

In this paper, patent pending substrate integrated waveguide (SIW) bandpass filters with moderate fractional bandwidth and improved stopband performance are proposed and demonstrated for a $Ka$ -band satellite ground terminal. Nonphysical cross-coupling provided by higher order modes in the oversized SIW cavities is used to generate the finite transmission zeros far away from the passband for improved stopband performance. Different input/output topologies of the filter are discussed for wide stopband applications. Design considerations including the design approach, filter configuration, and tolerance analysis are addressed. Two fourth-order filters with a passband of 19.2–21.2 GHz are fabricated on a single-layer Rogers RT/Duroid 6002 substrate using linear arrays of metallized via-holes by a standard printed circuit board process. Measured results of the two filters agree very well with simulated results, showing the in-band insertion loss is 0.9 dB or better, and the stopband attenuation in the frequency band of 29.5–30 GHz is better than 50 dB. Measurements over a temperature range of $-{hbox{20}} ^{circ}$C to $+{hbox{40}} ^{circ}$C show the passband remains almost unchanged.      

一种新型介质栅波导滤波特性的研究

提出了一种新型介质栅波导阻带滤波结构,并采用多模网络与严格模匹配相结合的方法对该阻带滤波特性进行了仔细分析,给出了主模TM模的Brillouin图及滤波结构的归一化中心频率、阻带的宽度和带内最大衰减等特性和结构参数的关系.与传统的介质栅滤波器相比,新滤波器结构不仅具有金属损耗小的优点,而且其阻带带宽和带内衰减都要比传统介质栅滤波器的大得多.文中所给出的计算结果对设计该新型带阻滤波结构有指导意义.     

Optimisation of SIW bandpass filter with wide and sharp stopband using space mapping

This work presents a substrate integrated waveguide (SIW) bandpass filter with wide and precipitous stopband, which is different from filters with a direct input/output coupling structure. Higher modes in the SIW cavities are used to generate the finite transmission zeros for improved stopband performance. The design of SIW filters requires full wave electromagnetic simulation and extensive optimisation. If a full wave solver is used for optimisation, the design process is very time consuming. The space mapping (SM) approach has been called upon to alleviate this problem. In this case, the coarse model is optimised using an equivalent circuit model-based representation of the structure for fast computations. On the other hand, the verification of the design is completed with an accurate fine model full wave simulation. A fourth-order filter with a passband of 12.0–12.5 GHz is fabricated on a single layer Rogers RT/Duroid 5880 substrate. The return loss is better than 17.4 dB in the passband and the rejection is more than 40 dB in the stopband. The stopband is from 2 to 11 GHz and 13.5 to 17.3 GHz, demonstrating a wide bandwidth performance.     

Design of filters with prescribed time response and Chebyshev stopband attenuation

This paper presents a new class of low pass filters with Chebyshev stopband attenuation which are intended for pulse applications and characterized by very small values of the dominant polo Q-factor, Their transfer functions are obtained by computational optimization in the time domain of either step response or impulse response under the constraint of double or higher-order multiplicity of the dominant pair of poles. The comparison with Schüssler filters, which are known for their excellent rise-time-overshoot characteristics, reveals that the new filters yield superior frequency and time domain characteristics and yet they have much smaller values of the dominant pole Q-factor. The pole locations and other important frequency and time-domain parameters are tabulated for optimum step response and for optimum impulse response for n = 5, 6, 7, 8 and several values of the maximum tolerable overshoot.     

A new method for the design of IIR filters with flat magnitude response

This paper presents a new direct design of infinite-impulse response (IIR) filters with a flat magnitude response in both passband and stopband (Butterworth filters). The design specifications are passband and stopband frequencies and passband droop and stopband attenuation. The approach is based on an allpass filter with flatness at frequency points /spl omega/=0 and /spl omega/=/spl pi/. Depending on the parity of the IIR filter order, the allpass filter is either real or complex. However, in both cases, the resulting IIR filter is real.     

Synthesis of RC Bandpass Filters

For the first time a method of designing RC bandpass filters is presented. The method consists of two steps. The first step is a scheme to locate the necessary poles and zeros that are RC realizable to produce certain bandpass characteristics. The second step is the synthesis of RC networks to produce these poles and zeros. In the first step, the conformal transformati begin{equation*}s(z) = {left(frac{sn^{2}(z,k) - sn^{2}(alpha{K,k})}{sn^{2}(alpha{K,k})[1 - k^{2}sn^{2}(alpha{K,k})sn^{2}(z,k)]}right)}^{1/2}end{equation*} is used to map the complex frequency s plane into a rectangle in the z plane such that the passband becomes one side, and a part of the negative real axis becomes the opposite side of the rectangle. In the z plane, if poles are located along certain portions of the border and zeros in the interior of the rectangle, certain passband and stopband behavior can be achieved. Among the useful characteristics obtainable by this scheme, the following are three outstanding examples: 1) characteristics that are equal-ripple in the passband and monotonic in the stopband; 2) characteristics that are equal-ripple in the passband and have a number of transmission zeros in the stopband; and 3) characteristics with a maximum gain at the band center and monotonic elsewhere. The steepness of attenuation outside the passband can be altered by a change in the numbers of zeros at the origin and infinity.     

应用缺陷地结构设计低通滤波器

对缺陷地结构(DGS)实现的等效均匀传输线提出了一种简单有效的由S参数求其特性阻抗和有效相对介电常数的方法。而后比较了缺陷地结构和微带线的特性阻抗和有效介电常数随频率变化的规律。最后,应用缺陷地结构设计了两个Chebyshev低通滤波器,并进行了制作和测试。所得滤波器与采用微带线设计的相同参数的低通滤波器相比,阻带最大衰减有超过5dB的改善,并避免了实现高阻抗微带线的工艺困难。     

Automatic generation of CMOS continuous-time elliptic filters

A procedure for the generation of CMOS, continuous-time, high-frequency g/sub m/-C filters with finite transmission zeros is presented. A third-order elliptic filter with 0.5 dB equiripple passband, 15 MHz cutoff frequency and -23 dB attenuation in the stopband is given as an example. The automatic generation method can be generalised to arbitrary high-order prototypes and higher-frequency filters derived from LC ladders.<>