Wideband Bandpass Research Articles

Analysis and design of an unequal termination impedance power divider with bandpass filtering response

The design of an unequal termination power divider (PD) with a bandpass filtering response and wide out-of-band suppression characteristics is presented. The two-cascaded coupled lines can be designed with a low impedance transforming ratio. For the validation, a 50-to-5 Ω termination impedance PD was implemented at a centre frequency (f 0) of 2.6 GHz. The measured results are in good agreement with the simulations, showing input and output return losses that are better than 19 dB over a passband bandwidth of 190 MHz (2.51–2.7 GHz), and an out-of-band suppression that is better than 19.6 dB from DC to 2.25 and 2.9 to 7.2 GHz. The isolation between the output ports is 39.2 dB at f 0, and it is better than 19 dB with a broadband frequency (DC to 7.2 GHz).

Rectangular optical filter based on high-order silicon microring resonators

The rectangular optical filter is one of the most important optical switching components in the dense wavelength division multiplexing (DWDM) fiber-optic communication system and the intelligent optical network. The integrated highorder silicon microring resonator (MRR) is one of the best candidates to achieve rectangular filtering spectrum response. In general, the spectrum response rectangular degree of the single MRR is very low, so it cannot be used in the DWDM system. Using the high-order MRRs, the bandwidth of flat-top pass band, the out-of-band rejection degree and the roll-off coefficient of the edge will be improved obviously. In this paper, a rectangular optical filter based on highorder MRRs with uniform couplers is presented and demonstrated. Using 15 coupled race-track MRRs with 10 μm in radius, the 3 dB flat-top pass band of 2 nm, the out-of-band rejection ratio of 30 dB and the rising and falling edges of 48 dB/nm can be realized successfully.

Compact Wideband Bandpass Filter for TETRA Band Applications

This letter proposes a compact wideband bandpass filter using Short Circuited line Loaded Triangular Stub Resonator (SCLTR). The SCLTR makes the filter compact and simultaneously shifts the harmonics to higher frequencies. Six transmission poles generated by six resonators provide wide passband bandwidth and three Transmission Zeros (TZs) escalate the selectivity of the bandpass filter response. Two transmission zeros are created by virtue of Simultaneous Electric and Magnetic Coupling (SEMC) and one because of source to load cross coupling. The designed and fabricated filter is very compact with a size of $0.127 \lambda _{g} \times 0.133 \lambda _{g}$ , providing −3 dB fractional bandwidth of 20.5% and wide stopband bandwidth from 0.42 to 1.55 GHz. The experimental results are in compliance with the simulated results, which show that the filter is viable for practical use.

A Wideband Balun Filter on a Triple-Mode Slotline Resonator With Controllable Bandwidth

In this letter, a wideband balun bandpass filter (BPF) composed of a triple-mode slotline resonator and a couple of microstrip–slotline cross-junction is presented. The proposed triple-mode resonator consists of a half-wavelength ( $\lambda $ /2) uniform impedance resonator (UIR) and two different short-circuited slotline stubs installed in middle of slotline UIR. The first three modes of the cross-shaped slotline resonator are then excited and utilized to achieve the balanced-to-unbalanced passband. By tuning the short-circuited stub length, its controllable bandwidth can be realized. Owing to the intrinsic 180° phase difference at two output ports of the microstrip–slotline cross-junction, a wideband passband is achieved with improved magnitude balance and out-of-phase properties. To validate our design concept, a wideband balun BPF operating at 4 GHz with 0.6-dB magnitude imbalance and 8° phase imbalance is designed and fabricated. Both simulated and measured results are found in good agreement.

Design of a Compact UWB Bandpass Filter using Via-Less CRLH TL

A novel compact ultra wideband (UWB) bandpass filter (BPF) based on composite right/left handed transmission line (CRLH TL) is reported in this paper. The proposed UWB BPF is designed and developed by coupling of two unit-cells of via-less CRLH TL, excited by asymmetrical coplanar waveguide (CPW) feed-line. The unit cell of CRLH TL is designed using series interdigital capacitor (IDC) in shunt with the shorted inductive stub. Because of the CPW-fed, no via is required to get the shunt inductance for the realization of CRLH TL, which minimizes the fabrication steps. The filter is compact in size 11.9 x 6 mm 2 . The proposed filter exhibits the return-loss (|S 11 |) more than 11.2 dB and insertion-loss (|S 21 |) less than 0.5 dB and low and flat group delay response throughout the passband, 3.3 GHz to 13.0 GHz. The proposed UWB BPF also shows the good stopband rejection (|S 21 | > 20 dB and |S 11 | < 0.8 dB) from 13.6 GHz to 15 GHz and steep roll-off from passband to stopband. The fractional bandwidth (FBW) of the filter is found to be 119 %. The equivalent lumped circuit model of the filter is obtained through Ansoft Designer. All simulated results are extracted through method of moment based simulator, IE3D. Agilent vector network analyzer (VNA) is used to get the measured results. All measured results are found in close similarity with the simulated results.

Single- and Dual-Band LTCC Filtering Switch With High Isolation Based on Coupling Control

This paper presents a novel method for designing single- and dual-band filtering switches based on coupling control. First, the ON- and OFF-state coupling matrices are analyzed to achieve bandpass responses and high isolation, respectively. Then, they are used to guide the low temperature cofired ceramic circuit realization. The ON- and OFF-states are enabled by controlling the PIN diodes in the filter feeding structures. In the ON-state, the circuit is equivalent to a bandpass filter without signals passing through the PIN diodes, which avoids additional loss introduced by the PIN diodes. For the OFF-state isolation, it is realized by controlling the coupling of the filtering circuit, which is different from that of conventional switches by turning off transistors or diodes to obtain isolation. Thus, isolation is considerably enhanced. For demonstration, a single-band filtering switch is implemented with a compact size of 0.050 λg × 0.048 λg × 0.023 λg . Furthermore, a dual-band one of the same dimension is realized with controllable passband frequencies and bandwidths in the ON-state as well as high isolation in OFF-state. The presented filtering switches feature compact size, low ON-state insertion loss, high OFF-state isolation, and high reliability, which are suitable for industrial applications.

A Compact UWB Bandpass Filter using Hybrid Fractal Shaped DGS

In this paper, a novel compact ultra wideband (UWB) bandpass filter (BPF) based on fractal-shaped defected ground structure is designed and developed with more than -20 dB out-of-band rejection level. It is made of stepped impedance line and composite right/left handed-transmission line (CRLH-TL) constructed with capacitive gap in conductor strip and a hybrid fractal-shaped ring slot in ground plane. The proposed UWB bandpass filter has good passband performance with -10 dB return-loss bandwidth of 2.2 GHz to 10.6 GHz with fractional bandwidth of 131%. The prototype of proposed filter is fabricated and measured. Good agreement is seen between simulated and measured results. The designed and developed filter is compact in size, simple in geometry and owns good S-parameters performance characteristics in both passband as well as in stopband. Return-loss better than 10 dB and insertion-loss less than 0.4 dB (except at some higher frequency) is obtained throughout the passband whereas, in stopband, insertion-loss more than 20 dB and return-loss better than 0.8 dB is observed up to the stopband frequency of 20 GHz. Moreover, UWB BPF also shows the flat group delay (variation ≤ 0.75 ns) performance. Thus the proposed filter can be a useful candidate for low profile future wireless communication systems.

Wideband Single-Ended and Differential Bandpass Filters Based on Terminated Coupled Line Structures

In this paper, a novel terminated coupled line structure (TCLS) is introduced, which is constructed by a coupled line section and four terminations loaded on it. Introducing different kinds of terminations, three types of bandpass filters (BPFs) based on TCLSs are proposed, theoretically analyzed, and fabricated, including two single-ended wideband BPFs with fractional bandwidths (FBWs) of 67% and 40% respectively, and a wideband differential BPF with 74% differential-mode FBW. These BPFs can achieve wide passband bandwidth, low in-band insertion loss, high passband selectivity, as well as deep stopband rejection performance simultaneously, benefited from the multiple transmission zeros and transmission poles obtained by the TCLSs. The practical design procedures of these BPFs are presented and explained. The agreement among theoretical predictions, EM-simulated, and measured results validates our proposed filter structures. Finally, the generalized multistage filter topology based on TCLSs is proposed to design high-order filters with better filtering performances.

Compact tri-band bandpass filter with two closely frequency spaced passbands

A compact tri-band bandpass filter based on a novel six-mode resonator is proposed. The filter has three passbands centered at 2.45, 5.2, and 5.8 GHz for WLAN applications. Among them, two closely frequency-spaced passbands with a small center frequency ratio (1/1.11) are realized. The 3 dB bandwidth of the two passbands are 5.8 and 5.2%, which means they have equal absolute bandwidth. Source-load-coupling structure is adopted to enhance the high-isolation performance. And the filter has six transmission zeros, resulting in high-frequency selectivity. The passband frequencies and bandwidths of the filter can be controlled. The measured results are in good agreement with electromagnetic simulation. Its circuit only occupies 0.14 λg × 0.09 λg (11.2 mm × 7.1 mm), where λg is the guided wavelength at the lowest passband center frequency.

Novel Wideband Bandpass Filter with Dual Notched Bands Using Stub-Loaded Resonators

In this letter, a novel wideband bandpass filter with dual notched bands using stub-loaded resonators is proposed. By using the signal interaction of two transmission paths, a wideband passband and two notched bands can be independently achieved and designed. By cascading two back-to-back vertical transitions, a six-pole wideband filter with equal ripple filtering response is synthetically analyzed. The dual notched bands are controlled by the even- and odd-mode resonant frequencies of the stub-loaded resonator. As a design example, the proposed wideband filter with dual notched bands is simulated and fabricated. The desired wideband filtering response is experimentally validated, and two notched bands are measured at 3.04 and 3.85 GHz, respectively.

Design of a SIW Bandpass Filter Using Defected Ground Structure with CSRRs

In this paper, a substrate integrated waveguide (SIW) bandpass filter using defected ground structure (DGS) with complementary split ring resonators (CSRRs) is proposed. By using the unique resonant properties of CSRRs and DGSs, two passbands with a transmission zero in the middle have been achieved. The resonant modes of the two passbands are different and the bandwidth of the second passband is much wider than that of the first one. In order to increase out-of-band rejection, a pair of dumbbell DGSs has been added on each side of the CSRRs. The structure is analyzed using equivalent circuit models and simulated based on EM simulation software. For validation, the proposed filter is fabricated and measured. The measurement results are in good agreement with the simulated ones.

Compact Tunable Balanced Bandpass Filter With Novel Multi-Mode Resonator

A novel multi-mode resonator is presented to design compact tunable balanced bandpass filters (BPFs). From the theoretical analysis, the common-mode (CM) resonant frequencies are different from that of the differential-mode (DM) response, so the CM suppression can be achieved without adding any extra lumped elements. For the DM response, the modal frequencies of odd and even modes can be adjusted simultaneously by varying the varactors. This helps to design the DM response with tunable passband center frequency. Moreover, the even-mode resonant frequency can be tuned independently, leading to controllable passband bandwidth of the DM. To verify the design method, a compact tunable balanced BPF is developed, fabricated and measured. Good agreement can be attained between the measurement and simulation.

Highly compact UWB bandpass filter based on composite right/left-handed transmission line and meander fractal like ring slot in ground

An ultra-wideband (UWB) highly compact bandpass filter with extremely high passband bandwidth is presented. The proposed structure is made using three-staged stepped-impedance lines and a composite right/left-handed transmission line (CRLH-TL) synthesized with meander fractal like ring slot in the ground and series capacitive gap in conductor strip. The capacitive gap in conductor strip and meander fractal like ring slot in the ground plane play major role for controlling the lower and higher cut-off frequencies. The equivalent circuit model of proposed filter is demonstrated and lumped parameters are extracted. A prototype is fabricated to experimentally validate the performance of proposed filter. The proposed UWB filter has extremely wide −10 dB return loss passband bandwidth from 3.14 to 18.26 GHz with relative bandwidth of 142% and insertion loss better than 0.5 dB. Also it achieves a wide upper-stopband from 19.7 to 24.4 GHz with insertion loss better than 13.0 dB, return loss &lt;1.5 dB and sharpened rejection skirts outside the passband at both lower and upper frequency ends. Good agreement is found between simulated and measured results with measured group delay variation in the passband &lt;0.65 ns.

A constant absolute bandwidth tunable band-pass filter based on magnetic dominated mixed coupling and source–load electric coupling

In this paper, a constant absolute bandwidth (CABW) band-pass filter based on magnetic dominated mixed coupling and source–load electric coupling is proposed. Specially, a novel mixed electric and magnetic coupling structure is presented to control the coupling coefficient variation and thus realize a narrow CABW width. Two transmission zeros are added to the filter response using a source–load coupling technique, leading to a better selectivity. The measurement shows that the –1 dB absolute and fractional bandwidth is 29 ± 3 MHz and 1.8–2.6%, respectively, while the central frequency of the passband varies from 1.11 to 1.51 GHz.

A new approach to construction of extended kit for M-Sequence UWB sensor system based on LTCC

Purpose The purpose of this paper is to introduce modified in–phase and quadrature components (I–Q) demodulator based on low temperature co-fired ceramics (LTCC) dielectric substrate GreenTape 951PX for M-Sequence ultra-wide band (UWB) sensor system. Design/methodology/approach Microstrip low pass (LP) and band pass (BP) filters for UWB sensor systems with required properties (for both filters, minimum attenuation is −40dB in stopband, bandwidth of pass band is 6 to 8.5 GHz for BP filter and cutoff frequency is 2.5 GHz for LP filter) were designed, simulated, fabricated and measured using dielectric substrates Du Pont GreenTape 951 PX. The developed microstrip filters were integrated with all parts of I–Q demodulator on one multilayer structure based on LTCC substrate Du Pont GreenTape 951 PX. Findings Both type of microstrip filters integrated in the I– Q demodulator achieved better transmission characteristics in comparison with commercial available filters. It was shown that LTCC technology based on GreenTape 951PX proves good stability in gigahertz frequency and suitability for fabrication of I–Q demodulator with a multilayer approach. Originality/value The novelty of this work lies in substituting commercially available LP and BP filters used in I– Q demodulator by microstrip LP and BP filters with better performance and furthermore the I– Q demodulator is fabricated based on LTCC instead of previously used PCB.

A compact wide bandwidth bandpass filter with SIR and S‐shaped coupled spiral resonator

ABSTRACTThis article proposes a compact wide bandwidth band pass filter (BPF) with a stepped impedance resonator (SIR) and an S‐shaped coupled spiral resonator. The SIR has a wide bandwidth while the S‐shaped coupled line has a compact structure due to the spiral type resonator. The BPF used the S‐shaped folded structure instead of the λg/4 transmission line to reduce the size and to enhance the performance of the BPF. The via‐hole was not used in order to keep the design simple. Due to the narrow coupling gap, the bandwidth of conventional BPFs can barely exceed 40%. However, in this work, the proposed BPF achieved a bandwidth of 68%, which is larger than the conventional filter. The experimental results in terms of insertion loss (S21) and return loss (S11) are 0.61 dB and 15.7 dB at 5.3 GHz. The smaller size of the BPF is suitable for microwave communication systems. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2334–2336, 2016

Research of dual-band microwave photonic filter for WLAN based on optical frequency comb.

This paper presents a dual-band microwave photonic filter for a wireless local area networks with independently tunable passband center frequencies and bandwidths. The two bands of the filter were 2.4 GHz and 5.725 GHz, respectively. The filter was based on a stimulated Brillouin scattering and an optical frequency comb (OFC) scheme. We created this filter using OFC pumps instead of a single pump. The OFC scheme consists of a cascaded Mach-Zehnder modulator (MZM) and a dual-parallel MZM (DPMZM) hybrid modulation that generated seven and 11 lines. The experimental results show that the two passbands of the filter were 80 and 130 MHz.

Stub-Loaded Theory and Its Application to Balanced Dual-Band Bandpass Filter Design

Novel stub-loaded theory is presented and applied to design balanced dual-band bandpass filter with independently controlled passband frequencies and bandwidths. According to the presented stub-loaded theory, the first differential-mode resonance can be independently designed by the loaded stubs, while not affecting the second one. Besides, except for the main coupling path, one more coupling path between the loaded stubs can be used to independently control the coupling coefficient of the first passband. Therefore, both the passband frequencies and bandwidths of each differential passband can be easily designed. To validate the proposed idea, the balanced dual-band BPF is designed, simulated and measured. Simulated and measured results are well agreed.

Bandpass frequency selective surface using asymmetrical slot four arms star geometry

ABSTRACTIn this article, the authors proposed a bandpass frequency selective surface using the slot four arms star geometry. An expression to calculate the resonance frequency is introduced, for which results with difference &lt;6%, when compared to measured ones, were obtained. The polarization dependence was discussed and a model based on two independent equivalent structures was successfully presented. Three prototypes were designed, fabricated, and characterized. A good agreement between simulated and measured results is observed. With the asymmetrical geometry, two bandpass bandwidths, separated by a notch band‐rejection, were achieved, a suitable characteristic to avoid co‐channel interferences. Furthermore, if an orthogonal polarization is applied, this notch band‐rejection can be converted to a bandpass bandwidth, providing a polarization filter behavior. The geometry simplicity and observed frequency response make the proposed FSS potentially attractive for many telecommunication systems. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1105–1109, 2016

Perturbed Sierpinski carpet resonator and its usage in compact dual and triple band bandpass filters

In this paper, perturbed Sierpinski carpet fractal shaped resonator is characterized and applied in the design of multiband band pass filters (BPFs). The route to achieving compact multimode resonators starting from the Sierpinski carpet fractal shaped resonator is detailed. The proposed resonators are used to demonstrate two topologies of dual band bandpass filters with passband center frequencies at 3.5 GHz as well as 5.5 GHz, respectively. Both the designs exhibit nearly identical passband bandwidth. In the second design, it is observed that the second passband gets slightly shifted towards 5.85 GHz. However, with edge loading this shift is nullified. A scaled down version of the same resonator is designed and three such resonators are interdigitally coupled in conjunction with complementary split ring resonators to exhibit a novel technique of achieving compact triband bandpass filter. All designs have acceptable passband insertion loss in the respective bands. Accessories are used to improve passband selectivity in all designs and also a wide stop band till 10 GHz is obtained. Fabrication prototypes for all the variants are realized with simulated and measured results in good agreement. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:418–425, 2016.