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With the rapid growth of terrestrial and mobile telecommunications, companies in this sector need highly selective equipment, lightweight with low manufacturing costs, hence the interest in miniaturizing front-end electronic components such as filters, antennas, mixers etc. In this paper, a novel structure of a passband and highly selective filter is proposed and discussed. The design involving two complementary split-ring resonator filter (CSRRF) configurations in microstrip technology operating at 6 GHz is investigated. To achieve the goal of this research the "N + 2" cross-coupling matrix method is used. The step-shaped CSRR filter that yields better electrical performance, smaller size, and low weight is realized. Its frequency responses simulated with HFSS software are compared with experimental measurements. An excellent agreement is observed in terms of bandwidth and center frequency. [ABSTRACT FROM AUTHOR]

A quad-band microstrip bandpass filter (BPF) based on a 13-mode resonator is proposed in this article with compact size, high band‐to‐band isolation, and multiple transmission zeros (TZs). The proposed filter is constructed by two transmission paths from the input to the output port, which employs the transversal cancellation mechanism of two transition paths to introduce extra nine TZs. Therefore, a total of 12 TZs are located at 0.2, 1.8, 2, 3.88, 4.61, 5.24, 5.9, 9.26, 9.51, 12.32, 12.75, and 13.27 GHz, respectively, realizing high selectivity. Moreover, the designed filter can achieve quad passbands with centered frequency at 0.95, 2.78, 7.32, and 10.63 GHz for the requirement of multi-service in modern communication systems, with wide bandwidth of 235, 790, 2200, and 1540 MHz, respectively. The measured results agree well with the simulation results, which proves the feasibility of the design method. [ABSTRACT FROM AUTHOR]

In this article, a low loss and compact microstrip ultra-wideband bandpass filter (UWB-BPF) with a narrow-notched band is recommended for suitable applications in ultra-wideband wireless communication systems. The design methodology is presented to develop the microstrip structure of the UWB-BPF pursued by a single notched band (NB) in the passband of the UWB filter. An array of I-shaped defected ground structures and L-shaped defected microstrip structures based lowpass filters is cascaded with a shorted stub based highpass filter to achieve a UWB-BPF response. The two identically folded open stubs are loaded to obtain the narrow NB. The center frequency of the UWB-BPF without the NB is 3.5 GHz, and the stopband is suppressed up to 14.5 GHz. The fractional bandwidth achieved is 160%, with a circuit area of 0.11 ${\rm{\lambda }}_{\rm{g}}^{\rm{2}}$ λ g 2 . Furthermore, the single NB is attained at 5.7 GHz to reject interferences of signal from the 5G network with an attenuation level of 59 dB. The electromagnetic simulated and experimental responses of the designed structures demonstrate a well-matched behavior among them. The NB at 5.7 GHz in the UWB-BPF passband region suppresses the signal interference from the 5G network (5500 MHz), WLAN (5900 MHz), and WiMAX (5800 MHz). [ABSTRACT FROM AUTHOR]

A super-compact ultra-wideband (UWB) microstrip band-pass filter (BPF) with triple-notched bands and wide stopband is proposed in this paper. The super-compactness of the proposed filter is achieved by integrating the modified SCRLH-TL UWB-BPF and backbone-shaped defected ground structure (DGS). The equivalent LC circuit models of the DGS and the modified SCRLH-TL UWB-BPF with the DGS are analyzed to validate their numerical simulation results. To introduce the triple notched-bands to mitigate the interference the two triple-mode SIRs are designed and loaded on the modified UWB-BPF without increasing the circuit size. The proposed filter was fabricated by using a conventional PCB process with the substrate of FR4. The measured 3-dB passband ranges from 2.8 through 10.2 GHz with the fractional bandwidth (FBW) of about 114%. The triple-notched bands with attenuation of more than 15 dB are measured at 4.4, 5.3 and 8.2 GHz, respectively. The filter exhibits a high selectivity with steep skirt property and has a wide upper stopband with an out-of-band rejection of −10 dB at 11.8−20 GHz. Its total dimension, including the rectangular substrate with feed lines, occupies only 16mm × 8 mm. [ABSTRACT FROM AUTHOR]

In this paper, a novel Ultra-Wideband (UWB) Bandstop Filter (BSF) with five Transmission Zeros (TZ) and three Transmission Poles (TP) is presented. This filter is designed with a new type of resonator. Validation of the proposed filter with the lumped model is also investigated. Further, the transmission line circuit model of the filter is proposed, and consequently even and odd mode impedance is calculated analytically. Furthermore, a compact size of 16.8 mm × 14.98 mm (0.2λg × 0.18λg) is achieved by employing folded stubs. The proposed filter offers an Ultra-wide bandwidth of 7.5 GHz (2.9 –10.4 GHz) with a rejection depth of greater than 20 dB over the entire stopband. Moreover, the upper and lower skirt factors of 70 dB per GHz are achieved. A prototype of the proposed UWB BSF is fabricated and measured. Simulated and measured results are in good agreement, which validates the proposed design. [ABSTRACT FROM AUTHOR]

In this paper, a high-efficiency class-F power amplifier with a harmonic control circuit is proposed. The harmonic control circuit is realised by loading microstrip branch lines to achieve a short-circuit state for the second harmonic. The double spiral defected ground units are loaded on the ground of the microstrip line of the drain bias circuit to produce a low-pass filtering and stopband suppression effect outside the passband, so as to suppress the third harmonic. Meanwhile, it would provide an open-circuit state for the third harmonic, and finally meet the harmonic impedance tuning demands of class-F power amplifier. Through theoretical analysis and simulation, a high-efficiency class-F power amplifier operating at 2.5 GHz ~2.7 GHz is designed. The measured results show that in the working frequency band, the drain efficiency is 66.3%~71.1%, the output power is 40.9 dBm ~42.1 dBm and the gain is 10.9 dB ~11.8 dB. [ABSTRACT FROM AUTHOR]

In this work, an ultra-wide stopband low-pass filter (LPF) is proposed using tapered step impedance resonators. The distributed equivalent of the proposed step impedance LPF is extracted, analyzed, and legitimated with simulated and fabricated results. The fabricated prototype has a 3 dB cut-off frequency (fc) of 2.92 GHz and an ultra-wide stop band extended up to 25.7 GHz (8.8fc) with an attenuation level of >20 dB. The transition bandwidth (from 3 to 20 dB) is 0.20 GHz and the roll-off factor is 112 dB/GHz (a reference to 30 dB). The passband insertion loss is 0.32 dB at 1.5 GHz and the normalized circuit size of the filter is 0.055. [ABSTRACT FROM AUTHOR]

A stub-loaded U-shaped microstrip resonator (U-SLR) exciting two odd-modes and two even-modes and its applications to single-wideband and dual-band bandpass filter (DB-BPF) are introduced. The parallel-coupled lines (PCLs) at input/output (I/O) ports can provide a wideband response by exciting two additional modes in the passband, so-called PCLs modes. In addition to the transmission poles (TPs) in the passband, two transmission zeros (TZs) in the lower and upper stopbands can be created by the loaded stubs. A compact size, high-selectivity, and low insertion loss WB-BPF is designed, fabricated, and tested. Moreover, a compact and low loss DB-BPF with closely spaced passbands is designed and tested. TZ-shifting method is used to design a DB-BPF by splitting the wideband. To achieve this, it is sufficient to change the length of only one of the loaded stubs. The calculated, simulated and measured frequency responses for both single-wideband and DB-BPFs are in very good agreement. [ABSTRACT FROM AUTHOR]

A novel four-element MIMO antenna with reconfigurable bandwidth characteristics is reported in this paper. The proposed antenna is evolved using a chamfered rectangular monopole operating from 2.2 GHz to 11.3 GHz. The frequency selectivity of the antenna is accomplished by introducing a bandstop filter adjacent to the microstrip feed line of the UWB monopole. The proposed bandstop filter is constructed by introducing a notch in an all-pass filter. The notch band is carefully chosen such that the integration of the filter with the UWB radiator provides resonances centred around 2.4 GHz and 3.6 GHz suitable for WLAN communications. The bandwidth selection is accomplished using feed selection which is enabled using a set of PIN diodes. This makes the antenna work in two distinct operating modes, namely, the UWB mode (2.2 to >12 GHz) and the dual-narrowband mode (D-NB) (2.4 & 3.6 GHz). The research is further extended towards the construction of a MIMO antenna suitable for mobile networks. The prototype of the proposed four-element antenna is fabricated and analysed for S-parameters, radiation, and diversity characteristics. The average gain of the MIMO antenna array is greater than 4.5 dBi in the UWB/D-NB mode. The proposed antenna is suitable for low power UWB communications and high throughput WLAN such as IoT, sub 6 GHz 5 G communications, etc. [ABSTRACT FROM AUTHOR]

In this paper, a miniaturized tri-band microstrip bandpass filter is designed using three sets of shorted stub-loaded stepped impedance resonators (SSLSIRs). One pair of resonators have meandered short stub-loaded resonator (MSSLSIR) to further reduce the dimensions of the whole tri-band filter. The operating frequencies of the SSLSIRs and MSSLSIR are designed for the applications in the WLAN (2.45/5.2 GHz) and Wi-MAX (3.5 GHz) systems, respectively. The proposed filter is advantageous in terms of size miniaturization up to 0.013 × 0.012 λ g ( λ g is guide wavelength) and in terms of good control over the passbands. The simulated and measured results are both in good agreement. [ABSTRACT FROM AUTHOR]

This paper discusses a new method for designing a microstrip dual-mode, sharp skirt, wideband bandpass filter with controlled center frequency and bandwidth from bandstop filter topology. A meander closed loop resonator with directly connected orthogonal feed lines provides a Bandstop filter (BSF) with reduced size. A pair of L-shaped open stubs introduced along the diagonal axis D-D1 realizes a wide passband within the rejection band (0.93–4.13 GHz) of the bandstop filter with sharp stopbands on either side of the passband. Furthermore, the effect of L-shaped open stubs susceptance on passband edges is demonstrated. A quarter wavelength stepped impedance shunt stub (SISS) connected at θ = 170 ∘ is proposed to achieve additional transmission zeros in the upper and lower rejection bands to improve the sharpness of filter response. Both center frequency and bandwidth of the proposed filter are controlled by the impedance ratio (R) of the SISS element. The proposed filter is simulated using ADS, fabricated and measured using Vector Network Analyzer (VNA). A good agreement is achieved between simulated and measured results. [ABSTRACT FROM AUTHOR]

A novel compact ultrawideband (UWB) filter with reconfigurable band notch property is presented. Stepped impedance slotline (SISL) resonator along with two open-ended coupled microstrip is used for the realisation of UWB filter. The WLAN band of rejection is obtained by placing the U-shaped DGS near the SISL resonator. Furthermore, two capacitors are placed in the active slot of U-shaped DGS to obtain WiMAX band of rejection. The proposed UWB filter with reconfigurable band notched characteristics is fabricated and measured. The measured results agree well with the simulated results. [ABSTRACT FROM AUTHOR]

This work presents balanced microstrip filters with asymmetrical frequency response based on a balanced trisection topology. The proposed balanced trisection topology has the feature of being used in single and multiband microwave filters. In this work, in order to test the topology flexibility, we address two applications, one for a single-band filter and the other for a dual-band filter. This topology introduces TZs on either side of the passband edges, improving the selectivity on one side of the passband. The non-adjacent resonators of the single-band trisection balanced filter are based on a Pi-network balanced resonator which is composed by six transmission lines (TLs) and two inductors (Ls). The differential-mode (DM) and common-mode (CM) resonances can be chosen independently with a proper selection of the impedances and the electrical lengths of TLs in order to have high DM stopband and intrinsic high common mode rejection (CMR). The Pi-network was modified and analyzed under the even and odd mode technique to have a dual-band behavior. Good agreement between simulation and measurement was achieved. [ABSTRACT FROM AUTHOR]

A bandstop filter is proposed, where the resonant element is a slot that is folded to the shape of the letter U and embedded into the microstrip line so that no extra width is required. Moreover, the folding of the slot reduces its length to 1/4 the effective wavelength. This is a considerable size reduction in comparison with the filters using the resonant elements like rings or coupled shortcircuited and open-circuited stubs. The designed prototype at the WLAN frequency of 2.45 GHz was investigated using the CST software package and showed low insertion loss at the passbands and high rejection across the stopband. The folding of the slot offered very low radiation at the stopband. The simulation results are validated by measurements on the fabricated prototypes. [ABSTRACT FROM AUTHOR]

In this paper, a compact quint-band microstrip bandpass filter (BPF) based on multiple mode resonating technology is proposed. It is composed of a symmetric dual-mode λ/4 resonator loaded with a shorted stub, two inverted F-shaped resonators, and two pairs of coupling configurations. To miniaturize the filter, the three resonators are bent and cross coupled together. Considering that the BPF has a symmetric structure, the even-odd mode analysis method is employed. On the basis of the simulation, the presented filter was fabricated by using a conventional PCB process with the substrate of Rogers RT/Duroid 5880. The measurement results are consistent well with the simulated data. The measured operating bands are centered at 1.8, 3.5, 4.5, 5.8 and 6.8 GHz, respectively, which are suitable for GSM, WiMAX, 5G, RFID and WiFi6 applications simultaneously. The measured in-band minimal return losses within five passbands are better than 15 dB. Furthermore, the filter exhibits a high selectivity with steep skirt property and the four band-to-band isolations among the five passbands are higher than 27 dB, and the out-of-band rejection is better than 25 dB. The filter's total dimension occupies only 0.18λg × 0.15λg, where λg represents the free space wavelength corresponding to the center frequency of the lowest passband. [ABSTRACT FROM AUTHOR]

A millimeter wave dielectric resonator antenna (DRA) array with high-gain and high-selectivity filtering response is proposed, which is composed of stacked feeding network and stacked DRA. The stacked feeding network consisting of two layers of thin substrate has the efficient characteristics to expand and integrate. The band-pass filter formed by complementary split ring resonator (CSRR) structure generates radiation nulls at the edge of the high-frequency band. With the improved filtering stubs loaded at the end of the H-shaped microstrip power divider, a radiation null at the edge of the low-frequency band is obtained and the roll-off degree at the edge of the high-frequency band is improved. By embedding the metal column in the fork-shaped stub, the suppression level of the low-frequency stopband is improved. A prototype of the proposed DRA array is fabricated and measured, which shows 7.2% relative bandwidth and a stable directional pattern in the range of 26.28–28.25 GHz with an average gain of 9.57 dBi. And an out-of-band suppression level of 18 dB is achieved. The DRA array can be applied for 5 G millimeter wave band to support high-speed communications at short distance. [ABSTRACT FROM AUTHOR]

In this paper, a 4-pole quasi-elliptic planar bandpass filter at Q-band on the liquid crystal polymer (LCP) is presented. The conventional design and development process of millimetre wave filters required to consider the surface roughness effects from the design stage for accurate development of filter at high frequency. Finite surface roughness of rolled copper and its impact on electrical performance are studied. Polishing is one of the methods to improve the conductor surface roughness. An improvement of 50% in surface roughness is reported for the rolled copper on the LCP, resulting in better than 1 dB insertion loss of the bandpass filter. Commensurate simulation and measurement results are presented. [ABSTRACT FROM AUTHOR]

This study presents new miniaturized designs of microstrip multiband bandstop filter (BSF) and multiband bandpass filter (BPF) employing step impedance resonators (SIRs) and RT/Duroid 6010 substrate. The projected bandstop filter can be adopted in applications for removing the interference of narrowband signals from the allocated bands of other wireless systems operated under 2.5, 5.84, and 9.79 GHz. On the other hand, the designed bandpass filter can be used in RF transceivers operating in various isolated narrow frequency bands at operating frequencies of 5.35, 5.555, 6.36, 7.84, 8.385, and 9.5 GHz. The novelty of this paper comes from the considerable smallness of the designed filters and extremely low fractional bandwidths (less than 1%) as compared with numerous reported filters in the literature, especially the superconducting filters. Both filter designs have been verified through measurement, and the measured consequences are in line with the simulation ones. [ABSTRACT FROM AUTHOR]

In this paper, a new compact dual-band filter based on closed-loop rectangular ring resonator is presented. Two passbands are designed to operate at L1 and L2 global positioning system (GPS) bands, respectively. The first passband is established by utilizing the dimension of square ring resonator that resonates at L1 band. Then, a perturbation mode element is applied to the upper and lower sides of the ring to separate the other degenerate mode and allocate the second passband of the filter at L2 GPS band. The dual passband can be adjusted to meet the designer requirements. The frequency selectivity of the filter is improved by using two symmetric parallel-coupled 0-degree feed structure that introduce a pair of transmission zeros around the passband. A practical dual-band bandpass filter is fabricated and measured. The measured results show good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

This paper presents a reconfigurable loop-based filter performing compound reconfiguration. The designed filter is capable of functioning as a bandstop or bandpass filter by a simple approach of cascading the resonator to the transmission line connecting source and load. Shifting of operating frequencies is characterised by switching between a loop and a C-shaped resonator. To demonstrate the working of the proposed concept, a compound reconfigurable filter operating at 1.5 GHz and 1.6 GHz is developed. The filter is developed on a compact layout of size 0.27 × 0.12 λg2. The proposed prototype is fabricated and measured for real-time validation. [ABSTRACT FROM AUTHOR]

In this article, a high-selectivity double-mode substrate integration waveguide bandpass filter utilizing modified parallel coupled microstrip lines (MPCML) is presented. The designed method is analyzed in detail. Six metal vias are designed to perturb TE-101 mode and TE-103 mode. The resonant frequency of the perturbed TE-101 mode is shifted to high frequency, close to that of TE-102 mode, which caused the formation of passband. The resonant frequency of the perturbed TE-103 mode is shifted to high frequency, improving out-of-band performance. Simultaneously, the coplanar waveguide structure is used to adjust the external quality factor. Two rectangular slotlines are introduced to adjust center frequency and bandwidth slightly. Two rectangular stubs are designed for better source and load matching. Three transmission zeros (TZs) are obtained to improve the selectivity. The designed MPCML promotes the generation of TZs. Another TZ is obtained by the coupling between TE-102 mode and TE-103 mode. The designed filter operates at 14.4 GHz with bandwidth of 800 MHz. The measured return loss is better than 15 dB, and the minimum insertion loss is 1.60 dB. The measurement is agreed with the simulation. [ABSTRACT FROM AUTHOR]

In this paper, a microstrip low-pass filter (LPF) using folded-flag-shaped resonators is designed and presented. Its base resonator length is 12.4 mm, and the proposed low-pass filter has a sharpness of 0.08 GHz. The filter cut-off frequency is 1.44 GHz, and the return loss is reduced to a level of −17 dB, indicating a flat pass-band. Also, the suppressing cell is used to weaken the disturbing harmonics by a stepped impedance structure and two high-impedance stubs with an L-shaped structure, which results in a bandwidth of 17.78 GHz. The circuit area of the LPF is 20.9 × 7.5 mm2, which it has created a suitable normalized circuit size (NCS) rate due to the −3 dB cut-off frequency. The figure of merit (FOM) of the proposed filter is 114450, and it indicates that the microstrip LPF responses are optimal as compared to previous works. [ABSTRACT FROM AUTHOR]

Bandstop filters with single and dual stop-bands were implemented using coupled mode microstrip slot resonators (MSRs) for the first time. With compact and ease of fabrication, the MSRs provide excellent filter response as desired. It is found that the MSRs can offer narrow bandwidth of less than 20% fractional bandwidth and large isolation of more than 40 dB. The designs of MSRs and filters are systematically demonstrated with the method of coupled mode resonator theory. MSRs may be potential alternative for complicated and arbitrary design of BSFs to achieve desired frequency response. [ABSTRACT FROM AUTHOR]

A compact, low-cost microstrip bandpass filter (BPF) with low insertion loss and wide attenuation band is presented in this article. The proposed structure consists of multiple interdigital capacitor sections and a T-shaped stub which is connected to the ground using via. The wide stopband response is achieved by the inclusion of defected ground structures (DGS). Addition of these defected ground structures also reduces the circuit size. The designed BPF of centre frequency 0.9 GHz is fabricated, measured, and its lumped equivalent circuit is also obtained. A good agreement is found among IE3D simulated results, circuit simulated results, and the measured results. The obtained results for the proposed bandpass filter (BPF) are −3 dB fractional bandwidth (FBW) of 63% and minimum insertion loss of 0.59 dB. The relative stop band (RSB) rejection is found up to 177% and the normalized circuit size (NCS) is found 0.012 λ g 2 . This proposed filter can be used for GSM and other microwave circuitry in wireless communication system. [ABSTRACT FROM AUTHOR]

Based on the multi-coupled line, a novel compact microstrip diplexer with high isolation and low insertion loss is developed. The presented diplexer consists of five short-ended parallel coupled lines to implement the desired channel selections while exempting the use of extra T-junction matching networks, as compared with the conventional case. The design concept is detailed and a prototype diplexer is developed and examined experimentally, where the two channels are of center frequencies of 1.8 and 2.4 GHz, respectively. On the other hand, a figure-of-merit (FOM) is, for the first time, presented to evaluate the comprehensive performance of a diplexer. Results indicate the demonstrator diplexer has a size of 0.18 λg×0.34 λg and a very high FOM of 19301. Measurements match well with the simulations. [ABSTRACT FROM AUTHOR]

In this paper, the design of a tunable and compact metamaterial microstrip band-stop filter is proposed. The device is designed to operate in the X band, it is based on a metamaterial pattern (single-turn square planar resonator) implemented on a ferrite substrate. The study focuses on the metamaterial band-stop filter and on the way to tune its frequency properties. For this reason, the magnetic material is a perfect solution, using YIG (Yttrium Iron Garnet) substrates. As a result, the central frequency of the filter can be tuned by varying the magnetic bias applied to the YIG substrate. A tunability up to 10.81% is obtained. The size of the proposed filter is electrically reduced to 3.7 mm2. [ABSTRACT FROM AUTHOR]

In this paper, a new microstrip low-pass filter will be presented for achieving high ability to choose wide stopband and suitable operation. This filter is built after design and simulation, and results of measurement will confirm the design accuracy. The results show that the overall performance of the recommended structure is improved in terms of physical dimensions, sharpness of response, and width of stopband, compared to old structures. Cut-off frequency of filter is 1.1 GHz. The stopband is so wide, and the amount of weakness in this band is equal to −20 dB. Roll-off rate parameter of the proposed filter is equal to 240 dB/GHz. This means that changing filter condition moves rapidly from passing to stop state. Size of proposed filter is small and equal to 27 mm × 16 mm. Results of simulation and measurement of the fabricated sample exhibit the same reaction. [ABSTRACT FROM AUTHOR]

A reconfigurable balanced resonator and a reconfigurable Balanced Band-Pass Filter (BBPF) are presented in this work. The resonator is based on closed-loop transmission lines, two parallel lines and two T-sections. Reconfigurability is achieved using Eutetic Galium–Indium (EGaIn) liquid metal. A third-order reconfigurable filter was designed, fabricated, and measured to work at 2 and 1.65 GHz. [ABSTRACT FROM PUBLISHER]

The reason of a pair of transmission zeros located near the passband of a cross-coupled microstrip filter is discussed. Moreover, with the use of tapped transmission line, another two transmission zeros are generated. To verify the analysis, a two-layer cross-coupled microstrip filter with tapped-line technique is developed, where four transmission zeros are found close to the passband, thus, realizing an enhanced filter selectivity. The two-layer cross-coupled microstrip filter is fabricated and examined experimentally. Measurements agree with the simulations. [ABSTRACT FROM PUBLISHER]

This paper deals with a flexible CAD methodology for the design of a microwave extra wideband filter introducing a notch at a desired frequency. The structure, designed in a cost-effective planar microstrip technology to operate in the 5–20 GHz frequency band, is capable of covering up to 120% of fractional bandwidth. It shows good performance in terms of in-band and out-of-band insertion loss and group delay. Furthermore, a simple relationship between the notch frequency and a single geometrical parameter of the structure has been extracted, thus making the component highly flexible to design. The procedure steps and the relevant design results are reported, including the electromagnetic analysis of the port connectors. Finally, different samples of the filter have been realized and measured to test the procedure. The experimental results have shown a good agreement with the expected performance thus confirming the effectiveness of the proposed methodology. [ABSTRACT FROM PUBLISHER]

A novel electrically tunable filtering power divider, based on liquid crystal (LC) technology, is designed and experimentally demonstrated in this paper. Using low-cost T-shaped inverted-microstrip structures integrated with two dual-mode open-loop resonators, the tunable power divider possesses bandpass-filtering frequency response. Moreover, transitions between inverted-microstrip and microstrip structures are specifically designed at the I/O ports for the self-packaged. The experimental results indicate that the central frequency can be tuned from 5.75 to 6.25 GHz, i.e. a relative tuning range of 8.3%, the 3-dB bandwidth is 6.8 ± 0.2% over the whole tuning range, and the maximum amplitude and phase imbalance are less than 0.8 dB and 2.5°, respectively. In addition, the proposed filtering power divider has three transmission zeros to improve the frequency selectivity. [ABSTRACT FROM PUBLISHER]

In this paper, we describe a method to implement compact multiband bandpass filters with suppression of second harmonic frequency. This filter design approach is based on decreasing the coupling gap between adjacent resonators of a parallel-coupled-line bandpass filter in order to achieve both the desired multiband frequency response and the spurious suppression. We present the theoretical analysis of the proposed structure that consists of modeling the frequency dependence of the even- and odd-mode characteristic impedances as well as due to the different phase velocities of the parallel-coupled microstrip lines. As an example, a compact tri-band parallel-coupled-line bandpass filter with suppression of second harmonic frequency was implemented operating at 1.9/3.2/4.6 GHz to cover PCS1900, WiMAX, and C-band applications. A three-pole Chebyshev parallel-coupled microstrip bandpass filter was designed at a center frequency of 3.2 GHz and used as the basis to validate the gapping effect on the filter response which also achieves a narrower bandwidth for the second harmonic. Finally, the filter performance with minimized coupling gap is compared to a filter enhanced by the insertion of apertures in the ground plane. Generally speaking, good agreement was accomplished between simulated, calculated, and measured results. [ABSTRACT FROM PUBLISHER]

This document presents a dual-band bandpass filter with fully independent passbands. The filter is based on a novel dual-band resonant junction (DBRJ) andλ/2 resonators. This approach allows different filter order at each passband, independent fractional bandwidth tuning, and independent filter response at each band. The DBRJs consist of a short-circuited quarter-wavelength resonator. One prototype is presented with Butterworth and Chebyshev responses and center frequencies at 1.8 and 2.45 GHz. [ABSTRACT FROM PUBLISHER]

In this paper, a microstrip tri-band bandpass filter (BPF) utilizing square ring loaded resonator is proposed. A pair of bent perturbation stubs is installed to the ring resonator so as to control resonant modes of the ring. The first three modes are used for tri-band BPF design. In order to control the second and third resonant modes, two pairs of square patches and loaded open stubs are added, and then two asymmetric resonators are cascaded for tri-band operation. Based on the transmission line theory, even- and odd-mode analysis method is used to deduce the resonant frequencies. According to the resonant conditions, a kind of tri-band BPF can be flexibly designed. Finally, two filters are designed as examples in a comprehensive way for demonstration, and one design with passbands located at 2.4, 3.5 and 5.2 GHz is fabricated. Measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

In this paper, a microstrip lowpass filter with ultra-wide stopband is proposed. To achieve a wide stopband, the semicircle stepped impedance is connected in series with the triangular shaped compact microstrip resonance cell (CMRC). The lowpass filter with 3 dB cut-off frequency at 2.38 GHz and stopband region with the attenuation level better than –21 dB from 2.7 to 23 GHz has been designed, fabricated and measured. The filter has the transition band of 0.45 GHz. There is a good agreement between the simulated and measured results. [ABSTRACT FROM AUTHOR]

A compact tri-band bandpass filter using input/output cross coupling is proposed. Three passbands can be adjusted by changing the characteristic impedance of the T-shaped structure with a shorted stub. The three passbands are designed to operate at 1.85, 3.5 and 5.2 GHz based on the T-shaped structure. Four transmission zeros are used to realise high selectivity for the passbands. Good agreement can be observed between the measured and simulated results. [ABSTRACT FROM AUTHOR]

In the design of bandpass filters, the use ofλ/2 stubs of shunt configuration had been mostly unacceptable due to their effect of narrow stopband bandwidths in the ensuing filters. The design of bandpass filter presented in this article introduces 360° series transmission line segments to increase the stopband bandwidths to an acceptable level without affecting the wide passband. This designed filter has low insertion loss of less than –1.98 dB and a fractional bandwidth of 50% at 6 GHz mid-band frequency. A sharp rejection in the stopband is observed. To further widen the bandwidth of stopbands, a series capacitor and a shunt stub are used. The transmission line model of the filter is in good agreement with measured results. The filter is planar and is fabricated on FR-4 substrate which makes it cost-effective and easy to fabricate. [ABSTRACT FROM AUTHOR]

In this article, a new compact microstrip bandpass filter with ultra-wideband passband is implemented and proposed. The filter is constructed of only one-stage parallel-coupled line and two symmetric short-circuited stubs which are quarter wavelength long at the center frequency. The short-circuited stubs are connected at the input/output ends of the parallel-coupled lines to improve the selectivity at both edges of the desired passband. The design of the proposed filter is successfully realized in theory and verified by full-wave electromagnetic simulation and the experiment. An excellent agreement between the expected and measured results is obtained. [ABSTRACT FROM AUTHOR]

A microstrip-based Ultra-Wideband Bandpass filter with a controllable notch and suppressed stopband is proposed. Dumbbell-shaped defected ground structure (DGS) etched in the ground and the double equilateral-U (DEU) DGS units under the input and output feeding lines provide the controllable notch and suppressed stopband, respectively. For optimum design of both the DGS (Dumbbell and DEU), a notch at WLAN frequency of 5.8 GHz and simultaneous stopband till 18 GHz is reported. Experimental results are in favor of the simulated data. [ABSTRACT FROM AUTHOR]

A compact microstrip dual-band bandpass filter with multiple transmission zeros is proposed. This filter is composed of input/output (I/O) coupling structure with source-load cross-coupling and two pairs of short-ended resonators resonating at 2.4 and 5.8 GHz, respectively. By proper arrangement of the I/O coupling structure with source-load cross-coupling, multiple transmission zeros are introduced. In this way, high selectivity of both passbands and good out-band rejection level better than 20 dB up to 9 GHz are achieved. Good agreement can be found between the full-wave electromagnetic simulations and measured results, which verifies the proposed design concept. [ABSTRACT FROM AUTHOR]

In this work, a planar microstrip tri-band filter based on quarter-wavelength resonators is presented, which allows independent control of the positions of all three passbands. Furthermore, the topology of the filter provides five transmission zeros and thus results in a highly selective response in all passbands. A synthesis procedure of the filter is presented and used to design a tri-band filter which operates at WLAN frequencies of 2.4/3.5/5.2 GHz. The designed filter outperforms all other state-of-the-art tri-band filters in terms of compact size, high selectivity and transmission, and return-loss characteristics. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel capacitor-based coupling scheme for realizing both harmonicsuppressed and miniaturized microstrip bandpass filters. The proposed coupling scheme employs lumped-/distributed-capacitors to provide the desired coupling strength between the resonance elements instead of traditional parallel-coupled lines. Certain coupling regions are replaced by coupling points resulting in high freedom degree of the filter topologies. Thus, the filter structure can be effectively miniaturized by meandering microstrip lines. To investigate the properties of the novel coupling scheme, an analytical equation is derived for describing the coupling coefficient variation vs. the positions of coupling points and the values of coupledcapacitors. Theoretical analysis indicates that several zero-voltage points can be chosen to suppress the harmonics, and the coupling coefficient can be easily tuned in a wide range by adjusting the capacitance of the coupled-capacitor. For demonstration, two sample filters are designed and fabricated. Simulation and experimental results agree well, validating the proposed methodologies. [ABSTRACT FROM AUTHOR]

A tunable dual-band microstrip filter using step-impedance resonators with harmonic suppression and compact size is presented in this paper. The second passband frequency of the filter can be flexibly controlled by tuning the bias voltage across the varactor whereas the first passband frequency is fixed. The structure is composed of couple lines and capacitiveloaded stepped-impedance resonator to provide frequency tunability and folded to reduce the size of the filter. The coupling scheme applied in this paper helps to reduce insertion loss and eliminate parasitic parameters, which is due to that extra blocking capacitances that are needless compared with the conventional coupling structure. To certify the validity, a prototype dual-band filter is designed, fabricated, and measured. The measured results show good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

A novel microstrip tri-band bandpass filter (BPF) based on stub-loaded triple-mode resonator is proposed. The open- and short-circuited stubs are asymmetrically loaded to a uniform impedance open-loop resonator, constructing a triple-mode resonator. Benefiting from the proposed asymmetrical loading scheme, the designed tri-band BPF not only possesses the controllable bandwidths of the three passbands, but also shows very wide stopband. Finally, a tri-band microstrip BPF with good performance is designed at 1.5, 2.57, and 3.83 GHz. Three transmission zeros near the passbands are obtained to improve the selectivity of the tri-band BPF. Meanwhile, the other transmission zeros produced in the stopband enhance the harmonic suppression level. The rejection level from 4.3 to 13.7 GHz is better than 20 dB. The measured results are in good agreement with the simulated data. [ABSTRACT FROM PUBLISHER]

Design and fabrication of compact dual-mode dual-band microstrip bandpass filters with a novel feed scheme is presented. The proposed filters have two square loop resonators for two passbands, and each resonator is fed by the feedlines located at the upper corners of the resonators. By using the perturbation elements such as patches or corner-cuts, two degenerate modes of each passband can be easily excited, so mode frequencies and transmission zeros of the passbands can be controlled independently. Also, the proposed feed scheme provides the harmonic suppression for the first passband. In addition, theoretical results have been obtained by using an equivalent circuit model, and a coupling scheme is also presented. The designed filters have an electrical length offor the quarter wavelength resonator, whereis the guided wavelength at 1.8 GHz. Two bandpass filters having elliptical and linear phase filtering characteristics in each passband have been designed, fabricated, and tested. Measured results are in an excellent agreement with simulated and calculated ones. In all frequency responses, return losses are better than 15 dB and insertion losses are at acceptable values for both passbands. [ABSTRACT FROM PUBLISHER]

A fourth-order dual-band microstrip band-stop filter is proposed in this paper. Folded stepped impedance resonators are implemented as well as capacitive gap and inductive grounded via, thus the dual-band performance can be obtained in merely one resonator. Besides its compact size, simplicity, and good spurious band suppression, the filter also features its excellent mid-band rejection and skirt characteristic which is achieved by four reflection zeros adjacent to the dual resonating frequencies. Controllable response of filter is realized by tuning of gap capacity and via inductance, and the theory is verified by both simulation and experimental results that agree well with each other. [ABSTRACT FROM PUBLISHER]

To design a bandpass filter with good performance, an open loop resonator within an inverted Y-type microstrip line is discussed in detail in this paper. Using a microstrip struc-ture, the resonator is introduced in the filter design, and single- and dual-band bandpass fil-ters, with dual-mode and more compact size, have been investigated. The single band bandpass filter is much smaller in size than conventional filter with a single-mode open loop resonator operated around the same frequencies and two transmission zeros existing in the stopband. The position of transmission zeros can be easily adjusted by using a source-load structure. Moreover, based on the research above, two symmetric resonators are com-bined, and a dual-band bandpass filter is designed with sharp rejection and wide stopband due to four transmission zeros. The fabricated samples are tested to verify the design. Very good results have been obtained. [ABSTRACT FROM AUTHOR]

In this paper, a novel bandstop filter based on microstrip LC resonators and 1-bit frequency reconfigurable bandstop filter are presented. The configuration of the proposed LC resonators has open structure and is suitable to load with reconfigurable capacitors. Lumped elements models have been developed, and the frequency tuning capability of the bandstop filter is studied, and it is shown that the filter stopband can be reconfigured by the loading capacitance. A 1-bit reconfigurable bandstop filter is designed based on the proposed novel bandstop filter loaded with two switchable 3.5mm × 6.5mm × 0.508mm Rogers 5880 single metal plane PCB capacitors. The prototype with compact overall size of 22mm × 39mm was designed and fabricated to validate the new structure. The measured stop-band central frequency is 3.04GHz and 2.513 GHz in cutoff state and connected state, respectively. 500 MHz central frequency reconfigurable capability is obtained. [ABSTRACT FROM PUBLISHER]

A microstrip bandpass filter (BPF) using a novel defected ground structure (DGS) resonators and inter-digital capacitors is proposed in this paper. The BPF is designed by cascading a novel microstrip highpass filter (HPF) and a lowpass filter (LPF). The LPF with a 3 dB cutoff frequency of 6GHz is constructed by a laddershaped transmission line on the top plane and a combined open loop DGS on the bottom one, resulting high selectivity and good stopband performance. The HPF consists of a ladder-shaped transmission line with zigzag slot on the top plane and the open loop DGS on the bottom one, providing two transmission zeros and steep rejection slope. The designed BPF with a 3 dB bandwidth of 2GHz and center frequency of 5GHz exhibits sharp cutoff frequency response. The BPF also shows good stopband performance with rejection better than 20 dB from DC to 3.55GHz in lower stopband and 6.2 to 14GHz in upper stopband, respectively. The measured results agree well with the simulations. [ABSTRACT FROM PUBLISHER]

It considers uncertainties in future load demand and market price and uses particle swarm optimization for the solution. The cost function incorporates feeder installation cost, power loses cost, cost of purchased active power and reliability costs and incorporates several constraints. A modification of the DV-Hop method is presented that uses a particle swarm optimization technique to address the positioning error. [Extracted from the article]