An equivalent circuit model for the wide‐band band‐pass filter with the modified Minkowski‐island‐based fractal patch

An equivalent circuit model for the wide‐band band‐pass filters (BPFs) using modified Minkowski‐island‐based (MIB) fractal patch are proposed in this article. The BPF is mainly formed by a square patch resonator in which a modified MIB fractal configuration with second‐order iteration is embedded in the patch. By the equivalent circuit model with diamond structure, the wide‐band responses are analyzed. The design procedure included equivalent circuit model is available for wide‐band design. For wide‐band characteristics, at 5.0 GHz central frequency, it has good measured characteristics including the wider bandwidth of 3.14–6.89 GHz (3‐dB fractional bandwidth of 75%), low insertion loss of 0.39 dB, and high rejection level (?48.5/?44.9 dB). The patch size is 7.4 λ 7.4 mm² (0.25 λ_g × 0.25 λ_g) with 14.1% reduction. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:170–176, 2014.     

A tunable balanced dual‐band BPF with quasi‐independently controlled center frequency and bandwidth

In this paper, a balanced dual‐band bandpass filter (BPF) with high selectivity and low insertion loss performance is presented by employing stub loaded resonators (SLRs) and stepped impedance resonators (SIRs) into balanced microstrip‐slotline (MS) transition structures. The balanced MS transition structures can achieve a wideband common‐mode (CM) suppression which is independent of the differential‐mode (DM) response, significantly simplifying the design procedure. Six varactors are loaded into the resonators to achieve the electrical reconfiguration. The proposed balanced dual‐band BPF can realize quasi‐independently tunable center frequencies and bandwidths. A tuning center frequency from 2.48 to 2.85 GHz and a fractional bandwidth (20.16%‐7.02%) with more than 15 dB return loss and less than 2.36 dB insertion loss are achieved in the first passband. The second passband can realize a tuning center frequency from 3.6 to 3.95 GHz with more than 12 dB return loss and less than 2.38 dB insertion loss. A good agreement between the simulated and measured results is observed.     

A 1‐to‐n way single‐ended‐to‐balanced substrate integrated waveguide filtering power splitter

An approach to 1‐to‐n (n = 3, 4…) way single‐ended‐to‐balanced filtering power splitter (SETBFPS) is proposed. The properly placed balanced ports with 0.5λ_g (λ_g is the substrate integrated waveguide [SIW] guided wavelength at f₀) space make the TE32nd 103 and TE32nd 105 modes of n 32nd‐mode SIW multimode resonators form differential‐mode (DM) passband of the SETBFPS. Compared with the state‐of‐art single‐ended‐to‐balanced power splitters, the proposed approach has all the functions of 1‐to‐n way, filtering, and common‐mode (CM) suppression. A 1‐to‐3 way prototype is exemplified at 3.5 GHz with the minimum insertion loss (IL) of 0.09 dB, a fractional bandwidth (FBW) for a 15‐dB return loss of 35%, and a FBW for 15‐dB CM suppression of 52%. Low IL and wide bandwidth can be observed.     

Wide stopband harmonic suppressed low‐pass filter with novel DGS

In this article, a wide stopband 20 dB harmonically suppressed low‐pass filter (LPF) using novel defected ground structures (DGSs) is proposed. The DGSs has been analyzed as a low pass filter which shows a significant harmonics suppression in the stopband. The lumped parameter equivalent of the DGSs has been developed to show its effectiveness. The modified equivalent circuit model of the filter helps in placing the transmission zero near ?3 dB cutoff frequency. The LPF is designed on a 0.10 λ_g× 0.09 λ_g substrate size where λ_g is guided wavelength at ?3 dB cut‐off frequency (f_c) equal to1 GHz. The simulation shows a 20 dB harmonic suppression up to 50 f_c. The prototype of the LPF has been developed and with the available vector network analyser, the S‐parameters have been measured upto 20 GHz (20 f_c).The state of the art comparison of the LPF shows a high figure of merit equal to 26 250 which is higher than many recently published works.     

Ultracompact two‐way and four‐way SIW/HMSIW power dividers loaded by complementary split‐ring resonators

In this paper, two ultracompact power dividers based on the substrate integrated waveguide (SIW) and half‐mode SIW (HMSIW) technologies loaded by complementary split‐ring resonators (CSRRs) are presented. The presented structures are designed based on the theory of evanescent mode propagation. To obtain a size reduction, the CSRR unit cells are etched on the metallic surface of the SIW and HMSIW structures. First, a two‐way HMSIW power divider is reported. In this circuit, the concept of HMSIW is utilized aiming at a further size reduction in addition to the size reduction by the CSRR unit cells. Then, a four‐way SIW power divider is designed so that the direct coaxial feed is used for the input port and microstrip transmission lines are used for the output ports. Both two‐way and four‐way SIW/HMSIW power dividers at 5.8 GHz covering WLAN are designed, fabricated, and measured. They respectively have 0.18 × 0.21 λg² and 0.38 × 0.21 λg² total size. A fair agreement between simulated and measured results is achieved. The measured insertion losses are 0.5 ± 0.5 and 0.6 ± 0.5 dB for the two‐way and four‐way SIW/HMSIW power dividers, respectively, in the operating band of interest.     

A compact balun‐diplexer using interdigital line resonators

A novel compact balun‐diplexer applying new interdigital line resonators (ILRs) is presented in this article. It is found that the proposed ILR can not only reduce circuit size and but also realize high common mode rejection in differential mode operation frequency. By properly converting the symmetric four‐port balanced bandpass filter (BPF) to a three‐port device, a balun BPF with high selectivity and compact size are accomplished using ILRs. Then, the balun‐diplexer can be realized by combining two well‐designed balun filters with two 50 Ω transmission lines. The demonstrated balun‐diplexer with operation at 1.8 and 2.45 GHz have been designed, fabricated, and measured. Excellent performances have been observed. Specifically, 0.4 dB in‐band amplitude error, 1.8 in‐band phase error, more than 50 dB selectivity and 45 dB isolation are obtained. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:485–489, 2015.     

A novel dual‐band bandpass filter using co‐directional split ring resonators with closely spaced passbands and wide upper stopband

In this article, interdigital capacitor loaded co‐directional split ring resonators (CDSRRs) and their dual‐band bandpass filter applications are proposed. The proposed resonator is formed by nested open loop resonators having open ends at the same place unlike conventional split ring resonators (SRRs). In addition, the inner open loop resonator has interdigital capacitor located between the open ends. The proposed resonator exhibits dual resonance behavior with a small center frequency ratio. Both of resonance frequencies can be controlled due to the changes in the interdigital capacitor and the electrical length of the outer resonator. A dual‐band microstrip bandpass filter is designed by using the proposed CDSRR. Two CDSRRs are used to obtain two poles in each passband. Overall electrical length of the designed filter is 0.23 λ_g × 0.14 λ_g (0.0329 λ_g²), where λ_g is the guided wavelength for the used substrate at the lowest passband center frequency of 1.8 GHz. A small center frequency is obtained by adjusting the second passband at 2.27 GHz. A very wide upper stopband, closely spaced passbands, low insertion losses and high selectivity at both passbands can be obtained by means of the proposed structure. The designed filter was also fabricated and tested. The measured results show a very good agreement with the predicted results.     

A balanced dual‐band bandpass filter with independently tunable differential‐mode frequencies

A balanced dual‐band bandpass filter (BPF) with independently tunable differential‐mode (DM) frequencies is proposed in this letter. The proposed BPF is composed of complementary split‐ring resonators (CSRRs) etched on the ground and varactors loaded on the resonators. A balanced stepped‐impedance microstrip‐slotline transition structure is introduced to transfer the DM signals successfully and block the common‐mode (CM) signals transmission. Good DM transmission and CM suppression can be achieved. Moreover, by changing the reverse bias voltages of the varactors loaded on coupling CSRRs, two DM resonant frequencies of the proposed balanced BPF can be tuned independently. To verify the feasibility of the design method, a balanced BPF with DM frequency ranging from 0.80 GHz to 1.12 GHz and 1.55 GHz to 2.05 GHz is fabricated and measured. Good agreement between the simulation and measurement results demonstrate the validity of the design.     

Compact dual‐ and triband bandpass filter using frequency selecting coupling structure loaded stepped‐impedance resonator

This article presents two novel resonators, that is, frequency selecting coupling structure loaded stepped‐impedance resonator (FSCSLSIR) and π‐section loaded FSCSLSIR. The resonator behaviors and guidelines are given to design FSCSLSIR dual‐band bandpass filter (BPF) and π‐section loaded FSCSLSIR triband BPF. The proposed dual‐ and triband BPF have very compact sizes of 0.13 λ_gd × 0.06 λ_gd and 0.115 λ_gt × 0.074 λ_gt, respectively. Moreover, good return loss, low insertion loss, and high band‐to‐band isolation can be observed, and the proposed FSCSLSIR dual‐band BPF has an ultrawide stopband from 5.79 to 36 GHz. The experimental results are in good agreement with the simulations. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:427–435, 2015.     

Novel slotted stepped‐impedance resonator and its application to compact and high performance bandpass filter and diplexer design

By etching slots in the low‐impedance section of the conventional stepped‐impedance resonator, a novel slotted stepped‐impedance resonator (SSIR) is proposed. As two examples, a fourth‐order bandpass filter (BPF) operating at 1 GHz with a size of 0.078 λ_g × 0.062 λ_g and a miniaturized diplexer operating at 0.9/1.57 GHz with a size of 0.054 λ₀ × 0.086 λ₀ are designed based on the proposed SSIR. The fabricated BPF exhibits a high selectivity and a wide ?30 dB rejection upper stopband from 1.13 f₀ to 6.52 f₀, while the fabricated diplexer has up to ?60 dB output isolation. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

A tunable third‐order bandpass filter based on combining dual‐mode square‐shaped substrate integrated waveguide resonator with triangular‐shaped resonator

A frequency reconfigurable third‐order bandpass filter based on two substrate integrated waveguide (SIW) cavities is presented in this article. The purposed filter consists of a dual‐mode square‐shaped resonator and a triangular‐shaped resonator. In the square‐shaped cavity, four lumped capacitors are loaded as electrical tuning elements in the area where the electric fields of diagonal TE₂₀₁ and TE₁₀₂ modes are strongest. And an another capacitor is loaded at the suitable region of the triangular‐shaped cavity. Square‐shaped cavity introduces two transmission zeros and the triangular‐shaped cavity can suppress out‐of‐band spurious modes. The method that combines the resonators with different shapes and multiple modes into an organic whole cannot only achieve synchronous tuning but also have complementary advantages and improve out‐of‐band rejection. To verify its practicality, a SIW reconfigurable bandpass filter is simulated when the capacitance value varies from 0 to 1.4 pF and measured at 0.7, 0.8, and 0.9 pF, respectively. Measured results show that when the center frequency is tuned from 3.42 to 3.52 GHz, the proposed filter exhibits good tuning performance with insertion loss of less than 2.5 dB and return loss of better than 10 dB, which is suitable for fifth‐generation communication system.     

Coplanar waveguide wideband bandpass filter and its application to ultra‐wideband pulse generation

A technique to design wideband coplanar waveguide bandpass filters is reported. The filter is realized by etching a slot on the ground plane around a gap on its central conductor and modifying the gap in the form of parallel lines. It is shown that the 3‐dB fractional bandwidth of the filter can be varied from 60 to 110% by tuning the size of the slot aperture and the length of the parallel lines. Equivalent circuit and design steps are presented. Implementation area of the filter having passband 3.2–10.5 GHz is 0.90 λ_g × 0.26 λ_g, λ_g being the guided wavelength at 6.85 GHz while 20‐dB stopband is at least up to 18 GHz. Insertion loss is less than 2 dB up to 9 GHz. Area of the filter having fractional bandwidth 60% at 3.85 GHz is 0.67 λ_g × 0.11 λ_g. Passband loss is within 1.5 and 20 dB stopband is at least up to 12 GHz. The proposed filter structure is very simple to integrate, and the ultra‐wideband filter is used to generate an ultra‐wideband pulse as defined by the US Federal Communication Commission. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Compact dual‐band bandpass filter and diplexer using hybrid resonant structure with independently controllable dual passbands

In this article, a compact dual‐band bandpass filter (BPF) is developed using a hybrid resonant structure, which consists of a microstrip stub‐loaded dual‐mode resonator and a slotline stub‐loaded dual‐mode resonator. These two resonators, both having two controllable resonant modes and one transmission zero (TZ), are analyzed and used to construct two desired passbands of a dual‐band BPF. Multiple TZs are generated by introducing a source‐load coupling, thus improving the selectivity of the passbands. Then, the dual‐band BPF is reshaped to configure a compact diplexer. The inherent TZs of the two proposed resonators are designed to improve the frequency property and port isolation of the diplexer. Finally, a dual‐band BPF and a diplexer with the lower and upper passbands centered at 2.45 and 3.45 GHz, respectively, are designed, fabricated, and measured to verify the proposed structure and method.     

Compact ultra‐wideband bandpass filter with configurable stopband based on diamond‐shape resonator

An ultra‐wideband compact bandpass filter (BPF) with configurable stopband by tuning transmission zeroes is proposed in this paper. The ultra‐wideband bandpass response is based on a diamond‐shape resonator consisting of a pair of broadside coupled diamond‐shape microstrip lines, within which a diamond shape defected ground structure (DGS) is etched in the middle. Flexible transmission zeros realized by open and short stubs can be easily adjusted to improve band selectivity and harmonic suppression. Measurement result shows that the dedicated device has a 3 dB fractional bandwidth of 148% (0.94‐6.36 GHz) with 20 dB rejection stopband from 6.87 to 9.7 GHz (77.5%) which agrees good with the simulate performance. The overall size of the proposed BPF is 0.27 λ_g × 0.23 λ_g.     

A self‐packaged wideband filtering power divider based on substrate‐integrated suspended line

In this study, a filtering power divider (FPD) is proposed by utilizing one T‐shaped tri‐mode stepped‐impedance resonator with input/output coupling structures based on substrate‐integrated suspended line (SISL). The circuit topology and SISL technology are combined together to reach balance in performances such as compact size, wideband, high frequency selectivity, low loss, good in‐band isolation, wide stopband, and self‐packaging so that there are no obvious flaws. Wide bandwidth and two near‐band transmission zeros are contributed by the proposed circuit topology. Good isolation can be obtained by comparing different coupling schemes with one resistor. An additional transmission zero for extending the upper stopband can be achieved by the two closely placed stubs without increasing the size of the design. Low loss and self‐packaging can be realized by SISL technology. For demonstration, a prototype is implemented with the size of 0.5λ_g × 0.28λ_g, which exhibits the 1‐dB fractional bandwidth of 26.3%, the frequency selectivity of 0.25/0.37 at the lower/upper edges of the passband, and the insertion loss of 1.1 dB (including transition) at the center frequency (f₀) of 3.34 GHz, while the in‐band isolation is higher than 20 dB and the 15‐dB stopband is achieved up to 3.74 f₀.     

High isolation,proximity‐fed monostatic patch antennas with integrated self‐interference cancellation‐taps for ISM band full duplex applications

This work presents two dual polarized proximity‐fed monostatic patch antennas with improved interport isolation for 2.4 GHz industrial, scientific and medical band same frequency full duplex wireless applications. The presented antennas achieves the high interport decoupling through intrinsic isolation of the polarization diversity in conjunction with a simple single‐tap and two‐taps self‐interference cancellation (SIC) topologies. The polarization diversity isolation is achieved through two perpendicular microstrip feeds for proximity feeding to excite orthogonal polarization mode for transmit (T_x) and receive (R_x) modes. The prototype for proposed antenna with integrated single‐tap and two‐taps SIC circuit is tested to record its interport isolation, impedance bandwidths and gains for both T_x and R_x ports. The implemented antenna with single‐tap SIC circuit demonstrates 10 dB return‐loss bandwidth of ≥100 MHz for both T_x and R_x ports. The measured isolation exceeds 40 dB over the 40 MHz bandwidth. Moreover, the recorded peak isolation is better than 74 dB for implemented antenna prototype. Furthermore, the 40 MHz bandwidth with 40 dB isolation can be tuned with the help of SIC‐tap as demonstrated through the experimental results. The measured gain levels are around 4.6 dBi for both T_x and R_x port. The same antenna structure with integrated two‐taps SIC topology features better than 55 dB isolation within 10 dB return loss bandwidth of 100 MHz. The peak isolation exceeds 97 dB and isolation levels are better than 60 and 80 dB over 50 and 20 MHz bandwidths, respectively, for presented antenna with two‐taps SIC configuration. The compact antenna offers comparatively wider impedance and isolation bandwidth with improved SIC levels compared to previous designs.     

A dual‐polarized low‐profile microstrip patch antenna with U‐ or M‐shaped feed network

In this article, a dual‐polarized low‐profile microstrip patch antenna with U‐ or M‐shaped feed network is presented. The U‐ or M‐shaped feed network is printed on the same layer, which can achieve dual bands (5.3 and 5.8 GHz) and low profile (0.06 λ_g). Dual polarizations and high isolation are realized by making use of a quasi‐cross‐shaped slot feeding. Moreover, the port isolation is better than 25 dB, and the antenna gain is above 8.4 dBi for the two ports. And the cross‐polarization levels in both E and H planes are better than ‐30 dB for the two polarization ports, respectively. The design is suitable for array application in MIMO system. Details of the proposed design and experimental results are presented and well agreed.     

Compact dual bandpass filter for terrestrial radio and GSM applications

A Compact Dual Band‐Bandpass Filter (DB‐BPF) with wide stopband rejection is proposed in this article. The basic tools used in the structure are Short Circuited Stepped Impedance Resonators (SCSIR), Open Stub Resonators (OSR). First, a Single Band‐Bandpass Filter (SB‐BPF) is designed with wide stopband rejection, and then it is modified to DB‐BPF. Both the SB‐BPF and DB‐BPFs have similar type of construction except for an additional SCSIRs used in DB filter. The structure of the filters, use the source‐load coupling and OSR to generate transmission zeros, which suppresses harmonics and achieves wide stopband. The use of SCSIRs make the SB and DB bandpass filters size compact to 0.099λ_g×0.094λ_g and 0.118λ_g×0.092λ_g, where λ_g is guided wavelength with a wide stopband upto 6.85f₀ with 22 dB suppression for SB‐BPF and 2.78f₁/7.57f₀ with 22 dB suppression for DB‐BPF, where f₀ and f₁ are centre frequencies of first and second passbands respectively.     

Design of second‐order lumped‐element reconfigurable diplexers

This paper presents a new type of second‐order reconfigurable diplexers by using common lumped‐element dual‐resonance resonator (LE‐DRR) and LC resonators. As examples, a 0.9/1.8 GHz second‐order diplexer is firstly designed to investigate the design theory, which has merits of wide passband, low insertion loss and extremely compact size. Then, a second‐order switchable diplexer is simply designed by embedding two p‐i‐n diodes in two end‐stage LC resonators of the above diplexer to switch on/off each channel independently. Finally, the capacitors of the above diplexer are replaced by the varactor diodes, so that a second‐order tunable diplexer with two independently tuned channels is proposed. Measured results of proposed tunable diplexer show that its lower channel can be tuned from 0.492 GHz to 0.995 GHz with corresponding frequency tuning range (FTR) of 66.58%, while its upper channel can be tuned from 0.974 GHz to 1.7 GHz with FTR of 51.92%.     

Five‐order narrow‐band tunable superconducting filter

This article designed a five‐order narrow‐band tunable superconducting filter. The superconducting microstrip circuit was loaded by varactors diode. The center frequency of the tunable can be tuned through the changing of the bias voltage added in the varactors diode. The whole device has a parallel coupling structure and the filter circuit was fabricated by DyBa₂Cu₃O₇ superconducting film with 0.5 mm thickness and 2 in. LaAlO₃ as the substrate. The frequency can be continuously adjusted from 235 MHz to 250 MHz. The insertion loss of the filter was in the range of 2.51 dB to 9.64 dB. The bandwidth of the tunable filter was in the range of 0.5 MHz to 0.9 MHz. The out‐of‐band rejection was better than 70 dB. The measured results are in good agreement with the simulated ones.