Wideband balanced microstrip‐to‐microstrip vertical transition

A wideband balanced microstrip‐to‐microstrip vertical transition is proposed. This vertical transition is based on the back‐to‐back hexagonal microstrip lines with a slot on the common ground. The etched slot is used to achieve the vertical transmission of differential‐mode signal and the suppression of common‐mode (CM) signal. The back‐to‐back hexagonal microstrip lines enable the transition to obtain wide bandwidth. One prototype shows the fractional bandwidth (|S_dd11| ≤ ?15 dB) of 63%, the minimum (maximum) insertion loss of 0.7 dB (1.9 dB), and the minimum CM suppression inside passband of 27 dB.     

Compact wideband microstrip bandpass filter with wide upper stopband based on coupled‐stub loaded resonator

A novel wideband microstrip bandpass filter (BPF) based on a coupled‐stub loaded resonator (CSLR) is presented in this article. The CSLR is constructed by attaching one short‐circuited parallel coupled microstrip line (PCML) in shunt to a high impedance microstrip line. The filter bandwidth can be conveniently controlled via reasonable adjusting of the impedance of PCML. Moreover, new defected microstrip structures (DMSs) introduced in the PCML functions as a means of adjusting the positions of transmission zeros, created by the PCML. The resonant mode and transmission zero chart are given, indicating that the higher modes could be suppressed by the transmission zeros. Finally, to validate the proposed method, two wideband BPF filters with and without DMSs centered at 3 GHz with 3 dB fractional bandwidth of 87% are designed and fabricated. The measured results show that both the return losses are better than 15.8 dB, while the BPF with DMSs has a ?19.4 dB isolation wideband from 1.57 to 4.23 . The measured results are in excellent agreement with full‐wave electromagnetic simulation results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:122–128, 2015.     

Design of wideband slot‐coupled microstrip vertical transition

A wideband slot‐coupled microstrip‐to‐microstrip vertical transition is presented in this paper. The transition consists of upper/lower microstrip patch, a metallized via, a wide slot, and a CPW patch on the ground plane. The CPW patch is connected to the upper microstrip patch through the metallized via. The upper microstrip patch, the CPW patch, and the metallized via together constitute a hybrid resonator. By introducing the fundamental resonance of the hybrid resonator into the passband, a broadband microstrip vertical transition can be realized. A sample transition has been designed and measured. Experimental results indicate that a broad frequency range of 2.3 to 8.4 GHz with return loss better than 10 dB can be obtained.     

New multi‐standard dual‐wideband and quad‐wideband asymmetric step impedance resonator filters with wide stop band restriction

New multi‐standard wide band filters with compact sizes are designed for wireless communication devices. The proposed structures realize dual‐wideband and quad‐wideband characteristics by using a new skew‐symmetrical coupled pair of asymmetric stepped impedance resonators, combined with other structures. The first and second dual‐wideband filters realize fractional bandwidths (FBW) of 43.2%/31.9% at the central frequencies (CF) of 1.875/1.63 GHz, and second bandwidths of 580 MHz/1.75 GHz at CF of 5.52/4.46 GHz, respectively. The proposed quad‐band filter realizes its first/second/third/fourth pass bands at CF 2.13/5.25/7.685/9.31 GHz with FBW of 46.0%/11.4%/4.6% and 5.4%, respectively. The wide pass bands are attributed to the mutual coupling of the modified ASIR resonators and their bandwidths are controllable by tuning relative parameters while the wide stop band performance is optimized by the novel interdigital cross coupled line structure and parallel uncoupled microstrip line structure. Moreover, the quad band is generated by introducing the novel defected rectangle structure. These multi‐standard filters are simulated, fabricated and measured, and measured results agree well with both simulated results and theory predictions. The good in‐band and out‐of‐band performances, the miniaturized sizes and simple structures of the proposed filters make them very promising for applications in future multi‐standard wireless communication.     

Wideband and wide stopband superconducting bandpass filter using asymmetric stepped‐impedance resonators connected to open stub

A wideband wide stopband filter is designed using asymmetric stepped‐impedance resonators (ASIRs) connected to a large open stub. The capacitive open stub and the parallel‐coupled microstrip line are used to achieve the strong couplings for large fractional bandwidth (FBW). For a wide‐stopband performance, the proposed filter uses ASIRs to improve the high‐order spurious resonant frequency. The first and last resonators of the proposed filter are further optimized to suppress the spurious resonant frequency caused by open stub. The final filter has a 70% FBW centered at 4.87 GHz with 20‐dB‐rejection stopband up to 15.78 GHz (approximately 3.24 f₀). The measured insertion loss is less than 0.15 dB and the return loss is better than 17 dB.     

High selectivity wideband BPF with very wide stopband characteristic

This paper describes the design and evaluation of a highly selective wideband microstrip bandpass filter with a near brick‐shaped transmission response and a very wide stopband characteristic. The proposed filter structure excites multimode resonances that combine to realize a wideband filter response and excited too are transmission zeros that create a highly selective filter with wideband suppression in the upper and lower stopbands. The filter configuration comprises electromagnetically coupled resonators that are stub loaded. The input and output feedlines are interdigitally coupled to the resonators. Measured results confirm the low‐loss and via‐free wideband filter exhibits an elliptical response with a wide stopband with a rejection greater than 30 dB. The selectivity factor and stopband performance of the proposed filter is better than that obtained with the high‐temperature superconductor (HTS) filters. Design of the filter is relatively simple and easy to manufacture using standard PCB technology. There is good correlation between the simulation and measured results. The proposed wideband bandpass filter is suitable for applications in high interference environments and cognitive radio systems.     

Compact planar substrate‐integrated waveguide diplexers with wide‐stopband characteristics

Compact planar substrate‐integrated waveguide (SIW) diplexers with wide‐stopband characteristics are presented for the first time based on collaborative multispurious mode suppression techniques including the harmonic staggered technique, centered coupling windows, and offset‐centered output ports. The coupling scheme using common dual‐mode resonator coupled with multiple single‐mode resonators is adopted here to eliminate the T‐junctions for size and loss reduction, and the dual‐mode coupling controlling technique we previously proposed is also employed to allocate the fractional bandwidths (FBWs) of the two channels flexibly based on the FBW design graph. Additionally, by combining the harmonic staggered technique, centered coupling windows, and offset‐centered output ports, good out‐of‐band rejections can be achieved and excellent wide‐stopband characteristics have been implemented intrinsically. Two prototypes including second‐order and third‐order SIW diplexers are synthesized, designed, fabricated, and tested as demonstrations, extending the stopbands to 1.78f₁ and 2.04f₁ with the rejection levels better than 17.5 and 20 dB, respectively.     

A modified design approach for compact ultra‐wideband microstrip filters

A modified design approach for compact ultra‐wideband microstrip filters with cascaded/folded stepped‐impedance resonators is described. The key feature of the proposed method is to facilitate stronger coupling between stepped‐impedance resonators and, at the same time, eliminate the requirement of extremely small gaps in coupled‐line sections, as found in traditional designs. Simulations and measurements demonstrate that the filters designed with this technique exhibit good reflection, insertion‐loss, and group‐delay performance within the 3.1–10.6 GHz band. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2010.     

High‐order dual‐band superconducting filter with independently controllable passbands and wide stopband

A stepped‐impedance‐stub loaded stepped‐impedance resonator (SISLSIR) is proposed to design a dual‐band bandpass filter. The even‐ and odd‐mode frequencies and the coupling strength of the proposed resonators can be independently designed and adjusted. A dual‐feedline structure is used to meet the required external couplings of the 2 passbands. Thus, both the center frequencies and the bandwidths of the 2 passbands can be independently controlled. A 6‐pole dual‐band filter with the passbands of 3300～3600 MHz and 4800～5000 MHz is successfully designed using the proposed method and fabricated with YBCO/MgO high‐temperature superconducting (HTS) wafer. The measured results of the filter exhibit high performance and match well with the simulations. The measured insertion losses are less than 0.2/0.3 dB, and the return losses are greater than 15/14 dB for the lower/upper passbands, respectively. The out‐of‐band rejection is greater than 68 dB up to 12 GHz.     

High‐rejection wide‐stopband lowpass filters using signal interference technique

A design of compact, sharp rejection microstrip lowpass filters (LPF) with wide‐stopband is presented by using signal interference technique. The filter parameters can be easily controlled by the characteristic impedances of the configuration. Explicit design equations with graphs are presented. To validate the theoretical prediction, two prototype LPFs are fabricated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

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.     

Compact ultra‐wideband slot antenna with three notched‐band characteristics

A very compact ultra‐wideband (UWB) slot antenna with three L‐shaped slots for notched‐band characteristics is presented in this article. The antenna is designed and fabricated using a new stepped slot with different size, integrated in the ground plane, and excited by a 50 Ω microstrip transmission line. The stepped slot is used to minimize the dimensions of the antenna and to achieve an impedance bandwidth between 2.65 and 11.05 GHz with voltage standing wave ratio (VSWR) less than 2. The length of the stepped slot is equal to a quarter wavelength to create a resonance in the desired frequency. Three L‐shaped slots with various sizes are etched in the ground plane to reject three frequency bands in C‐band (3.7‐4.2 GHz), WLAN (5.15‐5.825 GHz), and X‐band (7.25‐7.75 GHz), respectively. The notched‐band frequency can be controlled by changing the length of the L‐shaped slot. The proposed antenna has a very small size (20.25 × 8 × 1.27 mm³) compared with previous works. The measured and simulated results show a good agreement in terms of radiation pattern and impedance matching.     

A novel balanced wideband power divider based on microstrip‐slot transitions

A novel design of a balanced wideband power divider (PD) with enhanced common‐mode (CM) suppression is proposed. The top and bottom layers of the structure contain tapered microstrip line. Those microstrip lines are coupled via slotline in the ground plane, which is located at the middle layer. With appropriate placement of the slotline, the coupling between the slotline mode and the differential‐mode (DM) signals can be maximized, while that between the slotline mode and the CM signals can be minimized. Simulated and measured results show that the proposed PD has equal power division, low insertion loss, and good return loss. In the measurement, the fractional bandwidth of the measured ?10 dB (DM) return loss is about 101% (1.82–5.35 GHz), the insertion loss for the DM signals is less than 5 dB, the suppression of the CM signals is higher than 45 dB, and the DM isolation is better than 10 dB over the fractional bandwidth. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:437–442, 2014.     

Compact low‐cost microstrip lowpass filter with sharp roll‐off and wide attenuation band

A compact low‐cost lowpass filter (LPF) with sharp roll‐off and wide attenuation band using stepped impedance resonator loaded with interdigital fingers and U‐shaped resonator is recommended in this article. The proposed LPF has a cut‐off frequency of 1.2 GHz with a sharp roll‐off 135 dB/GHz and passband insertion loss 0.35 dB. An array of two different shapes of defected ground structures are etched in the ground plane for introducing additional transmission zeroes to enhance the stopband performance. The relative stopband suppression is achieved up to 171% with a suppression factor of 2. The proposed structure is modelled, fabricated, and measured. The measurement results are found to be well‐matched with the simulated ones. Eventually, a high figure of merit of 21 600 is achieved.     

Novel compact dual‐narrow/wideband branch‐line couplers using T‐Shaped stepped‐impedance‐stub lines

This article presents a compact model to reduce the physical size and increase the frequency ratio between the second and first resonance frequencies of a dual‐function stepped‐impedance‐stub (SIS) line, which was subsequently employed in the realization of dual‐band branch‐line couplers. The proposed model comprises of a loaded spiral T‐shaped SIS that reduces the size of a conventional SIS line as well as improving its frequency ratio. The proposed model behaves exactly similar to the recently developed dual‐band resonators with the advantage of size reduction of ～35% as well as having a wide range of realizable frequency ratios between 1.4 and 3.7 compared to 1.7–2.7 and 1.8–2.3 for the conventional SIS and T‐shaped transmission‐lines, respectively. Dual‐narrowband and wideband branch‐line couplers were developed based on the spiral T‐shaped SIS lines. The dual‐wideband device's bandwidth was enhanced by 2.7% accompanied by a size reduction of 58.6% in comparison with the conventional dual‐wideband couplers operating at the same frequencies. The theoretical results were verified by measurement. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

A microstrip wideband monopole antenna for multisystem integration by utilizing stepped‐impedance structure and L‐shaped slot

In this article, a coplanar‐waveguide (CPW)‐fed dual‐band antenna for applications of the multisystem integration has been demonstrated. The resonance analysis of the stepped‐impedance (SI) monopole is presented by using the transmission‐line analysis method. The frequency‐response characteristics of the SI‐monopole, such as the resonance condition and harmonic response, are systematically summarized. Furthermore, utilizing several simple techniques, such as bent feeding topology, asymmetric ground plane, and an L‐shaped slot etched in the ground plane, a right‐hand circularly polarized (RHCP) radiating wave at 1.57 GHz and a left‐hand circularly polarized (LHCP) radiating wave at 2.33 GHz are excited for the applications of the global positioning system (GPS) and the satellite digital audio radio (SDAR) service system. After optimization of the geometrical parameters of the proposed antenna, the measured impedance bandwidths of a reflection coefficient less than ?10 dB range from 1.40 to 2.98 GHz and from 4.48 to 6.27 GHz, and thus covers most of the commercial wireless communication systems, such as GPS, digital cellular system (DCS), personal communication system (PCS), international mobile telecommunications (IMT)?2000, wireless local area networks (WLAN), and long‐term evolution (LTE) 2300/2600. The measured 3‐dB axial ratio (AR) bandwidths are about 80 MHz at 1.57 GHz and 100 MHz at 2.33 GHz.     

Compact ultra‐wideband bandpass filter with variable notch characteristics based on transversal signal‐interaction concepts

A novel technique is presented to design highly compact microstrip ultra‐wideband (UWB) bandpass filters that exhibit high selectivity quasi‐elliptical response. The design is based on transversal signal‐interaction concepts that enable the inclusion of single or dual notch‐bands within the filter's passband to eliminate interference from other services that coexist within the UWB spectrum. The filter configuration comprises of two transmission paths which include folded T‐shaped stepped impedance resonators (SIRs) that are capacitively coupled with the input/output lines to enable signal transmission. It is shown that by combining the filters of different passband centre frequencies an UWB filter can be realised with either a single‐ or dual‐notch function. The theoretical performance of the filter is corroborated via measurements to confirm that the proposed filter exhibits UWB passband of 123% for a 3 dB fractional bandwidth, a flat group‐delay with maximum variation of less than 0.3 ns, passband insertion loss less than 0.94 dB, high selectivity, a sharp rejection notch‐band with attenuation of ?23 dB, and a good overall out‐of‐band performance. Furthermore, the filter occupies a significantly small area of 94 mm² compared with its classical counterparts. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:549–559, 2014.     

A balanced dual‐band bandpass filter with a wide stopband and controllable differential‐mode frequencies and fractional bandwidths

In this article, a balanced microstrip dual‐band bandpass filter (BPF) is designed. The proposed filter is achieved by employing a microstrip U‐shape half‐wavelength resonator, a folded stub‐loaded resonator and balanced microstrip/slotline transition structures. The center frequencies and the fractional bandwidths of the two differential‐mode (DM) passbands can be controlled independently by changing the physical lengths of the two resonators and the gaps between each resonator, respectively. The balanced microstrip/slotline transition structures can achieve a wideband common‐mode (CM) suppression. Meanwhile, the DM passbands are independent from the CM responses, which significantly simplify the design procedure. In addition, a wide DM stopband is also realized. In order to validate the design strategies, a balanced dual‐band BPF centered at 2.57 and 3.41 GHz was fabricated and a good agreement between the simulated and measured results is observed.     

A high BDR microstrip‐line fed antenna with multiple asymmetric elliptical wide‐slots for wideband applications

In this study, a novel printed wide‐slot antenna for wideband applications is presented. The designed antenna consists of four merged elliptical wide‐slots (EWSs) of different dimensions in the ground plane. An open‐ended microstrip line having a characteristic impedance of 50 Ω is used to excite the EWS. Each EWS corresponds to the different frequency of operation and hence when merged together give a wideband response. The fabricated prototype of the designed antenna shows the 10 dB return loss bandwidth (RLBW) of about 157.72% ranging from 2.21 to 18.7 GHz. The peak gain varies from 0.1 to 6.5 dB within the RLBW is reported. An almost constant group delay, low variation (<?40 dB) in the transfer function S₂₁ and linear phase variation for both side by side and face to face orientations of the designed antenna shows its applicability for wideband applications. The electrical dimensions of about 0.176λ _L × 0.162λ _L (where λ _L is the lowest operating wavelength) give rise to the bandwidth dimension ratio of about 5505 which is highest among the antenna structures reported in the literature. The measured results are found in good concordance with the results obtained from numerical simulations.     

Dual‐band filter with high selectivity and wide stopband rejection

This article presents a highly selective dual‐passband filter based on stepped‐impedance‐resonator (SIR) and mixed electromagnetic coupling. First, the surface area of the filter is effectively reduced by the triangular topology. Second, four controllable transmission zeros are introduced by source‐load coupling feed and mixed electromagnetic, which increases the selectivity of the filter. Third, a perturbation structure is added to independently control the resonance points of each passband. Finally, the improved defect ground structure (DGS) is integrated to obtain wide stopband rejection. The measured S‐parameters are well agreement with the simulated results, which show that the center frequencies of the two passbands are 2.4 GHz and 5.2 GHz; and the passband insertion losses are 0.85 dB and 1.6 dB; and the relative bandwidths are 14.6% and 5.7%, respectively. Besides, the structure is with six transmission zeros, and 20 dB suppression for the third harmonic and the fourth harmonic are achieved. Compared with the traditional SIR double‐passband filter, this filter has many advantages, such as simple design, small size, small insertion loss, controllable frequency, high selectivity, and high spurious suppression.