Open Stubs Research Articles

A microstrip bandpass filter using coupled lines loaded by open stubs

A compact simple structure bandpass filter based on terminated three coupled line structures with high selectivity is introduced through odd and even-mode analysis. The proposed filter consists of three coupled lines loaded by open and short circuit stubs. The parallel-coupled lines structure is used to obtain high selectivity with transmission zeros near the passband. Meanwhile, simultaneously tuning on bandwidth and center frequency are introduced by coupled line. One type of bandpass filter based on terminated coupled line structure is theoretically analyzed, simulated, and measured. The stepped impedance structures at the input and output ports have been used to improve the attenuation level at the stopband region and create the multiple attenuation poles. The center frequency of 1.3 GHz, the fractional bandwidth (FBW) of about 65%, the low insertion loss of 0.25 dB, and the high return loss of 30 dB are obtained. Also, a flat group delay lower than 1.4 ns is achieved. Experimental and simulated results are presented, which are in good agreement.

A dongle-sized bandwidth-reconfigurable filtenna for UWB/5G-n77 band applications

ABSTRACT This paper presents a frequency reconfigurable filtenna for efficiently switching between ultra-wideband (UWB) and 5G-n77 band. The filter section with the UWB state of operation is realised by a stepped impedance open stub loaded at the middle of a stepped impedance resonator. Switching to 5G-n77 band is accomplished by appending two open-circuited uniform impedance stubs to the UWB filter section through PIN diodes. The antenna section is coplanar waveguide (CPW) fed and is based on a quasi-self-complementary design with a half- hexagonal-shaped radiator. The microstrip to CPW transition is realised by connecting the ground planes through vias. The overall size of the filtering antenna is 18.5 mm × 57 mm. The filtering antenna has stable radiation patterns with good agreement between simulated and measured results. The peak gain in 5G-n77 band and UWB band is 4 dBi.

Transverse resonance technique for analysis of a symmetrical open stub in a microstrip transmission line

Open stubs in a strip (microstrip) transmission line are one of the most common elements of planar circuits used in numerous devices in the various types of wireless systems. Therefore, the urgent problem is to develop an analyzing method for discontinuities in the form of the open stub in a microstrip transmission line at frequencies at which the high-frequency effects must be considered. In the paper, a technique of scattering characteristics calculating on a symmetrical microstrip open stub by transverse resonance method is presented. Boundary value problems for a rectangular volume resonator based on a microstrip transmission line with a symmetric open stub are solved for the three options boundary conditions in the symmetry plane and on the longitudinal boundaries. The intersection of the spectral curves obtained by the numerical solution of the “electric” and “magnetic” boundary value problems determines the minima of a reflection or transmission coefficients of fundamental wave on discontinuities. To algebraize the boundary value problems for the eigen frequencies of volume resonator with discontinuity, the corresponding two-dimensional functions of the magnetic potential are constructed, through which the components of the current density on the strip are determined. The functions of magnetic potential were defined by decomposing them into expansion by Fourier series, which ensures stable convergence of the series and numerical calculation algorithm. The developed technique has been tested by calculating the eigenfrequency spectra of an open microstrip stub using the transverse resonance method on the example of an open stub in a microstrip transmission line with a resonant frequency of about 3.0 GHz. Also, a technique for numerical solutions of “electric” and “magnetic” boundary-value problems for resonators with two electrodynamically coupled symmetric open stubs in a microstrip transmission line is developed.

Compact transversal signal-interaction wideband bandpass filter with multiple transmission zeros and wide stopband

In this paper, a compact wideband bandpass filter with multiple transmission zeros and a wide upper stopband is proposed based on the transversal signal-interaction concept. The filter has two transmission paths for signals to travel from the input port to the output port. The wideband bandpass filter is designed with a center frequency of 4.29 GHz (f0) and a 3-dB fractional bandwidth of 71.3 %. Six transmission zeros from 0 GHz to 4.2 f0 can be achieved due to the superposition of signals of the two transmission paths and the virtual short effect of open stub. The designed and fabricated wideband bandpass filter is of minimum insertion loss of 0.3 dB, group delay in the passband below 1.1 ns, and upper-sideband rejection up to 18 GHz (4.2 f0). Additionally, the proposed filter possesses compact size, and the overall circuit only occupies 0.23 λg × 0.15 λg (λg is the guide wave length of 50 Ohm microstrip line at 4.29 GHz). Measurement and simulation results are in good agreement.

A Frequency-Reconfigurable Dual-Band RF Crossover Based on Coupled Lines and Open Stubs

A Frequency-Reconfigurable Dual-Band RF Crossover Based on Coupled Lines and Open Stubs

A Novel Dual-Band Omnidirectional Horizontally Polarised Antenna Using Slotted Ground for Wi-Fi Applications

This letter explores an innovative approach to designing a compact, dual-band, omnidirectional, horizontally polarised (OHP) patch antenna with a low profile. The antenna’s ground plane is meticulously etched with radial and arch slots to create open-circuited stubs. This design generates two circulating current loops: one beneath the circular patch and the other on the outer side of the circular patch, comprised of four circular stubs. These current loops operate in unison to produce dual-band resonance and in-phase circulating current on the ground at both resonance frequencies. The antenna’s configuration includes four circular stubs formed by printing sequential radial and bent slots beneath the patch. This arrangement generates an omnidirectional radiation pattern in the azimuth plane at the upper resonance frequency. In addition, four open circular stubs outside the patch are integrated into the ground plane cascaded to the inner four stubs to achieve resonance at the lower frequency. The complete dimensions of the proposed antenna configuration are 0.29λ0 × 0.29λ0 × 0.025λ0, with bandwidths of 2.84% and 2.77% corresponding to measured resonance frequencies of 2.457 and 5.27 GHz, respectively. The measured gains are 1.2 dBi at the lower resonance frequency and 0.8 dBi at the upper resonance frequency. Furthermore, the measured roundness of the radiation pattern remains within 1 dB at the lower frequency band and within 2.8 dB at the upper-frequency band.

Ka-Band Wide-Angle Scanning Phased Array with Dual Circular Polarization

A wide-angle scanning phased array with dual circular polarization in the Ka-band is presented in this paper. To improve the scanning capability of the phased array, the microstrip element is modified by loading many metal posts at its center and periphery. In addition, a stripline coupler is designed to achieve dual circularly polarized (CP) radiation, and the inner conductor of the subminiature micro-push-on (SSMP) connectors for feeding the coupler is extended to the top layer of the multilayer element by introducing an open stub, which simplifies the assembly process between the SSMP connector and multilayer printed circuit board (PCB) due to through-hole soldering instead of blind-hole soldering. The proposed element can cover a frequency range from 28 GHz to 30.5 GHz with a relative bandwidth of 8.5% in the Ka-band. An 8 × 8 phased array is constructed based on this proposed element, and a wide-angle scanning range from −65° to +65° is obtained for the dual circular polarization. The proposed array has a gain fluctuation of 5.1 dB and an axial ratio (AR) of less than 3.3 dB during beam-steering. The prototype is fabricated and measured, with a good agreement between the measured and simulated results. The proposed phased array can be applied in a Ka-band millimeter-wave (MMW) communication system.

Derivation of Generalized Design Formulas for Modified Branch-Line Coupler with the Second Harmonic Suppression Characteristics

We propose a modified branch-line coupler composed of the open stubs and stepped impedance lines. This structure allows the second harmonic suppression and size reduction. We present the steps to transform from a conventional branch-line coupler to the proposed structure using equivalent circuits and derive the generalized design formulas. From the results analysis of the design sample, we demonstrate the validity of the derived formulas. The fabricated branch-line coupler provides more than 30 dB the second harmonic suppression and about 30 % size reduction compared to a conventional branch-line coupler.

Dual-narrowband bandpass filter with exact equations of scattering parameters

Abstract In this article, a new microstrip dual-narrowband bandpass filter employing parallel-coupled transmission lines and open stubs is presented, investigated, and fabricated. The proposed dual-narrowband bandpass filter is analyzed and its exact scattering parameters are calculated, simulated, and measured. So, calculated scattering parameters offer a deep inside view of the performance of the proposed filter. To analyze the proposed filter, the even- and odd-mode excitation are utilized. The input impedance under even- and odd-mode excitation are achieved by transmission line theory and inserted in the scattering parameter equations. Finally, the accurate scattering parameters are derived and compared with simulation results. Simulation results prove the theoretical results. Then, an optimized proposed filter is fabricated and matched with simulation results. The center frequency bands are 4.5 and 6.8 GHz. The optimized filter occupies 0.12 $ \times $ 0.096 $\lambda _g^2$ , which is small. Its fractional bandwidth of the first and second passband are 1.5 and 2.5%, respectively. Furthermore, wide and strong rejection levels in the stopbands are offered. The structure of the proposed filter provides many freedoms to design. There is an agreement between experimental and simulation results.

Design of Series-Fed Circularly Polarized Beam-Tilted Antenna for Microwave Power Transmission in UAV Application

In response to the increasing deployment of unmanned aerial vehicles (UAVs) across various sectors, the demand for efficient microwave power transmission (MPT) systems for UAVs has become paramount. This study introduces series-fed circularly polarized (CP) and passively beam-tilted patch array antennas designed to enhance MPT in UAV applications, with the intention of addressing the needs related to extending flight times and improving operational efficiency. The radiating element of the proposed antennas employs the conventional model of the patch with truncated corners for CP operation, with transmission line lengths optimized for beam tilt to ensure precise energy transfer. Additionally, an open stub is integrated into the broadside series-fed antenna to improve impedance matching, which is crucial for maintaining signal integrity. The proposed design achieves right-hand circular polarization (RHCP) with an axial ratio (AR) below 3 dB across the operating band, indicative of its effectiveness in diverse UAV operational contexts. Prototypes of each proposed antenna were fabricated and measured according to the beam tilting angle. The measured RHCP realized gains of the proposed antennas are 14.59, 13.09, 13.07, and 10.71 dBic at the tilted angles of 0°, 15°, 30°, and 45°, respectively, at 5.84 GHz.

A new design approach of Rat-Race coupler based compact GaN HEMT power amplifier towards flat high efficiency over broadband

This paper presents a high efficiency Rat-Race Coupler based compact GaN HEMT power amplifier (PA) design over broadband for high power transmitter in wireless communication. The rat-race coupler integrated PA Compact design is proposed for the first time as per author best knowledge. The design methodology used a higher order two open stubs and a rat-race coupler (RRC) at input/output sections to control harmonics impedances. The RRC is used to enhance the i/o power, and efficiency over broadband, which provides a good insertion loss, and consumes the least power and non-crucial impedance bandwidth for the normalized frequency band of interest. As a proof of concept, a PA is fabricated using a monolithic microwave integrated circuit (MMIC) 0.15 µm gallium nitride high electron mobility transistor (GaN HEMT) process. The measured result shows that the designed PA achieves a flat power added efficiency (PAE) of 65 % − 74 %, output power (Pout) of 44.8 dBm − 46 dBm, and drain efficiency (DE) of 72 % − 85 %, over a record wide frequency of 1.8 GHz − 3.6 GHz, which is the highest one among all reported harmonic tuned PAs.

Design of highly selective balanced bandpass filter with wide differential-mode stopband and high common-mode suppression

A highly selective and wide stopband bandpass filter (BPF) with multiple transmission poles (TPs) and transmission zeros (TZs) has been proposed. The BPF employs a box-like coupling structure consisting of two half-wavelength resonators and a dual-mode open stub loaded resonator, enabling the generation of two TZs and four TPs. Three controllable TZs are obtained by adding an annular spiral open stub to the terminal of the input and output coupling lines, which significantly improves the selectivity of the BPF. To achieve a wide stopband characteristic, a wide stopband unit with three additional TZs is cascaded within the structure. A balanced BPF is realized by introducing a microstrip-slotline-microstrip balun structure to the input and output ports of the proposed BPF. Experimental results validate the feasibility of the proposed BPF and balanced BPF applied in 2.45 GHz ISM band. The introduction of eight TZs gives the BPF a 20 dB rectangular coefficient of 1.3 with an upper stopband exceeding than 12 GHz. The balanced BPF can achieve 40 dB of high common-mode(CM) suppression in the passband, while differential-mode (DM) transmission is close to the performance of the proposed BPF. The minimum insertion loss for BPF and balanced BPF is 0.8 dB and 1.3 dB, respectively.

A Low-Profile Metal-Backed Dipole Loaded With Closely Coupled Arc-Shaped Open Stubs for On-Metal Tag Design With Wide Frequency Tuning Capability

A Low-Profile Metal-Backed Dipole Loaded With Closely Coupled Arc-Shaped Open Stubs for On-Metal Tag Design With Wide Frequency Tuning Capability

Wideband filtering power divider based on D-CRLH resonator

In this paper, a wideband filtering power divider (FPD) based on dual-composite left–right-handed (D-CRLH) resonator is proposed. The D-CRLH filter unit, featuring a parallel stepped impedance resonator (SIR), is used to replace the λ/4 transmission line of the Wilkinson power divider, which can make the FPD more compact. Due to the inherent characteristics of D-CRLH resonator, two transmission zeros can be generated on both sides of the passband, so the proposed power divider based on the D-CRLH resonator can achieve a quasi-elliptic filtering response. To further enhance anti-interference ability at low frequencies, a pair of open stubs is added to the output feedline to introduce an additional transmission zero on the low-frequency side of the power divider passband. Finally, isolation resistors are introduced on the input and output feedlines to improve the isolation between the output ports. For validation, a prototype with a center frequency of 3.6 GHz is fabricated and measured, with −10 dB fractional bandwidths (FBWs) of 58.3 %(2.55–4.65 GHz). The measurement results are basically consistent with the simulation results, and its isolation in the passband is all more than 13.8 dB.

Compact lowpass filter with vast out-of-band rejection utilizing DGS

A unique low-profile microstrip lowpass filter (LPF) is introduced. It features a broad range of stopband and sharp roll-off. The suggested LPF is built utilizig a T-shaped configuration which includes a stub for resonance and utilizes open stubs as attenuator cells. To further improve the stopband, a double circular ring is engraved into the ground plane. The developed filter features a cut-off frequency of 3 dB at 3.4 GHz, a roll-off rate of 108 dB/GHz, and a stopband range from 3.7 to 22.8 GHz. The attenuation is less than −20 dB. The prospective LPF is designed using a lumped LC circuit model and validated using Keysight Advanced Design System (ADS) simulation and theory. The final design is realized using RT/Duroid 4003C, which boasts a small footprint of 12.4mm×8.69mm×0.8mm. The modelling findings and measurements of the suggested LPF are in fairly good agreement.

10–14GHz and 14–18GHz Interdigital Planar Bandpass Filters for Frequency Multiplexer

This paper presents the design of two wideband bandpass filters (BPF) operating in the 10–14 GHz and 14–18 GHz ranges for a five port 1-18GHz frequency multiplexer. The 10–14 GHz BPF utilises an interdigital array of resonators with asymmetrical widths and is combined with a low-pass filter for wide stopband characteristics. Sharp attenuation in the stop bands is achieved by including quarter wavelength open stubs. The 14–18 GHz BPF incorporates three interdigital resonators with a modified middle resonator, introducing a variable gap width for improved impedance matching. Open-circuited stubs and a bandstop filter further enhance attenuation in the stop bands. Equivalent circuit models accompany both filters. Both filters exhibit excellent performance, as evidenced by the reflection coefficients below −12 dB within their respective frequency ranges. The insertion loss remains below 2.5 dB throughout the passband, indicating efficient signal transmission. Moreover, the group delay for both filters is less than 0.8 ns, indicating minimal signal delay. These results demonstrate the high-quality characteristics of the designed filters, making them suitable for a wide range of applications requiring efficient signal filtering and multiplexing.

Novel EBG‐type power/ground network with open stub bridges for broadband SSN suppression

AbstractA novel electromagnetic bandgap power/ground (P/G) network is proposed by using λ/4 open stub resonators for the broadband suppression of the simultaneous switching noise. Since three λ/4 open stub resonators are linked to the bridge between the two cells as bandstop filter, the high‐order mode resonances can be effectively suppressed. The proposed P/G network is analyzed by the cavity modes, simulated by the full‐wave simulator, and validated by the measurement. A broadband simultaneous switching noise suppression from 0.6 to 7.6 GHz is achieved. Additionally, in comparison with the reference boards, the radiated emission has less electromagnetic interference, which validates the advantage of the proposed electromagnetic bandgap P/G network.

High common‐mode rejection balanced bandpass filter using novel coupling scheme and source‐loaded coupling technique

AbstractA balanced bandpass filter (BPF) with a novel coupling scheme and source‐loaded coupling (SLC) technique is proposed. The J‐inverter is directly connected to the source or load, and the single‐band cell (SBC) is fed by the J‐inverter. Meanwhile, the J‐inverter is also coupled to a resonator. Equivalent differential‐mode (DM) and common‐mode (CM) circuits are presented, and their ideal frequency responses under DM and CM are also provided. Furthermore, the SBC equals paralleled short‐ and open‐circuited stubs in DM and equals two paralleled open stubs in CM. To validate the design concept, a four‐pole balanced BPF working at 2.66 GHz with fractional bandwidth (FBW) of 13.8% is designed and fabricated. Three transmission zeros (TZs) are generated, and the upper stopband suppression level reaches 34 dB. Meanwhile, a high CM rejection level attains 54 dB within the DM passband.

Knowledge‐Based Methodology of CPW‐Fed Open Stub Loaded C‐Shaped Microstrip Antenna by Surrogate‐Based Modeling

Knowledge‐Based Methodology of CPW‐Fed Open Stub Loaded C‐Shaped Microstrip Antenna by Surrogate‐Based Modeling

A Compact Microwave Quadrature Hybrid Coupler Using Capacitive Composite Lines and Meandered Stubs

In this paper, a new structure of the quadrature hybrid coupler (QHC) with compact size is proposed using capacitive composite lines and meandered open stubs. The proposed coupler works at 1.6 GHz with a 0.4 GHz bandwidth, which shows 25% fractional bandwidth (FBW). The proposed QHC occupies only 15 mm × 15 mm (0.12 λ × 0.12 λ), while the typical QHC size is 32 mm × 32 mm (0.25 λ × 25 λ) at the same working frequency. In the designed structure, two symmetric meandered stubs and two symmetric π-shaped composite networks including capacitors and microstrip lines are applied together. The designed QHC has a small size and occupies only 22% of the area of the conventional QHC, resulting in a 78% size reduction. The designed prototype has been analyzed, fabricated and tested, and the experimental results verify the simulated and analysis results. The results show a better than 27 dB return loss, more than 28 dB isolation between the output ports and less than 0.4 dB insertion loss at the working frequency of 1600 MHz. With the achieved desirable specifications, the fabricated QHC is a suitable choice for wireless microwave applications.