Fractional Bandwidth Research Articles

Design of compact microstrip high gain filtering antenna array based on SIW cavity

ABSTRACT The article has designed a single-mode, substrate-integrated waveguide (SIW), high-gain filtering array antenna. The proposed filtering antenna array is implemented on a stack of metal and dielectric substrate layers with SIW cavity and CPW feeding at the bottom layer to excite the single T E 201 mode. It acts as the first stage of the filter resonator, facilitating the four-way power distribution through the slots to the 2 × 2circular patch array acting as the second stage of the filtering resonator. With the advantages of the reutilisation of the existing high-order SIW cavities, the presented filtering array antenna offers low loss, very high gain, high efficiency, miniaturised size, and simple construction. A filtering array prototype with dimensions 1.081 λ x0.752 λ x0.023 λ has been fabricated using a multi-layer printed circuit board method and measured to validate the proposed design.The structure offers a peak gain of 12.6 dBi, fractional bandwidth (FBW) of 4.6%, and 96% peak radiation efficiency at the centre frequency of 13.68 GHz. An excellent correlation is observed between the measured and simulation results. The proposed design has immense potential in high-frequency and wide-ranging filtering arrays for radar and satellite in Ku band applications.

A compact microstrip quint-band bandpass filter using shorted stub-loaded SIRs based on the interdigital feedline structure

ABSTRACT A compact microstrip quint-band bandpass filter (BPF) composed of two pairs of shorted stub-loaded step-impedance resonators (SSLSIRs) with interdigital feedline structure is designed in this paper. The two pairs of resonators are bent and placed back-to-back on the upper and lower sides of the feedline in order to miniaturise the filter. Due to the symmetric structure of the resonators, the even-odd mode analysis method can be used to derive the resonant frequency equations. Based on the simulation, the filter is fabricated on the substrate of Rogers 4350 and measured. The measured S-parameter results are in good agreement with the simulation results. The operating frequencies of five passbands are measured at 2.2/2.8/4.3/5.4/6.7 GHz and the 3-dB fractional bandwidth (FBW) is 12.7/3.8/6.6/3.2/6.9%, respectively. The measured in-band minimal return losses and the insert losses within five passbands are 11/12/13/12/13 dB and 1.7/2.5/2.7/1.5/1.6 dB. Furthermore, the proposed BPF has good frequency selectivity with steep skirt property via the interdigital feedline structure, which yields seven transmission zeros (TZs). The four measured band-to-band isolations among the five passbands are higher than 20 dB. The filter’s total dimension occupies only 0.18 λg × 0.15 λg, where λg represents the free space wavelength corresponding to the centre frequency of the lowest passband.

Analysis and Design of a Six-Port Network Based on a Modified Schiffman Phase Shifter

Purpose: This study presents a novel design of a six-port network based on a modified Schiffman phase shifter operating at a 90±2° phase shift. Design/ Methodology/ Approach: The research methodology encompasses a comprehensive literature review, the analysis, design and simulation of the novel phase shifter, its integration into a six-port network, layout design and subsequent post-layout simulation, and comparative analysis to evaluate the new design's performance. Findings: The schematic results showed an operational bandwidth from 5.52 GHz to 12.21 GHz, translating to a fractional bandwidth of 75.47% with a maximum phase error of ±1.8° for the 90° phase shift. Also, the post-layout simulation results from momentum demonstrated outstanding performance with an operation frequency band spanning from 5.52 GHz to 12.21 GHz, representing a factional bandwidth of 75.47% and ±2.1° phase error across the entire band. In addition, good impedance matching was achieved at all the ports well below -10 dB. Practical Implications: It also finds application in satellite communications, where beamforming enhances signal strength and quality by directing the signal towards specific locations on Earth, and antenna arrays for satellite uplink and downlink antennas adjust the beam direction and coverage area dynamically. Social Implications: The social impact of this work includes high-performing communication devices for current and future generations, more accurate measurements, particularly wearable devices in healthcare for monitoring human vitals, weather monitoring systems, high-precision radar systems, wireless gadgets, high-data-rate communication systems, and Internet of Things (IoT) devices. Originality and Value: The study contributes to the existing body of knowledge by introducing an innovative design that addresses the limitations of phase accuracy and bandwidth in Six-Port Networks.

Metasurface Based Dual Cp Antenna for S Band Communication

This article proposes a dual circularly polarized antenna with high gain, isolation and wideband characteristics. The proposed antenna consists of a microstrip patch antenna fed with 90° hybrid coupler. The gain of the parent antenna is increased from 3 dB to 7.1 dB. The high gain of 7.1 dB is due to superstrate based metasurface configuration consisting of periodic arrangement of unit cells placed on FR4 substrate and suspended by air gap with the help of non-dielectric spacers. The antenna is fabricated and measurement shows the antenna has good impedance matching across 2 to 3 GHz. The impedance bandwidth of the proposed antenna is 0.8 GHz (2.04–2.84 GHz) with fractional bandwidth of 32.78% and maximum return loss observed at 2.2 GHz and 2.7 GHz. The hybrid coupler provides LHCP and RHCP from 2–3 GHz. The antenna offers wide port isolation >13 dB. The proposed antenna can be promoted for satellite communication replacing bulk array antennas.

Bandwidth enhancement of resonating absorber using a lossy dielectric layer for RCS reduction in X-band

Abstract In this paper, a resonating absorber is proposed for radar cross section reduction in the X-band, with the inclusion of a high loss dielectric layer. The absorber consists of a pair of co-centered resonating Jerusalem cross printed on a FR4 substrate cascaded with a high-loss dielectric layer and a metallic back plane. The designed absorber offers 90 % absorption from 7.8–12 GHz with a fractional bandwidth of 42.42 %. The designed absorber is 0.106λ L thick with a compact square unit cell of size 0.076λ L (wavelength at the lowest frequency). An equivalent circuit model is developed to analyze the proposed absorber. The absorber is angularly stable for varying angle of incidences up to 40°–60° for TE and TM polarizations respectively. The planar as well as the conformal structure of the proposed absorber offer a minimum 10 dB radar cross section reduction in the X-band. The conventional approach which involves complex fabrication process of soldering thousands of lumped resistors to increase the bandwidth, whereas the proposed absorber is realized to offer wide absorption using simple PCB etching technique. To validate the design prototype is fabricated and the measurement is carried out.

Dual Band Modified Complementary Split Ring Resonator Loaded Substrate Integrated Waveguide Based Bandpass Filter

This study presents a dual-band bandpass filter design that implements microstrip to substrate integrated waveguide (SIW) transition to decrease radiation losses. The proposed filter is designed with using four complementary split ring resonators (CSRR) to minimize its size and to gain double negative property. A bowtie shaped slot is etched inside CSRR to have a second resonance at the spectrum. After the simulation results are performed the designed filter is fabricated on a Rogers RT5880 dielectric substrate and the experimental results are compared with the simulation results. The proposed filter has center frequencies at 6.57 and 12.55 GHz with fractional bandwidth (FBW) of 22.05% and 26.29%, respectively. Moreover, the presented filter offers the best bandwidth-to-size result with the size of 0.327λg×0.352λg (where λg is the wavelength at the first passband’s center frequency).

Broadband HMSIW antenna using a demi hexagonal ring slot for X-band application

Microstrip antennas offer several advantages, including small size, easy fabrication, controllable polarity and radiation patterns, and easy integration with other components. These qualities make microstrip antennas more reliable than other antenna types. However, they also have limitations, such as lower radiation efficiency and narrow bandwidth, primarily due to the thin substrate thickness. Substrate integrated waveguide (SIW) is a type of microstrip antenna. SIW antennas come in two forms: one with a rectangular shape, typically designed as a slot, and the other in the form of a horn. However, SIW slot antennas face challenges with narrow impedance bandwidth due to the thin substrate, unlike conventional bulky hollow waveguides. The half-mode substrate integrated waveguide (HMSIW) slot antenna, which is a 50% miniaturized version of the SIW slot antenna, also suffers from reduced fractional bandwidth, resulting from the miniaturization and the thin substrate. This paper focuses on enhancing the bandwidth of HMSIW antennas by incorporating a demi-hexagonal ring slot. The broadband impedance bandwidth simulation (27.36%) is achieved through triple resonance frequencies to address the issue of narrow impedance bandwidth. Both the simulation results and measurements show consistency, with the measured impedance bandwidth ranging from 8.91 to 12.62 GHz (34.46%), demonstrating at least triple resonance frequencies.

Design of Compact Differentially‐Fed End‐Fire Filtenna With High Selectivity

ABSTRACTIn this letter, a compact differentially‐fed end‐fire filtenna is developed. The developed filtenna consists of three drivers, a director, a reflector, and a pair of U‐shaped strips. Different from conventional Yagi antenna with a single driver, multiple drivers are employed to concurrently broaden the impedance bandwidth and facilitate the filtering response. To further improve the lower frequency selectivity, a pair of split rings is inserted between the driver and the director. And a radiation null at lower frequency is generated due to the out‐of‐phase surface currents on director and split rings. For verification, a prototype with a center frequency of 3.9 GHz is designed, fabricated, and measured. The measurement results have a good agreement with the simulation ones. The developed filtenna has a fractional impedance bandwidth of 14.4% (3.62–4.18 GHz), a peak realized gain of 5.8 dBi, a front‐to‐back ratio over 15 dB within the entire operational band. In addition, the filtenna also owns good filtering response with suppression levels higher than 16 and 25 dB for low‐ and high‐stopband, respectively.

Dynamically switchable multifunctional device for terahertz application using vanadium dioxide and graphene-based metasurface

Abstract In this article, a dynamically switchable and multifunctional metasurface is realized using a combination of vanadium dioxide (VO2) and graphene-based structures. The device can be tuned using the temperature transition property of vanadium dioxide from a wideband linear-to-circular polarization converter (LTCPC) to a wideband linear-to-linear cross polarization converter (LTLPC) and a dual-band absorber. The unit cell is designed with a gold-backed lossy-silicon dioxide (SiO2) substrate with a permittivity of 3.9, and the top metasurface layer is designed with a graphene-based dual triangle loaded split ring (DTLSR) and two stripes of vanadium oxide to cover the split partially. The proposed device can be used as a wideband LTCPC at normal temperature (298 K) from 1.43 THz to 2.85 THz, i.e., 66.35% fractional bandwidth (FBW). At temperatures greater than 341 K, VO2 exhibits metallic properties, and the structure functions as LTLPC from 1.82 THz to 3.31 THz (PCR ≥ 80%), i.e., 58.08 % FBW and maximum polarization conversion ratio (PCR) reported as high as 99.65 %. Furthermore, at this metallic condition, two absorption peaks are obtained at 1.22 THz and 3.30 THz with absorptivity of 93.5% and 100%, respectively. The device offers incident angle invariability up to 40° for LTCPC and up to 50° for LTLPC operation. Further insight into the mechanism of operation is developed using the surface current density and electric field distribution analysis. The advantage of the proposed metasurface over other similar structures is assessed with respect to multifunctional behavior, bandwidth, and stability under oblique incidence.

A Single‐Layer Wideband Differentially‐Fed Dual‐Polarized Filtenna With Low Cross‐Polarization

ABSTRACTIn this paper, a single‐layer differentially‐Fed dual‐polarized filtenna (DFDPF) with low cross‐polarization is developed. The developed DFDPF consists of four shorted driven patches and four triangular parasitic patches. First, each single‐feed driven patch resonates at its TM10 mode (corresponding to the antiphase TM20 mode of the two differentially‐fed patches). Incorporating shorting pins on the driven patches leads to a lower radiation null. Then, the parasitic patches are embedded into the gap between the driven patches to introduce an extra in‐band resonance operating in its TM1/2,1/2 mode, along with an upper radiation null, while the footprint remains unenlarged. This improves operating bandwidth and roll‐off rate on the upper passband edge. Finally, a pair of symbiotic open‐ended l‐shaped stubs are integrated into each driven patch to further enhance the suppression level of the upper stopband. The developed DFDPF was prototyped and measured for experimental verification. Experimental measurements validate the feasibility of the simulation results, demonstrating a wide –10 dB fractional impedance bandwidth of 19.5% and a peak realized gain of 6.6 dBi. In addition, the cross‐polarization level is lower than –40 dB.

A Simple Single‐Layer Wideband Filtenna With Multiple Controllable Radiation Nulls

ABSTRACTIn this letter, a single‐layer wideband filtenna with multiple controllable radiation nulls is presented. The developed filtenna has a very simple structure and is composed with a square substrate integrated waveguide (SIW) cavity, a square patch, and a pair of U‐shaped slots. Notably, the filtenna possesses three radiation nulls that can be tuned by adjusting specific geometrical parameters. To achieve a wide bandwidth and better frequency selectivity, the TM10 mode of the square patch is utilized to couple with the TE210 mode of the square SIW cavity. And a radiation null at upper and lower edge of the passband can be simultaneously obtained because of the effective multipath coupling and the impact of TE110 mode in SIW cavity. An extra in‐band resonance and out‐of‐band radiation null are concurrently introduced by etching a pair of U‐shaped slots at the metal ground plane so as to further expand the bandwidth and enhance the frequency selectivity. To validate the design method, a prototype of the filtenna operating at center frequency of 4.76 GHz was fabricated and measured. The measurement results show an impedance fractional bandwidth of 15.8% (4.38‐5.13 GHz) and a peak realized gain of 6.1dBi.

Dual-Band Gysel Filtering Power Divider with a Frequency Transform Resonator and Microstrip/Slotline Phase Inverter

This paper presents a novel dual-band Gysel filtering power divider (FPD) with an excellent isolation performance and a significantly wide isolation bandwidth. Although Gysel power dividers have been extensively studied in the field of radio frequency (RF), the integration of filtering functionality and the expansion of isolation bandwidth remain challenging. The proposed design addresses these challenges by incorporating frequency transform resonators (FTRs) and a microstrip/slotline (M/S) phase inverter into the classic Gysel topology. The FTR is directly connected to the output port to provide a dual-band response, enabling the Gysel FPD to operate without external coupling between the resonator and the port. The M/S phase inverter is a dual-layer 180° phase shifter, designed to replace the conventional 180° transmission lines loaded between the two isolation resistors of the Gysel FPD, achieving a wide isolation bandwidth. To validate the proposed design method, a dual-band Gysel FPD with center frequencies of 1.4 GHz and 1.7 GHz is designed, fabricated, and measured. The measured results show that the in-band return loss is greater than 20 dB, and the in-band insertion loss is about 0.6 dB, and the amplitude and phase imbalance characteristics are good. In addition, the 20 dB-isolation fractional bandwidth achieves 97% (0.78–2.25 GHz). The measured results show excellent agreement with the simulation results, validating the effectiveness of the proposed design methodology.

Research on the miniaturization method of the broadband linear-to-circular polarization conversion metasurface based on genetic algorithm

The size of the metasurface unit cell increases with the decrease of its center working frequency (CF). This is not conducive to the integrated design of the metasurface. To address the problem, a miniaturization design method based on genetic algorithm (GA) is proposed. Firstly, an element library is established. By randomly selecting and combining these elements, various structures are generated as the initial population of GA. Secondly, a Python-CST joint simulation program is constructed to automatically model the metasurface unit cells and extract their electromagnetic parameters. Finally, after multiple iterations of optimization, the optimized unit cell is obtained. This paper takes the transmissive-type linear-to-circular polarization conversion metasurface (LTCPCM) as a research object. The simulation results show that the size of the designed unit cell is only 0.18 λ of the CF (3.86 GHz). The LTCPCM exhibits broadband and wide-angle characteristics, with a fractional bandwidth (FB) of 71% (incident angle θ = 0°) and an angular stability (AS) of 45°. The experimental validation and the simulation result are consistent, proving the effectiveness of the proposed method. The research results can provide a reference for further miniaturization design of metasurface unit cells.

A Fluted E‐Shaped Antipodal Vivaldi Antenna With Rectangular Strips for Surface Scanning Application

ABSTRACTIn this paper, a fluted E‐shaped antipodal Vivaldi antenna (AVA) loaded with rectangular‐shaped strips is proposed for ground‐penetrating radar (GPR) application. The corrugation method is implemented by introducing multiple slots in the uppermost and lowermost arms of the antenna, followed by adding additional 10 strips to broaden and stabilize the impedance bandwidth. The electrical dimension of the antenna is 1.07λ × 1.8λ × 0.004λ. The proposed modified AVA (MAVA) exhibits a high fractional bandwidth of 144.8% over an ultrawideband of 1.6–10 GHz. The peak gain achieved by the antenna is 8.97 dBi. The proposed antenna offers a stable unidirectional radiation pattern along E‐ and H‐plane throughout the spectrum with maximum radiation efficiency of 96%. A prototype of the proposed antenna has been fabricated and tested where the measured results bear close resemblance with the simulated results. The pertinence of proposed antenna for GPR subsurface scanning was examined through a field test where scanned result signifies its aptness for such submissions.

Compact wideband tunable phase shifter with minimal in-band phase deviation

ABSTRACT This brief presents a novel design of a compact wideband tunable phase shifter with low in-band phase deviation. Different from the implementation structures of conventional tunable phase shifters, the proposed design is composed of two microstrip lines, two varactor-loaded coupled lines, and an open-circuit stub, which can perform the characteristics of low phase error, large phase shift range, wide operating bandwidth, and compact size simultaneously. Theoretical analysis demonstrates that a relatively large phase shift range and small phase error can be realized by choosing appropriate electrical parameters of the coupled lines and microstrip lines. The measurement results indicate that the fabricated tunable phase shifter operating at 1.9 GHz can provide a maximum continuously tunable phase shift up to 225.5° within the 21.1% fractional bandwidth, with a maximum in-band phase error of ± 3.22°. Meanwhile, the insertion loss is less than 3.95 dB over the operating band.

A Filtered Differential Phase Shifter with High Selectivity

In this paper, a filtered differential phase shifter with good selectivity is proposed and constructed. This study proposes and builds a filtered differential phase shifter with good selectivity. The main and reference lines in the suggested filtered differential phase shifter are structurally identical. The main line’s bandpass filtering function is achieved by a new coupled feeder, a parallel coupled line loaded with shorted branches, and a coupled resonator at the load end. It has impedance matching and additional transmission zeros/poles. By loading the coupled resonator at the load end, the selectivity of the phase shifter can be improved and the passband and transmission zeros/poles of the phase shifter can be equitably distributed by varying the coupling coefficients and the electrical lengths of the loaded branches. The reference line is a coupled resonator with the same structure and its electrical length is related to the number of degrees of phase shift. Finally, a differential phase shifter is designed and measured. The fractional bandwidth of the proposed phase shifter is about 38%, the return loss reaches −11 dB, the insertion loss is about 1.02 dB, the deviation of the simulated results in terms of the number of degrees of phase shift is about 2.5 degrees, and the deviation of the tested results is about 6 degrees. The trend of the simulation results and the actual measurement results are in good agreement.

Constructing a Microstrip Phase Shifter with Low Phase Error Using a Y-Resonator

In this paper, we propose a Y-type dual-mode microstrip phase shifter that utilizes input–output cross-coupling. The structure comprises a main line and a reference line, with the main line designed in a cross-coupled parallel-feeding configuration to create a band-pass filter. The single-mode resonance frequency is fine-tuned to meet the bandwidth requirements of the band-pass filter. Additionally, by introducing new symmetric transmission zeros in the upper and lower cutoff bands through the cross-coupling of the input and output feed lines, we achieve a quasi-elliptic response. This design significantly enhances both the passband and out-of-band performance of the filter. The reference line functions as a uniform transmission line, and the phase shift value of the phase shifter is achieved by adjusting its electrical length. Compared to conventional phase shifters, this design offers several advantages, including a simpler structure, reduced phase error, and a wider phase shift range. Ultimately, a 90° to 225° phase shifter was designed and simulated, while a 90° phase shifter was fabricated and tested. Measurement results indicate that the designed phase shifter successfully achieves a phase shift of 90° ± 1.2°, with S11 less than 16.5 dB and a fractional bandwidth (FBW) of 60.8%.

Miniaturized IPD-based bandpass filter chip with edge self-coupled SRR and mixed coupling structure for 5G new radio

ABSTRACT A miniaturised millimetre-wave bandpass filter chip based on the integrated passive device (IPD) process for 5 G new radio is proposed in this paper. Two techniques are utilised to minimise the circuit footprint. Firstly, the innovative edge self-coupled split ring resonator (ES-SRR) is proposed, which incorporates a self-coupled effect by narrowing the gap between the vertical microstrip line and the two split stubs. The theoretical model of the ES-SRR is examined to identify its resonating characteristics. Secondly, the magnetic dominant mixed-coupling structure is implemented in the planar filter by meticulously adjusting the resonator line widths. This configuration generates two transmission zeros at each side of the passband. To demonstrate their effectiveness, a sixth-order bandpass filter, operating within the frequency range of 24.25–29.5 GHz, is simulated and fabricated using 100-µm-thick GaAs IPD technology. Experimental results reveal an insertion loss of 2.95 dB and a minimum return loss of 17 dB, achieving a fractional bandwidth of 21%. Notably, the filter exhibits two transmission zeros at 21 GHz and 33 GHz with rejection levels of 55 dB and 60 dB, respectively.

Reflectionless filtering power divider with wide passband using LTCC technology

Abstract This paper presents a reflectionless filtering power divider (FPD) in low-temperature co-fired ceramic (LTCC) technology. The proposed FPD consists of a pair of parallel-coupled lines (PCLs), an absorptive bandstop filtering (ABSF) section and a Wilkinson power divider section, which are distributed in different LTCC layers. A controllable wide passband is realized by quarter-wavelength PCLs and reflectionless performance at the out-of-band is achieved by employing a lossy resistor loaded in the ABSF section. For demonstration, a prototype of the proposed FPD operating at 6.5 GHz with a 3 dB fractional bandwidth of 60% is designed and fabricated using LTCC. The measured results are in good agreement with the simulated ones, which validates the theoretical prediction and design idea.

A compact wideband coupler design for 5G applications

Abstract This paper presents the design of a compact broadband coupler specifically dedicated to 5G applications. The innovative approach proposed skillfully merges two distinct methods: the use of stepped impedance structures and meanders. The aim is not only to miniaturize the structure and extend the bandwidth, but also to maintain high performance, particularly within the 3.5 GHz core frequency band. The effectiveness of this approach is reflected in a remarkable reduction in size, down by 59% compared with conventional designs. In addition, the achievement of a large fractional bandwidth 40% is a significant result of this study. Equally important, this coupler offers a precise quadrature phase difference between its two output ports. The extensive experimental results confirm the relevance of this innovative approach, making it a promising choice for the design of compact, high-performance couplers for state-of-the-art 5G applications.