Reconfigurable Frequency Research Articles

Ionic Liquids‐Based Reconfigurable Frequency Selective Rasorber with Thermally Tunable Absorption Band

This article proposes a novel ionic liquids‐based reconfigurable frequency selective rasorber (FSR) at microwave bands. The ionic liquids‐based FSR consists of a bandpass‐type frequency‐selective surface, a 3D resin container, and an ionic liquid layer. Numerical simulation analysis demonstrates that the transmission loss of the FSR is less than 3 dB within the range of 4.3–5.3 GHz, and the absorption rate exceeds 90% within the range of 8–27.5 GHz. The FSR exhibits reconfigurable characteristics: when the cavity is filled with the ionic liquid [EMIm][N(CN)2], it demonstrates low‐frequency transmission and high‐frequency absorption. In contrast, when no ionic liquid [EMIm][N(CN)2] is in the cavity, it exhibits low‐frequency transmission. The proposed ionic liquids‐based FSR also has a wide incidence angle with polarization‐insensitive characteristics. By studying the electromagnetic characteristics of frequency‐selective rasorbers at different temperatures, it is found that the frequency‐selective rasorber has a stable passband at low frequencies and the absorption bandwidth decreases with increasing temperature at high frequencies. Finally, a prototype of the FSR based on ionic liquid has been fabricated, and the experimental results are presented to demonstrate the validity of the proposed structure, indicating potential applications in antenna stealth technology.

Design of a metasurface loaded with RF varactor and PIN diode integration dual-band reconfigurable antenna for bluetooth, Wi-Fi, WLAN and wireless 5G applications

Abstract This article presents a compact dual-band reconfigurable antenna design utilizing a metasurface integrated with an RF varactor and PIN diode for Bluetooth, Wi-Fi, WLAN, and 5G wireless applications. The results of the study show that using the metasurface reflector (MSR) structure gives a much higher gain than using a decagon antenna without a metasurface reflector. This antenna is designed and fabricated on FR4 epoxy substrate materials with a dielectric constant of 4.4 and the thickness of the substrate is 1.6 mm. The metasurface reflector (MSR) loaded antenna has a total electrical dimension of 0.51λ0 × 0.49λ0 × 0.013λ0, where λ0 represents the resonating wavelength at a 2.6 GHz center frequency. In the proposed work, the slotted decagon patch antenna consists of a complementary split-ring resonator constructed on its ground plane. Moreover, for the frequency reconfiguration, a PIN diode switch and an additional varactor diode switch are used for tuning the frequency band. Furthermore, without affecting the radiator structure, the varactor diode is placed on the upper side of the patch and the PIN diode switch is integrated into the ground plane. The proposed antenna has reconfigurable and tunable operating frequencies of 2.6 GHz and 3.4 GHz. The operational frequency of the band is switched between 2.6 GHz to 3.4 GHz. The switching operation of the dual configuration of 2.6 GHz with the PIN diode ON and 3.4 GHz with the PIN diode OFF. However, simultaneously applying a reverse bias voltage to the varactor diode from 0-10 V shifts its resonance frequency from 2640-2510 MHz and frequency tuning is done in respective bands. The proposed antenna achieved a peak gain of 7.5 dBi, and a radiation efficiency range of 72– 82% in the overall operating bands of interest. The proposed work is used for Bluetooth, Wi-Fi, WLAN, and wireless 5G applications. Performance verification is done by fabricating prototypes and verifying their performance using simulation and testing results.

Ultra-flat electro-optic frequency comb based on a chirp-modulated lithium niobate resonator.

Chirp modulation can generate a relatively flat electro-optic frequency comb (EO comb) and offers the advantage of frequency reconfigurability, demonstrating significant potential in high-precision sensing and absorption spectroscopy measurements. However, nonresonant devices such as waveguides are susceptible to limitations in modulation efficiency and bandwidth during electro-optic modulation. In this paper, by utilizing chirp modulation resonance mode, we have realized an EO comb based on a lithium niobate resonator with small tooth spacing and high flatness. Theoretically, the chirp modulation of phase is achieved by modulating the dispersion coupling term in the resonant mode transmission equation. Compared with conventional waveguide-based EO combs, the resonant mode chirp modulation is capable of generating a multistage flat comb, and thus the bandwidth of the comb is significantly expanded. In the experiment, with a repetition rate as low as 20 kHz and a bias voltage of 1 V, the comb bandwidth extended to over 150 MHz, where the number of 3 dB flat comb teeth for a single stage exceeds 2,000. Finally, we evaluated the measurement capability of the frequency comb at different temperatures by utilizing the transmission spectrum of the germanium-doped silica waveguide cavity as the absorption spectrum, measuring a temperature sensitivity of 1505.00 MHz/K and a temperature instability of 1.13 mK/Hz1/2.

Millimeter-wave frequency-reconfigurable filtering antenna with high frequency turning ratio

To solve the problem of small frequency turning ratio of the frequency-reconfigurable antenna operating in the millimeter-wave band, a millimeter-wave dual-band frequency-reconfigurable filtering antenna is proposed in this work. The proposed filtering antenna consists of a reconfigurable bandpass filter and an ultra-wideband double layer Vivaldi antenna. The reconfigurable bandpass filter is comprised of several components, including parallel coupled lines, stepped impedance resonator (SIR), PIN diodes, U-shaped branches, and bias network. The reconfigurable filter is integrated in the feedline of the Vivaldi antenna, which provides a simple structure and possesses flexibility for further expansion. The reconfigurable characteristic is realized by controlling the electrical length of the open circuit stepped impedance resonator through two PIN diodes, which not only acts as a switch but also affects the impedance matching within the millimeter wave band. Firstly, the equivalent circuit model of the SIR loaded with PIN diode and bias network is analyzed and simulated to achieve dual-band reconfigurability in the Ka-band. The bias network consists of fan-shaped branches and high-impedance microstrip lines, which suppresses the flow of RF signals. Two notches are introduced by the two U-shaped branches, which are arranged beside the parallel coupling line without affecting the performance of the reconfigurable filter. The realized two notches are located in the non-operating frequency band between the two reconfigurable bands, which enhances the out-of band performances of the reconfigurable filter. Then, to suppress the unnecessary coupling effect and concentrate the energy on the feedline of the Vivaldi antenna, some metallized vias are loaded on the two sides of the feedline. Finally, a metal cavity is introduced to isolate the radiation from filtering components, and some metal columns are loaded inside the cavity for improving the self-resonance of the metal cavity, which effectively improves the cross-polarization level of the filtering antenna. The measured results show that the proposed antenna operates in a range from 25.9 to 28.6 GHz with a maximum gain of 8.83 dBi when the PIN diodes are in the on state, and in a range from 32.6 to 35.9 GHz with a maximum gain of 9.97 dBi when the PIN diodes are in the off state. The center frequency ratio between two reconfigurable frequency bands reaches 1∶1.26, and the cross-polarization levels are all less than –20 dB in both operating bands.

Reconfigurable 28/38 GHz wideband and high isolation MIMO antenna for advanced mmWave applications

Abstract This research presents a high-performance MIMO antenna for 5G and next-generation wireless communication. Operating in the millimeter wave (mmWave) band, the antenna offers frequency and radiation pattern reconfigurability. A compact-size antenna, with dimensions of 22.5×30×0.787 mm3, exhibited peak gains of 7.5 and 6.5 dBi at 28 and 38 GHz, respectively. The envelope correlation coefficient (ECC) was improved through proper spacing and adopting a simple decoupling technique, ensuring efficient MIMO operation. Based on the evaluated reflection coefficients, bandwidths of 2.3 and 12.9 GHz at 28 and 38 GHz, respectively have been accomplished. The mutual coupling between antenna elements was minimized achieving improved isolation of −37 and −40 dB at the desired frequency bands. This corresponds to an envelope correlation coefficient and diversity gain of 1.6×10−4 and 9.99, respectively. The antenna gain was enhanced by incorporating a metasurface designed to optimize gain and improve isolation. For a single-element antenna, the gain was enhanced to 7.9 and 7.3 dBi at frequencies of 28 GHz, and 38 GHz, respectively. The antenna design incorporates frequency and pattern reconfigurability through switching selected antenna ports and patches. The proposed design’s simplicity and antenna compactness make it practical for various mmWave communication systems.

A High-Performance Antenna With Simultaneous Frequency and Polarization Reconfigurability

A High-Performance Antenna With Simultaneous Frequency and Polarization Reconfigurability

Reconfigurable frequency selective surface based absorber realized using interlocking blocks

Abstract A reconfigurable frequency selective surface (FSS) based absorber structure has been designed using a novel, cost-effective, simple to operate and easy to fabricate 3D printed interlocking blocks. Four different topologies have been investigated and validated through simulation and experimental studies. The basic geometry comprises a 3D printed mounting board, on which different blocks can be attached using interlocking studs. The frequency reconfigurability has been obtained by mechanically changing various resonating blocks on the board, which results in four distinct absorption frequencies at 4.89 GHz, 4.02 GHz, 2.92 GHz and 2.25 GHz achieving the absorptivities of 98.92 %, 96.52 %, 99.3 % and 99.5 % respectively in S and C bands. The absorption characteristics are further justified by evaluating the surface current distribution and impedance responses. The prototypes have been fabricated and tested, and they have attained a good agreement with the simulated responses. The absorption characteristics and operational frequencies remain the same, for all four cases during variations in the polarization angle for oblique incidence for both TE and TM polarizations up to 45°, as studied in the simulation. These have been experimentally verified up to 30° for TE polarization, thereby demonstrating the polarization-independent and angularly stable responses.

Design of band reconfigurable Koch fractal antenna for wideband applications

In this communication, a band reconfigurable fractal antenna with modified partial ground is proposed for wireless applications. Four switches using PIN diodes supported by the antenna biasing circuit provide frequency reconfigurability, while star-shaped fractal geometry is used to achieve both miniaturisation and wideband functioning in the proposed antenna. The surface current distribution of the radiating patch is altered by the ON and OFF states of the PIN diode, which leads to the multiband resonance and reconfiguration features of the designed structure. The designhas an overall electrical size of 70 × 45 × 1.6 mm3 and is made on a commonly available FR4 substrate with a thickness of 1.6 mm and a dielectric constant of 4.4. The three operational bands are as follows: case I, which covers 3.7–5 GHz (30 %); case II, which covers 1.7–3.5 GHz (71 %); and case III, which covers 1.4–4 GHz (96 %). Two distinct bands are obtained in cases I and II; and case III nearly covers the frequency band of cases I and II. Therefore, the impedance bandwidth (IBW)offers continuous wideband frequency coverage from 1.4 to 5 GHz (110 %). To sense the full band and then modify its bandwidth to choose the appropriate sub-band and prefilter out the others, the proposed antenna may switch between a wide operational band of 1.4–5 GHz with three distinct subbands. The antenna could potentially be useful for wireless communication systemsin the future due to its frequency-selective feature and stable radiation patterns.

Ultra-miniaturized HMSIW cavity-backed reconfigurable antenna diplexer employing dielectric fluids with wide frequency tuning range

This communication presents an ultra-miniaturized two-way frequency tunable antenna diplexer based on cavity-backed slots and dielectric fluids. The proposed antenna utilizes two half-mode substrate-integrated rectangular cavities loaded with slots and fluidic pockets. The conventional size reduction is achieved by employing half-mode cavities, whereas ultra-miniaturization is obtained by applying the slots, which provides additional capacitive loading. As the cavities are of unequal sizes, a weak cross-coupling path is created between the ports to obtain high isolation (> 30 dB). The isolation is further enhanced by loading the slots. Two mechanisms are analyzed to tune the frequency bands individually or simultaneously. Firstly, the width of the slots can be altered to tune the frequency bands. However, this method involves modification of the physical dimensions of the antenna. Secondly, fluidic vias are created on the bottom plane of the cavities. These can be filled with various dielectric liquids to achieve frequency reconfigurability without altering the physical dimensions of the antenna. To demonstrate the concepts considered, the prototype of the proposed antenna was fabricated and experimentally validated. The structure has a footprint of 0.045λg2 and an isolation exceeding 33.4 dB. The operating frequencies are tunable in the range from 3.08 to 3.84 GHz (lower band) and from 4.97 to 6.33 GHz (upper band) by varying the dimensions of the slots whereas the operating frequencies are reconfigurable in the range from 2.74 to 3.38 GHz (lower band) and from 4.54 to 5.58 GHz (upper band), by employing microfluidic approach. As a result, the working frequencies may be varied in the range from 2.74 to 3.84 GHz (lower band) and from 4.54 to 6.33 GHz (upper band), making this antenna diplexer a competitive candidate for several communication systems. The cross-polarization levels, front-to-back ratio, and realized gain are greater than 19 dB, 18 dB, and 2. dBi, respectively. Excellent consistency is observed between full-wave simulation results and the measurement data.

A Dual-Band Reconfigurable Frequency Selective Surface With Independent Tuning Capability

A Dual-Band Reconfigurable Frequency Selective Surface With Independent Tuning Capability

A novel miniaturized metamaterial inspired frequency reconfigurable antenna with switchable polarization for sub 6 GHz band

Abstract A metamaterial-inspired frequency reconfigurable antenna with switchable polarization realized for 2.4 GHz, 3.5 GHz, and 5.8 GHz frequencies, is reported in this work. Initially, a conventional rectangular patch is designed to resonate at 3.5 GHz. A regular square-shaped SRR (Split Ring Resonator) is a metamaterial-inspired structure that excites additional resonance at 5.8 GHz, without increasing the antenna form factor. Further, a parasitic patch is introduced to create one resonance at 2.4 GHz. Reconfigurability of frequency and polarization is achieved using MPP4203 series PIN diodes. The antenna is simulated using CST Microwave Studio Suite 2019. The designed antenna, characterized by reflection coefficient and bandwidth is analysed for three diode states. The devised antenna operates at 2.4 GHz, 3.5 GHz, and 5.8 GHz, with a maximum bandwidth of 346.2 MHz at the 5.8 GHz frequency band. The radiator outperformed other similar antennas reported in the literature in terms of antenna size, bandwidth, and frequency cum polarization reconfigurability.

Reconfigurable dielectric resonator antenna and array with frequency and polarization flexibility

To implement frequency and polarization hybrid reconfiguration, a 4 × 4 array has been investigated. The radiation elements of the antenna array consist of cylindrical dielectric resonators, Wilkinson power divider, PIN diode, and dielectric substrate. The PIN diode controls the states of each branch in the Wilkinson power divider to achieve frequency and polarization reconfigurability. To verify the feasibility of the design, a fabricated sample of the proposed antenna array has been measured. The results demonstrate that the antenna array can be switched freely between its operating frequencies and polarizations. It operates within a bandwidth of 1.93 to 4.6 GHz for frequency reconfiguration, and three common polarization states—linear polarization, left-handed circular polarization, and right-handed circular polarization—can be continuously tuned from 2.96 to 3.39 GHz.

A Gain‐Enhanced Multiband Frequency and Pattern Reconfigurable Antenna for Wi‐Fi 6E and 5G New Radio Wireless Standards

ABSTRACTIn this paper, a multiband hybrid reconfigurable antenna with enhanced gain is reported to support Wi‐Fi 6E, indoor WLAN, and 5G new radio (NR) wireless standards. The reported structure consists of a half‐hexagonal‐shaped radiating element along with two symmetrical rectangular single‐split resonators interconnected via two PIN diodes to achieve multiband frequency and pattern reconfigurability of the proposed antenna and a single‐layer frequency selective surface (FSS) to enhance the gain. By configuring these PIN diodes in three distinct modes, the reported antenna allows for independent reconfigurability to support multipurpose sub‐6GHz and Wi‐Fi 6E (3.3, 3.5, 5.1, 5.3, and 6.5 GHz) wireless standards, respectively. The results also showed that the antenna is capable of maintaining a frequency of 6.5 GHz in all modes while reconfiguring its radiation pattern in three different directions, namely, 265°, 13°, and 337° on the xz plane. The gain of the proposed hybrid reconfigurable antenna is enhanced by an FSS‐based reflector placed below the radiating structure at a distance of to the lowest operating frequency (3.3 GHz), and the gain is enhanced by 2–4 dBi as compared without FSS. The reported hybrid reconfigurable antenna is implemented on an FR‐4 substrate with a depth of 1.6 mm and a relative permittivity of 4.4. For validation of the proposed structure, the experimental results are compared with the simulated results.

Dual-comb source with a reconfigurable repetition frequency difference using intracavity Brillouin lasers

A Brillouin-assisted 80-GHz-spaced dual-comb source with a reconfigurable repetition frequency difference ranging from 48 MHz to 1.486 GHz is demonstrated. Two pairs of dual-pump seeds with an interval offset produce the corresponding dual Brillouin lasers in two fiber loops, and then the Brillouin lasers give rise to dual combs via the cavity-enhanced cascaded four-wave mixing effect. The repetition frequency difference is determined by the interval offset of the dual-pump seeds, which is induced by the Brillouin frequency shift difference between different fibers in a frequency shifter. Each comb provides 22 lasing lines, and the central 10 lines in a 20-dB power deviation feature high optical signal-to-noise ratios exceeding 50 dB. The linewidths of the dual-comb beating signals are less than 300 Hz, and the absolute linewidths of the comb lines are around 1.5 kHz. The dual-comb source enables substantial repetition frequency differences from 48 MHz to 1.486 GHz by changing the pluggable fibers in the frequency shifter.

Frequency-reconfigurable liquid crystal metasurface array

In this paper, a frequency-reconfigurable metasurface (MS) circularly polarized antenna array (CPAA) based on liquid crystal (LC) is presented. The antenna features a multilayer structure. Design of the MS circularly polarized antenna unit using the characteristic mode analysis method, the combination of MS structure, temperature-controlled LC, and sequential feed network not only enhances the impedance bandwidth (IBW), axial ratio bandwidth (ARBW), and gain. By adjusting the temperature to change the relative dielectric constant of the LC, further frequency reconfigurability of the CPAA is achieved. Under different temperature control settings, the effective IBW and ARBW of the antenna can be shifted from 39.0% (4.51–6.70 GHz) to 40.3% (4.61–6.94 GHz), while the peak gain moves from 11.59 dBi at 5.31 GHz to 11.71 dBi at 5.41 GHz. The results demonstrate that the proposed MS CPAA offers advantages of wide bandwidth, high gain, low profile, and frequency reconfigurability.

A Reconfigurable Frequency Selective Rasorber With Switchable Transmission/Reflection/Absorption Band

A Reconfigurable Frequency Selective Rasorber With Switchable Transmission/Reflection/Absorption Band

Highly-miniaturized microfluidically-based frequency reconfigurable antenna diplexer employing half-mode SIRW

This article introduces a super-miniaturized frequency reconfigurable antenna diplexer based on microfluidic techniques. The proposed structure is developed using a half-mode substrate-integrated rectangular waveguide (HMSIRW). The antenna architecture consists of two HMSIRW cavities loaded with L-shaped slots, which are excited by two microstrip feedlines to realize two distinct radiating frequency bands. The footprint of the antenna diplexer is miniaturized by using the half-mode cavities. Further size reduction is achieved by the capacitive loading of the slots. The design evaluation, radiation mechanism, parametric analysis, and equivalent circuit model are discussed in detail. The empty fluidic vias are drilled on the bottom plane of the cavities and poured with various dielectric liquids to obtain independent frequency reconfigurability at two operating bands. For validation, a frequency reconfigurable antenna diplexer is designed, manufactured, and demonstrated experimentally. The measured results show that the return loss, isolation, and realized gains are greater than −20 dB, 28 dB, and 3.3 dBi, respectively, while ensuring small footprint of only 0.071λg2. The fabricated diplexer exhibits a frequency reconfiguration range greater than 17 % at both frequency bands.

A compound reconfigurable series-fed microstrip antenna for satellite communication applications

PurposeThis paper aims to present an innovative reconfigurable series-fed microstrip antenna using radiofrequency positive intrinsic negative (RF PIN) diodes for cognitive S-band and C-band satellite communications. The antenna can dynamically reconfigure its frequency, polarization and radiation pattern to meet diverse application needs.Design/methodology/approachThe design involves a reconfigurable four-element microstrip antenna using FR4 substrate and copper patches. RF PIN diodes enable dynamic frequency, polarization and radiation pattern reconfiguration. Simulations and optimizations are performed using CST and HFSS, using techniques like the Nelder-Mead algorithm, particle swarm optimization, covariance matrix adaptation and trust region framework. An antenna prototype is also fabricated to validate the simulations.FindingsThe proposed antenna demonstrates significant reconfigurability: it switches between S-band (2.45 GHz, 2.52 GHz) and C-band (5.55 GHz, 5.59 GHz) with bandwidths of 120 MHz and 550 MHz, respectively. It transitions between circular and linear polarization in the S-band and modifies the radiation pattern by 45 degrees, providing an alternative radiation direction in the C-band. The antenna achieves a maximum gain of 5.95 dBi at 2.52 GHz and 93% efficiency at 5.55 GHz. Simulated results closely match those from the fabricated prototype, confirming the design’s validity.Originality/valueThe innovative use of RF PIN diodes enables comprehensive reconfigurability in frequency, polarization and radiation patterns within a single microstrip antenna, meeting the demands of S-band and C-band satellite communications. This study demonstrates superior performance, significant gains and efficiencies across various reconfiguration modes, validated by rigorous simulation and practical fabrication. The simple structural design further distinguishes this study from others in the field.

MXene-based kirigami designs: showcasing reconfigurable frequency selectivity in microwave regime

Today’s wireless environments, soft robotics, and space applications demand delicate design of devices with tunable performances and simple fabrication processes. Here we show strain-based adjustability of RF/microwave performance by applying frequency-selective patterns of conductive Ti3C2Tx MXene coatings on low-cost acetate substrates under ambient conditions. The tailored performances were achieved by applying frequency-selective patterns of thin Ti3C2Tx MXene coatings with high electrical conductivity as a replacement to metal on low-cost flexible acetate substrates under ambient conditions. Under quasi-axial stress, the Kirigami design enables displacements of individual resonant cells, changing the overall electromagnetic performance of a surface (i.e., array) within a simulated wireless channel. Two flexible Kirigami-inspired prototypes were implemented and tested within the S, C, and X (2-4 GHz, 4-8 GHz, and 8-12 GHz) microwave frequency bands. The resonant surface, having ~1/4 of the size of a standard A4 paper, was able to steer a beam of scattered waves from each resonator by ~25°. Under a strain of 22%, the resonant frequency of the wired co-planar resonator was shifted by 400 MHz, while the reflection coefficient changed by 158%. Deforming the geometry impacted the spectral response of the components across three arbitrary frequencies in the 4-10 GHz frequency range. With this proof of concept, we anticipate implementing thin films of MXenes on technologically relevant substrates, achieving multi-functionality through cost-effective and straightforward manufacturing.

Multi-functional active frequency reconfigurable polarization converter using a simple DC bias circuit.

A multi-functional active converter with frequency reconfiguration is proposed and experimentally verified. The unit cell is composed of two T-shaped metal patches connected with a PIN diode. Two metal vias are designed to connect the T-shaped metal to the ground. The T-shaped metal patches are slantly arranged to provide circular polarization conversion. By switching on and off the PIN diode, frequency reconfiguration can be realized. The DC bias is exerted to the PIN diode through two metal vias connecting to the ground. The ground is gracefully designed so that a very simple bias circuit is developed. It is demonstrated that three frequency bands are generated for both off and on states. An incident linear polarization can be converted to right-hand circular polarization, linear polarization, and left-hand circular polarization in these frequency bands, respectively. A circuit model is established to understand the principle of this design. It is found that circuit simulation is consistent with full wave simulation. Measurements conducted during the frequency range of 20-40 GHz shows that good agreement with simulation has been reached.