arXiv subjects

Fan Qin

Publications and source records attributed to Fan Qin.

At least 19 recordsLinked to original sources

arXiv2026

An Ultra-Low Profile Metasurface for Enhanced Non-Diffractive OAM Beam Generation Based on Sparse Feed Array

This paper proposes a novel ultra-low profile transmitted metasurface to generate enhanced non-diffractive orbital angular momentum (OAM) beams, employing a sparse feed array (SFA) to create a quasi-plane wave excitation for the first time. Our simulation indicates that with uniform amplitude excitation, the non-diffraction performance of Bessel beam produced by metasurface, surpasses that of conventional single-feed excitation. Based on this principle, a 5 * 5 sparse feed array is introduced and positioned less than one wavelength from the metasurface, ensuring a quasi-uniform amplitude excitation across all units. Further, this metasurface leverages its flexible phase control capability and integrates the spatial phase, OAM phase, and axicon phase to generate an enhanced high-order Bessel beam. The simulated results confirm a successful non-diffractive Bessel beam generation carrying OAM with mode l = +2, exhibiting reduced beam divergence and higher gain. This design also offers benefits of ultra-low profile, high aperture efficiency, low structural complexity.

eess.SP↗

arXiv2026

Flexible Wideband Filtering Monopole Antenna With Stable High Omnidirectionality

This article presents a wideband flexible filtering monopole antenna with symmetric structure for stable high omnidirectionality. It is based on a monopole antenna, which is printed on a single-layer flexible substrate. Two folded parasitic strips with different length are devised on both sides of the driven monopole, giving filtering responses in the higher and lower band without filtering circuits. Since the asymmetric filtering structure adversely affects in-band omnidirectionality, this baseline design is extended with symmetric filtering structure to improve omnidirectionality and bandwidth. In the proposed design, a pair of parasitic strips are devised on the both sides of monopole antenna symmetrically, achieving a radiation null in the higher band. Then, by loading a pair of folded parasitic strips on the both sides of feed line with slotted metal ground, a radiation null is realized in the lower band. Besides, the driven monopole is slotted symmetrically for wideband operation. By adopting a fully symmetric filtering structure, the proposed design effectively suppresses the impact of the parasitic elements on the in-band omnidirectional radiation pattern, thereby achieving high omnidirectionality. Furthermore, the proposed antenna exhibits stable performance under different bending radii. To verify our design concept, an antenna prototype is fabricated. Both the flat and bent antennas are measured. The results show that the proposed antenna has a -10 dB impedance bandwidth of 45.6%, an in-band gain about 2 dBi, and an out-of-band radiation suppression more than 11 dB. The measured omnidirectionality has variations less than 0.8 dB without bending and 1 dB with a bending radius of 30 mm. This design offers several advantages including stable high omnidirectionality across a wide bandwidth, flexible conformal capability, and filtering property.

eess.SP↗

arXiv2026

A Wideband Multibeam Planar Quasi-Yagi Array Antenna Based on Parasitic Pixel Strips

This letter presents a low-complexity parasitic pixel strip (PPS) structure for array antenna to generate six radiations with flexible beam control. To realize multibeam operation, three groups of symmetrical strip-shaped pixels are integrated with the feed antenna, the connection state of which can be controlled by PIN diode. Leveraging the reconfigurable parasitic configuration, the coupling path of the antenna can be strategically manipulated, achieving the desired multibeam property. Thus, by utilizing the PPS structure in conjunction with a planar quasi-Yagi antenna, this single antenna can operate at four states with beam direction towards 40{\deg}, -40{\deg}, 0{\deg}, along with a dual-beam at +/-45{\deg}, within the frequency range from 5.0 to 5.6 GHz. Moreover, a prototype of a 1 * 2 array with the PPS structure is also fabricated to achieve six beams with a scan range of 40{\deg}, 20{\deg}, 0{\deg}, -20{\deg}, -40{\deg} and a dual-beam at +/-30{\deg}. Notably, only four PIN diodes are utilized to implement six radiations, verifying that this approach effectively minimizes the excessive use of switches and extends the variety of beams, which provides a low complexity method for multibeam array antenna without complicated beamforming network. These antennas satisfy the benefits of wideband, planner structure, low structural complexity, low cost, and flexible beam control.

eess.SP↗

arXiv2026

Flexible Wearable Filtering Antenna With Stable Performance for IoT Devices

In this article, a flexible and lightweight filtering wearable antenna without extra circuits is presented. The proposed antenna starts from a flexible directional antenna with lightweight structure, which includes a layer of ultra-thin flexible substrate, a metal ground layer, and a flexible foam layer sandwiched between them. Then, by introducing two pairs of vertical slots to the radiation patch printed on the flexible substrate, two radiation nulls are realized at both band edges without extra circuits. Moreover, to mitigate the deterioration of in-band radiation under different curvature, a pair of inverted Fshaped slots are loaded on the radiation patch. The coupling of Fshaped slots suppresses non-radiated lateral current components along the curvature direction, maintaining stable performance after bending. In addition, deformation analysis of the proposed antenna with a three-layer human tissue model under different bending radii is carefully carried out, showing stable bandwidth, effective out-of-band radiation suppression, and low specific absorption rate (SAR) value. To verify this method, a prototype is fabricated. Measurements are conducted both in free space and conformal on the curved body tissue. The results show that the proposed antenna achieves a bandwidth from 2.7 GHz to 3 GHz, an out-of-band radiation suppression more than 11 dB with maxmium suppression of 23 dB, and an average gain of 8.5 dBi. As a flexible wearable antenna with stable performance and integrated reliable filtering features, it has several advantages including flexible wearable structure, stable filtering properties, lightweight characteristic, and low SAR. This makes it an excellent candidate for wearable IoT applications.

eess.SP↗

arXiv2026

Band bases as common triangular bases in cluster algebras from surfaces

We consider the skein algebra of an unpunctured marked surface. Thurston previously constructed its band basis topologically. We show that this band basis coincides with the common triangular basis, which is a Kazhdan-Lusztig type basis for quantum cluster algebras analogous to the dual canonical basis of quantum groups. Our result confirms a conjecture of Thurston. It also provides new cases for the existence of the common triangular basis. In addition, we discover a phenomenon where certain unknots are arranged in configurations resembling beads on a necklace.

math.QA↗

arXiv2026

Freezing operators in representation theory of quantum loop algebras

We prove the Hernandez conjecture on the simple $(q,t)$-characters (an analog of the Kazhdan--Lusztig conjecture) for untwisted quantum loop algebras of classical type. This result is new in type $\mathrm{C}$. We also prove that the folding homomorphism, introduced by Hernandez, gives a dimension-preserving bijective correspondence between the finite-dimensional simple representations (in a skeletal subcategory) of untwisted quantum loop algebras of classical simply-laced type and those of the corresponding doubly-twisted quantum loop algebras. This result is new in type $\mathrm{D}$. In our approach, we develop a bootstrapping method for $q$ and $(q,t)$-characters, based on the freezing operator previously introduced in the context of cluster algebras by the second named author. This method allows us to reduce statements for general simple representations in all classical types to corresponding results on core subcategories in a uniform manner.

math.RT↗

arXiv2025

Integral cluster structures on quantized coordinate rings

We develop (quantum) cluster algebra structures over arbitrary commutative unital rings $\Bbbk$ and prove that the (quantized) coordinate rings of connected simply-connected complex simple algebraic groups $G$ over $\Bbbk$ admit such structures. We first show that the integral form of the quantized coordinate ring of $G$ admits an upper quantum cluster algebra structure over $\mathbb{A}=\mathbb{Z}[q^{\pm\frac{1}{2}}]$ by using a combination of tools from quantum groups, canonical bases and cluster algebras and a previous result of the second and third authors over $\mathbb{Q}(q^{\frac{1}{2}})$. We then obtain (integral) quantum versions of recent results of the first author: when $G$ is not of type $F_4$, the quantized coordinate ring of $G$ admits a quantum cluster algebra structure over $\mathbb{A}'$, where $\mathbb{A}'=\mathbb{A}$ when $G$ is not of types $G_2$, $E_8$, and $F_4$; $\mathbb{A}'=\mathbb{A}[(q^2+1)^{-1}]$ when $G$ is of type $G_2$, and $\mathbb{A}'=\mathbb{Q}(q^{\frac{1}{2}})$ when $G$ is of type $E_8$. We furthermore prove that the classical versions of these results hold over $\mathbb{A}'$ (where $\mathbb{A}'=\mathbb{Z}$ if $G$ is not of type $F_4$ or $G_2$ and $\mathbb{A}'=\mathbb{Z}[\frac{1}{2}]$ if $G$ is of type $G_2$) and that the integral form of the coordinate ring of $G$ of type $F_4$ is an upper cluster algebra. Finally, by using common triangular bases of (quantum) cluster algebras, we prove that the above results also hold under specializations of $\mathbb{A}$ and $\mathbb{A}'$ to commutative unital rings $\Bbbk$.

math.QA↗

arXiv2025

Dual-Band Flexible Endfire Filtering Antenna With Conformal Capability for Emergency Communication Applications

In this letter, a single-layer dual-band flexible conformal filtering endfire antenna is presented. The proposed antenna is based on two co-designed folded dipoles (FDs) working at two frequencies, where the lower-frequency FD acts as a reflector for the higher-frequency one. Then, by devising an additional reflector for lower-frequency FD, dual-band endfire radiation is realized. Parasitic strips are deliberately introduced around the FDs to generate electric coupling and magnetic coupling in the two operating bands, resulting in significant filtering performance with four radiation nulls. With flexible structure and single-layer configuration, the antenna design exhibits flexible conformability with cylindrical surfaces of diverse diameters, thereby enabling seamless integration into scalable emergency communication systems. To verify our design concept, an antenna prototype is fabricated and measured. The measured working frequency ranges from 1.37 to 1.45 GHz and 1.89 to 2.07 GHz. Out-of-band radiation suppression more than 11 dB is achieved under different bending radii. The proposed design offers several advantages including dual-band endfire filtering radiation, flexible conformability and low-profile.

eess.SY↗

arXiv2025

An introduction to representation-theoretic canonical bases of cluster algebras

This is an introduction to cluster algebras and their common triangular bases. These bases are Kazhdan-Lusztig-type and serve as the canonical bases of cluster algebras from the representation-theoretic point of view. We review seeds associated with signed words, cluster operations (freezing and base change), the extension technique from finite to infinite rank, which are convenient tools to study these algebras and their bases. We present recent results on the topic and provide examples. An appendix collects detailed examples of some cluster algebras from Lie theory, including those from Lie groups and representations of quantum affine algebras.

math.RT↗

arXiv2025

From i-boxes to signed words

The combinatorics of i-boxes has recently been introduced by Kashiwara--Kim--Oh--Park in the study of cluster algebras arising from the representation theory of quantum affine algebras. In this article, we associate to each chain of i-boxes a signed word, which canonically determines a cluster seed following Berenstein--Fomin--Zelevinsky. By bridging these two different languages, we are able to provide a quick solution to the problem of explicit determining the exchange matrices associated with chains of i-boxes.

math.RT↗

arXiv2025

A High-Efficiency Reconfigurable Bidirectional Array Antenna Based on Transmit-Reflect Switchable Metasurface

This paper proposes a reconfigurable bidirectional array antenna with high-efficiency radiations and flexible beam-switching capability by employing a novel transmit-reflect switchable metasurface (TRSM). To realize the electromagnetic (EM) wave transmitted or reflected manipulation, a dedicated transmit-reflect switch layer (TRSL) with periodically soldered PIN diodes is introduced between two transmitted metasurfaces. By switching ON/OFF the embedded diodes, the TRSL performs as a mesh-type ground layer or polarization-grid layer, exhibiting a reflect or transmit property to the incident wave respectively. Further, utilizing the above TRSM configuration in conjunction with a microstrip feed antenna, bidirectional radiations are obtained at the same frequency and polarization. To further reduce the number of PIN diodes and control complexity, an enhanced TRSM using a single diode to control two unit cells is also investigated, resulting in half PIN diodes reduction. Since the bidirectional beam-switching is achieved by only controlling PIN diodes integrated in the ground plane instead of directly acting on the radiation element, which reduces insertion loss and avoids phase quantization errors, the proposed antenna can maintain a high aperture efficiency. To verify this concept, a prototype was designed, fabricated, and measured, demonstrating a successful realization of backward and forward patterns with peak gains of 22.3 and 22.1 dBi, and aperture efficiencies of 47.2% and 43.8%. The 3-dB gain bandwidths of reflected and transmitted modes are 13.7% and 12.3%. This antenna has the advantages of high gain, high aperture efficiency, simple configuration, cost-effectiveness, and flexible and digital beam control.

eess.SY↗

arXiv2025

Partially compactified quantum cluster structures on simple algebraic groups and the full Berenstein--Zelevinsky conjecture

The construction of partially compactified cluster algebras on coordinate rings is handled by using codimension 2 arguments on cluster covers. An analog of this in the quantum situation is highly desirable but has not been found yet. In this paper, we present a general method for the construction of partially compactified quantum cluster algebra structures on quantized coordinate rings from that of quantum cluster algebra structures on localizations. As an application, we construct a partially compactified quantum cluster algebra structure on the quantized coordinate ring of every connected, simply connected complex simple algebraic group. Along the way, we settle in full the Berenstein--Zelevinsky conjecture that all quantum double Bruhat cells have quantum cluster algebra structures associated to seeds indexed by arbitrary signed words, and prove that all such seeds are linked to each by mutations.

math.QA↗

arXiv2024

Fast square-oscillations in semiconductor VCSELs with delayed orthogonal polarization feedback

We present an experimental investigation into the generation of self-sustained and fast square oscillations from the TE mode of semiconductor VCSELs with delayed orthogonal polarization feedback. We find that the low frequency switching originates from the rotation of the TE and TM modes facilitated by a long time delay, but the fast oscillations are anchored to the frequency beating between the TE and TM modes and are modified by a half-wavelength ($\lambda/2$) plate. A comprehensive analysis of the evolution of the nonlinear dynamics is conducted and the related mechanism is discussed. Our study not only deepens our comprehension of laser nonlinear dynamics but also offers an all-optical approach for producing specialized signals, which could be instrumental in applications such as optical communications and photonic computing leveraging the complexity of long-delay systems.

physics.optics↗

arXiv2024

A New Channel Model for OAM Wireless Communication at 5.8 and 28 GHz

Orbital angular momentum (OAM) in electromagnetic (EM) waves can significantly enhance spectrum efficiency in wireless communications without requiring additional power, time, or frequency resources. Different OAM modes in EM waves create orthogonal channels, thereby improving spectrum efficiency. Additionally, OAM waves can more easily maintain orthogonality in line-of-sight (LOS) transmissions, offering an advantage over multiple-input and multiple-output (MIMO) technology in LOS scenarios. However, challenges such as divergence and crosstalk hinder OAM's efficiency. Additionally, channel modeling for OAM transmissions is still limited. A reliable channel model with balanced accuracy and complexity is essential for further system analysis. In this paper, we present a quasi-deterministic channel model for OAM channels in the 5.8 GHz and 28 GHz bands based on measurement data. Accurate measurement, especially at high frequencies like millimeter bands, requires synchronized RF channels to maintain phase coherence and purity, which is a major challenge for OAM channel measurement. To address this, we developed an 8-channel OAM generation device at 28 GHz to ensure beam integrity. By measuring and modeling OAM channels at 5.8 GHz and 28 GHz with a modified 3D geometric-based stochastic model (GBSM), this study provides insights into OAM channel characteristics, aiding simulation-based analysis and system optimization.

eess.SP↗

arXiv2024

Based cluster algebras of infinite rank

We extend based cluster algebras from the finite rank case to the infinite rank case. By extending (quantum) cluster algebras whose initial seeds are associated with signed words (arising from double Bott-Samelson cells), we recover infinite rank cluster algebras arising from representations of (shifted) quantum affine algebras. As a main application, we show that the fundamental variables of the cluster algebras arising from double Bott-Samelson cells can be computed via a braid group action when the Cartan matrix is of finite type. We also obtain the equality A=U for the associated infinite rank (quantum) cluster algebras. Additionally, several conjectures regarding quantum virtual Grothendieck rings due to Jang-Lee-Oh and Oh-Park follow as consequences. Finally, we show that the cluster algebras arising from representations of shifted quantum affine algebras, discovered by Geiss-Hernandez-Leclerc, admit natural quantizations.

math.QA↗

arXiv2024

Multibeam Hybrid Transmitarray Based on Polarization Rotating Metasurface With Reconfigurable Bidirectional Radiation

This paper proposes a bidirectional multibeam hybrid transmitarray (HTA) employing a transmission polarization-rotating metasurface (TPRM). A novel configuration is introduced to facilitate bidirectional beam scanning by combining the transmitarray (TA) and folded-transmitarray (FTA). To accomplish the reconfiguration of both unidirectional and bidirectional radiation states in the +z, -z, and +/-z directions, a polarization switchable multi-feed array (MFA) is placed at the focal plane between the TA and FTA, radiating x-polarization, y-polarization, and 45-degree oblique polarization waves, respectively. Meanwhile, the proposed antenna can achieve multibeam radiation in the three aforementioned states by switching the polarization of the MFA. To demonstrate the operating principle, a prototype has been designed, simulated, and fabricated. The measured results agree well with the simulated results. The simulated and measured results indicate that the proposed design can generate reconfigurable multibeam in both forward and backward directions, either separately or simultaneously. In the unidirectional states, forward and backward beam scanning is achieved within an angular range of +/-30{\deg} and +/-22{\deg}, respectively, with peak gains of 23.6 dBi and 23.1 dBi. A simultaneous forward and backward beam scanning of +/-40{\deg} and +/-22{\deg} is achieved in the hybrid radiation state, with peak gains of 19.4 dBi and 19.3 dBi, respectively. The proposed antenna array design offers several advantages, including bidirectional low-loss beam scanning, a simple structure, low power consumption, and a low profile.

eess.SY↗

arXiv2024

Applications of the freezing operators on cluster algebras

We apply freezing operators to relate different (quantum) upper cluster algebras. We prove that these operators send localized (quantum) cluster monomials to localized (quantum) cluster monomials. They also send bases to bases in many cases. In addition, the bases constructed via freezing coincide with those constructed via localization.

math.QA↗

arXiv2024

Analogs of the dual canonical bases for cluster algebras from Lie theory

We construct common triangular bases for almost all the known (quantum) cluster algebras from Lie theory. These bases provide analogs of the dual canonical bases, long anticipated in cluster theory. In cases where the generalized Cartan matrices are symmetric, we show that these cluster algebras and their bases are quasi-categorified. We base our approach on the combinatorial similarities among cluster algebras from Lie theory. For this purpose, we introduce new cluster operations to propagate structures across different cases, which allow us to extend established results on quantum unipotent subgroups to other such algebras. We also obtain fruitful byproducts. First, we prove A=U for these quantum cluster algebras. Additionally, we discover rich structures of the locally compactified quantum cluster algebras arising from double Bott-Samelson cells, including T-systems, standard bases, and Kazhdan-Lusztig type algorithms. Notably, in type ADE, we obtain their monoidal categorifications via monoidal categories associated with positive braids. As a special case, these categories provide monoidal categorifications of the quantum function algebras in type ADE.

math.RT↗