This paper investigates a multiple array structures-based OAM inverse scattering imaging method. To enable efficient OAM wave generation and inverse scattering imaging, we design an 18-element circular array and a square-shaped array (SQA) to decouple the OAM waves and scattering information. The geometric asymmetry of the squared array allows the beam to focus on specific directions, thereby enhancing the inverse scattering imaging performance. The study shows that square arrays contain imaging results similar to those of larger circular arrays and effectively reduce the formation of side lobes, improving image quality and accuracy. Therefore, the square array provides more precise imaging results. This method effectively addresses the limitations of traditional OAM wave generation techniques and demonstrates strong potential for practical applications.

In this letter, a multifunctional reconfigurable metamaterial (MRMM), featuring three operating states is introduced based on the multi-scale integration of hierarchical microchannel configuration and liquid metal (LM) regulation strategy. The MRMM can flexibly switch among full-band transmission from 8 GHz to 15 GHz with an insertion loss (IL) of 1 dB, second-order bandpass from 11.64 GHz to 13.72 GHz (also featuring an IL of 1 dB), and full-band shielding from 8 GHz to 15 GHz with a reflection loss (RL) of -15 dB, while exhibiting reliable polarization and angular stability. Subsequently, the physical mechanisms of the MRMM at different states are analyzed using the equivalent circuit method (ECM). Finally, a physical sample of the proposed design is manufactured and tested to validate the effectiveness of simulation results. Both numerical simulations and experimental verifications confirm the wide switchable bandwidth and multistate characteristics of the MRMM.

The paper proposes a wideband circular polarized (CP) antenna, its phased array and Van Atta array. Broad impedance bandwidth and axial ratio bandwidth can be realized through the adoption of multilayer structures and slotting techniques in the patch antenna design. The developed circular polarized antenna operates at 5.6GHz achieving 16% impedance matching range and 8.3% AR (axial ratio) bandwidth. The corresponding phased array exhibits a 3dB scanned beamwidth of +/- 51 degrees. The proposed Van Atta retrodirective array exhibits a 5-dB beamwidth of 95 degrees in monostatic radar cross-section (RCS) performance.

A four-stage ultra-wideband 15-50 GHz LNA in 0.15 um GaAs pHEMT process is presented in this paper. A RLC feedback with a virtual ground capacitance (RLC&VGC) topology used in current-reuse structure is proposed, which enables flexible adjustment of both low- and high-frequency gain. Moreover, a RC parallel circuit and LR series circuit are exploited to improve gain flatness. Several bandwidth extension techniques are employed to expand the bandwidth up to 50 GHz. A prototype of a four-stage common-source (CS) LNA with the proposed techniques is designed and fabricated in a 0.15 um GaAs pHEMT process. Measurement results show a noise figure (NF) of 2.4 dB, a gain exceed 24 dB with the gain flatness of +/- 1.4 dB. Due to the utilization of the self-biasing technology, the chip consumes a DC power of 168 mW with a single DC supply of +4V. The amplifier achieves good linearity, with an output 1 dB compression point (OP1dB) of 13.4 dBm and a third-order intercept point (OIP3) of 23 dBm.

This paper presents a multispectral compatible stealth metamaterial (MCSM), which consists of two functional layers including a radar-infrared compatible stealth screen (RICSS) and an adjustable pixelated visible camouflage screen. The proposed MCSM achieves a microwave absorptivity greater than 90% over 8.9-13.75 GHz under normal incidence and an infrared emissivity of 0.35 within 3-14 mu m. To enhance optical compatibility, the upper-layer RICSS incorporates transparent materials and a coplanar design, achieving a high visible light transmittance of 79.32%. Three different pixelated camouflage patterns (i.e. forest, ocean, and desert) can be adjusted due to the thermochromic mechanism. Finally, the multispectral compatible stealth performance of the MCSM is demonstrated by visible light, microwave and infrared experiments separately. The integration of these multifunctional properties in a single structure highlights the potential of the MCSM for applications requiring multispectral stealth and tunable optical properties.

In this paper, a reconfigurable frequency selective surface (FSS) is presented for integrating rapid switching and wideband tuning functions into a single design. The proposed design mainly consists of two layers. Metallic patterns, integrated with two PIN diodes, are embedded on the F4B substrate on the top layer. A microfluidic channel layer, incorporating two coarse-tuning channels and one fine-tuning channel, is set at the bottom. This design facilitates fast switching between reflection and transmission states by actively controlling the PIN diodes. Meanwhile, liquid metals (LMs) are employed in the microfluidic channels for the frequency tuning function. In the transmission state, the design enables wideband and discrete frequency tuning from 7.36 GHz to 8.76 GHz by injecting or discharging LMs in the coarse-tuning channels. In addition, it can realize high-precision and continuous frequency tuning by adjusting the relative position of the LM segments in the fine-tuning channels.

In this work, a novel switchable band-notched absorber is presented, which employs the use of liquid metal. The design is composed of two principal elements: a microfluidic layer and a band-notched absorbing structure, combining the functionalities of electromagnetic (EM) switching and polarization selection through the control of liquid metal within microfluidic channels. Four combined states of wideband reflection and band-notched absorption for different polarizations can be independently attained. The simulation results indicate that the design exhibits the advantages of wideband switching capabilities, polarization insensitivity, and multifunctional features, rendering it a potential candidate for practical scenarios of electromagnetic stealth.

This paper proposes a metasurface design method to achieve bistatic radar cross-section (RCS) pattern synthesis in space, based on a receiver-transmitter metasurface (RTMS) and a genetic algorithm for phase distribution optimization. Due to the slots on the ground between the adjacent metasurface elements, the unwanted interunit coupling effect is significantly reduced. Based on the theoretical analysis model of the phased array, the corresponding phase distribution of the required RCS pattern is optimized by a genetic algorithm. According to the required phase distribution, the corresponding RTMS units are designed, and the overall RTMS structure is finally constructed. The simulated results demonstrate that the electromagnetic (EM) waves scattered by the proposed RTMS are concentrated in the desired directions of 0 degrees and +/- 49 degrees which is consistent with the design intention. Both simulated and measured results verify that the proposed RTMS design methodology can realize the bistatic RCS control in space with a customized shape.

In this paper, an aperture-coupling and cross-coupled mechanism are put forward to exploit two bandpass unit cells for a dual-band bandpass filter (BPF) with a large frequency ratio. It includes a cascaded step-impedance resonator (SIR) BPF and a low-pass filter (LPF) on the top layer and a sixth-order SIW BPF with cross-coupling on the bottom layer. As for the SIW BPF of the bottom layer working at the millimeter-wave (MMW) frequency band, a specific-length microstrip line is utilized as an inverter to connect two non-adjacent resonate cavities, which can introduce the inverse cross-coupling and improve the frequency selectivity of the filter. On the top layer, a BPF operating at the microwave band was designed using a cascaded form of SIR BPF and LPF. Based on the proposed design theory, a dual-band BPF with a large frequency ratio up to 6.83 was carefully designed and simulated. The desired results can be obtained and the concept of the proposed structure can also be verified. Thus, both two frequency bands exhibit the characteristics of flat group delay.

AbstractThis letter presents a Ka‐band low‐cost microstrip line phase shifter based on liquid crystal (LC) technology. Furthermore, a sum‐difference beamforming antenna array based on the LC phase shifter is designed. The phase shifter is composed of two coaxial connectors, a metal base, an intermediate dielectric layer, a gradient metal sheet and a top glass layer. The simulated results show that a nearly 360° phase shift coverage can be achieved with the effective permittivity of LC varying from 2.5 to 3.5. The sum‐difference beam antenna array is composed of a circulator, a sum‐difference network, a one‐to‐eight power‐division network, eight liquid crystal phase shifters, and a serious fed antenna array. The simulation results show that the antenna array can achieve sum‐difference beam scanning range of ±30°. A prototype of LC phase shifter is fabricated and tested. The results show that the designed LC phase shifter can achieve a 360° phase coverage by applying a direct current (DC) voltage ranging from 0 to 12 V. Compared to traditional phase shifters, the proposed design offers a simple structure at a lower cost. When applied in the design of a sum‐difference beam antenna array, it can reduce the producing cost and enable integrated design.

This paper introduces a novel Fabry-Perot cavity (FPC) antenna design based on metasurface technique to achieve bi-directional radiation with independent forward and backward beam control capability and a low-profile configuration. Two pieces of partially reflective metasurface (PRMS) based on receiver-transmitter architecture with independent control of transmission and reflection phases are designed to serve as the upper and lower layers of the FPC antenna, respectively. By manipulating the transmission phase distribution of the two pieces of PRMS, designable independent multi-beam bi-directional radiation patterns can be achieved. For validation, two FPC antennas based on the proposed configuration are designed with different bi-directional radiation patterns. Proved by simulated results, Antenna 1 can achieve forward dual-beam and backward single-beam radiation simultaneously with a return loss of less than -10 dB at 10.4 GHz. The two beams of forward radiation point in the -45 degrees and 35 degrees directions, respectively, with gains of 7.42 dBi and 7.70 dBi. The gain of the single beam of backward radiation is 10.82 dBi. Antenna 2 can achieve a four-beam radiation pattern with both forward and backward dual beams. The beam directions of the four beams are -153 degrees, -44 degrees, 37 degrees, and 146 degrees, respectively. The gains in each direction are 5.45 dBi, 6.63 dBi, 5.97 dBi, and 5.22 dBi, respectively. The overall profile is 23.72 mm (0.81 lambda) for both antennas. The prototype of Antenna 1 is fabricated and measured. The results are in good agreement with the simulated counterparts, which demonstrates the feasibility of the proposed design methodology.

This paper presents Ka-band power divider and coupler based on the air-filled substrate integrated waveguide (AFSIW) technology. The utilization of air as the dielectric material in SIW structures offers reduced dielectric losses and enhanced performance for high-frequency applications. The AFSIW devices demonstrate lower loss, higher quality factor, and increased power handling capabilities compared to conventional SIW designs. These compact and lightweight components provide improved efficiency and isolation for millimeter-wave wireless communication systems.

In this letter, a broadband filtering power divider (FPD) based on a quarter circular/cambered substrate integrated waveguide (QCCSIW) cavity and microstrip line (MSL) resonators is proposed. First, a second-order bandpass filter (BPF) is designed based on the arc-shaped coupling of the QCCSIW. Second, a pair of quarter-wavelength (lambda/4) MSL resonators are integrated into the QCCSIW cavity to form a fourth-order asymmetric BPF with a pair of transmission zeros (TZs). Finally, a hybrid QCCSIW and MSL FPD with isolation is investigated. For verification, all BPFs and FPD are simulated, fabricated, and measured. The proposed FPD demonstrates a center frequency of 4.99 GHz, a 3-dB fractional bandwidth (FBW) of 37.11% (1.85 GHz), and an insertion loss (IL) of 0.8 dB. The port isolation is greater than 11 dB within the entire passband. Meanwhile, a pair of TZs are generated at 3.62 and 6.35 GHz respectively. The proposed hybrid QCCSIW and MSL FPD possesses an overall size of 1.73 x 1.74 lambda( g ), featuring advantages of broad bandwidth, compact size, and superior selectivity.

This paper presents a modularized reconfigurable functional electromagnetic surface (MRFES) for broadband absorption and polarization conversion by using tightly coupled dipole antennas (TCDA) and back-loaded radio frequency (RF) circuits (BLRFC). A dual-polarized antenna array with tight coupling and wide angular scanning characteristics is designed. By loading different RF circuits on the back side of the antenna array’s ground plane, switchable broadband absorption and polarization conversion functions are achieved. The design adopts modularization to facilitate the replacement of back-loaded RF circuits for diverse electromagnetic (EM) control functions. The final design of the tightly coupled antenna array has a thickness of 13.437 mm and a size of 119.5 mm × 119.5 mm. It works in a bandwidth range of 4.14–13 GHz. Upon loading the absorption circuit board, a broadband absorbing electromagnetic (EM) surface is formed, achieving dual-polarization absorption within a bandwidth of 4.14–12.4 GHz. With the polarization conversion circuit board attached, polarization conversion effects are realized within a bandwidth of 4.4–12.9 GHz. Both simulations and experiments verify that the designed EM surface possesses modular reconfigurable functions for broadband absorption/polarization conversion. The proposed design scheme holds promising prospects for applications in active stealth, adaptive camouflage, intelligent communication and other fields.

A dual-polarized multifunctional reconfigurable band-notched absorber (MRBNA) based on Galinstan is presented in this paper. The proposed MRBNA comprises a liquid metal transmission/reflection switchable layer (LM-T/RSL) and a wideband band-notched absorber (BNA). The MRBNA represents a paradigm shift in adaptive electromagnetic (EM) solutions, offering unprecedented wideband switching capabilities between superior band- notched absorption and full-band reflection states. By harnessing the potential of LM-T/RSL and innovative polarization selection mechanisms, this design sets a new benchmark for advanced stealth systems. The impact of LM-T/RSL on transmission and reflection characteristics is investigated, followed by experimental investigation of fluid flow in microfluidic channels. Then, the structural conception of the MRBNA is examined, employing the equivalent circuit method (ECM) and surface current distributions for a better understanding of its operating mechanism. Finally, a prototype is fabricated and empirical validation is conducted to demonstrate the simulated results. Positioning it at the forefront, the seamless adaptability of the proposed MRBNA to changing EM conditions promises to revolutionize modern stealth operations.

AbstractRetrodirective arrays have attracted a lot of research interest due to their unique characteristic of automatically responding to an interrogator without any prior information on the source location. As a unique member in the family of retrodirective arrays, the Van Atta array reflectors have features of simple structure and low cost and hold great potential for use in military and commercial applications, such as mobile communication, vehicle radar, radio‐frequency identification (RFID), and wireless power transfer (WPT). The Van Atta arrays are composed of an even number of radiation elements connected by transmission lines with equal electrical lengths. This article provides a detailed overview of the most recent research on the Van Atta array reflectors. Firstly, the development of the Van Atta arrays is briefly reviewed, and the basic design ideas are introduced. Then, the detailed operation principle of the Van Atta arrays is described, together with the theoretical analysis and experimental measurement to obtain the scattering field patterns in both monostatic and bistatic cases. After that, the latest research progress including the designs of one‐ and two‐dimensional Van Atta arrays is discussed. Besides the passive reflectors, the active Van Atta arrays can be implemented by introducing amplifiers or modulation circuits. In addition, this article also presents a short review of some typical applications of the Van Atta arrays, including the fields of vehicle‐mounting reflectors associated with the intelligent transportation systems (ITSs), the wireless charging of electronic devices, and ultralong‐range chipless sensing. Some examples of transponders using the Van Atta structures for these applications are introduced. Finally, some challenges and future research directions for Van Atta reflectors are presented.

In this paper, an X-band mixed microstrip and substrate integrated waveguide (SIW) four-way power combiner network with fully isolated performance is proposed. The power combiner network provides a high power capacity while maintaining the miniaturization of the structure. The input network can be considered as a four-way power divider composed of three microstrip 3-dB couplers, while the output network consists of three SIW 3-dB couplers. The directional couplers can enhance the isolation among the high-power signals of the four transmitting paths. In addition, the active power combiner utilizing X-band Gallium Nitride (GaN) power amplifier MMIC chips has also been designed. To demonstrate the feasibility of the above concept, the proposed prototype is developed. The experimental results show that the proposed power combiner attains a bandwidth ranging from 8.8 to 10.5 GHz, with a minimal insertion loss of 2.3 dB.

In this paper, a design and implementation of a low-noise amplifier (LNA) Monolithic Microwave Integrated Circuit (MMIC) chip operating at Ka-band (30-40GHz) is presented. The proposed chip utilizes a current-reuse structure, which significantly simplifies the design and save the current consumption from one DC supply. A three-stage common-source amplifier is fabricated in 100nm GaAs pHEMT process. Measurement results show a noise figure of less than 2.2dB, gain of 18dB, power consumption of 70mW from 5V supply, and an output 1dB compression point (P1dB) of 4.5dBm.

In this letter, a dual-band filtering 4×4 Butler matrix (DB-F-BM) based on a stub-loaded resonator (SLR) is proposed, operating at 12 and 17 GHz. The dual-band filtering (DB-F) 180° hybrid coupler can provide power allocation, phase shifting, and frequency selection at both frequencies. Each operating band reveals a second-order bandpass filtering response. This hybrid coupler is designed based on SLR and exploits different electromagnetic coupling to realize desired phase characteristics. A DB-F-BM was built, using DB-F 180° hybrid coupler, wideband 90° coupler, and phase shifter. The DB-F 180° hybrid coupler and DB-F-BM are fabricated and measured. The measured results are in good agreement with the theoretical ones. The lower and higher frequency bandwidth of DB-F-BM is approximately 8% and 3%, respectively. It also exhibits good out-of-band suppression. Furthermore, the DB-F-BM is applied to construct a 1 × 4 antenna array and verified the designed concepts and beamforming performance.

In this brief, an X-band low phase noise oscillator based on the substrate integrated waveguide (SIW) filtering rat-race coupler (FRRC) is proposed. The FRRC in the oscillator design is utilized to act as the frequency-stabilized component, power splitter and matching network simultaneously. It exhibits the merits of high quality factor, high circuit integration and decent impedance matching. For verification, the proposed prototype exploiting an improved SIW FRRC has been investigated, fabricated and measured. It demonstrates that the parallel-feedback oscillator works at 11.03 GHz. The rejection of second and third harmonic signals is up to 49.6 dBc and 48.8 dBc, respectively. In addition, the oscillator exhibits a low phase noise performance of −142.9 dBc/Hz at 1-MHz frequency offset from the oscillation frequency.