Boyu Sima

Computational microwave imaging (CMI) based on metasurface apertures effectively simplifies the system hardware. However, conventional random-field approaches suffer from low energy efficiency, leading to a poor signal-to-noise ratio (SNR) that severely degrades imaging quality. To address this, this letter proposes a bunching imaging method featuring a steerable region of interest (ROI) utilizing a 1-bit transmissive coding metasurface and experimentally validates its performance. By partitioning the aperture into subarrays and programming each to focus on a random point within the ROI, the proposed strategy addresses the trade-off between energy concentration and pattern diversity. Experimental results demonstrate that this transmissive implementation increases the peak power of the radiated field by approximately 13 dB over the conventional method while maintaining low mutual coherence. This enhancement leads to improved imaging quality under real experimental conditions, validating the proposed system as an effective solution for high-SNR computational imaging.

With the continuous expansion of electromagnetic application scenarios for retrodirective systems, reconfigurable retrodirective arrays featuring multiple operating modes and flexible control capabilities have gradually emerged as an important research and application direction. In this paper, an active reconfigurable function‐switching network operating over 6.4–11.2 GHz is designed. A broadband filtering magneto‐electric dipole antenna is proposed that inherently fuses filtering selectivity with radiation, thereby effectively suppressing out‐of‐band interference without requiring additional filter circuits. By integrating the developed filtering magneto‐electric dipole antenna, a broadband active reconfigurable retrodirective array system with three functional states (absorption, active retrodirective array, and active phased array) is developed. In the active retrodirective mode, the developed system achieves a monostatic radar cross section (RCS) angular coverage of ± 50° (angular range within a 6 dB drop from the RCS peak) within the operating band, along with an RCS dynamic modulation range exceeding 20 dB. In the active beamforming mode, a 3‐dB beam scanning range of ± 45° is realised.

A millimeter‐wave (MMW) voltage‐controlled oscillator (VCO) with parallel feedback architecture is proposed in this paper. A diplexer with large frequency ratio is exploited to act as a fundamental frequency stabilization and third‐harmonic frequency extraction component, simultaneously. It consists of an X‐band microstrip bandpass filter (BPF) and a Ka‐band substrate integrated waveguide (SIW) BPF. The characteristics of the proposed diplexer possess a decent performance of high isolation between the two output ports. To verify the proposed architecture, a Ka‐band VCO prototype is designed, fabricated, and measured. The observed outcomes indicate that the frequency tuning range is from 26.19 to 26.76 GHz, and the designed VCO achieves a superior phase noise (PN) of −128.7 dBc/Hz and the corresponding figure of merit (FOM) indicates −203.8 dB/Hz at 1‐MHz offset frequency.

This paper presents a hybrid-controlled multifunctional metamaterial (HCMM) that integrates electromagnetic switching and frequency tuning through combined active and microfluidic modulation. The HCMM achieves rapid switching between shielding and transmission states via active control of PIN diodes, while wideband frequency tuning is accomplished by manipulating liquid metals (LMs) in embedded microfluidic channels. Wideband frequency adjustment is demonstrated through discrete coarse-tuning (LM injection/discharge) and continuous fine-tuning (precise LM segments repositioning). The underlying operational mechanisms are analyzed by establishing an equivalent circuit model (ECM). Finally, experimental measurements of a fabricated prototype validate the design, confirming its dual-function reconfigurability in both state switching and frequency adaptation.

Metasurfaces (MSs) have been an effective method for the manipulation of electromagnetic (EM) radiation. However, this research mainly focused on controlling single-directional radiation. In this paper, a Fabry–Perot cavity (FPC) antenna based on the MSs technique is proposed, which obtains a bi-directional radiation with independent control of the forward and backward radiation patterns. The antenna is located in an FPC with two MSs forming the top and bottom surfaces. The MSs can partially reflect the x-polarized incident wave, i.e., it is a partially reflective metasurface (PRMS). Meanwhile, it can transform a specific incident component from x-polarization into y-polarization with a transmittance around −9.2 dB. In addition, the phase of the x-polarized reflection and y-polarized transmission can be controlled independently. So, a bi-directional radiation, of which the forward and backward radiation can be independently controlled, is obtained by the FPC antenna by manipulating the transmission phase distribution of the two PRMSs. As validation, two bi-directional radiation FPC antennas are designed based on the proposed method. Antenna 1 achieved a bi-directional single-beam radiation, of which the forward and backward radiation radiate to 2° and 177° with a gain of 13.4 dBi and 12.3 dBi, respectively. Antenna 2 achieved a bi-directional multibeam radiation, which radiates dual beams forward and a single beam backward. The two beams forward fire to 37° and 322° with a gain of 9.53 dBi and 9.3 dBi, while the beam backward fires to 178° with a gain of 7.8 dBi. At last, the first antenna is fabricated and measured for experimental validation, achieving the coincident results as simulation. This research can be potentially applied in research on antennas, communication, and wireless sensors in several practical scenarios, such as multibeam electromagnetic radiation, multi-user communication, multi-target monitoring, and sensor–communication system integration.

This article proposes a comprehensive design methodology for a broadband filtering Doherty power amplifier (FDPA) incorporating an integrated harmonic suppression network (IHSN) as post-matching network (PMN). First, unlike the conventional Wilkinson power divider, the input stage of the proposed Doherty power amplifier (DPA) employs a third-order cascaded trisection (CT) filtering power divider (FPD) network, implemented using a twelfth circular SIW (TCSIW) resonator. The proposed structure exhibits a bandpass response featuring a transmission zero at the upper stopband. Moreover, the physical footprint of the FPD is significantly decreased to 36.2% of its original size through the integration of L-shaped slots into the circular SIW, achieving a more compact design. Second, the PMN at the output of the DPA incorporates a pair of radial stubs and high-impedance short-circuited microstrip lines. The combination exhibits a bandpass response with an extended stopband to mitigate the high-order harmonic components generated by the nonlinearity of the DPA. Finally, to expand the bandwidth, a quarter-wavelength transmission line is added to the output of the peaking amplifier as an integrated compensating reactance (ICR). For verification and comparison, two types of DPAs are designed and fabricated: a conventional DPA with a Wilkinson power divider and a stepped-impedance PMN, and a filtering DPA with enhanced harmonic suppression characteristics. Measurement results reveal that the proposed DPA exhibits a filtering response with a wide suppression band up to the fifth harmonic frequency. Meanwhile, the proposed FDPA maintains a 6-dB back-off efficiency of 45%–55% and a saturated efficiency of 57%–69% over the operational frequency band of 1.8–2.6 GHz (36.4% fractional bandwidth), with a saturated output power exceeding 42.5 dBm. Furthermore, the proposed DPA achieves a maximum suppression level of 34 and 71 dBc for the second- and third-harmonic components.

Driven by the growing demand for electromagnetic wave modulations, programmable metasurfaces are expected to achieve wider spatial coverage and higher phase modulation accuracy. However, existing solutions cannot simultaneously satisfy the requirements of full-space propagation and continuous phase modulation. To address this issue, this letter proposes a metasurface unit topology based on receiving-reradiating structure that enables continuous phase modulation in full space. Based on this topology, a switchable transmissive-reflective metasurface unit with continuous 360-degree phase modulation capability is designed. Simulations and measurements validate a phase modulation range of over 360 degrees in both transmission and reflection modes.

To fulfill the continuously developing requirements of satellite communications and radar detection, this paper demonstrates a theoretical and experimental investigation of dual-circularly polarized (CP) transmitarray antennas (TAs) capable of generating spin-decoupled flat-top beams with customized gain differences. The constituent element for the transmitarray is a high-efficiency receiver-transmitter structure composed of a CP receiving antenna and a polarization-adjustable transmitting antenna. By rotating these two antennas jointly and modifying dimensions of transmitting patch, independent phase shifts and flexible energy allocations can be imparted to dual-CP transmitting waves, respectively. Then, a circular array is implemented by using the proposed element, specifically, a modified intersection approach is employed to synthesis a fan-shaped and a circular-shaped flat-top beam for the left-handed CP (LHCP) and right-handed CP (RHCP) channels, respectively. Three TAs, achieving −6, 0, 6 dB realized gain differences between the fan-shaped and circular-shaped beams, are separately implemented and verified through full-wave simulations, while the 6 dB-case TA is also fabricated, assembled and validated through experimental tests. All the simulated and measured results verify the high-quality flat-top beam, tailorable energy allocation and wide-angle beam-scanning properties for the dual-CP TAs.

Traditional antenna arrays for direction-of-arrival (DOA) estimation typically require numerous elements to achieve target performance, increasing system complexity and cost. Reconfigurable intelligent surfaces (RISs) offer a promising alternative, yet their performance critically depends on phase coding design. To address this, we propose a phase coding design method for RIS-aided DOA estimation with a single receiving channel. First, we establish a system model where averaged received signals construct a power-based formulation. This transforms DOA estimation into a compressed sensing-based sparse recovery problem, with the RIS far-field power radiation pattern serving as the measurement matrix. Then, we derive the decoupled expression of the measurement matrix, which consists of the phase coding matrix, propagation phase shifts, and array steering matrix. The phase coding design is then formulated as a Frobenius norm minimization problem, approximating the Gram matrix of the equivalent measurement matrix to an identity matrix. Accordingly, the phase coding design problem is reformulated as a Frobenius norm minimization problem, where the Gram matrix of the equivalent measurement matrix is approximated to an identity matrix. The phase coding is deterministically constructed as the product of a unitary matrix and a partial Hadamard matrix. Simulations demonstrate that the proposed phase coding design outperforms random phase coding in terms of angular estimation accuracy, resolution probability, and the requirement of coding sequences.

Reconfigurable intelligent surfaces (RIS) offer efficient control over the amplitude/phase of reflected/transmitted signals, providing a cost-effective solution for direction of arrival (DOA) estimation. Existing RIS-aided DOA systems suffer from poor sensing matrix orthogonality due to random phase coding, limiting performance when using compressive sensing-based algorithms. To address this issue, we propose a reconfigurable coding design method for transmissive RIS-aided DOA estimation by single receiving sensor. We reformulate the reconfigurable coding design as a Frobenius norm minimization problem, where the Gram matrix of the equivalent sensing matrix is rendered to approximate with an identity matrix. The reconfigurable coding is deterministically designed as the product of a unitary matrix and a partial Hadamard matrix. Simulation results show superior angle estimation accuracy over random coding under the same SNR, reducing the number of measurements by at least 25%.