Search Results (37)

We propose a tunable multi-functional metamaterial composed of two pairs of gold corner resonators interconnected with photosensitive silicon, operating in the terahertz range. This design achieves dual-band unidirectional reflectionlessness, polarization conversion, and asymmetric transmission for linearly polarized waves, regardless of whether the photosensitive silicon is in the insulating or conductivity state. When the photosensitive silicon transitions from the insulating state to the conductivity state, its conductivity increases significantly, resulting in a frequency shift phenomenon in the functional peak frequencies. Numerical simulations demonstrate the structure’s robust performance in dual-band unidirectional reflectionlessness and its significant asymmetric transmission, with minimal sensitivity to variations in the incident angle and photosensitive silicon sheet length. By integrating multiple functionalities and enabling frequency tunability through the control of photosensitive silicon conductivity, this design offers a reconfigurable solution for THz applications, such as switches, polarization converters, and modulators. Full article

A dual-band dual-circularly polarized transmitarray antenna (TA) operating in the 28/39 GHz millimeter-wave band is proposed in this article. The TA unit consists of two parts: a broadband linearly polarized (LP) receiving part and a dual-band dual-circularly polarized transmitting part. An over-2-bit phase compensation is achieved by changing the size of the U-shaped slot and the rotation status of the receiving part. A 24 × 24 TA model with an aperture size of 88.8 mm × 88.8 mm is built up by using the proposed units and fed by a wide-band corrugated horn antenna. The simulated results show that the maximum gain of the dual-band dual-circularly polarized TA is 26.28 dBic within the low-band (26.5–29.5 GHz) and 27.4 dBic within the high-band (37–40 GHz). To verify the accuracy of the simulation, a prototype of the proposed TA is fabricated and measured. The measured maximum efficiencies are 53.56% and 42.89% in low and high bands, respectively. The proposed TA covers two bands (28/39 GHz) for fifth generation (5G) millimeter-wave applications. Moreover, it features low cost, high gain, and high efficiency. Full article

The integrated imaging of LWIR cameras and SAR is one of the important directions of multi-sensor integration. In order to reduce the structural complexity of LWIR cameras and SAR-integrated imaging antenna, a dual-polarized metasurface-integrated antenna (MIA) is designed in this paper. It is composed of a microwave metasurface antenna and an optical metalens, and the metalens is embedded in the center of the metasurface antenna. The MIA uses the powerful electromagnetic wave control ability to simplify the optical and microwave signal transmission paths and reduce the number of devices. At the same time, in order to expand the function of the MIA, based on the principle of metasurface, the dual-linearly polarized and dual-circularly polarized MIAs are designed and simulated, respectively. The results show that the designed dual-polarized MIA has good performance. This paper provides a new scheme for the integrated imaging system of LWIR cameras and SAR with simple structure, diverse functions and easy integration. Full article

A novel common-aperture miniaturized antenna with wideband and dual-polarized characteristics is proposed, which consists of a circularly polarized (CP) and a linearly polarized (LP) antenna. The circularly polarized antenna stacked on the upper layer adopts asymmetrical ground and introduces the patch and T-type feed network. On this basis, the meshed reflector structure, which also works as a ground plane for the LP antenna, is added to reduce the influence on circular polarization and achieve directional radiation. The LP antenna stacked in the lower layer uses a monopole structure, and the coaxial feed line perforates the reflector, and thereby the common-aperture antennas are tightly stacked together from top to bottom. Simulation and test are in good accordance, and the results show that the two ports of the antenna are well matched in the range of 5.5 GHz to 7.8 GHz, where peak gains of 8.5 dB and 6 dB are realized for circular polarization and linear polarization, respectively. Moreover, the 3 dB axial ratio (AR) bandwidth of the CP antenna is 34.3% and the isolation between the two ports is better than 15 dB, suggesting potential applications in the relay platform or drone detection for signal transmission and reception. Full article

We report a photonic-assisted method for measuring the frequencies of a multi-tone microwave with high accuracy based on pulse identification. The unknown microwave signal and a linearly chirped signal are modulated to an optical carrier using a dual-polarization Mach–Zehnder modulator. Carrier-suppressed single-sideband modulation avoids the generation of undesired frequency components after photodetection. An electrical bandpass filter with a narrow bandwidth selects the beat signal between the unknown signal and the linearly chirped optical tone. A pulse, generated by the beat signal, can be observed using an oscilloscope (OSC). By identifying the beating pulse position, we can accurately determine the frequency of the unknown signal. The single-tone and multi-tone microwave signal ranges of 6–16 GHz and 26–36 GHz are successfully measured, respectively. The measurement errors for single-tone and multi-tone signals are both less than ±1 MHz. Full article

A THz-to-IR converter can be an effective solution for the detection of low-IR-signature targets by combining the advantages of mature IR detection mechanisms with high atmospheric transmittance in the THz region. A metallic metasurface (MS)-based absorber with linear polarization dependence based on a split-ring resonator (SRR) unit cell has been previously studied as a preliminary example of a THz-to-IR converter structure in the literature. In this simulation-based study, a new cross-shaped unit cell-based metallic MS absorber structure sensitive to dual polarization is designed to eliminate linear polarization dependency, thereby allowing for incoherent detection of THz radiation. A model is developed to calculate the temperature difference and the response time for this new cross-shaped absorber structure, and its performance is compared to the SRR structure for both coherent and incoherent illumination. This model allows for understanding the efficiency of these structures by considering all loss mechanisms which previously had not been considered. It is found that both structures show similar performance under linearly polarized coherent illumination. However, under incoherent illumination, the IR emittance efficiency as gauged by the temperature difference for the cross-shaped structure is found to be twice as high as compared to the SRR structure. The results also imply that calculated temperature differences for both structures under coherent and incoherent illumination are well above the limit of the minimum resolvable temperature difference of the state-of-the-art IR cameras. Therefore, dual-polarized or multi-polarization-sensitive MS absorber structures can be crucial for developing cost-effective THz-to-IR converters and be implemented in THz imaging solutions. Full article

Multifunctional integrated meta-devices are the demand of modern communication systems and are given a lot of attention nowadays. Most of the research has focused on either cross-polarization conversion (CPC) or linear-to-circular (LP–CP) conversion. However, simultaneously realizing multiple bands with good conversion efficiency remains crucial. This paper proposes a multiband and multifunctional dual reflective polarization converter surface capable of converting a linearly polarized (LP) wave into a circularly polarized (CP) wave, in frequency bands of 12.29–12.63 GHz, 16.08–24.16 GHz, 27.82–32.21 GHz, 33.75–38.74 GHz, and 39.70–39.79 GHz, with 3 dB axial ratio bandwidths of 2.7%, 40.15%, 14.6%, 13.76%, and 0.2%, respectively. Moreover, the converter is capable of achieving CPC with a polarization conversion ratio (PCR) that exceeds 95%, within the frequency ranges of 13.10–14.72 GHz, 25.43–26.00, 32.46–32.56 GHz, and 39.14–39.59 GHz. In addition, to identify the fundamental cause of the CPC and LP–CP conversion, a comprehensive theoretical investigation is provided. Furthermore, the surface current distribution patterns at different frequencies are investigated to analyze the conversion phenomena. A sample prototype consisting of 20 × 20 unit cells was fabricated and measured, verifying our design and the simulated results. The proposed structure has potential applications in satellite communications, radar, stealth technologies, and reflector antennas. Full article

A 1550 nm all-fiber dual-polarization coherent Doppler lidar (DPCDL) was constructed to measure the depolarization ratio of atmospheric aerosols. In lidar systems, the polarization state of the laser source is typically required to be that of linearly parallel polarization. However, due to the influence of the fiber-optical transmission and the large-mode field output of the telescope, the laser polarization state changes. Hence, a polarizer was mounted to the emitting channel of the telescope to eliminate the depolarization effect. A fiber-optical polarization beam splitter divided the backscattered light into components with parallel and perpendicular polarization. The DPCDL used two coherent channels to receive each of these two polarization components. A calibration procedure was designed for the depolarization ratio to determine the differences in gain and non-responsiveness in the two polarization channels. The calibration factor was found to be 1.13. Additionally, the systematic error and the measured random error of the DPCDL were estimated to evaluate the performance of the system. The DPCDL’s systematic error was found to be about 0.0024, and the standard deviation was lower than 0.0048. The Allan deviations of a 1-min averaging window with a low SNR of 19 dB and a high SNR of 27 dB were 0.0104 and 0.0031, respectively. The random errors at different measured heights were mainly distributed below 0.015. To confirm the authenticity of the atmospheric depolarization ratio measured with the DPCDL, two field observations were conducted with the use of a co-located DPCDL and micro-pulse polarization lidar to perform a comparison. The results showed that the correlation coefficients of the aerosol depolarization ratios were 0.73 and 0.77, respectively. Moreover, the two continuous observations demonstrated the robustness and stability of the DPCDL. The depolarization ratios were detected in different weather conditions. Full article

We numerically and experimentally demonstrate a terahertz metadevice consisting of split-ring resonators (SRRs) present within square metallic rings. This device can function as a dual-band polarization converter by breaking the symmetry of SRRs. Under x-polarized incidence, the metastructure is able to convert linearly polarized (LP) light into a left-hand circular-polarized (LCP) wave. Intriguingly, under y-polarized incidence, frequency-dependent conversion from LP to LCP and right-hand circular-polarized (RCP) states can be achieved at different frequencies. Furthermore, reconfigurable LCP-to-LP and RCP-to-LP switching can be simulated by integrating the device with patterned graphene and changing its Fermi energy. This dual-band and multi-state polarization control provides an alternative solution to developing compact and multifunctional components in the terahertz regime. Full article

We propose and experimentally demonstrate a tunable frequency-doubling optoelectronic oscillator (FD-OEO) based on a single-bandpass dispersion-induced microwave photonic filter (MPF) consisting of a Mach–Zehnder modulator (MZM), a linearly chirped fiber Bragg grating and polarization-multiplexed dual-loop. Thanks to the polarization dependence of the MZM, a special double sideband modulation is implemented where the optical carrier (OC) and subcarriers are orthogonally polarized. By simply tuning the PC in the OEO loop, the phase difference between the orthogonal polarization carrier and two sidebands can be controlled, and thus the center frequency of the fundamental OEO can be tuned. Furthermore, a PC and a polarizer are placed outside the OEO to achieve optical carrier suppression (OCS) modulation, which ensures that a frequency-tunable microwave signal at the second-harmonic frequency is generated. In the experiment, a fundamental frequency signal with tunable frequency from 3.6 to 6.85 GHz and FD-OEO with a tunable frequency range from 7.2 to 13.7 GHz are generated. Full article

In this work, a dual-band transmissive polarization conversion metasurface (PCM), with omnidirectional polarization and low profile, is proposed. The periodic unit of the PCM is composed of three metal layers separated by two substrates. The upper patch layer of the metasurface is the patch-receiving antenna, while the bottom layer is the patch-transmitting antenna. Both antennas are arranged in an orthogonal way so that the cross-polarization conversion can be realized. The equivalent circuit analysis, structure design, and experimental demonstration are conducted in detail, the polarization conversion rate (PCR) is greater than 90% within two frequency bands of 4.58–4.69 GHz and 5.33–5.41 GHz, and the PCR at two center operating frequencies of 4.64 GHz and 5.37 GHz is as high as 95%, with a thickness of only 0.062${\lambda }_L$, where ${\lambda }_L$ is the free space wavelength at the lowest operating frequency. The PCM can realize a cross-polarization conversion, when the incident linearly polarized wave at an arbitrary polarization azimuth, which indicates that it has the characteristics of omnidirectional polarization. Full article

This paper presents a linear-to-dual-circular polarization metasurface decomposer, which decomposes a linearly polarized (LP) planar incident wave into a pair of circular polarized (CP) waves, namely, a right-handed circular polarized (RHCP) wave and a left-handed circular polarized (LHCP) wave, and scatters them into different directions. The proposed metasurface polarization decomposer is composed of a series of rotated trimming stub loaded circular patches. The two CP components are excited due to the perturbation introduced by the trimming stubs, and the different phase gradients added to the RHCP and LHCP components are realized by rotating the circular patches with different angles. A $12\times 12$ metasurface polarization decomposer is designed, fabricated, and measured, which scatters the RHCP and LHCP into $-{30}^{\circ }$ and ${30}^{\circ }$, respectively. The simulated and measured results agree well with each other, which demonstrates the proposed design. Full article

Using polarization-maintaining fiber (PMF) in dual-frequency heterodyne interferometry has the advantages of reducing the laser’s own drift, obtaining high-quality light spots, and improving thermal stability. Using only one single-mode PMF to achieve the transmission of dual-frequency orthogonal, linearly polarized beam requires angular alignment only once to realize the transmission of dual-frequency orthogonal, linearly polarized light, avoiding coupling inconsistency errors, so that it has the advantages of high efficiency and low cost. However, there are still many nonlinear influencing factors in this method, such as the ellipticity and non-orthogonality of the dual-frequency laser, the angular misalignment error of the PMF, and the influence of temperature on the output beam of the PMF. This paper uses the Jones matrix to innovatively construct an error analysis model for the heterodyne interferometry using one single-mode PMF, to realize the quantitative analysis of various nonlinear error influencing factors, and clarify that the main error source is the angular misalignment error of the PMF. For the first time, the simulation provides a goal for the optimization of the alignment scheme of the PMF and the improvement of the accuracy to the sub-nanometer level. In actual measurement, the angular misalignment error of the PMF needs to be smaller than 2.87° to achieve sub-nanometer interference accuracy, and smaller than 0.25° to make the influence smaller than ten picometers. It provides theoretical guidance and an effective means for improving the design of heterodyne interferometry instruments based on PMF and further reducing measurement errors. Full article

This paper describes the design steps carried out to prove the concept of a wideband monopole antenna system to be used in a wearable device conceived for the evaluation of electromagnetic field radiation. Such a device is envisaged to be integrated into protective vests worn by professional users in their working space environment as part of intelligent multi-risk protection. Initially, the main characteristics of a simple straight monopole are reviewed to serve as a reference. A modified octagonal monopole antenna element is introduced, and a two dual-linearly polarized configuration of such monopoles is designed, fabricated, and tested to be used in the frequency range of 0.7–3.5 GHz. The expected radiation characteristics (input reflection coefficient and isolation between vertically and horizontally polarized ports) are confirmed experimentally. The effects of a thick lossy foam substrate layer used to mitigate the presence of the metal shield, employed in the vest lining as a Faraday cage protection, are analyzed both by simulation and experimentally. Finally, electromagnetic simulations are carried out to confirm that a system of five dual-linearly polarized monopole elements located in the chest, shoulders, back, and helmet of the user can provide an adequate estimation of the incident electromagnetic field radiation. Full article

Presented in this paper is a conceptual design by computer simulation of a monopulse reflector antenna with dual-circularly polarized sum patterns and linearly polarized azimuth and elevation difference patterns, which can be called a semi-dual polarized antenna. The proposed antenna consists of a five-element monopulse feed and a prime-focus parabolic reflector. The novelty of the proposed antenna is a monopulse feed consisting of a dual-circularly polarized square waveguide sum channel radiator and linearly polarized rectangular waveguide azimuth and elevation difference channel radiators. The separation of dual circular polarization is realized by a septum polarizer. The difference pattern is obtained by feeding two rectangular waveguides in opposite directions using a coaxial probe. The proposed monopulse feed geometry requires only two power combiners for a monopulse comparator network while providing dual-polarized performance comparable to the full dual-polarized sum and difference channel monopulse scheme. The concept of the proposed antenna is shown in a conceptual design by computer simulation. The monopulse feed is designed first, and then combined with a parabolic reflector. The designed monopulse reflector antenna operates at 14.5–16.0 GHz, and shows excellent sum and difference pattern characteristics: 36.1–36.7 dBc sum channel directivity with 0.65 dB boresight axial ratio and 32.6–32.9 dBi difference channel directivity with 1.56–1.66° crossover angle. Full article