A microstrip filtering power divider (FPD) with good isolation performance and harmonic suppression is presented. By replacing a simple resistor with a novel distributed stepped-impedance resonator ...network, better isolation and wider stopband are simultaneously attained. A transmission matrix-based analysis method is then extensively described to determine the circuit geometrical parameters at the synthesis level by facilitating the incorporation of design indexes and structure dimension. A prototype FPD is designed, fabricated and measured. The proposed FPD exhibits a center frequency of 2.2 GHz (f 0 ) with the isolation better than 17dB within the entire passband and a stopband extended to 12 GHz (5.45f 0 ).
The authors report a novel approach for designing tunable and reconfigurable bandstop filters by employing bias‐free optically‐controlled photoconductive radio frequency (RF) switching elements. To ...verify the effectiveness of the approach, a bandstop filter with two stopbands centred at 4.05 and 4.75 GHz was designed using a split‐ring‐coupled microstrip transmission line on RO3010 substrates. To enable reconfigurability, a micromachined Si chip with a thickness of ∼73 μm was embedded in the gap of each resonator. The tuning and reconfiguring of the filter are accomplished by selectively illuminating the Si chips using fibre‐coupled laser diodes with a wavelength of 808 nm. By turning on and off each laser diode, the filter stop bands can be dynamically reconfigured. In addition, the suppression of each stop band can be continuously and independently tuned by changing the light intensity from 0 to 20 W/cm2. With geometric scaling, this approach is promising for realizing a novel class of compact and high‐performance tunable and/or reconfigurable circuits from the microwave to mmW‐THz region.
A wideband filtering power divider (FPD) with good isolation and widen upper stopband is presented. A distributed stepped-impedance resonator (SIR) network composed of three short-circuited SIRs and ...one isolation resistor is introduced to obtain both port-to-port isolation and harmonic suppression. For demonstration, an FPD operating at 2.3 GHz with 3 dB fractional bandwidth of 31% is designed, fabricated and measured. In the operating band, the measured isolation is better than 17 dB, while out of band, the upper stopband is extended to 9.8 GHz (4.2f0) with a rejection level of 20 dB.
We report the design, simulation, and analysis of a THz phased array, using lens-coupled annular-slot antennas (ASAs) for potential beyond 5G or 6G wireless communications. For a prototype ...demonstration, the ASA employed was designed on a high resistivity Si substrate with a radius of 106 μm, and a gap width of 6 um for operation at 200 GHz. In order to achieve higher antenna gain and efficiency, an extended hemispherical silicon lens was also used. To investigate the effect of the silicon lens on the ASA phased array, a 1 × 3 array and 1 × 5 array (the element distance is 0.55λ) were implemented with a silicon lens using different extension lengths. The simulation shows that for a 1 × 3 array, a ±17° scanning angle with an about −10 dB sidelobe level and 11.82 dB gain improvement (compared to the array without lens) can be achieved using a lens radius of 5000 μm and an extension length of 1000 μm. A larger scanning angle of ±31° can also be realized by a 1 × 5 array (using a shorter extension length of 250 μm). The approach of designing a 200 GHz lens-coupled phased array reported here is informative and valuable for the future development of wireless communication technologies.
In this work, high-performance terahertz (THz) tunable/reconfigurable circuits/components using photo-patterned mesa array structures have been demonstrated for implementations in advanced imaging, ...sensing, and communications. In recent years, a variety of THz applications, from radio astronomy to medical imaging, have been explored and developed. Accelerated by significant progress in THz signal generation/detection techniques, growing interest has been drawn to more advanced THz applications. Tunable/reconfigurable circuits/components that can provide dynamic modulation of THz radiation for multi-band and multi-functional operation are needed in those applications. Several tuning approaches including mechanical, thermal, and electrical tuning, have been reported for realizing THz tunable/reconfigurable circuits. However, those approaches tend to show slow tuning responses, as well as limited tunability/reconfigurability due to the use of conventional pre-patterned circuits. This could be solved by using optically-generated free carriers in semiconductors to form photopatterned circuit structures and realize freely tunable/reconfigurable circuits without the need for mechanical tuning and prepatterned circuits/devices. However, the achievable resolution in unpatterned semiconductors is limited due to the carrier lateral diffusion. In this work, we propose and investigate a novel approach for realizing tunable and reconfigurable THz circuits on the basis of semiconducting micromachined mesa-array structures. The mesa-array structure consists of two-dimensional arrays of subwavelength and electrically isolated semiconductor mesas, thereby confining the free carriers within each mesa. Consequently, high-resolution photopatterns (e.g., with a spatial resolution on the order of 10 μm, compared to typical ~400 μm diffusion length in Si) can be generated for the implementation of high-performance tunable/reconfigurable circuits in the THz regime. In this work, the optical properties of the proposed mesa array structures have been investigated through theoretical calculation and full-wave electromagnetic simulations. A Si mesa array prototype structure was designed, fabricated, and tested. Measurements show that a modulation depth of ~20 dB was obtained in the frequency range of 740-750 GHz under a light intensity of ~12 W/cm2. The mesa array structure has been implemented in THz photo-induced coded aperture imaging (PI-CAI) to form high-fidelity tunable/reconfigurable aperture masks for subwavelength spatial resolution. This novel approach for PI-CAI with subwavelength spatial resolution is promising in advanced high-resolution THz imaging and sensing applications. In addition, mesa-array-based tunable/reconfigurable THz bandpass mesh filters have been demonstrated with insertion losses of 0.82-1.13 dB in the frequency range of 108-489 GHz. Other functionalities such as bandstop filtering can also be realized by optically changing photopatterns illuminated on the same mesa array structure. The wide tuning range and reconfigurability of the mesh filters demonstrate that the proposed approach is promising for developing tunable/reconfigurable circuits with multiple functionalities. Furthermore, tunable/reconfigurable THz sub-system components have also been designed and simulated using Si pillar arrays. SIW transmission line, as well as more advanced SIW-based circuits, including SIW bend, single-pole double-throw (SPDT) switch, and phase shifters have been demonstrated. The pillar-array-based universally tunable/reconfigurable SIW structures favorable candidates in more advanced THz sensing and adaptive telecommunication systems.
We report a novel approach for dynamically tuning and reconfiguring microwave bandpass filters (BPFs) based on optically controlled switching elements using photoconductivity modulation in ...semiconductors. For a prototype demonstration, a BPF circuit featuring a second‐order design using two closely coupled split‐ring resonators embedded with multiple silicon chips (as switching elements) was designed, fabricated, and characterized. The silicon chips were optically linked to fiber‐coupled laser diodes (808 nm light) for switching/modulation, enabling dynamic tuning and reconfiguring of the BPF without any complex biasing circuits. By turning on and off the two laser diodes simultaneously, the BPF response can be dynamically reconfigured between bandpass and broadband suppression. Moreover, the attenuation level of the passband can be continuously adjusted (from 0.7 to 22 dB at the center frequency of 3.03 GHz) by varying the light intensity from 0 to 40 W/cm2. The tuning/reconfiguring 3‐dB bandwidth is estimated to be ~200 kHz. In addition, the potential and limitations of the proposed approach using photoconductivity modulation are discussed. With the strong tuning/reconfiguring capability demonstrated and the great potential for high‐frequency operation, this approach holds promise for the development of more advanced tunable filters and other adaptive circuits for next‐generation sensing, imaging, and communication systems.
We report the design, fabrication, and prototype demonstration of a 200-GHz polarization-resolved quasi-optical detector employing monolithically integrated zero-bias heterostructure backward diodes ...(HBDs). In this design, polarization resolution is achieved by orthogonally integrating the detectors with a planar dual-polarization annular-slot antenna. The detector chip was fabricated and mounted on an extended hemispherical Si lens to enhance antenna efficiency in the millimeter-wave to terahertz region. The responsivity and radiation patterns of the detector were characterized experimentally; good agreement with theoretical calculations was obtained. By measuring the outputs of two orthogonal HBDs as a function of the polarization angle of the incident wave, the planar detector detects intensity and resolves polarization. On the basis of the polarimetric measurement, we further demonstrate the polarization imaging capability of the proposed detector by using it as an imaging system. The detector is promising for developing terahertz polarimetric sensors and imaging arrays in chemical sensing, biomedical imaging, and radio astronomy applications.
A fully integrated lens-coupled dual-polarization detector for imaging was designed, fabricated, and characterized in the terahertz (THz) region. Two zero-bias heterostructure backward diodes were ...monolithically integrated into a planar dual-polarization annular-slot antenna. An impedance matching network consisting of an interdigitated dc block and shorted stubs was implemented for maximum power transfer. The fabricated chip was then mounted on an extended hemispherical silicon lens for high antenna efficiency. The performance of the integrated detector has been characterized at 200 GHz. The detector module can simultaneously measure the two orthogonal linear-polarized components of the incident THz waves, and hence obtain the polarization direction. On the basis of this polarimetric detection, polarization-resolved imaging of a Gaussian beam, as well as birefringent samples, was performed using the integrated detectors. The angular resolution of the polarization detection has been demonstrated to be as small as 3°. The single-pixel detector demonstrated here is amenable to array applications for THz focal-plane arrays that will have a significant impact on a wide range of remote sensing, through-barrier imaging, and detection/identification applications.
We report a novel approach for realizing tunable/reconfigurable terahertz (THz) mesh filters on the basis of micromachined mesa‐array structures. In this approach, different filter patterns are ...generated virtually using photogenerated free carriers in a semiconducting mesa‐array structure to achieve superior tunability and reconfigurability. Micromachined mesa‐array structures enable the formation of high fidelity, optically generated mesh filter structures for THz frequencies. To evaluate the proposed filter designs, the optically patterned spatial modulation properties of mesa‐array structures were first evaluated. Reconfigurable mesh filter prototypes were then designed and simulated using silicon mesa arrays with 50 × 50 μm2 square mesa unit cells. Simulations show that reconfigurable bandpass filters (BPFs) operating in the frequency range of 108–489 GHz with insertion losses of 0.82–1.13 dB can be achieved. By employing smaller unit cells, the frequency tuning range and filtering performance can be further improved. In addition to BPFs, other filter functionalities can also be realized utilizing the proposed approach. The wide tuning range and reconfigurability of the mesh filters demonstrate that the proposed approach is promising for developing tunable/reconfigurable circuits and components for advanced THz sensing, imaging, and communications.
Ran is considered to be a promising target for tumor-specific immunotherapy because its protein is exclusively expressed in tumor tissues, though its mRNA can be expressed in most normal tissues. In ...our study, we obtained four candidate wild-type epitopes designated Ran1, Ran2, Ran3, and Ran4, derived from the Ran antigen with the highest predicted affinity with MHC-I, indicated by affinity prediction plots and molecular dynamics simulation. However, in vitro affinity assays of these epitopes showed only a moderate affinity with MHC-I. Thus, we designed altered peptide ligands (APLs) derived from Ran wild-type epitopes with preferred primary and auxiliary HLA-A*0201 molecule anchor residue replacement. Of the eight tested peptides, the 1Y analog had the strongest binding-affinity and lowest-dissociation rate to HLA-A*0201. Additionally, we investigated the CTLs activities induced by Ran wild-type peptides and the APLs in human PBMCs and in HLA-A*0201/K
b
transgenic mice. Ran1 1Y was superior to other APLs and wild-type peptides in eliciting epitope-specific CTL immune responses both in vitro and in vivo. In summary, a wild-type epitope of the tumor-specific antigen Ran, expressed broadly in many tumors, was identified and designated Ran1. An APL of Ran1, Ran1 1Y, was further designed and verified in vitro and in vivo and found to elicit a stronger Ran-specific CTL response, indicating a potential anti-tumor application in the future.
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