This paper presents a 220-320-GHz hemispherical lens antenna fabricated using photopolymer-based additive manufacture and directly fed by the standard WR-3 rectangular waveguide without any additional waveguide extension. The microfabrication process is based on digital light processing rapid prototyping using the Monocure 3DR3582C resin-based photocurable polymer. This gives various key advantages, including ease of antenna fabrication, manufacturing speed, and cost-effectiveness due to its rapid fabrication capability. Even though the photopolymer is found to have a loss tangent of 0.034 at 320 GHz, the all-polymer lens antennas still achieve a fractional bandwidth of 37%, covering the whole 220-320-GHz WR-3 waveguide band with a measured gain of approximately 16 dBi at 0° over the whole band. A measured return loss of better than 14 dB is achieved from 220 to 320 GHz with a half-power beamwidth of approximately 12°, which is relatively constant over the whole WR-3 band.

In this paper, the design and measurement of a three-dimensional-printed low-loss asymptotically single-mode hollow-core terahertz Bragg fiber are reported, operating across the frequency range from 0.246 to 0.276 THz. The HE11 mode is employed as it is the lowest loss propagating mode, with the electromagnetic field concentrated within the air core as a result of the photonic crystal bandgap behavior. The HE11 mode also has large loss discrimination compared to its main competing HE12 mode. This results in asymptotically single-mode operation of the Bragg fiber, which is verified by extensive simulations based on the actual fabricated Bragg fiber dimensions and measured material parameters. The measured average propagation loss of the Bragg fiber is lower than 5 dB/m over the frequency range from 0.246 to 0.276 THz, which is, to the best of our knowledge, the lowest loss asymptotically single-mode all-dielectric microstructured fiber yet reported in this frequency range, with a minimum loss of 3 dB/m at 0.265 THz.

This work presents, for the first time, an in-situ self-aligned fluidic-integrated microwave sensor for characterizing NaCl contents in NaCl-aqueous solution based on a 16-GHz bandpass combline cavity resonator. The discrimination of the NaCl concentration is achievable by determining amplitude differences and resonant frequency translations between the incident and reflected microwave signals at the input terminal of the cavity resonator based on the capacitive loading effects of the comb structure inside the cavity introduced by the NaCl solution under test. Twelve NaCl-aqueous liquid mixture samples with different NaCl concentrations ranging from 0% to 20% (0 - 200 mg/mL), which are generally exploited in most industrial and biomedical applications, were prepared and encapsulated inside a Teflon tube performing as a fluidic channel. The Teflon tube is subsequently inserted into the cavity resonator through two small holes, fabricated through the sidewalls of the cavity, which can be used to automatically align the fluidic subsystem inside the combline resonator considerably easing the sensor setup. Based on at least five repeated measurements, the NaCl sensor can discriminate the NaCl content of as low as 1% with the measurement accuracy of higher than 96% and the maximum standard deviation of only 0.0578. There are several significant advantages achieved by the novel NaCl sensors, e.g. high accuracy, traceability and repeatability; ease of sensor setup and integration to actual industrial and biomedical systems enabling in-situ and real-time measurements; noninvasive and noncontaminative liquid solution characterization as well as superior sensor reusability due to a complete physical separation between the fluidic and microwave subsystems.

This paper reports on a miniaturized lab-on-a-waveguide liquid-mixture sensor, achieving highly accurate nanoliter liquid sample characterization, for biomedical applications. The nanofluidic-integrated millimeter-wave sensor design is based on a near-field transmission-line technique implemented by a single loop slot antenna operating at 91 GHz, fabricated into the lid of a photolaser-based subtractive manufactured WR-10 rectangular waveguide. The nanofluidic subsystem, which is mounted on the top of the antenna aperture, is fabricated by using multiple polytetrafluoroethylene layers to encapsulate and isolate the liquid sample during the experiment, hence, offering various preferable features, e.g., noninvasive and contactless measurements. Moreover, the sensor is reusable by replacing only the nanofluidic subsystem, resulting in a cost-effective sensor. The novel sensor can measure a liquid volume of as low as 210 nanoliters, while still achieving a discrimination accuracy of better than 2% of ethanol in the ethanol/deionized-water liquid mixture with a standard deviation of lower than 0.008 from at least three repeated measurements, resulting in the highest accurate ethanol and DI-water discriminator reported to date. The nanofluidic-integrated millimeter-wave sensor also offers other advantages, such as the ease of design, low fabrication and material cost, and no life-cycle limitation of the millimeter-wave subsystem.

This manuscript presents a triple-port ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna designed for wireless communication. The antenna employs automobile window film as a substrate, which is a cost-effective, easily accessible, and ultra-thin material. The proposed structure comprises a monopole antenna featuring a circular patch pattern that is fed by a coplanar waveguide (CPW). Additionally, the internal ground plane has been modified by grooving both sides to form a rectangular slot antenna construction. As a result, the antenna possesses identical dimensions and is equipped with three ports. The antenna exhibits a frequency range spanning from 3.1 GHz to 10.6 GHz across all three ports. Additionally, the | S ₁₁ | at port 1 demonstrates an extensive operating bandwidth of 2.4 GHz to 10.6 GHz with a signal attenuation of less than -10 dB. Consequently, it has the capability to facilitate a diverse range of applications such as ultra-wideband (UWB), Worldwide Interoperability for Microwave Access (WiMAX), Wireless Personal Area Network (WPAN), Wireless Local Area Network (WLAN), and 5G. Furthermore, the antenna exhibits a gain of 5.8 dBi across its entire range, a correlation coefficient below 0.45, and a group latency of under 0.85 ns. The antenna exhibits both omnidirectional and bidirectional radiation patterns across its operational range at ports 1, 2, and 3.

This paper presents, for the first time, a microwave gas sensor utilizing Poly (styrene-co-maleic acid) partial isobutyl/methyl mixed ester (PSE), which is a sensing material, as a coating on an interdigital resonator. The proposed sensor is based on a near-field transmission-line technique to detect the changing of the dielectric properties of the sensing material. The sensor was designed based on a DiClad 880 substrate with an interdigital resonator, operating at 4 GHz, on the middle of an ungrounded coplanar waveguide transmission line structure with rejection characteristic by coating the PSE solution as a sensed-gas material. The measured transmission coefficient, S21, was changed depending on the dielectric properties of the PSE change due to various concentrations of gas targeted in a range of 50 to 1,000 ppm (50 ppm, 200 ppm, 500 ppm, 1,000 ppm) under a static system in a closed chamber at room temperature. The extracted results of differential transmission coefficient change, S21, from four samples of ammonia concentration can be separated impressively. To confirm the selectivity performance of ammonia gas, three interfering gases, i.e., acetone, ethanol and methanol, were investigated. The measured results show that the proposed sensor can discriminate ammonia gas from three interfering gases over the entire concentration range in only three minutes. Moreover, it has many advantages, such as low cost, real-time monitoring and room temperature operating. The PSE-coated sensor described in this paper is suitable for a high-performance selectivity in ammonia gas sensing applications both in industrial processes and in agricultural products.