Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications. By Christophe Caloz and Tatsuo Itoh.

Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

The development of efficient, low-cost and highly sensitive chemical sensors that can monitor trace amounts of volatile organic compounds (VOCs) has become indispensable for industrial and biomedical applications. Here, we demonstrate a high-performance and flexible VOC sensor based on a 3D Mxene framework (3D-M). The 3D-M was prepared through an effective electrospinning technique coupled with a self-assembly approach. The resulting 3D-M sensor can perform at room temperature, and displays a high sensitivity to extremely low concentrations of VOCs (ppb level) due to its highly interconnected porous structure, which enable the easy access and diffusion of gas molecules. Furthermore, the sensor also exhibits an ultra-wide sensing range (from 50 ppb up to a saturated vapor), fast response and recovery (less than 2 min), and good reversibility and flexibility (no performance decrease for 1000 bending cycles) for various VOCs (e.g. acetone, methanol and ethanol), demonstrating a great potential for both industrial and biomedical applications.

A flexible VOCs sensor based on a 3D Mxene framework with a high sensing performance

The operating frequency of future communication systems will cover unlicensed millimeter-wave bands as well as existing microwave bands. Large frequency ratio antennas that can be applied to both frequency bands simultaneously and maintain the high isolation between the two channels are difficult to design. This paper presents a new design of dual-band shared-aperture antenna based on the concept of structure reuse. The antenna consists of a patch antenna working at 3.5 GHz and a $12 \times 12$ substrate integrated waveguide (SIW) slot array antenna working at 60 GHz. The frequency ratio of this shared-aperture antenna is 17. In this design, the overall structure of the SIW slot array antenna is employed as the radiator of the patch antenna. With this new scheme, the high aperture reuse efficiency can be achieved. Meanwhile, the millimeter-wave antenna based on the SIW technology has the high-pass nature to reject the lower frequency signal. A compact microstrip resonant cell that acts as a low-pass filter is connected in series on the feedline of the microwave antenna to suppress the upper frequency signal. Thus, the channel isolation between the patch and the SIW slot array antennas can be more than 130 dB at 3.5 GHz and 65 dB at 60 GHz.

A Dual-Band Shared-Aperture Antenna With Large Frequency Ratio, High Aperture Reuse Efficiency, and High Channel Isolation

The utilization of novel comb copolymer phthalocyanine (Pc) thin films as sensitive layers for microwave gas sensors at room temperature under exposure to various volatile organic compounds are presented. The microwave gas sensors are based on an interdigital capacitor fabricated in a microstrip line technique with adequate layers and dimensions. The developed sensors were tested for acetone, ethanol and methanol in the range of 0–200 ppm with special emphasis to the range of 0–25 ppm. The presented sensors will be used as a part of a microsystem for exhaled breath analysis, i.e. diabetes biomarkers detection. All the measurements are carried out at room temperature. The obtained results confirmed the possibility of utilization the microwave Pc-based sensors for exhaled acetone measurements.

Microwave-based sensors with phthalocyanine films for acetone, ethanol and methanol detection

A novel realization of a broadband $8 \times 8$ Butler matrix having phase progressions 0°, ±45°, ±90°, ±135°, and 180° has been proposed. The presented network is composed of coupled-line 3-dB/90° directional couplers and Schiffman phase shifters that ensure its broadband amplitude and phase characteristics. The proposed solution allows for a fully planar realization without any interlayer connections, which has been achieved by both rearrangement of the matrix layout and realization of the selected crossovers as tandem connections of quadrature directional couplers. The proposed concept has been verified experimentally by the design of a Butler matrix operating within 2.5–3.5 GHz and applied in a multibeam antenna array with broadside beam.

Broadband Integrated $8 \times 8$ Butler Matrix Utilizing Quadrature Couplers and Schiffman Phase Shifters for Multibeam Antennas With Broadside Beam

A novel concept of a feeding network of a microstrip antenna array composed of series-fed linear subarrays has been shown. The proposed feeding network utilizes a concept of a slot coupler, in which two microstrip lines are coupled through a slot in a common ground plane. As it has been shown, such a slot coupler provides equal-amplitude and out-of-phase output signals and, therefore, can be used for appropriate feeding (at the center) of a single linear antenna subarray that utilizes “through-element” series-feeding technique. The proposed concept of a slot coupler has been used for the design of an 8 × 8 antenna array, in which all 8 × 1 linear subarrays are series-fed, whereas all 8 linear subarrays are fed by a parallel feeding network.

Microstrip Antenna Arrays Fed by a Series-Parallel Slot-Coupled Feeding Network

Design of broadband rat-race couplers with the use of a shorted coupled-line section and impedance transformers has been comprehensively investigated. A broadband rat-race coupler utilizing a shorted coupled-line section and two shorted quarter-wave long transmission lines has been modified allowing for achieving ideal isolations between two pairs of respective ports. Also it has been shown that the bandwidth of such couplers can be increased when multisection impedance transformers are applied, and that the Darlington synthesis procedure can be used for calculation of transmission-line impedances. A tabular data for rat-race couplers with up to four-section impedance transformers is given. The theoretical analysis has been verified by measurements of the manufactured broadband rat-race coupler operating within 0.8 to 2.8 GHz frequency range.

Broadband Rat-Race Couplers With Coupled-Line Section and Impedance Transformers

In this paper, we propose a novel low-cost microwave vector system dedicated for monitoring the properties of liquid samples. The system is composed of the differentially fed coupled-line sensor and five-port correlator allowing for measurement of both magnitude and phase of a signal dependent on material under test. An exemplary microwave vector system has been designed to operate at the frequency $f_{{0}} = \text{2.4}\, \text{GHz}$ , manufactured and experimentally verified. The measurement results have proven the increased sensitivity of the proposed sensor on the dielectric materials in comparison to the methods described in the literature. Moreover, the proposed sensor has been utilized for measurements of several milk samples with various fat content, and the obtained results prove the industrial application of the presented approach.

Krzysztof Wincza

Papers

Microwave-based sensors with phthalocyanine films for acetone, ethanol and methanol detection

Broadband Integrated $8 \times 8$ Butler Matrix Utilizing Quadrature Couplers and Schiffman Phase Shifters for Multibeam Antennas With Broadside Beam

Microstrip Antenna Arrays Fed by a Series-Parallel Slot-Coupled Feeding Network

Broadband Rat-Race Couplers With Coupled-Line Section and Impedance Transformers

Low-Cost Microwave Vector System for Liquid Properties Monitoring