Gap Waveguide Research Articles

Millimeter-Wave Fully Integrated Dielectric Resonator Antenna and Its Multi-Beam Application

To address the issues of the inconvenient fabrication and integration for millimeter-wave (MMW) dielectric resonator antennas (DRAs), a new configuration is proposed. First, a dielectric resonator with artificial electromagnetic boundaries is implemented by introducing the electromagnetic band-gap structure along the four side-wall boundaries of a certain dielectric region on a printed circuit board. The electromagnetic bandgap (EBG) structure is constructed using a printed array of periodic upside-down mushroom-type unit cells. The resonant-mode analysis reveals that the proposed DR can support conventional dielectric resonator modes and dense dielectric patch (DDP) cavity modes simultaneously. To excite the DR, a substrate-integrated gap waveguide transmission line is embedded in the proposed structure for implementing a fully integrated DRA. For demonstration, a fully integrated dielectric resonator antenna (FIDRA) operating at 31 GHz is designed. Simulated results show that the antenna offers an 11.5% −10 dB impedance bandwidth (29.6 to 33.2 GHz), in which a peak gain of 7.85 dBi is obtained. As an extension, a multi-beam antenna array composed of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \times 4$ </tex-math></inline-formula> FIDRA antenna array and a SIGW <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 4$ </tex-math></inline-formula> Butler matrix is designed and fabricated. The experimental results verified the effectiveness of the proposed configuration in integrating the DRA and feeding network.

A Broadband Low-Profile Monopulse Comparator for Dual-Circularly Polarized Feeder

This article proposes a scheme to design a broadband low-profile monopulse comparator for the dual-circularly polarized feeder. For obtaining a compact and easily integrated structure, a monopulse comparator with a ring-shaped symmetrical planner topology is proposed by using the 3 dB coupler and the phase shifter based on the groove gap waveguide (GGW). Then, in order to achieve the equal-amplitude distribution in a broad bandwidth, the asymmetrical coupling structure and the novel dispersion-matched transition are proposed to improve the directivity of a 3 dB coupler. Moreover, a ridge waveguide with periodic grooves featuring stable dispersion change is adopted to design the phase shifter, which contributes to obtain an accurate phase control in the broad frequency band. To validate experimentally the broadband performance, a dual-circularly polarized four-horn feeder with two identical monopulse comparators is designed and fabricated. The results show that the symmetrical radiation patterns with 32 dB null-depth can be obtained from 27 to 31 GHz. The monopulse comparator characterizes broad bandwidth, low loss, and a compact size, which provides a monopulse comparator with accurate amplitude/phase control for the research of the monopulse antenna.

Magnetoelectric Dipole Antennas Loaded With Meta-Lens for 5G MIMO Pattern Diversity Applications

This communication presents a unique design of a dual-polarized wideband passive beam-switching antenna at millimeter-wave (mm-wave) bands for multiple-input–multiple-output (MIMO) pattern diversity applications, which exhibits low correlation between the ports and a broad tilt bandwidth (BW). A magnetoelectric (ME) dipole fed by a printed ridge gap waveguide (PRGW) as a quasi-TE source is considered as the elementary antenna in the Ka-band. To achieve beam deflection in each quadrant, a four-port MIMO prototype consisting of four ME-dipoles, positioned perpendicular to each other, is integrated with a meta-lens that consists of three layers of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12\times12$ </tex-math></inline-formula> dual-polarized split-ring resonators (SRRs) offset from the center of each antenna. The beamforming structure is able to generate four fixed beams, one in each quadrant at an elevation angle of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 40^{\circ }$ </tex-math></inline-formula> with respect to the broadside direction by exciting each port sequentially, while the other ports are terminated. Moreover, the proposed orthogonal structure contributes to low correlation between the four ports, while achieving dual-polarization, which highlights the suitability of the antenna for 5G mm-wave applications. The measured results from a fabricated prototype demonstrate a −10 dB impedance BW of 40% over 24–36 GHz, tilting BW of 32.2%, and a peak gain of 13.4 dBi at 29 GHz, while an isolation better than 30 dB is achieved over the whole frequency band. Moreover, a measured radiation efficiency in excess of 85% is obtained, due to the use of the low-loss PRGW feedlines.

High-Gain 100 GHz Antenna Array Based on Mixed PCB and Machining Technique

A W-band 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 slot-enhanced antenna array with high gain and high aperture efficiency is proposed based on the mixed printed circuit board (PCB) and machining technique. The antenna array consists of 16 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 antenna subarrays. The substrate-integrated waveguide (SIW) cavity is used to feed the antenna subarray, where electromagnetic fields distribute in the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">220</sub> mode. The SIW cavity is fabricated by the PCB technology for low cost, low profile, and lightweight. To reduce the loss of the feeding network, a constant-amplitude in- phase power divider based on ridge gap waveguide (RGW) is adopted to feed the SIW subarray using the machining technique. Besides, the standard WR-10 waveguide to the RGW transition structure is designed for measurement. The entire antenna array is integrated and packaged in a metal box. The measured results show that the impedance bandwidth of the antenna array is 97.8–107 GHz with a reflection coefficient lower than −10 dB. Within the impedance bandwidth, the antenna array gain is higher than 24.0 dBi, and the peak gain is 26.5 dBi. Moreover, an aperture efficiency of the antenna is larger than 75%.

Fully Metallic Glide-Symmetric Leaky-Wave Antenna at Kₐ-Band With Lens-Augmented Scanning

A fully metallic leaky-wave antenna (LWA) with enhanced scanning rate is presented. The leaky waveguide is implemented in groove gap waveguide technology and is periodically loaded to produce backward radiation. Furthermore, glide-symmetric pins are placed inside the leaky waveguide to increase the dispersion. A parallel-plate waveguide metasurface prism lens is used to disperse the backward radiation and increase the scanning rate of the LWA. The designed antenna can steer the radiation from −26° to 26° from 27 to 35 GHz, and an average total efficiency of 74% is achieved. A prototype of the designed antenna is manufactured, and measurements corroborate the simulated results. The proposed concept is applicable to other frequency-scanning antennas and can be used to increase the scanning rate in radar and imaging systems.

X-Band In-Line Coaxial-to-Groove Gap Waveguide Transition

A coaxial-to-groove gap waveguide transition is proposed for the first time, addressing the lack of similar designs in the state-of-the-art literature. An in-line configuration is adopted in case of stringent space requirements in groove gap waveguide systems. This device has no dielectric and makes use of a waveguide multi-step ridged section connected to the inner conductor of a coaxial line. Three versions are presented, covering progressively wider bandwidths depending on the number of employed steps. The three configurations achieve 20-dB return loss fractional bandwidths of 2.63%, 16.79%, and 38.08%, and 30-dB return loss fractional bandwidths of 0.84%, 10.63%, and 33.49%, with a simulated insertion loss always better than 0.05 dB when a realistic metal conductivity of 2 × 10 7 S/m is assumed. A tolerance analysis on the most critical geometrical parameters is provided to assess the mechanical feasibility, preserving a remarkable performance at X band.

Peak Power Handling Capability in Groove Gap Waveguide Filters Based on Horizontally Polarized Resonators and Enhancement Solutions

This letter studies the peak power handling capability (PPHC) in groove gap waveguide filters based on horizontally polarized resonators. Moreover, a modification of the resonant cavity is proposed, where the central pins of the original structure are replaced by a rounded metal block. As a result of this change, the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> -like mode can still be excited, but the maximum electric field strength is shifted to the center of the cavity, which leads to a higher PPHC. The main advantages of the original structure are maintained, and greater robustness in the manufacturing process is achieved. Next, some guidelines for the design of the coupling windows and the dimensions of the blocks are shown to minimize the electric field strength and, consequently, maximize the PPHC. Finally, two third-order bandpass filters (with pins and with blocks) centered at 16 GHz have been manufactured and tested in a measurement campaign, where a PPHC enhancement of 8.7 dB at high pressures is achieved for the novel solution presented in this work.

Novel Hybrid Electric/Magnetic Bias Concept for Tunable Liquid Crystal Based Filter

This paper presents a novel hybrid bias concept for liquid crystal (LC) filter by using simultaneously electric and magnetic bias fields. It enables continuous tuning with a simplified electrode design, decreased number of electrodes and reduced bias voltage. Furthermore, the tuning efficiency is increased, since the homogeneous bias fields enable a full exploitation of the LC's anisotropy. To demonstrate this concept, a novel reconfigurable gap waveguide two-pole bandpass filter with tunable center frequency and coupling elements is designed at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$30 \,\mathrm{GHz}$</tex-math></inline-formula> . Liquid crystal technology is applied as tunable material, whereby tunability of the center frequency and coupling elements is obtained by controlling the LC's effective permittivity. The presented filter's center frequency can be tuned from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$28.88 \,\mathrm{GHz}\,\mathrm{to}\, 29.88 \,\mathrm{GHz}$</tex-math></inline-formula> with a maximum bias voltage of 100 V, with a return loss of 20 dB and low insertion loss of only 1.65 to 1.95 dB.

Single Layer Dual Circularly Polarized Antenna Array Based on Ridge Gap Waveguide for 77 GHz Automotive Radar

A single layer 77 GHz dual circularly polarized (CP) antenna array is proposed based on ridge gap waveguides (RGWs) technology. The antenna consists of eight U-shaped slots, fed by two feeding networks for generation of dual CP. The proposed antenna array has been fabricated and measured. The experimental results show good agreement with the simulations. The axial ratio is below 2 dB, and the return loss and port isolation are better than 13 and 18.6 dB over 76–81 GHz, respectively. The measured gain for the integrated array is 14.8 dBi at the center frequency of 78.5 GHz. With integration of feeding networks and the radiating elements in a single layer, this antenna has potential to be used in automotive radars.

Wideband mm-wave high-gain multibeam antenna array fed by 4 × 4 groove gap waveguide butler matrix with modified crossover

This paper presents a wideband millimeter wave (mm-Wave) high-gain multibeam antenna array fed by Butler Matrix (BM) based on groove gap waveguide (GGW) technology. First, the components of 4 × 4 GGW BM have been designed and analyzed, especially the proposed modified crossover, which greatly improves the performance of BM as feeding network. Then a 2 × 2-element subarray with three layers has been proposed, combined with the 4 × 4 GGW BM to form a 1 × 4 broadside antenna array. Finally, the prototype of high-gain wideband four-beam antenna array has been manufactured and measured. The measured results verify the superior performance of the multibeam antenna array between 26.3-29.7 GHz. The return loss (RL) can reach 15 dB and isolation between ports is also less than 15 dB, and the measured maximum gain of radiation patterns and the maximum radiation efficiency can also reach 19.05 dBi and 86.8%, respectively. The measured results have a good agreement with the simulated results.

Bandstop filtering for integrated substrate gap waveguide high‐gain and wideband slot antenna for 5G

Slot antenna based on microstrip line and waveguide is a popular design for future 5G antennas. To improve performance of slot antenna, a high-gain wideband slot antenna based on integrated substrate gap waveguide (ISGW) is presented, in which a stepped impedance feeding line is adopted to broaden bandwidth, and ISGW is used to increase gain. First, the transmission characteristics and the effective relative permittivity of ISGW is discussed and calculated, with operation band from 25 to 45 GHz. The antenna has a passband of 24.9–38.1 GHz, that is, almost Ka band, and an average gain of ~9 dB. Further, bandstop filtering (BSF) characteristic is introduced in the above wideband antenna to achieve filtering antennas for 5G millimeter-wave (mm-wave) bands of 24.75–27.5 GHz for China, and 26.5–29.5, 27.5–28.5, and 37–40 GHz for n257, n258, and n260 of 5G new-radio (NR). The BSF is obtained by etching U-shaped CSRR on feeding patch of the antenna. First- and second-order BSF are achieved by etching first and second U-shaped CSRR on the antenna feeding patch, respectively, thus correspondingly one bandstop resonance at 34.6 GHz, and two bandstop resonances at both 32.5 and 34 GHz are obtained. It is found that the passband performance is unchanged, but the stopband radiation drops sharply at the boresight direction. The three antennas (wideband, and first- and second-order BSF antennas) proposed are all fabricated and verified.

High-Isolation Power Divider Based on Ridge Gap Waveguide for Broadband Millimeter-Wave Applications

In this article, a high-isolation power divider with ultrawideband characteristics for simultaneous operation in two adjacent bands is proposed. The power divider is developed based on a four-port coplanar Magic-T. The difference port of the Magic-T consists of a double-ridge gap waveguide (RGW) that supports quasi-TEM mode transmission, which provides the benefit of its broadband characteristics and allows for facilitated assembly. In addition, an inline microstrip line (MSL) containing a probe is inserted into the opposite side of the difference port to form the sum port. This basic configuration has actually achieved high isolation between the output arms and low return loss at each port, and however, its isolation bandwidth is limited by the narrowband matching of the sum port. To overcome this difficulty, a three-port microstrip T-junction is connected in series to the sum port of the Magic-T, resulting in a five-port 3-dB power divider with a wide isolation bandwidth. The process of considering this solution is analyzed and explained in detail in this article and the corresponding simulations and experimental verifications are performed. According to the obtained results, the proposed power divider has excellent overall performance, in particular low loss, ultrawideband, high isolation, and good amplitude/phase consistency.

Ka-Band Integrated Multilayer Pyramidal Horn Antenna Excited by Substrate-Integrated Gap Waveguide

This work proposed a solution of structures built from stacking several dielectric substrates with the conducting cladding, aiming for electrical contact between them [perfect electric conductor (PEC)–PEC]. At mm-wave frequencies, surface roughness or imperfect flat surfaces present possible gaps that cause severe unexpected leakage. Many engineers overlooked this problem. To prevent this leakage, we propose transforming one of the PEC–PEC surfaces into artificial magnetic conductors (AMCs), creating a PEC–AMC layer that suppresses any leakage even with no contact between the surfaces where the gap is less than a quarter wavelength. A wideband multilayer pyramidal horn antenna using substrate-integrated gap waveguide (SIGW) technology is proposed as an example that highlights the proposed solution. In each layer of the horn, the opening is surrounded by periodic cells to suppress leakage and surface waves. In addition, the upper surface surrounding the horn’s opening is surrounded by EBG mushroom cells to act as a soft surface that suppresses the surface waves and reduces the edge diffraction, and, in turn, improves the radiation characteristics of the horn. The horn achieved a gain of 11.5 dBi and 20.5% bandwidth (28.5–35 GHz). The simulated and measured results show excellent agreement with each other.

A TE₀₁-Mode Groove-Gap-Waveguide-Based Wideband Fixed-Frequency Beam-Scanning Leaky-Wave Antenna for Millimeter-Wave Applications

A wideband fixed-frequency beam-scanning leaky-wave antenna (LWA) operating at the millimeter-waveband is presented in this article. A groove gap waveguide (GGW) supporting base is introduced as a transmission structure of the antenna with a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> -mode excitation, and two rows of longitudinal slots etched on top of the superstrate act as the radiating structures. Two rows of PIN diodes are soldered below the longitudinal slots, so that the long slots can be cut into a group of short slots. By controlling the PIN diodes, the working states of the slots can be switched between “ON” and “OFF.” Then, by selecting proper activation states, the fixed-frequency beam scanning can be obtained. In addition, the developed antenna is verified in practical fabrication and experiment. The experimental results have good agreements with that in simulations. The measured peak gain reaches at 16.8 dBi, and the beam-scanning range more than 70° from 23 to 29 GHz is realized.

High-Gain and Low-Loss Dual-Polarized Antenna Array With Reduced Sidelobe Level Based on Gap Waveguide at 28 GHz

In this letter, a 16×16-element dual-polarized antenna array with a reduced sidelobe level is proposed at 28 GHz for fifth-generation (5G) communication systems. The dual linear polarization operation is carried out through cross-shaped waveguide slots and multilayer feeding networks. Low-loss gap waveguide technology and Taylor distribution are applied in the feeding networks. A ridge unequal power divider with flexible power ratio and phase difference is devised and applied in the gap waveguide feeding network to reduce the complexity of unequal power structural design. A prototype of the proposed dual-polarized antenna array is manufactured by milling technology. Measured results show that the realized gains are higher than 28 dBi over the operating frequency band of 27.4–28.6 GHz. Moreover, the sidelobe level is lower than −18.5 dB for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -direction polarization and −19.5 dB for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -direction polarization.

Novel Band Gap Waveguide for Low-Loss and Dual Band Applications

In this article, the band gap waveguide (BGW) is proposed and studied. The BGW is formed by a groove gap waveguide (GGW) and a rectangular waveguide, and the former is totally integrated inside the latter. The units of the GGW form a stopband to confine the electromagnetic (EM) wave inside the groove of GGW and propagate the quasi-TE₁₀ mode at high frequencies. When operating at low frequencies, the units cannot block EM waves, and the latter can pass through them and propagate in the entire rectangular waveguide region as a TE₁₀-like mode. Besides, the characteristics, propagation modes, and designing methods of the BGW are illustrated and analyzed. Two transition structures corresponding to high- and low-frequency operations are then designed to verify the transmission performance of the BGW, as well as its integration capability with other passive components. A back-to-back transition prototype has been fabricated to evaluate its performance. The measured results are in great agreement with the simulated results. According to the experimental results, good impedance matchings and low insertion losses are achieved from 6.8 to 8.05 GHz for low frequency and from 71 to 86 GHz for high frequency, respectively.

Wideband Open-Ended Ridge Gap Waveguide Antenna Elements for 1-D and 2-D Wide-Angle Scanning Phased Arrays at 100 GHz

A new antenna element type based on the open-ended ridge gap waveguide (RGW) is proposed for phased array applications. This element type is of a particular interest at high millimeter-wave frequencies ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq$</tex-math></inline-formula> 100 GHz) owing to a contactless design alleviating active beam-steering electronic integration. The key challenge addressed here is a realization of a wide fractional bandwidth and a wide scan range with high radiation efficiency. We demonstrate a relatively simple wideband impedance matching network comprised of an aperture stepped ridge segment and a single-pin RGW section. Furthermore, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$E$</tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$H$</tex-math></inline-formula> -plane grooves are added that effectively suppress antenna elements’ mutual coupling. Results demonstrate a wide-angle beam steering ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq \text{50}^\circ$</tex-math></inline-formula> ) over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq {20\%}$</tex-math></inline-formula> fractional bandwidth at the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$W$</tex-math></inline-formula> -band with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq {89\%}$</tex-math></inline-formula> radiation efficiency that significantly outperforms the existing solutions at these frequencies. An experimental prototype of a 1 × 19 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$W$</tex-math></inline-formula> -band array validates the proposed design concept through the embedded element pattern measurements.

Wideband Circularly Polarized Septum Antenna Array With Ridge Gap Waveguide Feeding Network for Wireless Application

A full corporate feeding <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 circularly polarized (CP) planar antenna array using septum antenna elements for millimeter-wave (mmWave) frequency band applications is reported. Widebands for both the impedance and axial ratio (AR) bandwidths and high efficiency are guaranteed by the antenna array attributed to septum elements and feeding network based on the metal ridge gap waveguide (RGW). For the analyzing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> 2 sub-array containing a feeding structure, simulated results show that the impedance bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert &lt; -10$ </tex-math></inline-formula> dB) of 31.4%, AR bandwidth (AR < 3 dB) of 32.6%, and maximum gain of 29.2 dBic are realized. For the practical fabricated 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 antenna array prototype, measured results reveal that its impedance bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert &lt; -10$ </tex-math></inline-formula> dB) is 31.5%, overlap AR bandwidth (AR < 3 dB) is 33.1%, and maximum measured gain value is 28.4 dBic with a maximum aperture efficiency of 85%. With such performances, the proposed CP antenna array would be a promising candidate for mmWave communication systems.

Study of the Multipactor Effect in Groove Gap Waveguide Technology

This article presents a theoretical and experimental comparative study of the different multipactor threshold values obtained in the rectangular waveguide (RW) and the groove gap waveguide (GGW). To this end, the multipactor effect has been first analyzed in an RW with a recently developed theoretical model. Then, the multipactor breakdown power levels in the equivalent GGW have been predicted with an accurate electron tracking code, showing a significant increment compared with the RW case. In order to validate these results, two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -plane WR-90 RW transformers have been designed with a full-wave electromagnetic simulation tool. The central sections of these transformers have been implemented in RW and GGW, respectively, and their multipactor breakdown power levels have also been predicted. The two designed transformers have been fabricated in aluminum and then measured in terms of electrical response (scattering parameters) and RF multipactor effect (power threshold values). All the experimental results agree well with the set of simulated data, thus fully validating the performed study.

Novel Technique of Gap Waveguide Cavity Resonator Sensor with High Resolution for Liquid Detection

This article proposes a novel microfluidic sensor designed with a highly accurate Q-factor for liquid detection. The proposed sensor is developed and implemented with a gap waveguide cavity resonator (GWCR) approach. The GWCR approach is formed from the two metallic plates denoted as upper and lower plates. These plates are separated by an array of metallic pins attached to the lower plate, leading to high electric field concentration. A microfluidic channel is created at the midpoint of each plate to place the holder of liquid under test (LUT). The GWCR provides a high electric field, which increases Q-factor and is shown to exhibit a significant improvement in sensitivity and linearity. To characterise and evaluate the dielectric properties of the fluid, the LUT is placed inside a hairlike glass, which passes through the microfluidic channels. The LUT perturbs the electric field distribution inside the GWCR, known as the perturbation principle. The relation between the LUT and the electric field changes the electric field behaviours in terms of resonant frequency, Q-factor, and transmission coefficient. The analysis of these changes in the electric field behaviours leads to identifying the dielectric properties of the LUT. The anonymous dielectric characteristics of LUT, permittivity, and loss tangent formulas are derived utilising the polynomial fitting approach. The measurement outcomes reveal that the stated sensor can measure the permittivity and loss tangent for both LUT samples, such as ethanol and methanol, at 6.1 GHz and 23.4°C.