Double-ridged Waveguide Research Articles

Broadband complex permittivity measurements of nematic liquid crystals based on cavity perturbation method

ABSTRACTLiquid crystals (LCs) have already been widely used in reconfigurable microwave devices as an excellent phase change material for their electric tunable dielectric properties. An accurate value of complex permittivity on a given LCs is the most important parameter on designing microwave devices. In this paper, a novel method is proposed to realise a broadband permittivity measurement. On the basis of the theory of perturbation, it consisted of a double-ridge waveguide cavity and the given vector network analyser. In order to have a broadband measuring range and uniformly distribute operating frequency points, multi-mode double-ridged waveguide cavity is introduced to resonate at 11 operating modes (TE,n = 1,2, …, 11). Meanwhile, to suppress the undesired-modes effectively, several non-radiating slots are applied to keep the operating modes easily recognisable, so as to complete the broadband complex permittivity measurement in 5–40 GHz using only one cavity. Besides, another feature of this method is that the total-required sample is only about 0.02 mL because the sample loading area in the double-ridged waveguide cavity is perfectly designed very small. Therefore, several NLCs are measured, including a certain commercial mixture MM (Merck), and M1~ M7, as developed LC mixtures with large dielectric anisotropy and low microwave losses.

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A design of a double-ridge waveguide narrow-wall multiple-aperture coupler suitable for conventional machining is demonstrated. Different options for coupling levels up to 3 dB, all working over V-band (45–75 GHz) and W-band (75–110 GHz), are given. The narrow-wall coupler is designed in a custom-made transmission line, double-ridge waveguide, denoted by WRD45110. To experimentally validate the proposed design method and the performance of a selected component, a 15 ± 3 dB narrow-wall coupler is fabricated using computer numerical control machining in three individual pieces; the top section, the middle wall, and the bottom section. Two different H-plane cut assembly techniques utilizing male–female parts and pin walls are examined. The obtained results show a good agreement between simulations and measurements for both methods, therefore proving these components are now feasible.

Adaptive Cross Approximation Algorithm Accelerated Inverse Equivalent Current Method for Near-Field Antenna Measurement

The adaptive cross approximation (ACA) algorithm is adopted to efficiently compute the discretized forward integral equation operator in the near-field (NF)–far-field transformation process by utilizing the rank-deficient nature of the well-separated interactions between the equivalent sources and the measurement probes. The threshold of the ACA compression is carefully investigated to achieve results that are more accurate. Besides, an octree-based geometrical-adaptive grouping scheme is proposed where two different grouping strategies are designed for planar and spherical measurements, respectively. To further increase the accuracy and efficiency of the computation, the leaf-level cube size for the sources and probes are also flexibly decided, since the corresponding two spatial distribution densities vary significantly. The effectiveness of the proposed method is validated with synthetically generated NF data and with spherical measurements of a double-ridged waveguide antenna.

Design of Simple and Double Ridge Waveguide T-Coupler for Space Domain

The T-Coupler or the magic tee (or magic T or hybrid tee) is a hybrid or 3 dB coupler used in microwave systems. It is an alternative to the rat-race coupler. In contrast to the rat-race, the three-dimensional structure of the magic tee makes it less readily constructed in planar technologies such as micro strip or strip line. The magic tee was originally developed in World War II, and first published by W. A. Tyrell of Bell Labs in a 1947 IRE paper. Robert L. Kyhl and Bob Dicke independently created magic tees around the same time. This paper illustrates simple and double ridge waveguide T-coupler. The relationships between the scattering variables in this sort of network are fixed by the unitary condition. Such a network has the properties that it is a matched device with one adjacent port decoupled from any incident port. The object of this paper is to present some results of simulation on the coupling and directivity of double ridge cross-waveguide couplers in a field ridge waveguide. This results are obtain by Ansoft HFSS using the Finite Element Method (FEM) calculations and the Genetic Algorithms method, and which show good performance.

Vertical Coaxial-to-Ridge Waveguide Transitions for Ridge and Ridge Gap Waveguides With 4:1 Bandwidth

An ultra-wideband vertical coaxial-to-single-ridge waveguide transition is designed to cover Ku-, K-, and Ka-bands simultaneously. The simulated and measured back-to-back transitions have achieved better than 15-dB return loss within 12.8–40 GHz. The transition can also be a direct transition to the ridge gap waveguide (RGW). In addition, a similar concept is used to design a wideband coaxial-to-double-ridge waveguide transition to feed symmetric and asymmetric double ridge waveguide on a bandwidth ratio of more than 4:1. These transitions will be used to feed broadband ridge and RGW power splitters.

A 18–40 GHz Substrate Integrated Waveguide H-Plane Horn Antenna

A 18-40 GHz wideband substrate integrated waveguide (SIW) H-plane horn antenna is proposed for applications on both the K- and Ka-bands. By employing a grating transition in front of the horn aperture, the impedance bandwidth (IBW) of the proposed antenna is broadened considerably. A broadband double-ridge waveguide (DRW)-to-SIW transition is also developed as the feeding structure for the proposed SIW H-plane horn antenna. The DRW is adopted to support a wider IBW as compared to that of a rectangular waveguide. A prototype of the proposed antenna is experimentally verified. The measured results show that the IBW for |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | ≤ -10 dB ranges from 18 GHz to more than 40 GHz, covering the entire Kand Ka-bands. The measured gain varies from 7.52 to 15.37 dBi with an average gain of 11.58 dBi. In addition, the endfire radiation patterns are observed and maintained within the IBW.

3-D Printed Antenna for Snowpack Monitoring

Microwave radars represent a viable solution to perform rapid and nondestructive snowpack analyses. Depending on the working frequency, they are required to provide a suitable compromise between the penetration depth and the spatial resolution. For these reasons, antennas able to cover relatively large fractional bandwidths at a few gigahertz are fundamental, while minimizing the antenna mass and volume to do not jeopardize the portability often required to these systems. This letter presents the development and the experimental results of a novel antenna realized by three-dimensional printing, based on a double-ridge waveguide configuration and on the use of different infill percentages. The operation bandwidth is from 2.3 to 6 GHz, with a gain at the central frequency of around 5 dBi. The antenna is fabricated using low-loss filaments, with a relatively high dielectric constant (4.5); thus, maintaining the mass in the order of 100 g, with an encumbrance of 5.16 × 2.40 × 6.78 cm 3.

Linear Array of Center Line Longitudinal Slots Excited by Double Ridge Waveguides

Linear Array of Center Line Longitudinal Slots Excited by Double Ridge Waveguides

Robust Design of 3D-Printed 6–18 GHz Double-Ridged TEM Horn Antenna

A robust design of a 3D-printed 6–18 GHz double-ridged TEM horn antenna is proposed in this paper. The designed TEM horn antenna has two parts: an adaptor and a horn aperture. The adaptor is realized using a double-ridged waveguide to extend the operating bandwidth of the dominant mode (TE10 mode). Meanwhile, the horn aperture section is implemented in an exponentially tapered configuration to match the impedance of the double-ridged waveguide with the intrinsic impedance. The performance of the initially designed antenna shows that the reflection coefficient and gain levels are less than −13 dB and greater than 5.5 dBi within the 6–18 GHz band, respectively. The initial design was well done, but the noise factors that may occur during the manufacturing process were not taken into account. To design an antenna considering these noise factors, the parameters of the initial design are optimized by a novel robust design method also proposed in this paper. The robustness of the antenna optimized by the proposed method is approximately 12.4% higher than that of the initial antenna. The validity of the proposed method was tested by fabricating the antenna. A prototype of the optimized antenna with the proposed robust design method is fabricated using a 3D printer with a stereolithographic apparatus attached, and the surface of the frame is covered by a nano-silver plating. The measured results of the fabricated antenna are in good agreement with the simulation results over the operating band. The measured −10 dB reflection coefficient bandwidth of the antenna can cover 6–18 GHz. In addition, the measured gain ranges from 4.42 to 10.75 dBi within the 6–18 GHz band.

Novel ultra-wideband test fixture and method for attenuation of the attenuator-coated dielectric support rod in a helical slow-wave structure.

In order to measure the attenuation along the dielectric support rod in a helical slow-wave structure, a new test fixture and the corresponding test method are introduced. The proposed fixture is a transmission line that consists of three parts: angle gradient transitions, hyperbolical tapered lines, and parallel strips with a sample hole in the middle. The hyperbolical tapered lines on the top and bottom sides of the substrate were designed to realize an approximate Klopfenstein tapered line. The parallel strips provide a relatively reasonable electric field for measuring the attenuation of the dielectric support rod. Meanwhile, two modified metal blocks on both sides of each connector are designed to suppress unwanted radiation. The test fixture works in the ultra-wideband range from 7 GHz to 40 GHz, and it exhibits an insertion loss of less than 3 dB and a return loss of more than 10 dB over the whole frequency range. The sample hole was regarded as the mutually coupled parallel strip pairs (a four-port network), and the odd-even mode method was used to analyze the scattering parameters of the single parallel strip. The dielectric support rod deposited by the resistive thin-film was measured with the experimental test setup developed in this paper. Compared with the method of the double ridge waveguide, the measured results present a great agreement with the actual distribution of the attenuation in the length ranges from 12 mm to 15 mm, 25 mm to 27 mm, and 46 mm to 52 mm, and the differences in other length ranges are explained.

Double-Ridged Waveguide Orthomode Transducer (OMT) for the 67–116-GHz Band

A high-performance low-loss high-reflection-loss compact double-ridged waveguide orthomode transducer (OMT) for the 67–116 GHz band has been designed, fabricated, and tested. The focus in the design has been to achieve the best possible performance while keeping the design compact and fabrication as simple as possible. The designed OMT is based on a double-ridged waveguide Boifot junction followed by a main arm with an E-plane bend, and two side arms which are combined into a Y-junction. Wideband performance has been achieved by careful control of the waveguide width at the waveguide junction, and by the use of a variable width septum. The design is very compact and can be fabricated by conventional computer numerical control (CNC) milling techniques in two split blocks. The output waveguides are standard WR-10 rectangular waveguides. Prototype OMTs have been fabricated and tested with good agreement with simulations. The measured insertion loss is around 0.15 dB, the reflection loss is better than 23 dB, and isolation and cross-polarization are lower than – 45 dB at all frequencies. This OMT is intended to be used in cryogenic low-noise receivers for radio astronomy. To the extent of our knowledge, this is the best reported performance for an OMT over a 55% fractional bandwidth at W-band frequencies.

Hybrid Types of Waves Propagating in Double Ridged Waveguide with Piecewise-Layer Dielectric Filling

The algorithm for calculating electrodynamic characteristics of hybrid types of waves propagating in double ridged waveguide with piecewise-layered dielectric filling is presented. The double ridged waveguide structure with dielectric plates installed between the ridges, and with dielectric sample sandwiched between the dielectric substrates is consid-ered. The calculations are carried out using the method of partial regions. The presented algorithm takes into account the electromagnetic field components singularities near the dielectric and metal edges of the waveguide. The technique for calculating the electromagnetic energy losses in the double ridged waveguide with a piecewise layered dielectric filling is provided. The classification of hybrid waves is given. The spatial structures of electromagnetic fields and their planar projections (front view, top view, side view) for the first two HEwaves and the first EH-wave are demonstrated. Cutoff fre-quencies and propagation constants of HEand EH-waves are calculated. The results obtained using the described meth-od and numerical approach are compared. Then the results are analyzed.

Compact Full Band OMT Based on Dual-Mode Double-Ridge Waveguide

A nonstandard dual mode, double-ridge waveguide is utilized to design a compact orthomode transducer (OMT). The OMT is terminated with a standard circular waveguide common port and two standard isolated rectangular waveguide ports. The proposed structure exploits a one-fold symmetry to eliminate the coupling to the in-band higher order odd modes within the common port. The proposed concept is utilized to design a full ${K}$ 1-band OMT that is essential for space and mobile applications. Furthermore, the performance of the proposed OMT design is verified through a back-to-back measurement showing an excellent agreement between the full-wave simulations and measurements. Nevertheless, the proposed design achieves a measured matching level of 19 dB for the two modes and isolation level between them beyond 30 dB over the entire band.

Realistic Air-Filled TEM Printed Parallel-Plate Waveguide Based on Ridge Gap Waveguide

A double-ridge and double-sided textured surface waveguide based on the printed ridge gap waveguide (PRGW) is introduced. The structure acts as a parallel-plate waveguide supporting TEM waves, and it is referred to as TEM-PRGW. The TEM-PRGW has lower insertion loss and more confined power around the double ridges in comparison with the single-textured PRGW. The characteristic impedance of the TEM-PRGW is extracted from the conventional parallel-plate impedance expression. The TEM-PRGW is symmetric around the middle horizontal line splitting the gap. The modified unit cells of the periodic structure around the double ridges are also introduced to improve the TEM-PRGW performance in the presence of any discontinuities along the propagating direction, which might excite undesired horizontal polarization. Prototypes of the straight and double bend lines are fabricated based on the modified unit cells to prove the concept and have confidence in the simulation results.

On the Split-Block Realization of Millimeter-Wave Ridge Waveguide Components

A method to reduce RF leakage in split-block fabricated metallic ridged waveguide is presented. By placing a pin wall into the split-block seam, RF leakage and detrimental performance spikes are significantly reduced. Three different split-block double-ridge waveguide components of varying design complexity operating over 18–45-GHz bandwidth are fabricated and measured. It is shown that the addition of the pin wall improves the performance of each component such that results correlate well to simulated models with no split.

Electromagnetic radiation and behavioural response of ticks: an experimental test

Factors associated with the increased usage of electronic devices, wireless technologies and mobile phones nowadays are present in increasing amounts in our environment. All living organisms are constantly affected by electromagnetic radiation which causes serious environmental pollution. The distribution and density of ticks in natural habitats is influenced by a complex of abiotic and biotic factors. Exposure to radio-frequency electromagnetic field (RF-EMF) constitutes a potential cause altering the presence and distribution of ticks in the environment. Our main objective was to determine the affinity of Dermacentor reticulatus ticks towards RF-EMF exposure. Originally designed and constructed radiation-shielded tube (RST) test was used to test the affinity of ticks under controlled laboratory conditions. All test were performed in an electromagnetic compatibility laboratory in an anechoic chamber. Ticks were irradiated using a Double-Ridged Waveguide Horn Antenna to RF-EMF at 900 and 5000MHz, 0MHz was used as control. The RF-EMF exposure to 900MHz induced a higher concentration of ticks on irradiated arm of RST as opposed to the RF-EMF at 5000MHz, which caused an escape of ticks to the shielded arm. This study represents the first experimental evidence of RF-EMF preference in D. reticulatus. The projection of obtained results to the natural environment could help assess the risk of tick borne diseases and could be a tool of preventive medicine.

Bandwidth Investigation on Half-Height Pin in Ridge Gap Waveguide

Gap waveguide is a promising transmission structure, especially for millimeter-wave (mmW) and terahertz applications. It does not require conductive connection between the upper and the lower plates, which makes this technology gain advantages over conventional rectangular waveguides and substrate integrated waveguides in an mmW and terahertz regime. Different fabrication methods for gap waveguides should be employed for different frequency bands applied, such as molding, milling, die forming, electrical discharge machining, microelectromechanical systems, and 3-D printing. Therefore, different pin forms used in gap waveguides are required to match the applied fabrication methods. In this paper, a new pin form, the half-height-pin form, in gap waveguides is proposed for reducing the fabrication cost, and its stopband characteristics are investigated and compared with the previous full-height pins in gap waveguides at the $V$ -band. A device of a double-ridged gap waveguide with two 90° bends for verifying the stopband characteristic analysis of the new pin form has been designed and manufactured. The measured data confirm our analysis and simulations.

Millimeter-Wave Double-Ridge Waveguide and Components

A 45–110-GHz double-ridge waveguide, denoted by WRD45110, is designed, fabricated, and tested. A detailed parametric study is carried out to develop a cross section with in-band attenuation for the straight line below 0.06 dB/cm and group delay below 0.06 ns/cm. Ridges are rounded so that the theoretical peak power handling is above 400 W. For practical characterization, various straight lines are built with the direct metal laser sintering (DMLS) 3-D printing process in aluminum and stainless steel. Precision, repeatability, mechanical strength, and electrical performance are then evaluated. A 90° twist, a 90° E-bend, a 90° H-bend, and an open termination load are also developed, 3-D printed, and measured. Good performance of all lines and components and ability to cascade functional pieces are demonstrated.

Wideband Resistive Sensors for Double-Ridged Waveguides

Two types of resistive sensors with flat frequency response for WRD840 and WRD250 double-ridged waveguides were developed. The first type of sensors is optimized for microwave power measurements inside the waveguide. The second type of sensors is connected to the particular horn antenna and optimized for microwave pulse power density (or electric field strength) measurements in free space. The flat frequency response of the sensors was designed by changing the parameters of the sensing element. Proposed sensors can measure high-power microwave pulses covering frequency ranges 0.84-2.0 GHz and 2.6-7.8 GHz.

Ultra-Wideband Scanning Antenna Array With Rotman Lens

An ultra-wideband (6-18 GHz) phased-array antenna with a beam scanning angle of ±28° is proposed. A step-by-step design procedure consisting of beamforming network (BFN), end-launcher feed adapter, and the radiating element is presented. Microstrip Rotman lens has been designed to act as the BFN, and optimized to achieve minimum phase-error over the whole frequency range. In order to satisfy the condition needed for avoiding grating lobes, as well as achieving a wide radiation bandwidth and a high power handling capability, an E-plane double-ridged horn antenna is used as the radiating element. A novel wideband end-launcher coaxial to double-ridged waveguide transition has also been developed for connecting the BFN to the antenna array. Extensive optimization procedures have been applied to the end-launched adapter together with the antenna to achieve the best return loss over the frequency band of operation. The whole system has been simulated using CST full-wave simulator. An excellent agreement between the measurements of the fabricated system and the simulated results is observed.