Comments on “A Generic Approach for Permittivity Measurement of Dielectric Materials Using a Discontinuity in a Rectangular Waveguide”

Monopole antennas are widely used in communication systems because of features such as pure vertical polarization and omnidirectional radiation patterns in the horizontal plane. Conventionally, monopole antennas are fed through a ground plane by a coaxial probe. Recently, monopole antennas fed by printed transmission lines have attracted increasing attention. However, to the best of our knowledge, monopole antennas are seldom fed by a rectangular waveguide. We consider the problem of this type of feed because of our interest in designing an omnidirectional antenna at millimeter wave bands. At millimeter wave frequencies, rectangular waveguides are preferred to coaxial or microstrip lines because they exhibit very low loss, have a large power handling capacity and other waveguide components are readily available. The paper presents a design for monopole antennas fed by a rectangular waveguide. In order to achieve a good transition from a rectangular waveguide to the monopole antenna, a ridged waveguide section is introduced, and the vertical monopole is attached to the ridge through a circular aperture opened on the upper broad-wall of the rectangular waveguide, which is part of the ground plane. Two examples are provided and experimental tests of one of these antennas shows that the monopole can achieve about 24% bandwidth and 5 dBi gain.

A rigorous approach combining the orthogonal expansion method for modeling cylindrical posts in rectangular waveguides and the extension of the three short plane technique is introduced to obtain the S-matrix for a general coaxial probe in a rectangular waveguide. A cascading procedure is applied to solve the problem of a probe near a waveguide discontinuity and to obtain the response of a probe-excited band pass filter. The computed results are in excellent agreement with the measured results showing the usefulness of this method.

A new measurement technique is presented to determine the complex permittivity of a dielectric material. The dielectric sample is loaded in a short‐circuited rectangular waveguide. The reflection coefficient of the waveguide is measured by Network analyzer and calculated as a function of the complex permittivity using finite difference time domain method (FDTD). The Newton–Raphson method is then used to determine complex permittivity by matching the calculated value with the measured value. A comparison of determined values of the dielectric constant obtained from the Nicholson–Ross technique and the FDTD method is presented. Numerical resultants for complex permittivity of Teflon and Plexiglass measured at the microwave frequencies are presented. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1964–1968, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22611

To meet the packaging requirements of terahertz (THz) communication systems, a microstrip line (MSL) to rectangular waveguide (RWG) transition is proposed in this paper. In the transition, the MSL is connected to the corrugated substrate integrated waveguide (CSIW) by a tapered MSL for quasi-TEM to TE10-like mode conversion on substrate, which requires no via holes or shaped dielectric, and is easy to process in THz bands. Then, the CSIW is straightly connected to the RWG transformer and converted to standard RWG, resulting in a compact structure. The working principle of the proposed transition is analyzed, and the influence of several important parameters on the S-parameters of the transition is discussed. A single transition is designed for the 325–500 GHz operation, the S11 better than −14.5 dB and S21 better than −1.03 dB have been achieved in the entire frequency band.

In this paper, a simple waveguide measurement technique is presented to determine the complex permittivity of a dielectric material. The dielectric sample is loaded in a short-circuited rectangular waveguide. The reflection coefficient of the waveguide is measured by Network analyser and calculated as a function of the complex permittivity using theory of transmissions lines. The Newton Raphson method is then used to determine de complex permittivity by matching the calculated value with the measured value. The results obtained using Newton Raphson are in good agreement with the results obtained by the Nicholson-Ross technique.

In the millimeter wave band hybrid-integrated circuits take the form of waveguide-planar, which combines the advantages of planar technology and waveguides as low-loss systems. This makes it possible to successfully meet the high performance requirements of such devices as bandpass filters, multiplexers, etc. At the same time, elements that provide transitions between various integrated transmission lines and a waveguide become an important part of a complex microwave system, and the requirements for their characteristics - frequency band, losses, dimensions - become a challenge for designers. The article provides both an overview of the most successful designs aimed at solving this problem and a description of the transition topology proposed by the authors. The main attention is paid to the transitions between a rectangular waveguide and a microstrip line - all possible configurations of the joints of these waveguide systems are considered. It is shown that a number of designs make it possible to achieve a return loss at least 15dB in a frequency band, exceeding the operating frequency range of the waveguide with characteristic transition sizes not exceeding (0.2-0.3)λ0. It is proposed to use the results obtained to create efficient connections of the rectangular waveguides themselves with their complex mutual orientation. This solves many problems in the design of hybrid-integrated waveguide-planar microwave circuits, but can be successfully used in the development of purely waveguide systems, when the requirements of dimensions and cost in production are priority. The calculated data obtained in the article are compared with the results of an experimental study.

The scattering properties of the H‐plane waveguide discontinuities such as the cross junction, T‐junction, and right‐angle bend are analyzed taking their symmetry into account. the solutions are synthesized in two new and simple expressions. These solutions are treated rigorously by the mode‐matching method in which each junction section is divided by a circular region and the electro magnetic fields are matched with the scattered waves into waveguide regions at the boundaries. By means of the accurate numerical results obtained in a wide frequency range, the scattering properties of the H‐plane junctions in a standard waveguide and an oversized waveguide are examined in detail. the latter is believed to be useful for an approximnte estimation of the scattering properties of crossing roads in underground shopping centers.

Several RF and microwave radiating devices, such as horn antennas, Fabry–Perot cavity antennas, and aperture-fed focusing devices, are excited through rectangular waveguides. The impedance matching of the overall system (from the waveguide feed to the radiating aperture) is a task of crucial importance that is often addressed by means of brute-force parameter-sweep full-wave analyses or blind optimization algorithms. In both cases, a significant amount of memory and time resources are required. For this purpose, we propose here a simple, yet effective solution, which only requires a single full-wave simulation and a semi-analytical procedure. The former is used to retrieve the antenna input impedance at the end of the waveguide port excitation. The semi-analytical procedure consists in a transmission-line equivalent circuit that models two waveguide discontinuities (namely two capacitive irises) within the waveguide section, whose position and geometric features are finely tuned to obtain a satisfactory impedance matching around the working frequency. The proposed method is shown to be effective in diverse and attractive application-oriented contexts, from the impedance matching of a Fabry–Perot cavity antenna to that of a wireless near-field link between two aperture-fed focusing devices. A remarkable agreement between full-wave simulations and numerical results is found in all cases. Thanks to its versatility, simplicity, and a rather low demand of computational resources, the proposed approach may become an essential tool for the effective design of waveguide-fed antennas.

A two-layer dual-waveguide probe measurement geometry is proposed to nondestructively measure the complex permittivity and permeability of planar materials. The new measurement structure consists of two rectangular waveguides attached to a PEC ∞ange plate that is placed against the material under test, followed by a known material layer backed by a PEC. The purpose for this new measurement geometry is to improve the permittivity results obtained using the existing dual-waveguide probe geometries, namely, the PEC-backed and free-space-backed geometries, by permitting a larger electric fleld into the material under test and increasing the fleld coupling between the two rectangular waveguide apertures. The theoretical development of the technique is presented extending the existing single-layer PEC-backed method to the proposed two-layer dual-waveguide probe method. The new measurement structure is theoretically analyzed by replacing the waveguide apertures with equivalent magnetic currents as stipulated by Love's equivalence theorem. Making use of the magnetic-current-excited two-layer parallel-plate Green's function and enforcing the continuity of the transverse magnetic flelds over the waveguide apertures results in a system of coupled magnetic fleld integral equations. These coupled magnetic fleld integral equations are then solved for the theoretical re∞ection and transmission coe-cients using the Method of Moments. The desired complex permittivity and permeability of the material under test are found by minimizing the root-mean-square difierence between the theoretical and measured re∞ection and transmission coe-cients, i.e., numerical inversion. Last, experimental results utilizing the new two-layer technique are presented for two magnetic

The paper considers the general problem of a waveguide double junction consisting of three dissimilar waveguides coupled together via apertures. An equivalence theorem is utilized to set up an integral equation which is solved by using the method of moments. The method is attractive in that it forms the basis for a common computer code for a wide category of waveguide discontinuities. Numerical results are presented for a number of test problems which show the versatility of the method.

A simple analytical approach for determining the complex relative permittivity of dielectric and composite materials filling a rectangular waveguide is presented. The procedure requires the measurement of the reflection and transmission coefficient data of the test specimen by placing a thin slab of the material-under-test (MUT) at the center of a rectangular waveguide cross section. The dielectric constant and the loss tangent of the MUT are reconstructed from the measured reflection and transmission coefficient data using the newly proposed closed-form expressions, which represent the approximated form of the transcendental equation normally used to describe partially filled waveguides. A technique is also presented here to resolve the ambiguity problem generally associated with samples of electrical length greater than a wavelength. The applicability and range of validity of the proposed approach is tested by reconstructing a number of samples of varying dielectric properties

In this study, transmission characteristics of a novel THz wire waveguide — conical metal wire with dielectric coating at 0.1–1 THz are studied. The investigation results show that the coated conical wire with virtually low attenuation and high energy concentration is a promising candidate as THz transmission medium. The calculation results agree well with that of simulation such as high frequency structure simulation (HFSS), which is based on the finite element method. In this paper, a novel transition from a coaxial line to the coated conical metal wire is designed. Although coaxial probe excitation has been used in microstrip lines and rectangular waveguides in microwave, millimeter-wave frequency domains, the present study shows that it is also an effective method to excite conical wire at THz frequency. As shown in the investigation results, the return loss of coax-conical wire transition is better than 20 dB from 0.1–0.5THz, and the insertion loss is as low as 1 dB (the total length is 15 mm). It is a promising THz transition structure.

A low‐cost wide Ka‐band inline waveguide‐to‐microstrip transition is proposed, which facilities the integration of planar transmission lines with waveguide structures. By employing a circular patch above a wedge‐shaped cavity, the quasi‐TEM mode wave in the microstrip line can be transformed into the TE10 mode wave in the rectangular waveguide. A transition prototype in a back‐to‐back configuration is manufactured and experimentally tested. Measured results show that the return loss is greater than 13 dB from 28 to 38 GHz and the insertion loss remains less than 0.4 dB for the proposed single‐side transition. With the features of wideband, compact structure and easy integration, the proposed transition can be applied in the low‐loss and high‐integration millimeter‐wave systems.

The concept of transmission zero resonator pair (TZRP) is used in this paper. Based on this TZRP, a new method to induce a passband is demonstrated, by which different types of bandpass filters can be designed. The proposed TZRP is structured by a pair of resonators with different resonant frequencies, which lead not only to two transmission zeroes, but also to a transmission pole between them. Passband filters can then be built by designing the proximity coupling between the TZRPs, as the TZRP works as a basic resonant element. The passband of these filters can be flexibly controlled by the resonators of TZRPs, which determine the locations of the transmission zeroes and poles. By carefully allocating the transmission zeroes, high selectivity and large out-of-band rejection can be realized. This design method is applied to design filters in two different transmission media, namely, microstrip line and rectangular waveguide. Simulated and measured results demonstrate the effectiveness of this new approach of bandpass filter design. The designed filters have the properties of small size, easy fabrication, low cost, and low loss.

The presented paper reports a technique for modal analysis of waveguide loaded with composite dielectric materials using multi-scale finite element method. In this work, two-dimensional composite dielectric material loaded in waveguide is homogenized with an effective permittivity. By using a technique of finite element modal analysis in rectangular waveguide fully loaded with sample of composite dielectric and well known closed form dispersion formula of rectangular waveguide, the effective permittivity of the composite dielectric material can be explicitly determined. To validate the proposed homogenization technique, numerical examples of mode analysis in waveguides loaded with porous dielectric have been carried out. The dispersion characteristic, computed by meshing physical model and homogenized model are compared. The results show good agreement.