Waveguide longitudinal narrow wall slot radiating between baffles. Matching analysis

Rectangular waveguide slot arrays are commonly used in several microwave antenna systems. The slots are most often located in the broad wall of the rectangular waveguide, arranged longitudinally parallel with the waveguide axis, because this provides good control of the excitation of each slot over a large dynamic range by adjusting the offset of the slot from the center line of the waveguide. However, longitudinal slots can only radiate electrical fields that are transversely polarized with respect to the waveguide axis. If longitudinal (or dual) polarization is required, the slots (or half of them) must be located transverse to the waveguide axis. Transverse resonant slots in the broad wall are too strongly excited for use in large arrays, so transverse narrow slots in the narrow wall are preferred. In the latter case the slots are not excited unless they are tilted or coupled to tilted parasitic elements like wires or posts inside the waveguide. The purpose of the present paper is to analyse an untilted narrow wall slot excited by two tilted wires. An improved and extended analysis in which the slot extensions into the neighboring two broad walls are included, is described. The virtual cylinder method is applied to the calculation of the external admittances of the slot using wedge dyadic Green's functions and entire-domain basis functions in order to get good convergence of the integrals of the spectral domain formulations.

The symmetrically truncated right angle E-plane corner is investigated as a function of the position of the truncation plane. The problem is treated by placing electric and magnetic walls in the plane of symmetry of the bend and solving the resulting boundary value problems assuming an incident TEM mode in parallel-plate waveguide. The results are directly applicable to the same type of corner in rectangular waveguide. In analyzing the problem an infinite set of first order differential equations arise which are appropriately truncated and solved on an electronic computer by means of a fourth order Runge-Kutta scheme.

A thin wall leaky waveguide antenna (TLA) obtained by replacing one of the narrow walls of a rectangular waveguide by a film of metal with thickness less than the skin depth is discussed. The radiation pattern for TLA has been evaluated by using Kirchhoff-Huygens approach. In using this method, the dispersion relation has been solved for the complex propagation constants in a parallel plate waveguide with an imperfect plate ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma &lt; \infty</tex> ), the thickness of which is less than the skin depth. Separate approximate expressions for the propagation constants for TEM, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM_{n0}</tex> , and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TE_{n0}</tex> modes in this parallel plate structure have been obtained by considering the mode of propagation as a perturbation of the waveguide mode. Experimental results at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</tex> band frequencies with thin bismuth films are reported and are found to be in fair agreement with the theoretical results. Phase velocity ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c/\upsilon</tex> ) variation of TLA is essentially that of a simple rectangular waveguide. Very low values of attenuation constant can be obtained so that a long antenna can be used even with the beam directed away from endfire.

In this work, a comparative study of the susceptibility chart in a partially dielectric-loaded rectangular waveguide and in its equivalent partially dielectric-loaded parallel-plate waveguide with the same height is performed. This study shows how the inhomogeneity of the electric field inside the rectangular waveguide modifies the edges of the multipactor susceptibility chart with respect to that predicted by the parallel-plate waveguide case. Moreover, comparisons of the evolution of the population and the trajectory of the effective electron and the DC field appearing in the waveguide in a point well inside the multipactor region obtained with both models are performed, showing some quantitative differences in the multipactor evolution, but a similar qualitative behaviour is observed.

Slots in rectangular waveguides are often used at elements in linear array antennas. The polarisation of the radiated energy is usually linear. Circular polarisation can be obtained with compound slots in the broad wall. Experiments have shown that circular polarisation can be obtained from certain I-shaped slots in the narrow wall.

I Inrmrlucabn Rectangular parallel plate slotted my using dielectric substrate, named a post-wall waveguide my and show in Fig. 1 are athactive candidates for high efficiency and macs producible planar amy antennas in ter wave applications [l-31. The parallel plate is shorted by densely arrayed metal-surface via-holes. ATEM-like wave is excited at one end of parallel-plate by a feed waveguide through the coupling windows, which consist of posts as well. The aperture has an my of radiation units, each one of which consists of a reflection canceling slot set. In Fig. I, two slots (a pair) and three slots (a trio) compose a unit for Odeg- (a) and 4Sdeg-(b) linear polarization, respectively. Since the reflection from units is neghgible, TEM-like traveling wave option in the guide is expected [4]. For the slot design of Luge sized arrays, a pericdic boundary wall model was introduced and has been worked in illumination synthesis successllly [6], where dominant TEM-ke wave is attenuated gradually due to slot radiation during propagation. Figure 2(a) shows an example of the measured apem field distribution in Odeg linear polarkation my, with unifom apetture illumination designed [2]. The antenna parameters are given in Table 1. The am field is weak near the periphev, which reflects the boundary conditions at the post mw walls. The area with low illumination (black in color) becomes slightly wider with the wave propagation from the right to the lee. The illumination in the cenhal apemre has ripples of about 2dB. Figure 2(b) shows an example for 4Sdeg linear polarkition. [3]. The aperture field uniformity suffers 6um a triangular area of low illuminatioq in the lee bottom paa in the apem. All these observations imply the unique defects of oversized waveguide mys whch are large but are still finite (10-40 wavelength). Incident EM-Like wave is pertuhd due to waveguide narrow walls and slots. The objective of this paper is to provide the accumte and simple analysis model of the ape* ilIumination in the oversized waveguide mys for enhancing the qual~ty and the accuracy of the anay design. It is not realistic to conduct the full wave analysis of large two-dimensional slotted my with thousands of slots as it is. In this paper, the authors discuss effective analysis model for determining the slot excitation coefficients and apature illumination, which are perhrkd by the narrow walls of the waveguide as well as the coupling of radiation units in oversized waveguide. It is based upon the reflection canceling operation of the units and introduces patubation approximation which dispenses with the matrix calculation in the tidl wave analysis. 2 CaIcuWn ofhenkreNuminoli0n Excitation field for a radiation unit at some points consists of the two contributions, that is, unptuhd incident field and scattering fields fiom all the slots. For the latter, the rigorous analysis is not practical for larger anays with thousands of slots and patubation approximation is introduced here. The incident field ailer propagation in the overslzed waveguide [SI and scattering fields from slots result in non-muform excitation field for slots anayed in the x-direcbon The slots in the lower position in the waveguide in the traveling wave op-eration would be seriously p-erhukd. Figure 3

A full-wave numerical approach is proposed for analyzing rectangular waveguides with periodic slots. The approach is based on an aperture magnetic field integral equation in one unit cell. The presented technique can analyze both bound and leaky modes on rectangular waveguides with periodic slots that have a rather arbitrary shape on either the broad or narrow wall. Besides, the method can be used for a uniformly slit rectangular waveguide by taking the limit of the period. Using the proposed method, it is found that an air-filled rectangular waveguide with periodic longitudinal slots supports a leaky waveguide mode but no slot mode, while a uniformly slit rectangular waveguide (air-filled) can support a leaky waveguide mode as well as a slot mode. It is also found that an air-filled rectangular waveguide with cross slots supports a surface-wave mode in addition to a leaky waveguide mode.

With the advantage of small volume, light weight, high aperture efficiency and low side lobes, The Antenna Array of Slots in Rectangular waveguide is widely used in many microwave communication systems that requires narrow beam and shaped beam. This paper analyses the structure and design procedures of antenna array of slots in the narrow wall We first obtain the physical size of each slot by using the parameter sweep function of the Ansoft HFSS software. Then we created a complete model. Finally, we perform the simulation and compare against the design requirement There is a good agreement between simulation and design requirement.

An original 2D3V (two-dimensional in coordinate space and three-dimensional in velocity space) particle-in-cell code has been developed for simulation of multipactor discharge on a dielectric in a parallelplate metal waveguide with allowance for secondary electron emission (SEE) from the dielectric surface and waveguide walls, finite temperature of secondary electrons, electron space charge, and elastic and inelastic scattering of electrons from the dielectric and metal surfaces. The code allows one to simulate all stages of the multipactor discharge, from the onset of the electron avalanche to saturation. It is shown that the threshold for the excitation of a single-surface multipactor on a dielectric placed in a low-profile waveguide with absorbing walls increases as compared to that in the case of an unbounded dielectric surface due to escape of electrons onto the waveguide walls. It is found that, depending on the microwave field amplitude and the SEE characteristics of the waveguide walls, the multipactor may operate in two modes. In the first mode, which takes place at relatively low microwave amplitudes, a single-surface multipactor develops only on the dielectric, the surface of which acquires a positively potential with respect to the waveguide walls. In the second mode, which occurs at sufficiently high microwave intensities, a single-surface multipactor on the dielectric and a two-surface multipactor between the waveguide walls operate simultaneously. In this case, both the dielectric surface and the interwall space acquire a negative potential. It is shown that electron scattering from the dielectric surface and waveguide walls results in the appearance of high-energy tails in the electron distribution function.

In this paper, waveguide mode conversions in a parallel plate waveguide, rectangular waveguide, and circular waveguide are all demonstrated at terahertz frequencies. Different from the traditional ways to realize mode conversions, an ultracompact design method based on the inner-embedded subwavelength metallic gratings is provided. The principle of the method relies on modulating the phase velocities of spoof surface plasmon polaritons (SSPPs) supported on the gratings to generate π phase difference. Owing to the gradient matching the phase velocities of the waveguide modes and SSPPs, the efficiencies of the mode conversions are considerable. The output mode purities of the both demonstrations are very good. Besides, waveguide bend is also achieved by this method. The work in this paper hopes to establish a universal technique for compact waveguide mode control, especially in the terahertz frequency range.

Application of longitudinal slots with changing width is considered to be a prospective technique of excitation in the aperture of a slotted radiator cut in the walls of a waveguide structure amplitude and phase distribution which realizes optimal integral radiation characteristics, i.e., radiation far-field pattern and gain. The results of performance examination by the magnetomotive forces method are presented for longitudinal slots with changing width cut in the wide wall of a rectangular waveguide.

A method to reduce cross-polarization (X-pol) of narrow wall slotted waveguide is presented. A 10 inclined slot array cut in the narrow wall of a rectangular waveguide with the element spacing of d = 0.64Aµ 0 operating in Ku-band is employed. The proposed slotted waveguide antenna consists of a perforated-metallic plate which acts as a polarization filter. The polarization filter reduces the maximum cross-polarization level by 10 dB at the design frequency of 14 GHz and 5 dB over the frequency band 12 GHz to 18 GHz.

A V-shaped slot in the narrow wall of a rectangular waveguide is presented as a coupling element. Three- and four-port coupler parameters and the radiation characteristics of the slot were investigated using the finite-difference time-domain (FDTD) method. Two approximate numerical-analytical procedures are proposed to reduce the computer requirements and predict multislot device characteristics. A clear improvement in four-port coupler parameters was observed following the incorporation of a thin dielectric layer.

A problem of electromagnetic waves excitation by a structure, consisting of a narrow transverse slot in a broad wall of a rectangular waveguide and a vibrator with variable surface impedance, located inside the waveguide, is solved by the generalized method of induced electro-magneto-motive forces. Conditions, necessary for achievement of maximal slot radiation coefficient are defined. Calculated and experimental plots of energy characteristics of the vibrator-slot structure for different vibrator placement relative to the slot and for various dependencies of surface impedance upon the vibrator length are presented.

A high power, high gain, and beam-steerable array antenna for high-power microwave applications is presented in this paper, which is fed by rectangular waveguides. A C-shaped slot on the narrow wall of the rectangular waveguide is applied to couple energy from the waveguide to the helical unit, which is used to radiate circularly polarized microwave. 2-D beam scanning is achieved through fewer control units. Simulation results indicate that a 2-m-long linear array achieves a gain of 26.3 dB, an aperture efficiency of 90.43%, and a power-handling capacity of 96.5 MW. A prototype of 20 × 15 array shows the beam scanning range is about ±35° in both typical vertical planes, while the gain decreases by less than 2.0 dB.