Slot Admittance Research Articles

A Method for Low Sidelobe Substrate-Integrated Waveguide Slot Antenna Design Applied for Millimeter-Wave Radars

With the development of millimeter-wave radar systems, substrate-integrated waveguide (SIW) slot antennas have been widely used. This paper presents a computational approach for calculating the equivalent normalized admittance of slot in low sidelobe SIW longitudinal slot antennas. In contrast to the existing methods, this method takes into account the impact of the N-slots coupling on the admittance. Through this method, fitting functions for resonant length and conductance are obtained, which describe the relationship between the resonant length, resonant conductance, and offset of slots. Moreover, based on the two fitting functions, a low sidelobe SIW longitudinal slot linear antenna is designed for millimeter-wave radar applications at 77 GHz. This antenna consists of a transition from the standard WR-12 waveguide to the SIW and a set of radiating slots. The simulation results indicate an impedance bandwidth of 4.8% and a gain of 13.2 dBi. The sidelobe level in the H-plane is below −28 dB, which meets the desired specifications and confirms the accuracy of the presented method.

E- and H-Plane Constant Beamwidth Horn Antenna Over 4:1 Frequency Band

A wideband corrugation slot, called stepped-shape slot, is proposed in the design of E-plane corrugated double-ridged horn antenna (DRHA) with H-plane pin sidewalls to extend the constant beamwidth bandwidth (BW) of horn antennas. Closed-form expressions for the input admittance of the new slot are derived, and the BW is compared with the BWs of other conventional corrugations. The proposed slot presents wideband characteristics with a BW ratio of more than 4:1. The use of stepped-shape slot in a corrugated wall keeps the surface reactance capacitive over a relatively large frequency band. The H-plane sidewalls of the designed antenna are formed by curved pinwalls. The flare includes ridges to extend the frequency range, and the E-plane walls are corrugated with a wideband slot to improve the beamwidth constancy in elevation. Thus, constant beamwidth horn antenna (CBWHA) is obtained at both azimuth and elevation planes over the desired frequency band from 4.5 to 18 GHz. The measured performance of the proposed CBWHA reveals wideband characteristics with 31.0° ± 2.5° H-plane and 37.4° ± 5.2° E-plane half power beamwidths over 4:1 frequency range.

A Low Cross-Polarization Slotted Ridged SIW Array Antenna Design With Mutual Coupling Considerations

A novel shunt longitudinal slot planar array antenna based on a ridged substrate integrated waveguide (RSIW) with a good cross polarization and isolation is designed and fabricated. The slots in the proposed structure are placed on the centerline of the broad wall of the substrate integrated waveguide (SIW), in order to reduce cross polarization. Also, the asymmetric field distributions on both sides of each slot, which are required for making radiation possible, are realized through using ridges close to the narrow walls of the SIW. The admittance of a single slot in the proposed structure is obtained regarding the different values of the main parameters of the structure. An eight-element longitudinal slot array antenna on the broad wall of the RSIW is designed based on Elliots design procedure. In this design, internal and external mutual coupling effects are taken into account through calculating the active admittance for each slot of the array. A 2D graph is presented which contains the real and imaginary parts of the equivalent admittance of a slot based on the changes in the widths of the ridges and length of the slot. Using this graph, the widths of the ridges and length of the slot can be revised in a way that the mutual coupling effect is taken into account. Since the array antenna is composed of collinear elements, it demonstrates a better cross polarization and isolation in comparison with conventional slot array antennas. Simulation results show good agreement with measurement results of the fabricated proposed antenna.

밀리미터파 탐색기용 도파관 광벽 종방향 슬롯 배열 안테나

본 논문에서는 Ka-대역 모노 펄스 레이더용 도파관 광벽 슬롯 배열 안테나의 설계, 제작 및 측정 결과에 대해 기술하였다. 설계 방법으로는 개구면의 분포를 원하는 이득과 빔 폭 및 SLL을 고려하여 설계하였고, 등가 회로에서의 각 슬롯의 어드미턴스에 해당하는 도파관 슬롯의 옵셋과 길이를 Elliott 배열 합성 기법을 통해 구하였다. 설계한 도파관 슬롯 배열을 CST MWS로 해석한 결과, 주어진 대역폭 내에서 -10 dB 이하의 반사 손실, 32 dBi 이상의 이득, 3.7도의 3 dB 빔 폭, -20 dB의 SLL 결과를 얻었다. 또한, 설계한 안테나의 제작과 측정을 통하여 시뮬레이션 결과를 확인하였다. In this paper, the design and fabrication of slot array in the broad wall of the waveguide for Ka-band monopulse radar are discussed. The aperture distributions are designed for the desired antenna gain, beamwidth and Side-lobe Level(SLL), and then slot parameters, such as lengths and offsets, are obtained for corresponding to each slot admittance in the equivalent circuit by using Elliot's array synthesis procedure. MWS-CST simulation shows the return loss below -10 dB, antenna gain above 32 dBi, 3 dB beamwidth of 3.7 degree and SLL of -20 dB. In order to demonstrate the expected results, the designed antenna is fabricated and measured.

Full-Wave Design Considering Slot Admittance in 2-D Waveguide Slot Arrays with Perfect Input Matching

A novel design technique for two-dimensional (2-D) waveguide slot arrays is proposed in this paper that combines a full-wave method of moments (MoM) analysis and an equivalent circuit with the explicit restraint of input matching. The admittance and slot spacing are determined first in an equivalent circuit to realize the desired distribution of power dissipation and phase, with the explicit restraint of input matching. Secondly by applying a full-wave MoM analysis to the finite 2-D array, slot parameters are iteratively determined to realize the active admittance designed above where slot mutual coupling and wall thickness are fully taken into account. The admittance, treated as the key parameter in the equivalent circuit corresponds to the power dissipation of the slots but not to the slot voltage, which is directly synthesized from the radiation pattern. The initial value of the power dissipation is assumed to be proportional to the square of the amplitude of the desired slot voltage. This assumption leads to a feedback procedure, because the resultant slot voltage distribution generally differs from the desired ones due to the effect of non-uniformity in the characteristic impedance on slot apertures. This slot voltage error is used to renew the initial distribution of power dissipation in the equivalent circuit. Generally, only one feedback cycle is needed. Two 24×27-element arrays with uniform and Taylor distributions were designed and fabricated at 25.3GHz. The measured overall reflections for both antennas were suppressed below -18dB over the 24.3-26.3GHz frequency range. High aperture efficiencies of 86.8% and 55.1% were realized for the antennas with uniform and Taylor distributions, the latter of which has very low sidelobes below -33dB in both the E- and H-planes.

ANALYSIS OF AN INCLINED SEMI-CIRCULAR SLOT IN THE NARROW WALL OF A RECTANGULAR WAVEGUIDE

An inclined semi-circular slot cut in the narrow wall of a rectangular waveguide has been analyzed. By enforcing the boundary condition of continuity of the tangential magnetic field at the slot aperture, an integral equation with the aperture electric field as the unknown has been obtained and solved by the method of moments (MoM). The equivalent slot admittance is then determined. Different slot parameters, such as scattering coefficients, normalized resonant conductance, resonant length versus tilt angle, and radiation patterns, have been studied. The results obtained by the MoM have been verified by comparing them against those results obtained with HFSS.

비공진형 협벽 도파관 슬롯 배열 설계를 위한 효율적인 슬릇 어드미턴스 추출 방법에 관한 연구

In this paper, an analytic method is proposed to extract the reference slot admittance required for the design of a non-resonant waveguide edge slot array. A slot and two neighboring transmission line sections of the numerous alternately inclined slots with the identical inclination angle are modelled as a uniform lossy transmission line, and thus, the total ABCD matrix is easily calculated and compared with the simulated or measured one. From this procedure, the complex characteristic impedance and the complex propagation constant of the lossy transmission line are calculated and the normalized slot admittance is analytically obtained. In order to validate the proposed method, the admittance value of a reference slotted waveguide fabricated for designing the X-band edge slot array is extracted and it is compared with the one obtained by the other conventional method.

Analysis of Inclined I-Slots in the Narrow Wall of Standard X-Band Rectangular Waveguide

Different types of slot configurations in one of the walls of rectangular waveguides are analyzed by different researchers. In this paper different configurations of inclined I-slot radiators have been investigated and analysed. The analysis consists of evaluation of admittance characteristics of the slot as a function of slot parameters and frequency. Slot admittance characteristics are obtained from the concepts of self-reaction and discontinuity in modal current. On the other hand, coupling and VSWR are evaluated from the shunt equivalent network parameter making use of transmission matrix approach. The variations of normalized conductance, susceptance, coupling and VSWR as a function of frequency are presented. The advantage of such types of slots is that the entire slot geometry is confined only to narrow wall.

Extension of transmission‐line model for longitudinal‐slot dielectric‐filled waveguide

AbstractThis Letter presents a well‐suited model for the analysis of longitudinal‐slot dielectric‐filled waveguide antennas by extending the transmission‐line model used for printed slot antennas. The found slot admittance is calculated on the waveguide plane thanks to a transformation ratio that corresponds to the current discontinuity, taking into account the permittivity of the antenna. The results obtained with the use of this method are first compared to a commercial software based on the FDTD method, for two dielectrics, with different slot offsets, in the millimeter‐wave band. Second, the method is compared with a measurement. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 180–183, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10270

Admittance of transverse waveguide slots in cylindrical structures

The self and mutual admittances of transverse slots in arbitrary conducting cylindrical structures are computed. The analysis is performed in the spectral domain, where all fields and currents have been Fourier transformed along the structure. There are, however, no transformations in the transverse directions. A system of integral equations for cylindrical structures are formulated and solved with the moment method. The induced currents on the structure can thus be determined and used to compute the spectral self and mutual admittance of the slots. The spectral admittance is inverse transformed and included in the overall slot antenna analysis. The analysis is rigorous with trigonometric basis function expansions at the inner and outer slot apertures. Computed results on scattering parameters in the waveguide show good agreement with measured data.

A Rigorous Analysis of Dielectric-Covered Narrow Longitudinal Shunt Slots With Finite Wall Thickness

ABSTRACT The need for a protective dielectric cover is becoming more relevant in waveguide slot arrays, expecially in space applications. The aim of this paper is to describe a rigorous Method of Moment approach to the analysis of a dielectric-covered longitudinal shunt slot, taking into account the effect of the wall thickness. The whole procedure has been devised aiming at a time effective but precise way to compute the slot admittance, tailored to the needs of design procedures for slot arrays.

Admittance of Slots With Coordinate Boundaries in a Half-Infinite Rectangular Waveguide With Impedance Endface

Admittance of Slots With Coordinate Boundaries in a Half-Infinite Rectangular Waveguide With Impedance Endface

Analysis of an untilted wire-excited slot in the narrow wall of a rectangular waveguide by including the actual external structure

The admittance of an untilted slot in the narrow wall of a rectangular waveguide is calculated by including the actual external structure. The slot is excited by two tilted thin wires inside the waveguide. The slot is also allowed to extend into the two broad walls of the waveguide to make it sufficiently long for resonance to occur. The external slot admittance is evaluated by using a spectrum of two-dimensional solutions, a method which can handle the arbitrary cross section of the external structure, The analysis predicts that if both the slot and the wires are tuned to resonance, the transmission coefficient gets constant phase over a wide-frequency band. The results also show that resonance can be obtained for any slot length by adjusting the wire length, and this relation between the lengths is presented. The distance between the slot and the wires needed to maximize the radiated power is also shown; some results are confirmed by measurements.

Admittance of a longitudinal waveguide slot radiating into an arbitrary cylindrical structure

In this paper we use a hybrid method to calculate the admittance of a longitudinal slot (of finite length) in a rectangular waveguide, when the slot radiates into a cylindrical outer structure of arbitrary finite cross section. The analysis takes advantage of a Fourier transformation along the cylinder axis, by which the computational effort is drastically reduced. The harmonic spectral currents on the structure are expanded in subsectional triangular basis functions and determined using an electric field integral equation (EFIE) and the moment method. These currents and the corresponding fields are inverse Fourier transformed and matched over the slot to the fields inside the waveguide by an additional moment method approach using entire domain basis functions for the slot field. The calculated slot admittance has good accuracy when compared with measurements on a chosen geometry. >

Calculation of external aperture admittance and radiation pattern of a narrow slot cut across an edge of a sectoral cylinder in terms of a spectrum of two-dimensional solutions

A slotted triangular cylinder is a candidate for a base station antenna in mobile communications. This paper presents an analysis of the external aperture admittance and the radiation pattern of a transverse narrow slot cut across one of the wedges of a sectoral cylinder, the cross section of which approximates the actual triangular shape. Thereby, the external region can be described in terms of two canonical shapes, for which the dyadic Green's functions are obtained analytically. The aperture admittance of the slot is expressed in terms of the integrals of magnetic current over the slot aperture and the infinitely extended interface of the canonical regions. These integrals are evaluated in the spacial and spectral domains, respectively. This hybrid analysis provides good convergence of the results. The dependence of the 3-dB beamwidth and the front to back ratio of the transverse radiation pattern from the slot upon the size and the sector angle of the cylinder are also presented. >

Variational analysis of inclined slots in the narrow wall of a rectangular waveguide

A variational analysis for calculating the admittance of the inclined slots in the narrow wall of a rectangular waveguide is presented. The analysis uses the 90/spl deg/ wedge Green's function to model the scatterings off the waveguide corners and assumes an equiphase half-cosinusoidal electric field distribution along the slot aperture. Based on these, a variational equation is derived for the reflection coefficient due to the slot discontinuity, from which the slot admittance is calculated. Through comparisons between the computed results and the literature results, the analysis is found to be accurate, reliable, and efficient.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Admittance characteristics of narrow radiating slots in nonradiating dielectric waveguide

A study of an inclined slot cut in the metal wall of nonradiative dielectric (NRD) waveguide is presented. The modal expansion method is applied to the development of an equivalent network of a slot discontinuity in NRD waveguide, using the reciprocity and Poynting theorems. The effect of the metal wall thickness is taken into consideration by applying microwave network analysis. Numerical data for the normalised slot admittance is obtained and compared with experimental results. Good agreement is observed. Numerical data for the slot admittance for various dielectric materials is also presented and the radiation patterns of a single slot are included.

Broadwall-to-Broadwall Coupling between two Cross Rectangular Waveguides through an Offset Slot

The problem of coupling through a slot in the broadwall between two rectangular waveguides has been investigated and Method of Moments used to find the co-efficients of the field function. Convergence of solution requires inclusion of thousands of waveguide modes in the numerical solution. Number of basis functions less than 10 usually gives less accurate result in the computation of slot admittance. The resolant length has been found to change noticeably with offsets.

A Moment Method Solution for the Active- and Mutual- Admittance of Longitudinal Slots in a Rectangular Waveguide

This paper presents a moment procedure to study the admittance properties of mutually coupled longitudinal slots in the broad-wall of a rectangular waveguide. The method is attractive in that it takes into account the mutual coupling because of external fields and the internal fields due to both propagating and evanescent modes. It also incorporates, inherently, the effect of wall thickness, and utilizes the actual field distribution within the slot. The method is self-consistent, reliable, and accurate. Computed results for various slot-parameters at different offsets and various slot lengths are presented.

The aperture admittance of a circumferential slot in a circular cylinder

A circumferential slot in an infinitely long cylinder when fed with a tangential electric field is considered. Parseval's theorem, in which Fourier integrals appear, is used to express the aperture admittance as the integral from zero to infinity of an infinite series. Recognizing that the first two terms of this infinite series have a nonintegrable singularity when the variable of integration w is equal to the wavenumber k, the authors distort slightly the contour of integration to avoid k. The terms of the infinite series are then approximated when w is close to k. A combination of numerical and analytical schemes employing both large and small argument approximations of Hankel functions is used to perform the integration. It has been found that these integration schemes work very well, and a simple and fast algorithm has resulted. >