Circularly polarized rectangularly bent slot antennas backed by arectangular cavity

Rectangularly bent slot antennas backed by a rectangular cavity for circular polarization are proposed. Characteristics of three types of cavity-backed rectangularly bent slot antennas for circular polarization-the single square loop slot, the two-element square loop slot, and the two-arm square spiral slot antenna-are analyzed numerically. The generalized network formulation based on the equivalence principle is given in terms of the method of moments. The magnetic currents on the thin rectangularly bent slots in the presence of the backing cavity are obtained and used to calculate the input impedance, radiation pattern, and axial ratio. Experimental results on the input impedance, radiation pattern, and axial ratio are in good agreement with calculated data     

Ridged cavity backed slot antenna with dielectric loading

A reduced size cavity backed slot antenna, consisting of a transverse slot in the flat broadwall of a deep single ridge waveguide cavity is described. Partial dielectric loading achieves significant further reduction in electrical size. Moderate dielectric loss increases bandwidth (and significantly reduces antenna gain).<>     

Flush mounted rectangular cavity slot antennas--Theory and design

The loaded rectangular cavity slot antenna is analyzed using variational methods in conjunction with simplified equivalent circuit techniques to derive accurate design guides for efficiency, bandwidth, and resonant frequency. The aperture admittance is computed and the effects of a compound aperture plane iris and of material loading are analyzed. The aperture admittance of all such loaded cavity antennas is proportional tomu_{r},sqrt{mu_{r}/epsilon_{r}}, or1/epsilon_{r}, which characteristic lends to a common method of optimization of|T|^{2}(transmission cofficient). Experimental results include: 1) measurements of aperture field; 2) a comparison of theoretical and experimental value of bandwidth, efficiency, resonant frequency, and beam pattern for several experimental models; and 3) the measurement of the effect of applied dc magnetic field.     

Radiation from a short helical antenna backed by a cavity

The radiation from a short (1.5 turns) helical antenna backed by a cavity is evaluated on the basis of the numerically determined current distribution. Effects on the radiation field of the angle ψ between the cavity wall and the bottom plane of the cavity are discussed. It is found that the angle coverage of the circularly polarised wave can be widened by increasing ψ. The radiation field for ψ=75° is circularly polarised (an axial ratio within 3 dB) over a hemisphere     

Admittance of rectangular waveguide radiating from a conductingcylinder

Theory and experiment are compared for the admittance presented to a rectangular waveguide which terminates at an arbitrary angle in the surface of a conducting cylinder. Two methods are described for calculating the admittance: a single-mode approximation from the modal solution and an alternative asymptotic solution. Using these methods, the effect of aperture orientation on admittance, and the results obtained are compared with the experiment. The single-mode approximation is in good agreement with experimental results for the case when the input waveguide supports the TE₁₀ mode only. The accuracy of the approximate formula for waveguide admittance was also verified. The admittance is shown to be weakly dependent on aperture orientation for moderately large cylinders     

Admittance calculation of a slot in the shield of a multiconductortransmission line

The admittance calculation for a narrow slot in the conducting shield of a multiconductor transmission line (MTL) is presented. An approximate calculation is given for the admittance seen looking into a slot in the shield of a multiconductor transmission line when a uniform magnetic current is placed over the slot. The calculation presented is approximate in that only the transmission line mode is used in the calculation. All higher-order waveguide modes are neglected. This allows the magnetic current to be replaced by a point voltage source at the slot location. The admittance calculation then corresponds to calculating the driving point admittance of a point voltage source located in the shield of an MTL     

Admittance of a longitudinal waveguide slot radiating into anarbitrary 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     

A circuital approach to evaluating the electromagnetic field on rectangular apertures backed by rectangular cavities

In this paper, the problem of evaluating the electromagnetic field on rectangular apertures backed by rectangular cavities is investigated. The electromagnetic-field distribution is derived by using a circuital model of an aperture and suitable forcing terms introduced into the equations related to the aperture model. The effects of a rectangular cavity on the aperture-field distribution are assessed by considering the rectangular cavity as a load impedance. The impedance value is obtained by modeling the rectangular cavity as a length of rectangular waveguide back-ended by a short. The distribution of the electromagnetic field on the aperture is used as an exciting source to evaluate, through a modal expansion, the electromagnetic field inside the cavity. Numerical simulations are in a good agreement with both other theoretical models and experimental data.     

Admittance of a half-wavelength slot antenna radiating into a warm lossy two-layer plasma

The admittance of a half-wavelength slot antenna in a two-layer lossy plasma is shown to be greatly affected by moderate electron temperatures (T_{e} leq 1 eV) when the plasma is overdense. The effects of slot width and electron collision frequency upon the slot admittance also are investigated.     

Admittance of a slot antenna following r.f. voltage breakdown

An experiment to determine the input admittance of a slot antenna after r.f. voltage breakdown outside the aperture has occurred is described. It is found that the conductance decreases and the susceptance increases with input-power level.     

Single and stacked circular microstrip patch antennas backed by acircular cavity

In this communication, a full wave moment method solution for a probe-fed circular microstrip patch antenna, backed by a circular cavity both in single and in stacked configurations, is used to analyze the effect of a parasitic patch on antenna bandwidth. In addition, the effect of recessing a single patch into the antenna cavity is studied. In both cases, theoretical results for the scattering and radiation characteristics of the antenna are presented     

Admittance of an isolated waveguide-fed slot radiating betweenbaffles using a spectrum of two-dimensional solutions

An efficient method of computing resonant length and admittance characteristics of an isolated broad-wall shunt slot radiating between baffles of finite height is presented. The outer three-dimensional (3D) field problem associated with this geometry is reduced to a two-dimensional (2D) one via a Fourier transformation with respect to the longitudinal z direction. For each value of the longitudinal wave number k_z an integral equation is solved for the E field in the mouth of the plates using the method of moments. This procedure is repeated for several discrete values of k_z, to obtain a spectrum of 2D solutions which are then inverse-transformed to construct the 3D solution in the spatial domain for the exterior baffle region and the half space. The slot aperture field is determined by the conventional moment method solution to the integral equation that enforces the continuity of the H field across the slot. Scattering properties of the slot are then deduced. Numerical results for the resonant length and resonant conductance are presented. Computer results are found to be in good agreement with experimentally measured data     

Using electromagnetic scattering to estimate the depth of a rectangular slot

A theory for predicting the electromagnetic scattering from a rectangular slot is developed and is used to evaluate the possibility of determining the slot depth from scattering measurements. Experimental results obtained at 100 GHz are presented and compared with theory. Practical limitations of the technique are discussed.     

Characteristics of a longitudinal/transverse coupling slot incrossed rectangular waveguides

A rigorous analysis of a broad-wall slot coupler between two crossed rectangular waveguides is presented. The slot is longitudinal and offset from the center line in the main guide and is centered transverse in the branch guide. Integral equations are developed, taking into account finite wall thickness. The integral equations are then solved for the aperture electric field. Coupling slot characteristics are obtained, including the resonant length and dominant mode scattering. Numerical results for resonant length and scattering parameters are presented over a range of offsets, waveguide dimensions, and frequencies     

Admittance and resonant length of inclined slots in the narrow wallof a rectangular waveguide

The admittance properties and the resonant length of an inclined slot in the narrow wall of a rectangular waveguide have been investigated. The depth of cut of the slot in the broad walls of the waveguide has been taken into account. The internal power storage in evanescent modes in the waveguide, neglected in previous studies, is included. Theoretical results for the variations of conductance and resonant length with the angle of inclination of slots are presented. Through comparisons of the calculated results with previously available experimental data, the importance of the inclusion of the waveguide internal power storage is emphasized     

Analysis of L-shaped slot cut broadband rectangular microstrip antenna

Broadband microstrip antenna (MSA) is realised by cutting the slot at an appropriate position inside the patch. The bandwidth (BW) of the rectangular MSA (RMSA) has been increased by cutting an L-shaped slot inside the patch and it gives a BW of more than 550?MHz (>25%). The reported antenna has a peak gain of 9?dBi which reduces to less than 4?dBi towards the higher frequencies of BW. In this article, an analysis to study the broadband response of the L-shaped slot-cut RMSA is presented. Through the analysis, it was observed that the slot does not introduce any mode but modifies the orthogonal and higher-order TM₁₁ and TM₂₀ mode resonance frequencies of the patch and along with the TM₀₁ mode realises broader BW. Since TM₁₁ mode is dominant towards the higher frequencies of the BW, the cross-polarisation levels increases, which reduces the antenna gain to less than 4?dBi.     

The input admittance of the rectangular cavity-backed slot antenna

The input admittance of the rectangular cavity-backed slot antenna is investigated. The slot is assumed narrow so that the voltage distribution in its aperture is sinusoidal. Equations which represent the input admittance of this slot, backed by a rectangular cavity in which a single propagating wave is assumed to exist, are given. Calculations based on these representations are compared to available measured data. As the depth of the cavity increased the resonant frequency decreased and the bandwidth became narrower. Input admittance curves as a function of electrical slot length are also presented for several size cavities.     

Resonant electromagnetic field coupled into a lossy cavity through a slot aperture

A new approach is proposed for determining the electromagnetic fields coupled from an incident plane wave into a lossy conducting cavity through a slot aperture under resonant conditions. Use is made of the duality between a slot and a conducting strip and of the equivalence between a strip and a wire. Simplified formulas are derived that are explicit and flexible. Determination of resonant fields inside a cavity is reduced to simple calculations. Numerical examples are given.     

槽型腔表面等离子体滤波器特性研究

为了降低槽型腔滤波器透射频谱的FWHM(半高全宽),采用FDTD(时域有限差分法)对基于MIM(金属-介质-金属)波导的单槽型腔滤波器和级联槽型腔滤波器结构进行了数值模拟,并用耦合模理论对其透射频谱进行了分析。仿真结果表明,级联槽型腔滤波器能够有效抑制透射频谱的FWHM,其透射频谱的FWHM仅为单槽型腔结构的30%～40%。