3,049 research outputs found
Modified Dielectric Frequency Selective Surfaces With Enlarged Bandwidth and Angular Stability
No full textThe analysis of a dielectric stop band filter is performed in terms of modified dielectric frequency selective surfaces (MDFSS). In fact, an MDFSS can totally reflect the power if a plane wave impinging on it excites a leaky wave, acting thereby as a stop band filter. Its relative bandwidth is about 0.5-0.7 % and it can be enlarged by cascading MDFSSs. The development of such a cascade is analyzed in order to obtain a larger relative bandwidth. Unfortunately, the frequency behavior of the cascade is influenced the angle of incidence theta of the impinging plane wave. In fact, if the stop band filter is developed at f0 for normal incidence, not only does it not maintain the same bandwidth for theta=/0 but it also moves its central frequency toward other values with lower bandwidth and loses its stop band characteristic in a range of a few angles. This effect, known as angular stability, can be mitigated by cascading MDFSSs resonating at different angles of incidence. In this case, the choice of the MDFSSs plays an important role and it will be shown that the relative bandwidth can be maintained in the angular range 0 -30°
Reconstruction of the S-matrix of N-port waveguide reciprocal devices from 2-port VNA measurements
No full textTwo approaches to reconstruct the S-matrix of N-port waveguide reciprocal devices from 2-port S-matrix measurements are proposed and discussed. The main advantage of the proposed approaches is that measurements are done always at the same two ports, without moving the device. The remaining N-2 ports are loaded with different loads, either matched or short. The first approach, based on a manipulation of the 2-port S-matrices, requires N-2 matched and two other loads, while the second approach, based on the evaluation of an equivalent circuit, requires N-2 short and two other loads. The measurement technique is based on standard loads (short, shift and matched) in the waveguide calibration kit of the 2-port VNA
IDENTIFICATION OF EQUIVALENT CIRCUIT BASED ON POLYGON NETWORK FOR NONRECIPROCAL LOSSY N-PORT DEVICE
No full textIn this paper, a technique to identify/synthesize an equivalent circuit of nonreciprocal lossy N-port device is presented. The technique joins the classical procedure discussed in the '60s to the polygon network recently proposed in the literature, which permits to draw an equivalent circuit for reciprocal lossless N-port device in a very simple way. The identication is applied to two microwave devices, a reciprocal lossy iris in WR90 waveguide and a 3-port nonreciprocal lossy circulator. The proposed equivalent circuit could give some information about the agreement of the manufactured device and its design, which usually is developed in the hypothesis of ideal lossless components
Circuit approach to the analysis of microwave discontinuities
No full textAn equivalent circuit based on propagating and evanescent accessible modes is discussed and the numerical values of its elements (susceptances and electrical length) are obtained starting from the knowledge of the generalized scattering matrix S of microwave discontinuities. A database of the circuit elements is then defined in the frequency and geometric ranges of the analyzed discontinuities and is used to evaluate the generalized scattering matrix for values not contained in the database, with very simple formulas for any number of circuit ports. The obtained S matrices can be used to analyze very complex structures such as iris-based filters and manifold filters
"Natural" definition of the modal impedances in non-homogeneous dielectric loaded rectangular waveguide.
No full textIn this paper, the definition of the modal impedances of the electromagnetic field in a nonhomogeneously filled waveguide is discussed. The presence of TM modal impedances, which are functions of the transverse coordinate, does not permit us to obtain a unique Z matrix of these guides. Hence, the evaluation of the scattering matrix can be involved. The introduction of a “natural” EM expansion overcomes this problem leading to the definition of a unique modal impedance and a unique Z matrix. This approach is applied to the simulation of the effect of a block of dielectric in an empty waveguide by “cascading” the S matrices of the existing junctions. Finally, this “natural” EM expansion is applied to the junction between an empty waveguide and a completely filled waveguide, obtaining an equivalent circuit which better represents the physics of this problem, and to the optical fiber
On the definition of the Generalized Scattering Matrix for a lossless radial line
No full textIn this paper the Generalized Scattering Matrix for a radial line (rGSM) is defined. The main problem lies in the fact that, for a radial line, a unique characteristic impedance cannot be defined, since forward waves "see" an enlarging waveguide, while regressive waves a reducing one. Hence, two different impedances are defined and the usual normalization based on , valid for uniform lines, cannot be applied. An equivalent network, representing the transformation between voltages/currents and scattering amplitudes, is introduced. The transformers included in this circuit represent the normalization of electric quantities. The transformer ratios influence the properties of the rGSM, and this will be discussed at length. The rGSM is then applied to the analysis of a linear taper and the results are compared with those obtained with Generalized Telegraphists Equations. Finally, a double linear taper has been realized and the experimental and theoretical results, obtained with rGSM, are compared, showing a very good agreement in a wide band
Simple, Fast, and Effective Identification of an Equivalent Circuit of a Waveguide Junction With N Ports
No full textA simple, drawable and efficient equivalent circuit is proposed to represent a discontinuity/junction with N ports. The circuit is based on N transmission lines connected to the sides of a polygon with N side. N(N-1)/2 susceptances are placed on the sides and on the inner diagonals of the polygon. The circuit modularity permits to identify the N(N+1)/2 electrical parameters in a simple way. In fact, the lengths of the N transmission lines are obtained solving a system of N polynomial equations and the N(N-1)/2 susceptances are obtained solving a simple linear equation system.
The proposed circuit is used to evaluate the equivalent circuit of some directional couplers in the horizontal plane and of a 3D six-port coupler acting on the horizontal and vertical planes
Waveguide divider design based on null of electric field
No full textNowadays, the design of dividers is based on electromagnetic software that optimizes some geometric parameters to obtain the required performance. The choice of the geometry of the discontinuities contained in the divider and of the optimization initial point is quite critical to satisfy the divider requirements. In the last years, it is quite rare to find in the literature a theoretical approach helping the designers in the choice of the divider geometry. Helpful suggestion can derive by the analysis of the electric field in a trial divider that satisfies power division among the output ports in a thin band. In fact, the electric field null can be filled with metallic septa that ensure the same behavior at any frequency. The optimization of the septa position/form with numerical electromagnetic software permits to obtain divider with large bandwidth. A further analysis of the electric field null in the divider permits to add lateral metallic septa that further enlarge the transmission band. Finally, the design of an input matching network increases the transmitted power to the desired value
- …
