Waveguide divider design based on null of electric field

Nowadays, 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

An Equivalent Circuit for Discontinuities Exciting Evanescent Accessible Modes

An equivalent circuit for discontinuities exciting evanescent accessible modes is proposed. The key feature of this equivalent circuit is its capability for simplification if a port relative to an accessible evanescent mode is matched, or connected to a very long line. Circuit drawing is simple, fast, and based on a regular polygon with as many susceptances as the sides and diagonals. Each side is connected with a line of electrical length θk to the terminal ports, and if the port refers to an evanescent accessible mode, a series reactance is added. This reactance is the key to the evanescent part of the circuit because it is able to cancel the effect of the evanescent mode if the relative port is matched or connected to a very long evanescent line, reducing the complexity of the circuit by one degree. With the help of the proposed equivalent circuit, we can define some approximating functions for the elements of a circuit representing a post in a waveguide, which can be used to speed up the optimization of complex structures, like filters or diplexers, based on posts

IDENTIFICATION OF EQUIVALENT CIRCUIT BASED ON POLYGON NETWORK FOR NONRECIPROCAL LOSSY N-PORT DEVICE

In 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

Analysis of modified dielectric frequency selective surfaces under 3-D plane wave excitation using a Multimode Equivalent Network approach

In this paper, a novel modified dielectric frequency selective surface (MDFSS) is proposed and analyzed under 3-D plane wave incidence. Unlike classic DFSS, this MDFSS can easily be developed. The electromagnetic analysis is carried out using the Multimode Equivalent Network (MEN) approach. A new development of electromagnetic fields in non homogeneous dielectric regions is proposed in order to correctly define the Z or S matrix of these blocks. Results are shown for an MDFSS which ensures total reflection with a larger bandwidth than the classic DFSS. Bandwidth can be enlarged and modified by doubling the MDFSS. Similarly, two MDFSS can be combined to ensure total reflection for elliptically polarized wave incidence

On the definition of the Generalized Scattering Matrix for a lossless radial line

In 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 $sqrt{Z_0}$, 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

Optimization Procedure of Four-Port and Six-Port Directional Couplers Based on Polygon Equivalent Circuit

A new optimization procedure for four- or six-port couplers is proposed. The optimization is based on the equivalent polygon network that is constituted by a kernel made by a polygon with N sides, as the number of the coupler ports, with N(N−1) /2 susceptances placed at the sides and the diagonals. The kernel susceptances must have proper values to represent a coupler with the excited input port matched, the other N/2 -1 ports insulated, and the output N/2 ports sharing the same power. The procedure permits to optimize the coupler in two steps. In the first step, only the diagonal susceptances are optimized varying the geometrical parameters of the coupling region. In the second step, four or six irises are placed at a proper distance from the coupling region to synthesize the desired susceptances on the polygon sides. The optimization permits to exactly obtain the power division to the output ports at the design frequency. Finally, the optimization procedure is applied to the transitions between the coupler and the connecting standard flanged waveguide. The proposed optimization is efficient because a few geometric variables must be optimized. Moreover, with the equivalent circuit approach, the synthesis of the coupler and the connecting transitions is two separate tasks

Reconstruction of the S-matrix of N-port waveguide reciprocal devices from 2-port VNA measurements

Two 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

Scattering Matrix of 2N-port hybrid directional couplers

The derivation of the scattering matrix of hybrid directional couplers with more than four ports is rather difficult to find in the literature. Some particular cases can be found, but a general form is not yet discussed. The aim of this contribution is to develop a simple procedure to write the 2NX2N S-matrix for hybrid directional couplers with N input and N output ports. This procedure is based on the separation of the phase of the scattering coefficients in two terms. The first is related to the presence of transmission lines, or phase shifters, connected to the coupler ports and the second to the intrinsic nature of the coupler that impose particular phase relationships to the scattering coefficients to ensure that the S-matrix is unitary. These relationships are due to the presence of one polyphase systems of order N or to m polyphase subsystems of order N/m, if N is multiple of m. Finally, it will be shown that 2N port hybrid directional couplers with phase shift equal to 0 or pi are possible only if N is an integer power of 2