There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Dual-polarized antenna is widely used in communication systems such as ECM and DF systems. In this paper a novel doubleridged horn antenna with dual polarizations is introduced for frequency range of 8–18 GHz. Common double ridged horn antennas have single polarization over the operating frequency. We have used five layers polarizer to provide dual polarizations performance of the doubleridged horn antenna. In order to achieve dual polarizations the strips width, strips spacing and layers distances are optimized. It is worth mentioning that the corresponding VSWR of the antenna during the optimization process should be maintain below a certain value (VSWR< 2). Simulation results show that the proposed antenna yields dual polarizations performance and low VSWR over the operating frequency. We have used CST software for antenna simulation which is based on the finite integral technique.

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A Novel Dual-Polarized Double-Ridged Horn Antenna for Wideband Applications

This paper presents results of development and analysis of new Ku-band compact polarizers based on a square waveguide with irises. Main advantages of electromagnetic waves with circular polarizations, which are obtained in satellite antenna systems with polarizers, are listed and discussed in the article. The designs of compact waveguide polarizers with 3, 4 and 5 irises have been optimized to provide effective polarization and matching performance in the operating Ku-band 10.7-12.8 GHz. The dependences of electromagnetic characteristics of polarizers on frequency were simulated and optimized using finite integration technique. The alteration of sizes of optimal structures and improvement of their characteristics have been analyzed for the polarizers with number of irises from 3 to 5. The best performance among the considered designs is provided by the square waveguide polarizer with 5 irises. Voltage standing wave ratios of the polarizer with 5 irises for both linear polarizations are less than 1.13. The optimized differential phase shift lies within the range $90^{\circ}\pm 2.6^{\circ}$. The axial ratio of the polarizer with 5 irises is less than 0.40 dB. The XPD is higher than 32.9 dB. Therefore, developed new compact square waveguide polarizer with 5 irises provides efficient performance in the operating Ku-band 10.7-12.8 GHz and can be widely used in modern satellite television and other information systems.

Compact Polarizers for Satellite Information Systems

The results of numerical investigation of coaxial quad-ridged waveguides’ eigenmodes of two configurations (with ridges on inner or on outer perfectly conducting circular cylinder) for different cross-section dimensions are presented. In particular, dependences of cutoff wave numbers on geometrical dimensions ratios for the first three TE modes and for the first TM mode have been investigated and transversal electric field components distributions for these eigenmodes and for theTEM mode have been obtained. Besides, the optimization of coaxial quad-ridged waveguides has been carried out at antiphase excitation in order to provide maximal single-mode operation frequency band for the first TE mode. As a result two optimal configurations of coaxial quad-ridged waveguides with single-mode operation bandwidth ratios 4.6:1 have been designed. It has been defined that the waveguide with the ridges at the inner conducting circular cylinder has smaller cross-section dimensions at the fixed single-mode operation frequency band. Calculations are conducted utilizing the mathematical models obtained in [1] by the integral equations technique taking correctly into account of singular behavior of the field at ridges’ edges. Reliability of the results obtained is confirmed by the calculations based on finite difference time domain technique, which is implemented in the software package CST Microwave Studio at mesh size λ/100.

Eigenmodes of coaxial quad-ridged waveguides. Numerical results

This paper presents new simple analytical technique for the development and optimization of polarizers based on a square waveguide with irises. The presented technique applies scattering and transmission matrices of the structure elements for the calculation of general scattering matrix of the whole polarizer. For two types of fundamental modes polarizations the irises are simulated as inductances or capacitances, which are connected in parallel into the equivalent transmission line. In order to check the performance of developed simple analytical technique the polarization and matching characteristics of a square waveguide polarizer with two irises were calculated theoretically. The investigation of the influence of the iris parameters on the electromagnetic characteristics of the polarizer has been performed in the paper. In the operating frequency band 7.4–8.5 GHz the optimized design of a square waveguide polarizer with two irises provides voltage standing wave ratio less than 2.8 for both polarizations. Differential phase shift of the polarizer is $90^{\circ} \pm 8^{\circ}$. Axial ratio is less than 1.6 dB. Corresponding crosspolar discrimination is higher than 21.7 dB. Therefore, developed new simple analytical technique for the calculation of iris polarizer characteristics can be widely used for the approximate estimation of their performance. The subsequent optimization of the design must be carried out with the account of higher order modes or using accurate numerical simulation.

Analytical Technique for Iris Polarizers Development

The results of numerical investigation of sectoral coaxial ridged waveguides eigenmodes of two configurations (with a ridge on inner or outer wall) for different cross-section dimensions are presented. In particular, dependences of cutoff wave numbers on geometrical dimensions ratios for first four modes are investigated, electric field components distributions for these modes have been obtained and the optimization of sectoral coaxial ridged waveguides has been carried out to provide maximal single-mode operation frequency band. Two optimal configurations of waveguides with single-mode operation bandwidth ratio 5.6:1 are obtained. It is shown that smaller cross-section dimensions at the fixed single-mode operation frequency band has the waveguide with the ridge at the inner round wall. The size of the gap between the ridge and the round wall of optimal waveguide is identical for both configurations and is determined by the required ratio of cutoff frequencies of two lower TE modes. Calculations are conducted utilizing the mathematical model obtained in [1] by the integral equation technique with the correct account of singular behavior of the field at the ridge.

Eigenmodes of sectoral coaxial ridged waveguides

The electrodynamics eigenmodes boundary problem for sectoral coaxial single-ridged waveguides is solved by the integral equation technique utilizing the introduced system of orthogonal basis functions, which correctly take into account the singular field behavior at the ridge. The formulas obtained allow to compute cutoff wave numbers and electric and magnetic fields distributions of TE and TM modes in the presence of the ridge either on the outer or on the inner wall of the waveguide. The analysis of the dependence of cutoff wave numbers convergence on the type and the amount of basis functions and partial modes has been carried out. It is shown that for obtaining 0.1% residual error it is necessary to utilize in two times more unorthogonal basis functions, which correctly take into account singularity at the ridge, than introduced orthogonal basis functions, which correctly take into account singularity at the ridge, and in five times more orthogonal trigonometric basis functions, which don’t take into account singularity at the ridge. Besides the computing time increases in 4 and in 20 times, respectively.

Electrodynamics boundary problem solution for sectoral coaxial ridged waveguides by integral equation technique

The numerical optimization results of constant thickness septum polarizer’s performances for various operating fractional bandwidths (FBW) are presented in the paper. The polarizer’s structure includes a common input square waveguide, a constant thickness septum with several steps, and two output rectangular waveguides. The polarizer design of 2-, 3-, 4-, and 5-step septums is optimized for different narrow and wide operating FBWs to obtain the simultaneously maximum values of cross-polarization discrimination and isolation between rectangular ports and return losses. The optimized dimensions of the septums for FBW = 5, 10, 15, 18, and 20% are presented. Based on the obtained results, Q- and K-band prototypes were manufactured and their performances were measured. The measurements of the prototypes are in good agreement with simulations. These optimization results can be widely used for the development of septum polarizers and prediction of their performances for various FBW in the required frequency range.

Optimum Septum Polarizer Design for Various Fractional Bandwidths

This paper presents the results of development of a X-band compact stepped-thickness septum polarizer. All electromagnetic characteristics of the polarizer have been simulated and optimized numerically. A prototype of the polarizer has been designed, fabricated and tested. It has been shown that the use of a stepped-thickness septum instead of a constant-thickness one improves the return loss and XPD of the septum polarizer by 5 and 7 dB, respectively. Measured VSWR of the designed compact septum polarizer is less than 1.4 in the operating frequency band 7.70-8.50 GHz. Tested differential phase shift varies from 83° to 100°. Suggested compact septum polarizer is designed for a quasi-monopulse feed of a dual-polarized ground station antenna system. Measured XPD of the polarizer in an assembled feed system is higher than 30 dB.

Fedor F. Dubrovka

Papers

Eigenmodes of coaxial quad-ridged waveguides. Numerical results

Eigenmodes of sectoral coaxial ridged waveguides

Electrodynamics boundary problem solution for sectoral coaxial ridged waveguides by integral equation technique

Optimum Septum Polarizer Design for Various Fractional Bandwidths

Compact X-band Stepped-Thickness Septum Polarizer