This article presents results of optimization and development of X-band square waveguide stepped-thickness septum polarizers. Electromagnetic characteristics of the polarizers were simulated and ...optimized numerically using finite elements method. Optimal dimensions of the 2-, 3-, and 4-section stepped-thickness septum polarizers for various fractional bandwidths have been obtained. It is demonstrated that application of the stepped-thickness septum with 3 sections instead of it constant-thickness counterpart improves return loss and cross-polarization discrimination of the septum polarizer by 2–6 dB and 3–6 dB respectively, depending on fractional bandwidth. A prototype of the optimal waveguide polarizer with 3-section stepped-thickness septum configuration for the operating frequency range 7.70–8.50 GHz was developed, manufactured and tested. Measured values of VSWR and cross-polar discrimination of the prototype together with necessary transitions and bends within the stated above frequency range are less than 1.4 and higher than 30 dB, respectively. The developed compact stepped-thickness septum polarizer is a good candidate to be applied in the quasi-monopulse dual-circular polarization feed system of the ground station reflector antenna for tracking earth observing satellites.
The paper proposes a developed approximate analytical method of constructive synthesis of compact polarizers based on two reactive elements in a square waveguide. The analytical synthesis was carried ...out under conditions of the absence of reflection and obtaining a required phase shift. As a result, simple formulas have been derived that determine parameters of phase-shifting elements and the electrical distance between them. The constructive synthesis was performed under conditions of the equality of required and real admittances of posts and diaphragms in a square waveguide and their derivatives at the central frequency of the working frequency band. As a result, the real geometrical dimensions of polarizers based on two posts and based on two diaphragms in a square waveguide were determined that provided for maximally flat phase-frequency characteristic. It has been shown that the polarizer based on two posts in a square waveguide can ensure the working frequency band of 4% or 13% while reflecting the electromagnetic energy of less than 1% or 10%, respectively, and differential phase shift Δφ = 90°±1°. However, polarizer based on two diaphragms in a square waveguide under the same conditions can ensure the working frequency band of up to 11% or 18%, respectively. The theoretical results were confirmed by experimental data.
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.
The paper presents results of the development and performance optimization of 8-channel directional coupler (DC) of orthogonal type
H
21
modes in a circular multimode waveguide. This DC is designed ...for a high precision autotracking quasi-monopulse system of low-orbiting satellites for Earth remote probing. The design and testing of a prototype operating in the X-band 8–8.5 GHz were developed. The proposed simple and reliable DC design simultaneously performs an almost ideal power division of
H
21
mode into four equal parts. We obtain the coupling ratio –6.04…–6.2 dB, good matching (VSWR < 1.12), high isolation (
I
> 31 dB), and directivity (
D
> 25 dB). Transformation ratios of the working
H
21
mode into other types of modes in a circular DC waveguide are less than –70 dB. A manufactured prototype of the developed 8-channel DC is tested in the extended X-band of 7.7–8.5 GHz. The measured VSWR values do not exceed 1.25 for
H
11
modes with orthogonal circular polarizations. The measured isolation ratio of rectangular waveguide channels of tracking signal with respect to information signal in circular waveguide exceeds 32 dB.
This article presents results of electromagnetic (EM) simulation and experimental research of an original tapered slot antenna with modified topology and double-sided metallization. A comparison of ...this antenna with classical and antipodal topology is performed. Advantages and disadvantages of each of them are described. It is shown that due to the mirror symmetry planes in E- and H-planes, the proposed antenna has the highest crosspolar isolation and demonstrates electrodynamic characteristics acceptable for practice in the frequency range 0.5–6.6 GHz. Transition from an asymmetric 50-Ω coaxial line to a symmetric 100-Ω slotted line is made with the help of a balun placed in the same plane as the antenna. The latter simplifies the manufacturing process and radically reduces the longitudinal dimensions of the antenna. The research results indicate on potential application possibilities of the developed tapered slot antenna in various areas of wireless technologies.
The paper presents the results for estimating the potential coding efficiency of spectrum envelope waveform (SEW) of speech signals (SS) by using the linear prediction (LP) method and using different ...sets of alternative equivalent parameters (AEP) that include line spectral pairs/projections (LSP), line spectral frequencies (LSF), and alternative line spectral parameters of highest splitting (LSP-HS and LSF-HS). These results are derived by the proposed approach based on using the LP method for SS SEW coding with maximum frame overlap during its analysis. It includes the examination of such coding scheme as approaching an appropriate analog vector source in each of AEP spaces, the stepwise designing of an appropriate vector codebook in each of spaces with gradual increase of its size and employing the ideal scheme of vector quantization with exhaustive search at each stage. The distortions versus rate relationships have been calculated based on the results of analysis in each of AEP spaces. In addition, a generalized function is proposed for approximation of the specified relationships. The technique is presented that makes it possible in each AEP space to estimate Shannon’s lower bound, the dispersion of the Gaussian equivalent source, differential entropy, redundancy, values of the weighting constant in the generalized formula of entropy, and other entropy characteristics of coding the equivalent sources (parameters of SS SEW) in these spaces. The efficiency indicators of real and potential coding of corresponding AEP are proposed and calculated. It has been shown that in conjunction with the combination of proposed efficiency indicators, the best results demonstrate spaces of line spectral parameters of highest splitting (LSP-HS and LSF-HS).
This paper presents a new ultrawideband omnidirectional microwave biconical antenna having gain above 10 dB that has been proposed, developed, optimized and experimentally tested. The main feature of ...the developed biconical antenna is its possible use in uniaxial dual-band systems of omnidirectional radio monitoring. The possibility of arranging two omnidirectional antennas having different operating frequency bands on a single axis is provided by feeding a biconical antenna via a coaxial transmission line, the inner conductor of which contains another coaxial line for feeding the second antenna with smaller size conductors. For ensuring a high gain of biconical antenna (above 10 dB at diameter 21λ
0
), the antenna design included an axial-symmetric dielectric lens designed for equalizing the phase front at the aperture in the ultrawideband of frequencies with bandwidth ratio 2.3:1. The use of optimal dielectric lens makes it possible to achieve the same value of gain at the antenna diameter, which is 5 times as small as the one in the absence of lens. The veracity of theoretical results obtained is confirmed by a good agreement of calculated characteristics with measured ones for the developed prototype of biconical antenna. The proposed ultrawideband omnidirectional biconical antenna can be recommended for application in the state-of-the-art and future advanced systems of omnidirectional radio monitoring, radio intelligence, data transmission, and radio countermeasures.
A device developed on the basis of the state-of-the-art circuitry for radio path monitoring of the earth station of satellite system for remote sensing of the Earth has been proposed. The satellite ...communications, e.g., in the X-band of electromagnetic waves, are used for wireless communications in many branches of science and technology. Special devices are employed to monitor the radio path operation of the earth station of satellite system for remote sensing of the Earth. Developed on the outdated element base, the existing devices currently do not provide the necessary tactical and technical characteristics, namely: frequency retuning in a wide band, low stability of radiation frequency, insufficient noise immunity and reliability, etc. The developed device based on the state-of-the-art circuitry makes it possible to improve the above performance characteristics. It provides operation in a wide frequency range from 7.5 to 8.5 GHz; the output power is adjustable from 0.5 to 60 mW. The information signal bandwidth varies discretely from 1.5625 to 100 MHz. The paper presents a functional block diagram of the device, its structural and technological elements and test results. The paper also describes the process of development and testing of the device making it possible to monitor the radio path operation of the earth station of satellite system for remote sensing of the Earth, to estimate its parameters with remote control of retuning in the specified frequency range and to be capable of operating under adverse weather conditions.
This paper proposes a solution of the electrodynamic problem of determining the generalized scattering matrix of infinitely thin asymmetric one-sided inductive diaphragm in rectangular waveguide ...using the integral equation method. The problem is reduced to solving the system of integral equations in terms of the number of incident modes falling on the inhomogeneity from the left partial region. The efficiency of the new solution of electrodynamic problem is achieved owing to the correct way of taking into account the singularity of tangential electric field in the diaphragm aperture using the Gegenbauer polynomials. The Galerkin method is used to reduce each integral equation to the system of linear algebraic equations in complex coefficients of the expansion of tangential electric field in the diaphragm window. Numerical investigation of the obtained solution was conducted for determining the equivalent parameters of diaphragm in the frequency band where only the principal mode can propagate along the waveguide without attenuation. The possibility of effective high-accuracy calculation of the generalized scattering matrix of infinitely thin asymmetric inductive diaphragm in rectangular waveguide with due regard for singularity of tangential electric field at the sharp ridge in the diaphragm window has been confirmed.
This paper proposes an approximate analytical and numerical constructive synthesis method of optimal waveguide polarizers based on three irises in square waveguide. A mathematical model of polarizer ...has been developed on the basis of waveguide transmission and scattering matrices. The analytical expressions derived for elements of the scattering matrix were used for determining the electrical characteristics of polarizer. The synthesis conditions were developed in the form of a system of equations, the solution of which should ensure the minimal deviation of the differential phase shift with respect to 90°, the maximum possible flat phase frequency characteristic, and the best matching in the specified frequency band. The method was evaluated on the constructive synthesis of polarizers for three working frequency bands: 7.25–8.6, 7.75–8.5, and 8.0–8.5 GHz. The validity of constructive synthesis results was confirmed by the calculation data of characteristics of synthesized polarizers using the finite element method in frequency domain employing the CST Microwave Studio Software. A satisfactory matching of electrical characteristics calculated by both methods was achieved. For the working frequency band of up to 10%, the proposed method of constructive synthesis ensures a sufficient for practical purposes accuracy in determining the dimensions of polarizer and the corresponding electrical specifications. This method can be also recommended for rapid determination of initial values of polarizer dimensions guaranteeing the operation in the vicinity of global optimum and thereby speeding up the designing of optimal polarizers at the electrodynamic level. In addition, this method can be extended to the constructive synthesis of waveguide polarizers with a large number of irises.
