波纹波导极化器的分析

极化器是天线馈电系统中的重要器件,但传统的极化器带宽一般很窄。介绍了一种新型的宽带极化器(波纹波导极化器),其结构是在方波导的两壁加载横槽波纹,使波导中的2个正交模产生了90°的相位差。因而将线极化信号转化成圆极化信号。波纹波导极化器在超过30%的带宽内仍然有很好的相移特性,因此他在宽带反射面天线馈电系统中有着很广阔的应用。     

Optimum-Iris-Set Concept for Waveguide Polarizers

Novel profiled irises for the design of waveguide polarizers are presented. The two degrees of freedom of their piecewise-circular profile allow one to better control the frequency behavior of the differential phase shift. Thanks to this feature, an optimum iris set can be found by selecting the discontinuities for which the differential-phase-shift deviation from the average value is minimum in the operative bandwidth. This optimum iris set can be identified for several values of the ratio r/lambda₀, where r is the waveguide radius and lambda₀ is the free-space wavelength at the central frequency. Hence, even if both the waveguide size and central frequency are assigned in the specifications, polarizers with a very low deviation from 90deg of the total differential phase shift can be designed. In this way, the number of waveguide transitions in the antenna feed system can be reduced and the effect of spurious higher-order-mode coupling can be minimized. A Ka-band polarizer in circular waveguide with piecewise-circular-profile irises is described, showing a return loss better than 55 dB and a phase error of about 0.9deg in a 10% bandwidth     

8-18 GHz介质板极化器的分析与设计

介质板极化器在天线设计中的应用非常广泛。从介质板波导形成圆极化波的原理出发,推导出差相移与波导传播常数的关系式。因此只需利用数值方法计算波导的传播常数,从而减小了仿真计算量。分析表明在818GHz超宽带范围内,方波导中插入介质板的圆极化轴比理论上只能达到2．03dB。文中提出介质板插入结合波导口径变形的方法使圆极化轴比小于1．53dB,驻波比小于1．23。对介质板波导的关键参数进行误差分析,得到加工误差对圆极化性能的影响小于2．5％。     

Broad-Band Quarter-Wave Plates

Analytical expressions are given for the propagation constant for the two orthogonal dominant modes in a square waveguide loaded with a centered slab of dielectric. These are combined to find the differential phase shift in a loaded section. Solutions of these equations are given for polystyrene which enables one to design broad-band quarter wave plates. The problem of transforming from unloaded to loaded guide is discussed and two solutions are given and another suggested. Experimental results are given and it is found that the work in square guide carries over to circular guide almost intact. It is shown that quarter-wave plates may easily be designed to cover a normal waveguide bandwidth.     

A Broad-Band Dual-Mode Circular Waveguide Transducer

This paper describes a broad-band dual-mode waveguide transducer designed to couple two orthogonal TE/sub 11/ circular waveguide modes in separate rectangular waveguide ports. A compact, rugged, and economical junction has been developed to operate from 8600 mc to 9600 mc with a vswr of less than 1.15 at the rectangular port and a mode isolation of 50 db or greater. Developmental models are described to indicate the evolution from theory to the final model. Some problems encountered in attaining a small physical size are discussed in detail. The new junction has application to mode multiflexing, circular waveguide ferrite devices, circular polarization, and as a circular wave guide magic-T.     

Dual-Mode Canonical Waveguide Filters

This paper introduces a new form of dual-mode narrow-bandpass waveguide cavity filter. The filters, which can be constructed from either dual mode circular or square waveguide cavities, can realize the optimum transfer functions (including the exact elliptic function response). One of the unique features of these filters is that all the intercavity coupling irises may take the form of circular holes rather than long narrow slots. Several alternative input-output configurations are described. Experimental results on several filters indicate excellent agreement with theory.     

Circular TE01 periodic waveguide as delay line for pulse compression

An iris-loaded circular waveguide 1.3 m long, operating in the low-loss circular TE01 mode, produced 500 ns differential delay for a 50 MHz bandwidth at X band. The insertion loss was 2.2 dB.     

Dielectric-Lined Circular Waveguide with Increased Usable Bandwidth

This report describes how the useful (single-mode) bandwidth of circular waveguide can be significantly increased by using a smaller diameter with dielectric lining. The increased bandwidth results from an increase in the ratio of the cutoff frequency of the second, or TM-01, mode over that of the dominant, or TE-11 mode. A cavity test is described which permits the measurement of mode separation for any thickness of dielectric lining. A lining with a dielectric constant in the vicinity of 4 appears to be near optimum for maximum single-mode bandwidth. For a dielectric constant of 3.8 (fused silica), the greatest mode separation is obtained if the dielectric cross section has about 0.44 of the area of the entire cross section, in which case the useful bandwidth is about doubled (perhaps increased from 8 to 16 per cent, if the entire band is to clear the TE-11 cutoff frequency by 20 per cent). Over the useful bandwidth of such a waveguide, the guide wavelength may be calculated approximately by the simple waveguide formula in terms of the equivalent dielectric constant, as determined by the cavity measurement. Applications which would benefit from increased dominant-mode bandwidth in circular waveguide include rotary joints carrying circular polarization, rotary attenuators and phase shifters, and array radiators.     

Wide-Band Polarizer In Circular Waveguide Loaded with Dielectric Discs

A converter between linear and circular polarization has been designed in circular waveguide by the use of periodic loading with oblong dielectric discs. The disc loading increases the single-mode (TE-11) bandwidth relative to that of homogeneously filled circular waveguide. Moreover, periodic loading gives the designer freedom to adjust the disc thickness and shape to meet certain requirements. With the abutting disc-loaded waveguide as a reference, the dielectric loading is increased in one plane of polarization and decreased in the orthogonal plane. In a wide-band design, this differential loading gives nearly constant 90/spl deg/ difference in time phase between space-quadrature component waves, the condition for circular polarization. Such a polarizer has been constructed with four oblong discs. Across a frequency bandwidth of about 15 percent, the measured phase difference is within 2/spl deg/ of the desired value and the SWR is within 1.5 dB.     

Ultra-compact 90° twist based on a pair of two closely placed flat chiral irises

A new ultra-compact device for rotating the polarization plane of planar electromagnetic wave in a square waveguide by 90° whose dimension is almost ten times less than wavelength is suggested. It is based on strong interaction of near-fields in two closely placed flat chiral irises. It is shown that this approach due to strong multi-mode and near-field interaction allows rotating the polarization plane by 90° in the several percent bandwidth with the loss level not worse than 0.1 dB.     

Extension of Levy's Large-Aperture Design Formulas to the Design of Circular Irises in Coupled-Resonator Waveguide Filters (Short Papers)

This paper extends some results for waveguide irises to obtain accurate design formulas for the design of circular waveguide irises in coupled-resonator rectangular waveguide filters. Experimental results confirm the improved accuracy of the new design formulas. The new approach has been successfully applied to the design of a 12-GHz waveguide filter in WR90 waveguide for satellite transponder studies. Improved accuracy in the iris design enabled the filter to meet stringent group delay specifications.     

Some Results for Thin-Iris Loaded Periodic Waveguides

The planar waveguide holding planar obstacles is a prototype structure--its fields correspond to some sets of lowest modes in circular and coaxial line waveguides that use coaxial iris loading and in inductive iris loaded rectangular guides. An analysis of a periodically thin-iris loaded planar waveguide is offered, the procedure for which can also be applied to the other waveguides mentioned. A particular example for small iris separation is considered. Among the results of this study are adjustments to some formulas of Brillouin so as to allow consideration of large phase shifts per cell of periodic guide. The procedure, which can be recommended as a formula deriving technique, can find use with such other planar obstacles as the thick periodic iris, the interdigitally placed irises, or the single iris in a multimode guide. Some consideration is given to interdigital loading.     

Full-wave design and optimization of circular waveguide polarizerswith elliptical irises

We describe the design and optimization of a new polarizer structure realized in circular waveguide with insertion of elliptical irises. The device is compact, showing a considerable reduction in size and weight when compared to previously known realizations. It requires manufacturing by milling techniques only and, since it is composed entirely by waveguides with separable cross sections, it is also well suited for electromagnetic modeling. Measured and theoretical results for a polarizer with a 90°±1° differential phase shift and a return loss better than 35 dB for both polarizations over the operating frequency band confirm the validity of the proposed design     

Matched windows in circular waveguide

Design curves are presented for the matching of a dielectric window in circular waveguide propagating the dominant TE₁₁ mode. The matching is accomplished by thick or thin inductive irises which are in contact with the window on both sides. This configuration gives wide bandwidth and is mechanically convenient, but requires consideration of coupling of the higher-order modes generated by the closely spaced discontinuities. Mode matching and the generalized scattering matrix are utilized     

Compact HE11 to surface wave converters for high power waveguide dummy loads

The HE₁₁ mode in corrugated circular waveguide can be converted to the EH₁₁ mode (surface wave) by a short, smooth-waveguide phase shift section followed by a short corrugation depth taper. Low-power measurements at 110 GHz in 1.25 in. aluminum waveguide demonstrated approximately 99% conversion with the proper phase shift length. As expected, the conversion efficiency versus length of the phase shifter varied periodically with the period of the TE₁₁ to TM₁₁ beat wavelength. Since the EH₁₁ surface wave is highly attenuated, this type of converter can be used effectively in a compact high-power dummy load.     

Propagation In Dielectric-lined Square Waveguides

Symmetric structures such as circular and square waveguides may conveniently be used for dual polarization application. In this work the square waveguide with a dielectric lining of the same geometry is analyzed using a Galerkin-type method, with experimental verification. Modal characteristics, propagation constants, and bandwidth (BW) properties are outlined. Some interesting variations, depending on whether the value of the dielectric constant of the lining is higher or lower than that of the included material, are described and quantified to the extent possible by the accuracy of the method.     

The relationship between dual mode cavity cross-coupling andwaveguide polarizers

Cross-coupling in dual-mode cavity filters may be obtained by introducing an asymmetry within the cavity cross section at an angle of 45° to the two orthogonal modes. This paper presents a novel formula relating the resulting cross coupling coefficient between the orthogonal resonances to the polarization of a waveguide polarizer. Previous theories for such polarizers may then be applied directly to the dual mode filter situation. Formulas enabling the dimensions of the asymmetries for required coupling coefficients are presented for square and circular waveguide cross sections     

Intermodal dispersion and mode coupling in perfluorinatedgraded-index plastic optical fiber

Graded-index multimode perfluorinated plastic optical fibers typically exhibit bandwidths much greater than would be expected from their index profiles. To resolve this discrepancy, we have conducted the first measurements of differential mode delay in such fibers. These measurements show intermodal dispersion that increases as the square root of fiber length, implying strong mode coupling in these fibers. Significant power transfer between modes occurs at lengths less than 20 m, so that mode coupling results in improved bandwidth on length scales relevant for local area networks. The observed coupling arises from extrinsic nonuniformities of the waveguide     

Optimum field theory design of broad-band E-plane branchguide phase shifters and 180° couplers

Optimum rectangular waveguide E-plane branch guide phase shifters and 180° branch guide couplers are designed with the rigorous method of field expansion into normalized eigenmodes. The design includes both the higher order mode interaction between the step discontinuities and the finite step and branch heights. The phase shifter design applies the Schiffman principle to branch guide couplers where two ports are short-circuited. The 180° coupler design combines the advantage of the broadband potential of multiple-branch couplers with the low-insertion-loss qualities of E-plane stub-loaded phase shifters. A computer-optimized phase shifter prototype for the waveguide Ku-band (12-18 GHz) shows a 90°±1° differential phase shift with reference to an empty waveguide within about 23% bandwidth. Five-branch three-stub coupler prototypes, designed for 3±0.2 dB coupling, for the waveguide Ku- and Ka-bands (26-40 GHz) achieve a 180°±1° differential phase shift at the output ports within about 19% bandwidth, as well as more than 30 dB isolation and return loss. The theory is verified by measured results     

90° dielectric polariser in circular waveguide

Experimental results for a 90° dielectric polariser in a circular waveguide are presented. A small slot notched into the circular waveguide wall, used for the accurate alignment of the dielectric plate, has led to a decrease in the relative phase shift by 15.7%. A new U-shape impedance matching structure results in bandwidth of 12.4%