UAT analysis ofE-plane near and far-field patterns of electromagnetic horn antennas

The uniform asymptotic theory (UAT) of diffraction has been applied to arrive at expressions valid for both the near as well as far-field patterns of antenna with edges, namely an electromagnetic horn. It is found that the theoretically computed results agree very well with experiment. The agreement is found to be better than that reported by earlier authors in the far sidelobe and backlobe regions. The same theory is valid for near field as well with the pertinent values of radial distance where the uniform theory of diffraction (UTD) requires a slope diffraction correction.     

Reflection from the aperture of a longE-plane sectoral horn

The complex reflection coefficient of a longE-plane sectoral horn is derived using the geometrical theory of diffraction. Single diffraction alone is shown to be sufficient to describe the contribution from theE(widely separated) edges, while singly and doubly diffracted fields from theHedges are included by using an open waveguide result derived elsewhere. A relatively uncomplicated expression is obtained for the complex reflection coefficient of the horn which agrees well with experiment for horns with slant wall lengths greater than about3frac{1}{2}guide wavelengths.     

Mutual coupling between sectoral horns side by side

The mutual coupling between two sectoral horns side by side is formulated in terms of the rays, modes, and mode caustics excited in each horn. The coupling term is attributed to the multiple interaction between the aperture edges of both horns and is calculated using Keller's geometrical theory of diffraction. It is shown that this asymptotic method leads to an excellent agreement with experiment and is a considerable improvement over more complicated solutions based on the Huygens' principle.     

Complex radiation patterns of dual mode pyramidal horns

The radiation patterns of the dual mode horn and its related performance are influenced by the phase difference between component modes at the horn aperture and the phase distribution associated with the horn flare angle. Both effects are shown to deteriorate beam symmetry and increase sidelobe levels. Radiation pattern functions and fractional power distributions associated with the dual mode pyramidal horn are illustrated for a range of mode and distribution phase errors.     

Influence of the wall geometry on reflection and transmission in anE-plane sectoral horn

For a gradual waveguide-sectoral horn junction excited in the TEM mode, the influence of the wall geometry on reflection and transmission is investigated. The wall profile of the junction has the shape of a circular arc. When increasing the circle radius from zero, an abrupt junction changes to a smooth one. The magnitude of the reflection coefficient is reduced in a broadband manner whereas the phase variation increases. Clearly, the transmission increases too, but the ratio of dominant horn mode to the next higher mode will be diminished considerably. The analysis is rigorous and combines the "generalized telegraphist's equations" with a mode matching technique. This method is particularly suited for the calculation of waveguide-horn junctions.     

GTD analysis of the radiation patterns of conical horns

The far-field radiation patterns of conical horns of arbitrary flare angles excited in theTE_{11}mode are obtained employing the geometric theory of diffraction (GTD) based on the theory of Kouyoumjian and Pathak [3] and the slope diffraction technique [4]. The analysis presented enables one to predict accurately radiation patterns over the main beam, near and far sidelobes, and the becklobe of the horn. Validity of the analysis is established by satisfactory agreement between the calculated and measured patterns of an experimental conical horn. The radiation patterns of wide-flare corrugated conical horns excited in theHE_{11}mode of operation have also been calculated over the main beam, which contains most of the radiated energy (up to -40 dB with respect to boresight field), employing slope diffraction technique, and a good agreement is noticed between the calculated and measured radiation patterns.     

Near-field radiation characteristics of corrugated horns

The amplitude and phase patterns of corrugated feed horns are predicted in the near-field region by means of a spherical-mode-expansion method which has been previously applied only in the far field. Excellent agreement has been observed with experimental patterns, and typical results for horns with flare semiangles of 12° and 70° are described.     

GTD analysis of the E-plane patterns of conical horns

An analytical procedure for predicting accurately theE-plane patterns of conical horns with moderate aperture widths (ka < 10), based on uniform geometrical theory of diffraction (UGTD) and supported by measured data, is presented. This analysis predicts theE-plane patterns more accurately (over the main beam) than the one presented earlier.     

通过试飞测量大型直升机超短波天线的方向图

超短波天线方向图的精确测量对摸清机载通信系统性能底数,指导部队战术应用具有重要意义.针对传统试飞方法均不适用于大型直升机天线方向图测量的问题,通过分析大型直升机的飞行性能特点,提出了一种新的适用于大型直升机的超短波天线方向图试飞方法.通过分析计算给出了试飞中载机高度、速度、姿态等参数的限制数据,制定了详细的试飞流程,提出了逐架次、逐频点采集校准数据并完成校准曲线拟合的方法,得到了较高的测量精度.该方法已在某大型直升机定型试飞中进行了应用,试飞结果表明该方法的测量结果与传统测量方法之间的标准差在1.6 dB内,试飞效率提高了66%.     

Feed radiation patterns modified by a dichroic plate

The 20 GHz copolar radiation patterns of a feed 4.25 cm from a flat dichroic plate 15 cm in diameter have been computed using a mode-matching technique. The results are in good agreement with the measured patterns.     

Size reduction of microstrip antennas by means of periodic metallic patterns

A metallic electromagnetic bandgap material (EBG) is realised by combining 4/spl times/4 unit cells in a square geometry and excited by a microstrip line through a slot-aperture. It is shown that this structure is a radiating one, called an EBG patch, resonating at a lower frequency than the plain patch showing the same dimensions. An analytical model for the wavenumber of the EBG material facilitates the design of the EBG patch.     

Null placing in radiation patterns by shaping antenna edges

A simple null-placing technique is given by the shaping of antenna edges in the form of a step at the critical point of radiation. The E plane pattern of a pyramidal horn is used as an example, for which theoretical and measured results are given.     

Determination of modal amplitudes by resolution of radiation patterns

A simple and accurate method for the determination of the relative level of excitation of higher-order modes in over-moded waveguides is presented. The method relies on the change of amplitude and phase of the radiation fields of the open ended waveguide when the length of the guide is varied. Good agreement with the theoretical results is observed for a circumferentially corrugated waveguide operated near 10 GHz. Only the change in length and not the length of the guide itself need be precisely known.     

Far-field radiation patterns of multiple quantum well lasers grown by MO-CVD

The far-field radiation patterns of multiple quantum well lasers grown by metal-organic chemical vapour deposition (MO-CVD) with conducting stripe widths of 3, 5, 7 and 9 ?m were studied. The results show that the existing antiguidance effect in conventional heterostructure GaAs/GaAlAs lasers is stronger in quantum well lasers due mainly to the thinner active regions.     

Calculation of radiation patterns of paraboloidal reflectors by high-frequency asymptotic techniques

Radiation pattern of a paraboloid is calculated by asymptotic physical optics and geometrical theory of diffraction and the two are compared.     

Accurate determination of gain and radiation patterns by radar cross-section measurements

Using a two-port network and geometrical interpretation of equations involved in antenna scattering, it can be derived that antenna characteristics may be determined in properly designed scattering measurements. As an alternative to this approach it is shown that measurement procedures for gain and radiation pattern can be developed from simple considerations of the receiving, transmitting, and scattering properties of antennas. The main advantages of the technique are that no gain standard is required and a disturbing feedline to the antenna can be avoided. In addition to this the technique seems to be highly accurate. These general conclusions are well corroborated by experimental data on a standard gain horn. Sources of errors are outlined and compared with sources of errors in conventional techniques.     

Improving the symmetry of radiation patterns for offset reflectorsilluminated by matched feeds

The large difference between the dominant sidelobe levels in the asymmetric and symmetric plane radiation patterns of the short-focal-length offset paraboloids is minimized by illuminating the reflector with a prime-focus tilted matched feed. The amplitude of the asymmetric mode (TE₂₁) component in the matched feed is numerically evaluated for achieving an optimum peak cross-polar level. Effect of the feed tilt on the reflector efficiency is also indicated     

Electromagnetic radiation control in metallic waveguide with gyrotropic semiconductor wall

New possibilities of using magnetoplasma effects in semiconductors for the millimeter radiation control are discussed. For this purpose a highly-conductive semiconductor plate has been substituted for a part of the wide wall of metallic rectangular waveguide and the external magnetic field has been directed perpendicularly to the plate surface. It is shown that this construction can be used both as a second — harmonics filter and a directional coupler.     

Vertical radiation patterns of HF curtain arrays

The vertical radiation patterns of high-frequency (HF) curtain arrays are both expensive and time-consuming to measure. In addition, by the time the measurements can be made, it is usually too late to make significant changes to the array or its location. The paper describes a method of predicting the pattern over arbitrary ground and gives comparisons between predictions and measurements