Showing papers on "Reflective array antenna published in 1980"

Improved bandwidth of microstrip antennas using parasitic elements

Abstract: A method is described of doubling the bandwidth of rectangular microstrip patch antennas by locating capacitively excited λ m /4 short circuit parasitic elements at their radiating edges. The antenna characteristics are explained in terms of an antiphase mode of a pair of coupled resonators, and it is shown that the bandwidth improvement is independent of the coupling capacitance. Experimental results are presented for both linearly and circularly polarised antennas which support the theoretical predictions.

Systems study of overlapped subarrayed scanning antennas

Abstract: The properties of an overlapped subarrayed scanning antenna are studied, with emphasis on obtaining low sidelobes and large bandwidths.

Thinned array configurations for use with satellite-based adaptive antennas

Abstract: The nulling resolution of an adaptive antenna determines that the spatial extent about an interference source over which the communication system's link margin is unacceptably low when the radiation pattern is shaped to place a null on interference sources present over the antenna field of view. This resolution is inversely related to D/\lambda , indicating that large apertures are required to achieve very narrow resolution. In order to achieve good resolution with few elements, highly thinned arrays are commonly employed. Thinned array configurations optimized in performance in accordance with specific criteria are developed. These criteria are used to optimize the element positions within the array considering both the close-in nulling resolution and the average coverage area over a fixed circular field of view for which it is desired that system users have a positive link margin to a satellite at a geosynchronous altitude. It is determined that the circular array configuration, with elements equispaced on the circle, generally produces the best close-in nulling resolution against arbitrary interference scenarios for large values of D/\lambda . However, the average coverage area of this array is compromised due to the high sidelobes and grating lobes generated by this configuration. Thus other array configurations are considered. It is shown that exponentially space tapering the elements on the circle improves the average coverage area with little loss in resolution but leads to element spacings which might be incompatible with finite element size constraints in a practical design. Consequently, a third array configuration, developed according to standard synthesis techniques for nonuniform arrays, is also considered and shown to lead to good performance.

The phase centers of aperture antennas

Abstract: Two methods are given for the determination of the phase center of aperture antennas. These methods are used to obtain the phase centers of electromagnetic horn antennas treated as aperture antennas. The second-derivative method is more accurate and uses less computer time, while the two-point method is easier to understand and to derive. Calculated and experimental results are compared.

Resolution of coherent sources incident on a circular antenna array

Abstract: A method of processing voltages received on a circular antenna array which calculates the number, azimuths, and relative strengths of coherent sources is described. The method can be extended to any array geometry where inverse filtering (or deconvolution by the inverse beamspreading function) can be applied. In particular, it can be applied directly to a linear array geometry. In the analysis, the effects of mutual coupling between elements hasn ot been considered.

Unidimensionally scanned phased arrays

Abstract: Phased-array antennas operating in a linear or unidimensional scan mode are currently rising rapidly in importance with the emergence of a number of radar systems which employ advanced signal processing techniques but which do not require a full, and more expensive to implement, two-dimensional scanning capability. This simplification of the scanning feature permits the derivation of far more extensive array aperture design guidelines than is possible for a two-dimensional scan. It is shown that for waveguide arrays systematic procedures for manipulating a minimum number of parameters can be arrived at that lead to optimum performance reliably and efficiently. The approach ranges from the general, involving overall system aspects, to the specific, presenting a tableau of comprehensive practical design information not available elsewhere. In addition, various related subjects central to phased-array performance are discussed with particular attention on the increasingly important topic of wide frequency agility. A description of the antenna system of the multiple antenna surveillance radar (MASR) and its unique and unprecedented performance features is also included.

Phase error effects on gain and sidelobe level of a space-fed array

Abstract: A space-fed array is two back-to-back arrays that are connected together by a transmission line. The feed, which is located at the focal point, illuminates one side of the array and the energy which is intercepted by each of the elements is, in turn, transmitted to a corresponding element of the other array via a transmission line. This arrangement acting as a lens focuses the energy radiated into space. The effects of errors on the main beam gain and the average sidelobe level are treated. Two types of errors are considered: 1) random errors which are usually associated with manufacturing tolerance of the array, and 2) axial errors which tend to be somewhat compensating between the two sides of the array. The axial errors are usually associated with the effects of thermal gradients and structural motion that could be encountered in a large antenna system.

Crow's-nest antenna

Abstract: An experimental system of a phased array with 3π coverage is described, whose core component is the newly developed crow's-nest antenna, a phased-array antenna with spatially randomly distributed loop antennas.

Earth station antennas

Abstract: The author provides an overview of current Earth station antennas designed by Scientific-Atlanta Company.

Method for siting cosine-squared antennas and antenna array obtained thereby

Abstract: A method for optimally siting cosine-squared antennas in an array is taught, along with the array which is produced by use of the array. The array in question utilizes a dense hexagonal cellular grid, and each individual antenna is assigned a frequency group on which the antenna operates. The cells are ordered in such a fashion as to keep co-channel interference to a minimum.

Q-Band Short Backfire Antenna Arrays

Abstract: This paper presents experimental results at Q-band for a waveguide-excited short backfire antenna. Two examples of the application of such a highly efficient radiator as elements in antenna arrays are given. It is shown that the use of quarter wavelength slots on the common main reflector rim of the array leads to substantial improvement in the directive gain and sidelobe level. A designed two-element array exhibits a directive gain of 25 dB and sidelobe level of ?21 dB at 34 GHz whilst a four-element array shows corresponding values of 28 dB and ?12 dB at the same frequency.

Reflector radiation pattern from planar near-field measurements of array feed

Abstract: High gain shaped beam antennas for satellite frequency reuse applications are almost exclusively obtained by the use of complex multielement feed arrays to provide pattern control in conjunction with offset reflectors to remove blockage effects. In the design of complex multielement feed arrays for offset reflectors, the element excitations are usually synthesized using the isolated element properties. Proper performance of the array often requires that these theoretical excitations be modified to account for the effects on the feed elements due to the array environment. Near-field planar probing of the fields of the feed array have been found to provide an efficient and accurate method of predicting the secondary performances, including cross polarization and axial ratio. The nearfield measurement technique, moreover, provides an extremely effective method of determining the element performance and for determining the required compensation for desired antenna performance.

Phased-Array Antenna Processing With Titus Display: Technological Implications

Abstract: A general presentation of the holographic processing of antenna data is followed by a discussion of the practical possibilities using a 2-D Pockels modulator as real-time input. The complete processing of an active sonar circular array is described and other applications are suggested for passive sonar and active radar antennas, with consideration of actual technology limitations.

Efficient Small-Size Antenna for FM Radio Reception

Abstract: Functions required for the FM radio receiving system including antenna are mainly interference rejection and sensitivity, and are now demanded to be more improved in the face of an increase of FM broadcasting stations.

The hybrid slot, a low-profile energy-density antenna

Abstract: Low-profile antennas offer significant mechanical advantages over monopole antennas for mobile communications. At UHF and above, the required horizontal dimensions become reasonable. This paper describesa multi-port, stripline-fed, cavity-backed slot antenna which has several unique features that offer additional advantages over whip antennas for UHF mobile communications. (1) The reflection coefficient is small over a wide band. (2) Depending upon the external feed network, omnidirectional or one of several directive patterns can be selected. (3) The antenna responds to both the electric and magnetic fields to combat fading ina standing wave field.

An experimental study of the MEM applied to array antennas in the presence of multipath

Abstract: The paper presents some experimental results on the maximum entropy method (MEM) used to estimate the wavenumber spectrum produced by plane waves which are incident upon a receiving array antenna, as encountered in a low-angle tracking radar. The results show that, unless the direct and reflected signals in such a system are spatially uncorrelated, the use of the MEM in this application yields erroneous results.

Design for nonresonant type microstrip line slot array antenna

Abstract: There are two versions of the microstrip line slot array antenna: resonant array and nonresonant array according to its termination. Because microstrip loss is much larger than waveguide loss, a design method for the waveguide array is not applicable to the microstrip array. This paper proposes a new design method that utilizes nonlinear optimization and reduces the total loss; it is compared with a conventional design method. Two 2-array antennas with 64 elements were manufactured with new and old design methods. The antenna designed by a new method showed predicted properties.

Multiple beam feed networks using an even number of beam ports

Abstract: An aperture illumination compatible with the use of an even number of adjacent beam ports in a multiple beam feed network is discussed. The antenna pattern characteristics of near-in sidelobe levels, half-power beamwidth, aperture efficiency, and feed network loss are evaluated. Maximization of the available antenna gain at adjacent beam crossover points is shown to be possible for either sequential or simultaneons operation of a receiving system. The results presented indicate that lossy feed networks are quite suitable for certain array antenna applications.

Analysis and Tolerance Study of an Array Antenna for a New Generation of Secondary Radars

Abstract: An open array antenna is analyzed considering performance and tolerances with respect to the specifications given by Eurocontrol and F.A.A. Computed results and parametric charts are presented. The analytical methods used briefly described. Some considerations on the choice of the radiating element (slot or dipole) are given with respect to the wished performance.