Showing papers on "Reflective array antenna published in 1975"

Design of line source antennas for narrow beamwidth and asymmetric low sidelobes

Abstract: A design method is described for the creation of line sources that will yield antenna patterns consisting of a narrow main beam and low sidelobes, with the sidelobe levels different on the two sides of the main beam. The requisite aperture distribution is shown to be symmetrical in amplitude and asymmetrical in phase. Main beam offset and the characteristics of the associated difference pattern are discussed. The boresight error voltage curve is also displayed. Incremental gain resulting from asymmetric sidelobes is analyzed and data is given for typical cases. Experimental confirmation is, presented.

Phased array antenna with coarse/fine electronic scanning for ultra-low beam granularity

Abstract: An antenna and scanning means therefor particularly useful in an aircraft landing system operating in the microwave frequency range. The antenna is of the line phased array type which includes digitally controlled phase shifters for each of the radiating elements of the array. The beam formed by the antenna is steered by incrementing the phase shift applied at each of the array radiating elements by an amount of phase which is dependent in part upon the position of the radiating element in the array. Phase increments sufficient to shift the beam position by one coarse step (0.1°) are applied to symmetrically located radiating element pairs, pair by pair, until all elements have been incremented. The beam is thereby caused to move through one coarse step in a number of fine steps equaling the number of pairs of elements in the array. An additional feature of the scanning means is the application of phase increment to the array elements in a pseudo-random sequence.

Frequency scanning by leaky-wave antennas using artificial dielectrics

Abstract: Frequency-scanning characteristics of an artificial dielectric leaky-wave antenna are discussed. It is experimentally observed that the beam angle changes from 10\deg to 50\deg off broadside when the frequency is changed from 8.13 to 9.05 GHz. Over this frequency range the beamwidth does not vary monotonically and changes from 7.5\deg to 6.0\deg to 7.1\deg . It is found that the artificial dielectric antenna has a better temperature stability than that for frequency scanned arrays.

An Improved Element for Use in Array Antennas

Abstract: A new element is described which is useful in array antennas. This element has a circular symmetric radiation pattern, controllable beamwidth, and exhibits extremely low mutual coupling between elements in the array. A modification of this antenna element results in a single antenna having equal E- and H-plane patterns, no side lobes and extremely low back radiation.

Integrated Diode Phase-Shifter Elements for an X-Band Phased-Array Antenna (Short Papers)

Abstract: The design and production of 502 X-band P-I-N diode phase-shifter elements for a transmissive phased-array RADAR are presented. These elements consist of three phase-shifter states and two integrated dipole radiators formed using microwave integrated circuit techniques. The detailed design of loaded-line phase shifters and effects of circuit variations during production are examined in terms of measured performance. Finally, the performance of the phase shifters in the phased array is demonstrated through computed and measured antenna patterns giving quantitative results.

New Design Techniques for Microstrip Antenna Arrays

Abstract: The radiation resistance of an open-circuit microstrip termination is to a good approximation, a simple function of the strip width thus suggesting a straightforward yet effective means of element control when used in a large array; furthermore the array bandwidth can be controlled to some extent. The design of linear and two dimensional resonant arrays based on this design procedure is formulated and examples at X and J band are outlined; the beamwidths and sidelobe levels are of the order ± 4.5° and -16dB respectively. The extension of the new technique to travelling wave arrays, circular polarisation and various substrates is under investigation and will be mentioned; computational aspects throughout will be discussed.

Method of making an antenna array using printed circuit techniques

Abstract: Radio frequency array antenna structures and methods for fabricating such structures are disclosed wherein a plurality of radio frequency circuits forming the radiating face of an array antenna and a corporate feed are formed on one or more relatively flexible dielectric sheets and then bonded to a suitable core material to form a complete array structure which is light weight, inexpensive and structurally sound.

A Modified Monopulse Technique for Radar Tracking with Low-Angle Multipath

Abstract: In this paper a new monopluse technique for reducing radar multipath angle-tracking errors is proposed. The solution is achieved by using two monopulse antennas at different heights. The available signals allow one to control the antenna-height diversity so that the elevation angle control signal is not affected by reflected-wave components. The size of the antenna system may be reduced by properly using phase shifters. A possible configuration of such a system is considered and some practical data on the antenna-height diversity are discussed.

On the design of a circularly polarized waveguide narrow wall linear array

Abstract: The design characteristics of a circularly polarized linear array are presented. The array elements are crossed slot radiators on the narrow wall of a T-septated waveguide that supports Odd and even symmetry modes. These modes have the same phase velocities, if the dual mode waveguide is properly dimensioned, and they excite independently the shunt and series portions of the crossed slot element. Based on theoretical and empirical design criteria, a linear array of such elements was constructed and tested and the results proved very satisfactory.

The Effect of Rotating Antennas and Signal Polarization on Doppler Shift

Abstract: A study is made of a transmitting antenna spinning relative to a receiving antenna, showing that the received signal undergoes a phase shift which depends upon the relative orientation and the ellipticity conditions of the two antennas. It is shown that this phase shift is important in Doppler distance measuring equipment because it must not be confused with the phase shift caused by the changing distance between the antennas.

Dispersion measurements of one-element short backfire (SBF) antennas

Abstract: Three one-element short backfire (SBF) antennas at 40 MHz, 140 MHz, and 350 MHz were built in the institute for the use with the ATS-6 radio beacon experiment (RBE). Ehrenspeck's data experimentally measured in the GHz range were transformed into the VHF range. Since there were no relevant data available concerning the dipoles and feeder systems, various types were tested in combination with differently shaped SBF reflectors. The antennas were optimized with respect to gain, sidelobe suppression (ss), and forward-backward ratio (fbr). For all antennas ss was better than 20 dB and fbr better than 30 dB. The data, measured with the two identical antenna methods, are presented and compared with Ehrenspeck's data obtained with the pattern integration method. Ehrenspeck's gain seems to be about 0.8 dB higher than that measured at the antenna test range at Lindau, very likely due to the different measuring methods. In all other aspects the agreement of the data seems to be fairly good. The ATS-6 RBE yields the opportunity to measure the differential group delay of the RF signals. For this purpose the relative dispersion-phase shift \Delta_{D} -between the 40-MHz, 140-MHz, and 360-MHz carriers and their \pm1 -MHz sidebands has to be known fairly accurately. The following data were obtained: |\Delta_{D40/41}| \leq 4\deg /MHz; |\Delta_{140/141}| \leq 1.03\deg /MHz; |\Delta_{D360/361}| \leq 0.4\deg /MHz. Furthermore the total delay with respect to vacuum of the 360-MHz, 140-MHz, and 40-MHz SBF antennas was coarsely measured by using the two identical antennas method. We got the following figures 52.5 \times 10^{-9} s at 40 MHz, 15 \times 10^{-9} s at 140 MHz, and 5.8 \times 10^{-9} s at 360 MHz. These data are practically independent from azimuth and elevation angles of the antennas and from the conductivity of the ground as long as the elevation angle is larger than 15\deg . Similar measurements with Yagi antennas showed a strong variation of the aforementioned parameters when installing them at different locations. Thus the SBF antennas seem to be the best possible compromise of any antenna type for the specific purpose of the differential group delay measurements.

Far-Field Antenna Performance Investigations Concerning In-Band Effects of Near-Field Structures and Out-of-Band Phased Arrays

Abstract: : The report presents the results of studies involving (1) the effects on far-field antenna performance of obstacles located in the near-field of an antenna, and (2) derivation of statistical models for predicting the out-of-band performance of waveguide phased-array antennas. In the first area, empirical data were recorded to determine the degrading effects of near-field blocking obstacles and reflecting objects on gain loss (decoupling), beamshift, beamwidth, and sidelobe levels of microwave radar antennas. The data were recorded for two parallel-polarization senses. In the second area, a previously- derived basic theoretical statistical model for predicting out-of-band phased- array characteristics was expanded to include arrays of waveguide elements which randomly propagate higher-order modes. Statistical equations were derived to predict and describe the out-of-band radiation pattern characteristics and median gain as a function of the in-band scan angle of the array.

Design of optimal line-source antennas

Abstract: The design of optimal antenna patterns subject to sidelobe constraints is considered. A function space formulation of the antenna pattern shaping problem yields several advantages over currently available techniques for computing optimal line-source excitations. The two basic problems studied are a) maximizing directivity subject to hard, possibly angle-dependent, constraints on the sidelobe level and beamwidth; and b) antenna pattern shaping where the approximating pattern must fit into a known envelope.

Electromagnetic Direction Finding Techniques

Abstract: : The report summarizes research and development addressed to the problem of electromagnetic direction finding in the UHF frequency range. Both theoretical and experimental investigations are described under three topical headings. These include the analysis of slot antennas on a conducting cylinder, the hardware development of a T-bar fed slot antenna, and the computer aided design of a lossy wire (distributively loaded) circular array. The report concludes with recommendations for future investigations and hardware development.

The effect of tolerances on the isolation of frequency reuse antennas

Abstract: The expression for the expected isolation between two orthogonally polarized signals of a single beam frequency reuse array antenna when excitation, position, and orientation of the elements are subjected to independent random variables is derived. The isolation loss and the fundamental limitation of a multibeam frequency reuse antenna system are discussed.

A circular active reflector antenna (CARA), energy distribution calculations, and an experimental test

Abstract: Conventional high-frequency (HF) circular phased arrays, such as the Wullenweber circular array, have a cost factor that increases at a greater-than-square law rate as its radius is increased to produce larger apertures. A new method of forming simultaneous beams in an HF circular array has been proposed in which beams are formed in the space within the array from pickup element energy that has been amplified and reradiated. Such a device is called a circular active reflector antenna (CARA), and its cost increases at a substantially linear rate as its radius is increased to form larger apertures. This paper describes calculations of the distribution of reradiated energy within such an array in order to study the effect of changes in array configuration. A cost analysis is presented to establish the dependence of array cost on array size for both the conventional and CARA types of arrays. In addition, the performance of an experimental CARA array is reported. An experimental CARA array consisting of a 120\deg partially filled sector of 1500 m radius, forming six beams over a 2\deg field of view was constructed at a site in Utah to demonstrate the feasibility of the concept. Measurements made on the experimental array showed that at 14-MHz, it formed beams 0.7\deg wide at the 3-dB points, which agrees closely to the calculated value. The sidelobe response also compared closely to the level and angular position calculated for the sidelobes of the partially filled sector array tested. No evidence of instabilities or intermodulation distortion was noted.

Photography at Radiowavelengths.

Abstract: : The report contains the description of the concept and the instrumentation developed for imaging radiowave object fields. The electromagnetic field in the plane of an antenna array is specified by the waves arriving from different directions. The complex electromagnetic field may be sampled by the antennas in the array, faithfully amplified through those many identical receivers, to energize an equivalent array of ultrasonic emitters. The Fraunhofer image formed by the ultrasonic array may then be converted to yield a visible image. The imaging system developed is a one-dimensional version. It consists of a row of 20 antennas (equiangular spirals), 20 identical, high gain receivers and a linear array of ultrasonic emitters. The one-dimensional ultrasonic image is then detected by an array of 'pinducers', amplified and made to proportionately illuminate a row of L.E.D. light bulbs. The L.E.D. row is then photographed by means of a continuous run, 16 mm camera.

Sidelobe-Reduction Technique for Arrays with Block Phase Excitation

Abstract: Block phase excitation in a large phased array reduces circuit complexity and system cost but results in high side lobes in certain directions. This paper introduces a technique for determining the locations and levels of the prominent sidelobes when each phase shifter is used to control the phase of two array elements in a linear array. A steepest-descent iterative procedure ure which minimizes the high sidelobes in an optimum manner is presented. Numerical examples are given.