Studies on Difference Patterns from Cosecant Patterns

This chapter contains sections titled: Introduction Sum and Difference Patterns Dolph-Chebyshev Synthesis of Sum Patterns Sum Pattern Beamwidth of Linear Arrays Peak Directivity of the Sum Pattern of a Linear Array A Relation Between Beamwidth and Peak Directivity for Linear Arrays Taylor Synthesis of Sum Patterns Modified Taylor Patterns Sum Patterns with Arbitrary Side Lobe Topography Discretization of a Continuous Line Source Distribution Bayliss Synthesis of Difference Patterns Difference Patterns with Arbitrary Side Lobe Topography Discretization Applied to Difference Patterns Design of Linear Arrays to Produce Null-Free Patterns This chapter contains sections titled: References Problems ]]>

The paper describes monopulse radar with sidelobe-blanking system. The antenna of the sidelobe-blanking system is one subarray of the radar’s active phased array antenna. The elements of the subarray is also used for sum and difference pattern generation. It is shown that if aperture distribution required to produce low-sidelobe sum pattern is used, the pattern of one subarray will satisfy the requrements for antenna of the sidelobe-blanking system. An example of designing the monopulse radar with sidelobe-blanking system is presented. Sum pattern of the radar anettena is produced with different low-sidelobe pattern synthesis procedures. The analysis of monopulse radar parameters and sidelobe-blanking system performance is done.

A technique has been described which permits the design of linear and planar arrays for monopulse radar applications, using a small number of sub-arrays. The obtained results allows to build up an array antenna with a simple feed network. This technique let us keep other pattern parameters under control by simply including them in a cost function to to be minimized by a procedure such as simulated annealing.

In this paper, the optimization of both sum and difference patterns of linear monopulse antennas with low side lobe levels, high directivity and also narrow main beam width are efficiently solved by Continuous Ant Colony Optimization (ACO) Method. The synthesis problem is optimized by defining a suitable cost function which is based on limitation of the side lobe level. In this work, three different parameters are considered to be optimized separately which are the excitation amplitude of each element, the excitation phase of each element and finally the element-to-element spacing. Numerical results of each step, sum and difference patterns, are illustrated in each related part. Finally, we investigate placing some nulls in specific directions to suppress the jamming signals in both sum and difference patterns.

Recently a new method is introduced to synthesize low sidelobe patterns for planar array antennas with a periodic element arrangement. The method makes use of the property that for a planar array with periodic spacing of the elements, an inverse Fourier transform relationship exists between the array factor and the element excitations. This property is used in an iterative way to derive the array element excitations from the prescribed array factor. The same method is also able to partially compensate the degradation of the sidelobe and gain performance of array patterns due to element failures. Numerical examples of array-failure correction using this method are given for ultralow sidelobe sum and difference patterns of a 5800-element circular array where the failed elements are randomly dispersed across the aperture. The tapers in this array are created exclusively by active weighting in the transmit/receive (T/R) modules using variable gain control.

Summary form only given. Waveguide-fed slot array antennas have been employed in numerous ground and space based systems. Design and analysis techniques developed for such antennas are applicable to slot arrays in substrate integrated waveguides which are finding applications at millimeter wave frequencies and beyond. Slot array designs are generally based on Elliott's equations and variations thereof. Elliott's design procedure enforces the specified aperture distribution of the array elements and an impedance match at the input port at a single design frequency, generally at the center of the frequency band. Elliott's equations are not suitable for design optimizations or multi-objective designs. Previously we have used the moment method solution to the aperture electric field of all slots in a planar array in not only assessing the performance of the array but also for improving its design. Recently we reported the results of an investigation involving genetic algorithm optimization of a planar slot array using the moment method analysis (S. R. Rengarajan, RF and Microwave Computer Aided Engineering, 2013). The directivity and return loss were optimized over 5% frequency band. In this paper we demonstrate multi-objective optimization of a slot array using the genetic algorithm. In particular, for a planar array consisting of four quadrants, the sum pattern, and the azimuth and elevation difference pattern are all optimized. This is a challenging problem since the mutual coupling environment for each of the three patterns is different. A previous work employed an averaging technique to design such an array, thereby making a significant compromise on the performance (J. H. Schaffner, D. Kim, and R. S. Elliott, Alta Frequenza, pp. 312319, Nov. 1981). A novel technique to reduce the computation time used only one entire domain basis function for each slot aperture in the moment method. Subsequently an accurate equivalent solution corresponding to many basis functions was obtained. Numerical solutions validating our theory as well as optimum designs will be presented in the symposium.

In this paper, we designed a rectangular patch single and array antenna by using CST software version 18.0. First, we used a copper as radiating patch and then the nanomaterial conductor like carbon nanotube (CNT) to improve the antenna performance. In both cases, the operating frequency is 2.4 GHz, which is used for many communication applications including Wi-Fi and Bluetooth. We have designed the four-element patch array antenna in two forms of arrangement (series and corporate feed). We used the substrate FR4 (its height=1.6 mm, Єr=4.3) and copper as the ground in all our designs. The return loss (s parameter) Always less than 10 dB the value of voltage standing wave ratio (VSWR) was close to the one in the designs. The highest directivity obtained from a patch array (1×4) antenna was 13.5 dBi when using carbon nanotube. Finally, we made a comparison of the analyzed results after simulation in a detailed table of the basic antenna properties, Including Return loss, VSWR, gain and directivity at the resonant frequency.

This paper deals with the development of X-band array antenna with side lobe suppression implemented using Dolph Chebyshev power distribution. The array antenna which is fed using proximity coupling is intended to work around frequency of 9.3GHz for frequency-modulated continuous-wave (FMCW) radar application. The proposed antenna array consists of 5 microstrip patch antenna elements deployed on a grounded 0.508mm thick RT/Duroid® 5880 dielectric substrate wherein each antenna element is designed with a slot to obtain 90° rotated linear polarization. From the characterization results, it shows that the array antenna has shows side lobe level (SLL) around 20dB at frequency of 9.3GHz with simulated and measured return loss of 54dB and 30.45dB, respectively. Meanwhile, the simulated and measured gains at frequency of 9.3GHz are 12dBi and 11.39dBi, respectively. The result proves that the array antenna design by using Dolph-Chebyshev power distribution is appropriate for FMCW radar applications compared to the array antenna with uniform power distribution.

Array antennas for 77GHz automotive radar application are designed and measured. Linear series-fed patch array (SFPA) antenna is designed for transmitters of middle range radar (MRR) and all the receivers. A planar SFPA based on the linear one and substrate integrated waveguide (SIW) feeding network is proposed for transmitter of long range radar (LRR), which can decline the radiation from feeding network itself. The array antennas are fabricated, both the performances with and without radome of these array antennas are measured. Good agreement between simulation and measurement has been achieved. They can be good candidates for 77GHz automotive application.

This paper presents the design and development of wideband dual‐polarized microstrip array antenna at L‐band for spaceborne synthetic aperture radar (SAR) applications. A new type of electromagnetically coupled microstrip patch fed by strip‐loaded coaxial probe has been used as single antenna element. These radiating elements have been combined to form a 2×6 array antenna using feeder network in stripline configuration. The simulated and measured performance on return loss and radiation parameters has been presented. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:903–908, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27453

An antenna pattern design technique which results in a generalized Taylor pattern, except in a narrow region where a deep null is formed, centered at a preassigned position is presented. It is shown how this technique can be applied effectively to both linear arrays and line sources. The approach is direct so that the technique does not use either iterative sampling or a perturbation procedure. It is particularly useful in the design of a large array with a prescribed deep null. Numerical results indicate that to steer such a null, adjustment of the excitation is necessary near the edges only.

A narrow beam is formed by radiation from a large aperture having a flat phase front. Any curvature of the phase front, as by defocusing, causes widening of the beam and reduction of the directive gain. Certain symmetric and antisymmetric forms of aperture excitation, based on the probability function, have been known to yield radiation patterns of the same shape. It is found that these patterns retain their shape when widened by defocusing, so that the effects of defocusing can be expressed by simple and exact formulas. Also they retain some ideal relations that are peculiar to their use as sum and difference patterns in a tracking radar of the simultaneous-lobing or monopulse type. The simplification results from the fact that the attenuation for tapering the aperture excitation, and the phase shift by defocusing, are both proportional to the square of the aperture coordinates from the center. The amount of defocusing is then expressed by the constant ratio of these two quantities in radians per napier. While these forms ideally require a line or circle aperture of unlimited extent, they can be approximated with an aperture of finite extent. Therefore the resulting simple concepts and rules are helpful in practical situations.

The phase pattern of an antenna can be expressed with reference to an arbitrary point in space such that the phase over the range of directions of interest becomes constant. This point is called the phase center of the array, from where the antenna radiation appears to emanate. In general, an antenna does not have a unique phase center for all the directions of observation. This is due to the fact that theoretically a point emanates a spherical wavefront and the radiated wavefront from the array antenna, which has some finite dimensions, will not be therefore purely spherical with fixed curvature in all the direction of observations. The location of the phase center is a function of observation angle. An array antenna can be focused at some finite distance by moving the phase center of antenna and a flat-top beam can be obtained. This paper describes the effects of moving the phase center of an array antenna to change the shape of the beam by changing its beamwidth. It also discusses the movement of phase center in a planar array.

Smart antenna systems are of great importance in wireless communication and radar applications. They effectively enhance the system capacity and reduce the co-channel interference. Smart antenna is an array antenna that uses adaptive beamforming algorithms to steer the main beam toward the desired signal direction and reject the interfering signals of the same frequency from other directions without moving the antenna. This is achieved by continuously updating the weights of each radiating element (antenna). An algorithm with low complexity, low computation costs, high speed convergence rates and better performance is usually preferred. This paper introduces a new performance investigation and comparison between five different beamforming algorithms: Least Mean Square (LMS), Normalized Least Mean Square (NLMS), Sample Matrix Inversion (SMI), Recursive Least Square (RLS) and Hybrid Least Mean Square / Sample Matrix Inversion (LMS/SMI). In this investigation, the number of array elements and the displacement among them are changed in each algorithm. Simulation experiments are carried out, and the results are compared to verify the effectiveness of this investigation. The performance of each algorithm is optimized and demonstrated using MATLAB software package.

Design of large array antennas with contiguous subarrays and having very low sidelobe levels of the order of - 40 dB is discussed. The effects of the amplitude quantization, phase quantization and the number of subarrays on the radiation patterns of contiguous arrays are studied, and results are presented for both sum and difference patterns. A linear array of length <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">200 \lambda</tex> with different number of contiguous subarrays and having true time delay steering at the subarray level and phase steering at the element level is analyzed. It is shown that peak sidelobe/quantization lobe levels better than - 39 dB for the sum patterns and better than - 35 dB for the difference patterns can be realized within <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 60\deg</tex> scan and 0.3 percent bandwidth.