Mutual coupling compensation in small planar array antennas

Far-field pattern synthesis of small antenna arrays is a nontrivial problem, mainly due to mutual coupling, often precluding the use of conventional tapering algorithms. A technique to compensate for mutual coupling in small linear antenna arrays is described. The method consist of calculations of a coupling matrix, which is then used to compensate for the effects of mutual coupling. Two different methods of the calculation of coupling coefficients between the array elements are presented. In order to validate the methods, measured data for a small linear antenna array is presented and discussed.

Beam synthesis remains one of the most difficult problems for an antenna array designer, this task being made more difficult when one limits the number of elements to a handful. Pattern synthesis in planar arrays is often achieved by the sampling of a continuous aperture distribution at the element locations. In the case of arrays of limited numbers of elements this produces errors that can unacceptably distort the radiation pattern. When one also then considers the effects of mutual coupling between the antenna elements, the application of ideal element weights derived in this way are no longer valid. In the paper a technique is presented, using the concept of retrodirective beams, that can achieve a low sidelobe beam from a continuous distribution on a circular aperture. The theory is then extended to include a planar array of antenna elements. This is achieved by the addition of retrodirective beams to the uniform beam pattern of the array. Measured data is presented for a small planar array antenna using the derived method. A method for correction of the element weights, to minimise the effects of mutual coupling, producing low sidelobe radiation patterns is then applied. No knowledge of the antenna array's coupling coefficients are required.

A hybrid method that combines the theory of superstition of active element pattern (AEP) and invasive weed optimization (IWO) is proposed for calibrating the beam direction of small antenna arrays. For a small antenna array with only a few elements, the beam direction discrepancy of each element will arise due to the mutual coupling of antenna elements if the array is fed with phase distribution based on the array factor (AF) theory. In this paper, the mutual coupling effects among elements in a small antenna array are considered. AEP method is employed to synthesize the radiation pattern of the antenna array. The phase distribution is optimized by the IWO. With the proposed hybrid method, the beam peak of the small antenna array can accurately steer to the desired direction.

In this proposed work, a subspace based method of Direction of Arrival (DOA) estimation with Mutual Coupling (MC) compensation and wavelet denoising for Uniform Linear Array (ULA) is addressed. A preprocessing technique of denoising by Wavelet Transform (WT) is accomplished and followed by Mutual Coupling compensation algorithm to improve DOA estimation. A complex symmetric Toeplitz matrix is modeled and based on this matrix, mutual coupling between sensors is compensated. By denoising and mutual coupling compensation, this method accomplishes a satisfactory performance for weak signals in DOA estimation without array calibration. The effectiveness of the proposed method is studied through simulations.

Planar antenna array design is one of the most important electromagnetic optimization problems of current interest. This paper introduces a recently developed metaheuristic algorithm, known as the Invasive Weed Optimization (IWO), to the pattern synthesis of planar antenna arrays with desired pattern nulls and sidelobe level by amplitude-only and position-only optimization. The steps in the problem formulation are presented along with a design example that illustrates the performance of the IWO algorithm. Three examples have been presented and solved. Simulation results are proposed to compare with published ones to verify the efiectiveness of the IWO algorithm for planar arrays.

Every day on television there are weather forecast programs for several days in advance. Forecasted weather changes are obtained by analyzing and modeling the processed data collected from observing stations. One of the problems in carrying out measurements of atmospheric parameters is the tracking of a meteorological radiosonde in the air and providing two-way communication with it and the ground observing station. A new antenna system consisting of two antenna arrays is suggested for a meteorological radiosonde tracking radar. The small 4-element antenna array with a wide 35° beam switching in four directions is used in the near radar region. The small antenna array is suitable for quick target tracking at the initial stage of the weather balloon flight with high angular velocity. The large 48-element antenna array with a narrow 7° beam switching in four directions is used in the far radar region. Circular patch antennas are used as radiating elements. The large antenna array consists of eight 6-elements subarrays. The suggested design of the antenna was analyzed by using of ANSYS HFSS software. The proposed 52-element antenna system is compared with the existing one, but 24 elements larger. The paper contains the description of the antenna system and the modeling results.

This paper presents a novel bidirectional planar monopole antenna array, with its feeding network, to apply for WiFi/Bluetooth and LTE mobile standards. The planar array is comprised of monopole antenna elements that utilise Archimedean spiral slots, inspired as resonance paths, in order to generate multi-band performance. Contrary to conventional structures, the feeding network is composed of three Wilkinson power dividers, for the purpose of providing synchronised output signals over the required frequency range, miniaturising dissipation losses and decreasing mutual coupling. Simulation and measurement results are presented for a single antenna element, an initial Wilkinson power divider and a four-element planar array, which reside on FR4 substrates. Successfully comparison between simulated and measured results verifies that the single antenna element achieves a 10 dB reflection coefficient from 2.2GHz to 2.9GHz, and the planar antenna array illustrates a 10 dB return loss bandwidth from 2.4GHz to 3.1GHz, which could cover WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile applications. The proposed planar monopole antenna array also obtains large gain, high efficiency, narrow beam, low side lobe level and highly symmetric bidirectional radiation pattern in both E- and H-plane.

Radiation pattern synthesis of a planar antenna array using relative elements axial rotation is proposed to generate broadside flattop or cosecant beams for surveillance, radars, and mobile communications. For a proof of concept, 5 x 5 planar Hertzian dipoles are utilized to synthesize all space-desired radiation patterns over a solid angle ratio of 13.4%. The rotation of each element is adjusted using a built-in MATLAB-based particle swarm optimization (PSO) technique. The deployed algorithm can be extended to include more elements and deploy different radiating elements.

This paper presents the design of wireless power transmission circuit on a small planar wide-band antenna. The proposed rectifying circuit consists of a microstrip line, a Schottky detector diode and a capacitor. Our proposed rectifying circuit can work at 2.45 GHz, 3.8 GHz and 5.8 GHz, namely, multiband operation, and circuit size is 56 mm × 43 mm × 1.6 mm. The proposed small planar wide-band antenna has a maximum gain of 1.26 dBi at 2.5 GHz, 0.37 dBi at 3.8 GHz and 3.32 dBi at 5.8 GHz. The maximum conversion efficiencies of this circuit achieved at free space are 26.8%, 29% and 43.3% at 2.5, 3.5 and 5.8 GHz with load resistances of 2000 Ω, 510 Ω, 1300 Ω and 0 dBm input power level.

Removed.

At present, researchers generally believe that the change of maximum directivity of planar phased arrays in beam scanning process conforms with the cosine law, so that the wide-range beam scanning from broadside to end-fire is impossible to realize. There are three main factors that affect the scanning range of the planar phased array antenna: 1) array factor; 2) element pattern; 3) port impedance matching. Scholars have done a lot of researches on the element pattern and the port impedance matching. About the array factor, Elliott, a famous phased array scholar, made a theoretical study on the directivity of the linear array and the planar array in 1963 and 1964, concluding that the variation of directivity of planar phased array conforms with the cosine law. However, the above conclusion came from an approximate formula under certain conditions: 1) the element pattern in the half-space is omnidirectional; 2) the beam of a large array is narrow enough; 3) the beam cannot scan a range of several beamwidths close to end-fire. To make clear the scanning beam’s change law of planar arrays, the law of directivity changing with scanning angle of linear array and planar phased array with different sizes are analyzed by using the strict formula of array factor, and the directivity’s change law derived from strict formula of array factor is compared with the cosine law. The results show that 1) the variation law of the directivity of a linear array depends on the spacing between elements. When the spacing between elements is equal to half a wavelength, the directivity of the array does not change with the scanning angle. When the spacing between elements is less than half a wavelength, the directivity of the array increases with scanning angle increasing. 2) The directivity of a finite array decreases with scanning angle increasing. However, the scanning beam’s maximum directivity of a finite planar phased array does not satisfy the cosine law and it is not zero in the end-fire range. Based on the above conclusions, the idea that the change of array factor’s directivity is compensated for by element beamforming is further proposed, which points out a direction for realizing the ultra-wide-angle-range beam scanning of planar phased arrays.

This paper deals with the synthesis of monopulse antenna patterns, sum and difference ones, for planar phased array antennas with an elliptical aperture boundary featuring unequal ultra-low peak sidelobe levels (PSLLs) for the two principal planes of its far field. The used synthesis method is the iterative Fourier transform (IFT) approach. The elliptical planar phased array antenna involved in this synthesis contains 3656 open-ended waveguide radiating elements arranged in a triangular element grid and has an aperture width and height of 50λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and 25λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , respectively, where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength at X-band center frequency 1.0f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The simulated monopulse pattern results will be compared with those of a 4680-element rectangular planar phased array antenna having the same width, height, radiator type and triangular grid as the elliptical array antenna. The monopulse patterns of the rectangular array antenna meet the same unequal ultra-low PSLL requirements as those of the elliptical array antenna. It will be shown that the elliptical array antenna with a slightly enlarged aperture containing 4170 elements features on receive comparable or even better far-field performance characteristics as that of the rectangular array antenna. All reported far-field pattern simulations take mutual coupling between the array elements into account.

A planar array of 20 × 10 printed U-slot microstrip patch antennas is designed for the applications of high-resolution land-imaging using side-looking SAR systems operating in the C-band of the frequency. The planar array is designed to produce a three-dimensional beam of cosecant-squared shape in the ground-range direction and flat-topped shape in the azimuth direction. The mutual coupling between the adjacent patches is studied for investigating the controllability of the proposed array to achieve the required beam shapes. The desired radiation patterns are achieved by properly setting the complex excitation voltages of the array elements. A computationally-efficient Particle Swarm Optimization (PSO) algorithm is developed for this purpose. Instead of applying the PSO directly to obtain the excitation voltages of the entire planar array, which is computationally-expensive, it is applied to a 20-element and 10-element linear arrays to synthesize a cosecant-squared and flat-topped beams, respectively. Finally, the excitation voltages obtained from the optimization of the two linear arrays are simply used to determine voltage excitation of the entire planar array. The numerical solutions involved with the performance evaluation of the U-slot antenna, the mutual coupling between the elements of the array and the synthesized beam produced by the planar array for land imaging SAR applications are presented and discussed.

To effectively find the direction of non-circular signals received by a uniform linear array (ULA) in the presence of non-negligible perturbations between array elements, i.e., mutual coupling, in colored noise, a direction of arrival (DOA) estimation approach in the context of high order statistics is proposed in this correspondence. Exploiting the non-circularity hidden behind a certain class of wireless communication signals to build up an augmented cumulant matrix, and carrying out a reformulation of the distorted steering vector to extract the angular information from the unknown mutual coupling, by exploiting the characteristic of mutual coupling, i.e., a limited operating range and an inverse relation of coupling effects to interspace, we develop a MUSIC-like estimator based on the rank-reduction (RARE) technique to directly determine directions of incident signals without mutual coupling compensation. Besides, we provide a solution to the problem of coherency between signals and mutual coupling between sensors co-existing, by selecting a middle sub-array to mitigate the undesirable effects and exploiting the rotation-invariant property to blindly separate the coherent signals into different groups to enhance the degrees of freedom. Compared with the existing robust DOA methods to the unknown mutual coupling under the framework of fourth-order cumulants (FOC), our work takes advantage of the larger virtual array and is able to resolve more signals due to greater degrees of freedom. Additionally, as the effective aperture is virtually extended, the developed estimator can achieve better performance under scenarios with high degree of mutual coupling between two sensors. Simulation results demonstrate the validity and efficiency of the proposed method.

A research about design and realization of dual planar bow-tie dipole array antenna at 2.4 GHz will be presented for Wifi Outdoor BTS applications. The proposed antenna should have wide bandwidth, high gain, and ± 45° dual polarization. From the simulation and measurement results of realized antenna we can concluded that our proposed antenna has met the desired specifications; antenna reflection coefficient value <; -10 dB, mutual coupling <; -20 dB, antenna bandwidth exceeds 1.2 GHz, antenna gain reaches 16.62 dBi. Moreover, beside for Wifi Outdoor BTS applications, this implemented antenna actually can be used for another wireless systems simultaneously for GSM 1800 MHz, 3G 2100 Mz, and LTE/Wimax 2300/2500 MHz.