Synthesis of onboard array antennas including interaction with the mounting platform and mutual coupling effects

The performance of an antenna array is considerably affected by mutual coupling effects between antenna elements. When a large number of antenna elements are located close to each other, mutual coupling becomes more significant. In this study, by using a new mutual impedance matrix, a decoupling methodology for compensating mutual coupling effects in a practical very high frequency (VHF)/ultra high frequency (UHF) Yagi‐Uda antenna array is introduced. No previous publications have studied VHF/UHF Yagi‐Uda antenna arrays in this context. In the proposed scheme, extreme care has been taken to account for both self‐ and mutual impedance related to mutual coupling effects. Experimental and simulation results show that using the proposed method, a perfect decoupling is achieved. The application of high‐resolution direction of arrival (DOA) estimation algorithms in decoupled experimental data leads to excellent performance of DOA estimation, in terms of accuracy and resolution. In addition, it is concluded (from experimental and simulation results) that mutual coupling effects between array elements as well as the root‐mean‐square error of estimated parameters depend on the direction of arrival. It is also deduced that in the presence of mutual coupling, estimation of signal parameter via rotation invariance techniques algorithm performs better than other subspace‐based algorithms.

The performance of an adaptive antenna array is strongly affected by the electromagnetic characteristics of the array. The mutual coupling effect degrades the performance significantly, especially when the inter element spacing is decreased. A method to eliminate the effect of mutual coupling was proposed by R.S. Adve and T.K. Sarkar (see AP-S Int. Symp. Digest, p.1164-67, 1996). The method of moments (MOM) is used to model the mutual coupling effect on the weights and on the final directivity pattern of the adaptive array. Using an example of a two-element half wavelength adaptive dipole array, it is shown that the mutual coupling between the elements of an adaptive array causes significant degradation in the performance of the array and thus should not be neglected. It is demonstrated that, using the algorithm proposed by Adve and Sarkar, the effects of mutual coupling in adaptive arrays can be eliminated successfully.

The main problems in phased array antenna are mutual coupling and ground effects that destroys the designed radiation pattern. In this paper these undesired effects is compensated over 5 dB for mutual coupling effect and about 10 dB for both mutual coupling and ground effects in wide frequency band 30-88 MHz.

This article generalises a pattern synthesis technique to conformal arrays. An iterative method is used for optimisation of element excitations in an array of rectangular patch elements that are conformed to a hemispheric surface. The embedded-element co-polarisation and cross-polarisation patterns are evaluated using a full-wave method. These patterns are used in a newly introduced iterative synthesis algorithm to obtain the minimum sidelobe level (SLL) and cross-polarisation level (XPL). The mutual coupling effects on the synthesis results are investigated in this procedure. The synthesised patterns show adequate XPL and SLL comprised to other methods. The weighted alternating reverse projection (WARP) method is modified and it is shown that the WARP method can synthesise lower XPL and SLL than those of other methods. Compared with other synthesis method, the WARP improves SLL by 2 dB and XPL by about 1.5 dB in 19 element array.

Traditional direction of arrival (DOA) and polarization parameter estimation algorithms generally perform well under ideal conditions. However, their performance degrades significantly in practical scenarios due to mutual coupling effects among array elements. This work introduces an innovative method based on a distributed crossed dipole array to jointly estimate DOA and polarization parameters in the presence of mutual coupling effects. This work firstly eliminates the mutual coupling matrix (MCM) through subarray selection, without requiring prior knowledge of the array's mutual coupling. The DOA is then estimated using an improved high-resolution algorithm, followed by accurate estimation of the polarization parameters through parameter matching. The results from simulations confirm that the new method significantly improves the estimation accuracy in complex mutual coupling environments, showing notable potential for practical applications and robust performance.

Far-field pattern synthesis of small antenna arrays is a nontrivial problem. Typically radiation patterns are required to exhibit low sidelobe levels, whilst maintaining the ability to scan the main beam in space. Mutual coupling is a pertinent problem when the number of antenna elements is small, often precluding the use of conventional tapering algorithms. In this paper a technique previously employed to compensate for mutual coupling in linear arrays is extended to include small planar antenna arrays. The method consists of the calculation of the coupling coefficients between the array elements, which are then formed into a matrix and used to compensate for the effects of mutual coupling. It is then shown that this method is not suitable for all planar array configurations and a new technique is developed which allows the calculation of coupling matrices for these element configurations. Measured data from a small planar antenna array is presented, with the outlined methods employed to produce low sidelobe sum and difference beams.

SummaryThe optimization of the non‐uniform planar array antenna parameter in order to minimize the signal interference in the electromagnetic environment through null placement is one of the most important areas of investigation in the field of wireless communication. This study deals with an effective method of synthesis of a quadrant symmetric sparse planar array antenna using the novel implementation of the well‐known meta‐heuristic optimization algorithms, namely, symbiotic organism search (SOS) and moth flame optimization (MFO) algorithms. The objective of this work is to place multiple small and wide nulls at the desired angles and simultaneously minimize the side lobe levels using a nonlinear mathematical approach. Three examples are presented with constraints that include the inter‐elemental distance, fixed number of array elements in the aperture, and the aperture size. The radiating antenna array elements are considered to have fixed uniform current distribution. The meta‐heuristic optimization approach offers the advantages of avoiding the infeasible solution while finding the best optimal set of element positions to reduce side lobe level in the desired radiation pattern. The radiation pattern characteristics and the computation time associated with each example and each algorithm are recorded and compared for arriving at the conclusion. The superiority of SOS is found in terms of the optimized side lobe levels. At the same time, both algorithms are found to be efficient in positioning the symmetric nulls in desired locations in the radiation pattern successfully. When compared with the published papers, proposed approach yields better results confirming the effectiveness of the performance of these algorithms.

Because the maximum radiation direction of the end-fire array antenna points to the axis of the array and the small element spacing required to suppress the grating lobes, the mutual coupling effect between the arrays is more serious than that of the broadside array. The article first established the end-fire array antenna pattern model and clutter signal model with the effect of mutual coupling. The clutter signal model includes two cases, ideal mutual coupling effect and mutual coupling error. On this basis, we take a ten-element uniform linear array using CST Microwave Studio to validate our model. Then we analyze the clutter distribution characteristics of the end-fire array airborne radar and the effect of mismatch on the spatial steering vector. Finally, an adaptive mutual coupling compensation method based on covariance matrix reconstruction is proposed. In general, clutter suppression methods with end-fire array take no account of the mutual coupling error changing over time, but the proposed method first adaptively estimates the mutual coupling error based on the airborne radar echo data and uses the estimated normalized impedance matrix to compensate the spatial steering vector, then combines the system parameters to construct the clutter covariance matrix. The simulations indicate that this method accurately estimate the impedance matrix, and it eliminates the clutter power reduction and spatial steering vector mismatch caused by mutual coupling error. Moreover, it also solves the serious non-stationary clutter problem of the end-fire array airborne radar.

Ideal array responses are often desirable to a multiple‐input multiple‐output (MIMO) system. Unfortunately, it may not be guaranteed in practice as the mutual coupling (MC) effects always exist. Current works concerning MC in the MIMO system only account for the uniform array geometry scenario. In this paper, we generalize the issue of angle estimation and MC self‐calibration in a bistatic MIMO system in the case of arbitrary sensor geometry. The MC effects corresponding to the transmit array and the receive array are modeled by two MC matrices with several distinct entities. Angle estimation is then recast to a linear constrained quadratic problem. Inspired by the MC transformation property, a multiple signal classification‐ (MUSIC‐) like strategy is proposed, which can estimate the direction‐of‐departure (DOD) and direction‐of‐arrival (DOA) via two individual spectrum searches. Thereafter, the MC coefficients are obtained by exploiting the orthogonality between the signal subspace and the noise subspace. The proposed method is suitable for arbitrary sensor geometry. Detailed analyses with respect to computational complexity, identifiability, and Cramer‐Rao bounds (CRBs) are provided. Simulation results validate the effectiveness of the proposed method.

The 5th and 6th (5G and 6G) generation wireless communications exploit large antenna arrays to serve a large number of users over large distances. In 6G sky communication, large antenna arrays will be used for communications with unmanned aerial vehicles (UAV), satellites and high altitude platforms (HAP) along with terrestrial infrastructures. The manuscript at hand dispenses an organized technical survey of the effects of mutual coupling in massive MIMO (mMIMO) (multiple input multiple output) systems, subsuming the effects on te direction-of-arrival (DoA) of the signals and digital beamforming, which substantiate the performance of the design of smart antenna (SA). The mutual coupling distorts the wave front of the incoming signal, resulting in an erroneous DoA estimation and majorly degrading other performances of the antenna array in an mMIMO system. An assortment of compensation techniques is elucidated since it is unfeasible to completely eliminate the mutual coupling. Further, some investigated results of isotropic antennas and dipole arrays are explicated, screening the mutual coupling effects. For practical antenna array design, compensation for the effect of mutual coupling is necessary, especially for densely populated arrays in an mMIMO system. Investigations on various methods of compensation of mutual coupling in antenna array design are surveyed.

This study presents a hybrid electromagnetic isolation mechanism in a transceiver array antenna operating at 5.8 GHz. Maximum isolation between transmitting and receiving array antennas, at a very close spacing (3 mm = 0.058 λ 0 ), and minimum mutual coupling between each array elements is achieved without antenna radiation pattern degradation. The achieved separation is equivalent to 44% size reduction compared with conventional half wavelength spacing criterion. Each of the transmitting and receiving array antennas is a four-element linear microstrip patch array antenna. The employed hybrid isolation technique is composed of defected ground structure, to minimise coupling between array elements, and uniplanar electromagnetic bandgap, to minimise the coupling between the transmitting and receiving antennas. The resulting transceiver array antenna system fulfils -35 dB mutual coupling between array elements, and 60 dB isolation between opponent transmitting and receiving array antennas. The proposed design procedures are discussed and analysed using electromagnetic full wave simulations. Results were verified through experimental measurements for reflection coefficient, mutual coupling and radiation characteristics in which a good agreement with simulated results is granted.

The Knowledge of Direction of Arrival (DOA) of the signal impinging on a smart antenna enables us to reduce the effect of interference. In this paper, we investigate efficiency of multiple kernel learning SVR-based direction of arrival estimation in a smart antenna with mutual coupling effect. Mutual coupling effect can degrade performance of traditional DOA estimation methods such as MUSIC severely especially when the distance between elements is very small, but SVR-based methods such as MKL support vector regression method can deal with this problem very well. In this work, receiving mutual impedance method is used to calculate mutual coupling matrix. This method can deal with mutual coupling effect better than conventional mutual impedance method when the array is in receiving mode and the distance between elements is very small.

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.

In this paper, a novel hybrid Invasive Weed Optimization (IWO) and Cuckoo Search (CS) algorithm (IWO/CS) is presented for phase-only pattern synthesis of large array antenna. The hybrid IWO/CS algorithm embeds the Levy flight of CS algorithm into IWO algorithm as a global guide, thereby enhancing the global search ability of the algorithm. At the same time, in order to avoid trapping into the local optimal solution, mutation operator is introduced to enhance search ability of the algorithm. Finally, competitive exclusion operation is improved to maintain the diversity of population. The hybrid algorithm is applied to phase-only beam shaping to achieve main lobe broadening and side lobe depression. Simulation results demonstrate the superiority of the hybrid IWO and CS algorithm.

Wideband and multi-polarizations is the development trend of the conformal array antenna. Due to the variable curvature of the platform, one of the most serious challenges faced in the pattern synthesis of conformal array antenna is the serious cross-polarization. Based on element polarization diversity, a space-time-polarization weighting construct is proposed for frequency-invariant, low cross-polarization and low sidelobe pattern synthesis of conformal array antenna. The optimal weight vector is obtained by alternating projection method. Simulation results of the circular cylindrical array are provided to demonstrate the effectiveness and behavior of the proposed method.