Jianhui Bao

Mutual Coupling Calibration for Microstrip Antenna Arrays via Element Pattern Reconstruction Method

The element pattern reconstruction method is introduced to calibrate the mutual coupling effect of the microstrip arrays. This method is based on the fact that if the reconstructed pattern of the embedded element is consistent with that in the isolated state, then the corresponding calibrated received signal will be consistent with the received signal without mutual coupling effect. The calibration matrix is developed and is employed in the microstrip array to reconstruct the element patterns and in the direction-of-arrival (DOA) estimations. The new method has a wide adaptability for element structures and is very effective for the microstrip antenna array. Effectiveness of the new method is verified by the numerical examples.

Accurate DOA Estimations Using Microstrip Adaptive Arrays in the Presence of Mutual Coupling Effect

A new mutual coupling calibration method is proposed for adaptive antenna arrays and is employed in the DOA estimations to calibrate the received signals. The new method is developed via the transformation between the embedded element patterns and the isolated element patterns. The new method is characterized by the wide adaptability of element structures such as dipole arrays and microstrip arrays. Additionally, the new method is suitable not only for the linear polarization but also for the circular polarization. It is shown that accurate calibration of the mutual coupling can be obtained for the incident signals in the 3 dB beam width and the wider angle range, and, consequently, accurate [1D] and [2D] DOA estimations can be obtained. Effectiveness of the new calibration method is verified by a linearly polarized microstrip ULA, a circularly polarized microstrip ULA, and a circularly polarized microstrip UCA.

A CPW-fed slotted antenna with loaded split ring for multiband applications

This paper presents a coplanar waveguide (CPW)-fed slot antenna consisting of a slotted ground and a parasitically coupled split ring for multiband operation. In the design, the use of both the loaded split ring to rectangle wide slot and embedded L-slots into the ground is found an effective skill for exciting multiresonant modes as well as miniaturizing the slot antenna. The numerical and experimental results show that the optimal antenna has triple operating bands below – 10-dB reflection coefficients magnitude |S 11|) centered at 2.4/3.5/5.8 GHz covering the required bandwidths of various wireless communication standards. In addition, stable monopole-like radiation patterns and acceptable antenna gains are achieved across the operating bands.

Compact Multiband Slot Antenna for WLAN/WiMAX Operations

A novel compact triple-band slot antenna is proposed for WLAN/WiMAX applications. With the use of three L-shaped slots and an open-ended slot on the ground plane, three resonant modes centered at 2.4/3.5/5.8 GHz are excited. These modes cover the standards of 3.5 GHz WiMAX and 2.4/5.8 GHz WLAN, three useful frequency bands for present wireless communication systems. The proposed antenna fed by L-shaped microstrip line has a small overall dimension of mm2. The numerical and experimental results show that acceptable radiation characteristic is obtained over the operating bands.

Calibration of Mutual Coupling Effect for Adaptive Arrays Composed of Circularly Polarized Microstrip Antennas

Abstract In this article, a new mutual coupling calibration method, the element pattern reconstruction method, is proposed and utilized to calibrate the mutual coupling effect of circularly polarized microstrip arrays. Previous work has verified that the new calibration method is suitable for arrays composed of not only wire elements but also linearly polarized microstrip elements. The mutual coupling calibration of circularly polarized microstrip arrays employing the new method is presented in this work. For a well-designed circularly polarized microstrip array, the calibration matrix for the main polarization component can be used to calibrate the received signals with high accuracy. The numerical results verify the effectiveness of the new calibration method for the circularly polarized microstrip arrays.

A New Wideband Mutual Coupling Compensation Method for Adaptive Arrays Based on Cubic Hermite Interpolation

A new mutual coupling compensation method for wideband adaptive arrays is proposed. The new method is developed by combining the element pattern reconstruction method and the cubic Hermit interpolation method to achieve wideband mutual coupling compensation. For the employment of this method, mutual coupling matrices at some frequencies obtained by element pattern reconstruction method are needed and stored. By employing the cubic Hermit interpolation method, all entries of mutual coupling matrix for any frequency within the entire frequency band can be obtained accurately and efficiently. A uniform circular array with eight wideband dipole antennas is designed to verify the validity and effectiveness of the proposed wideband compensation method by the numerical examples.

An Improved Method for Mutual Coupling Calibration with Application in Wide-Angle Direction-of-Arrival Estimations

Abstract An improved element pattern reconstruction method is introduced to calibrate the mutual coupling effect of antenna arrays, and its applications in wide-angle direction-of-arrival estimation are presented. In this method, direction-of-arrival estimations and a calibration matrix are achieved by alternate iteration. The improved method can achieve a more accurate calibration matrix and direction-of-arrivals with less calculation time and iterations than the joint estimation methods for direction-of-arrivals and calibration matrix. Additionally, the angle ranges of direction-of-arrival estimations can be widened by this method for practical antenna arrays. The validity was verified by some numerical examples with a microstrip antenna array.

A Broadband Circularly Polarized Antenna Based on Cross-Dipoles

In this paper, based on cross-dipoles, a right-handed circularly polarized (RHCP) antenna with both broad impedance and axial-ratio (AR) bandwidth is proposed. Moreover, metal vias and branches are loaded to the cross-dipoles aiming to decrease the size of the antenna. The measured results show that a broadband impedance matching bandwidth ranging from 1.83 to 3.42 GHz for S11 less than �10 dB is obtained. Meanwhile, the 3-dB axial-ratio bandwidth is more than 29.0%, and the peak gain of the antenna is about 7.3 dBi with small variation at 2.5 GHz. A prototype is fabricated and measured for validating the design. The good agreements between the simulated and measured results show that the proposed antenna maybe a good candidate in circularly polarized (CP) antenna family.

Mutual Coupling Calibration for L-Shaped Microstrip Antenna Array with Accurate 2-D Direction of Arrival Estimation

An improved mutual coupling calibration approach based on the element pattern reconstruction (EPR) method is proposed in this paper. Compared to previous calibration methods in which the calibration is carried out in the entire space, the space angle ranges to be calibrated in this method is partitioned according to the interested directions. Through the partition of the space angle region, the angle ranges to calibrate are narrowed, and thus more accurate calibration matrix can be obtained in corresponding angle regions. With the employment of the calibration matrix on 2-D DOA estimation, more effective mutual coupling calibration and more accurate DOA estimations are achieved by alternate iteration in each angle region. The validity of this method is verified by an L-shaped microstrip antenna array, and the performance of mutual coupling calibration is presented by the better accuracy in 2-D DOA estimations.

Accurate mutual coupling calibration method for adaptive arrays with wide adaptability for element structures

The element pattern reconstruction method is proposed to calibrate the mutual coupling effect of adaptive arrays. The new method is characterized by the wide adaptability for element structures and high accurate calibration of mutual coupling effects. In the development of the new method, the relationship between the element patterns in the isolated state and those in the embedded state is established, and the calibration matrix is obtained by transforming the element patterns of the array. Two compact arrays composed of dipoles and microstrip antennas are designed to testify the effectiveness of the new method. For both arrays, more accurate DOA estimations are obtained due to the element pattern reconstruction method.