International Journal of Antennas and Propagation

In interference cancellation, the null at the angle of arrival (AoA) of interference can suppress interference. However, due to the large spacing between array elements and the periodicity of the array, some small nulls at the angles of noninterference are formed inevitably. When the AoA of the desired signal is in these small nulls, they impair the effectiveness of interference cancellation by attenuating the desired signal. This paper proposes the concept of a side null to represent these nulls in the noninterference direction. And the cancellation ratio of the desired signal (SCR) is deduced to quantitatively characterize the side null. The spatial noncooperative interference cancellation model based on the main-auxiliary antenna array is established. Based on this, the SCR is derived to evaluate the amount of desired signal attenuation. Then the simulation, respectively, in two-dimensional plane and three-dimensional space, describes the side null visually. Moreover, the method of side null reduction is discussed by modulation of the array. Finally, the existence of side null and its influence on interference cancellation are verified through the experiments. The results of the simulation and experiment are in good agreement, and both support the theoretical analysis.

This paper investigates different approaches for achieving isolation in a MIMO antenna design. It provides an in-depth comparison of these techniques, analyzing their advantages and disadvantages. The challenges of obtaining sufficient isolation in modern MIMO antenna design are discussed, and various isolation methods developed for the MIMO design are examined. The study introduces a compact 28 GHz 4-port MIMO antenna design, which is placed on a Rogers RT/Duroid 5880 substrate. The design includes a rectangular patch with semicircles at the ends and dual slots etched from it. A partial ground plane is integrated into the antenna to achieve an operating frequency range from 22 to 29 GHz, centered at 24 GHz. To reduce mutual coupling between elements, four elements are arranged orthogonally and four stubs are added at a specific frequency band to enhance isolation. The ground plane also incorporates a defected ground structure (DGS) to improve gain. To optimize the antenna’s bandwidth, a ground cut technique is used, resulting in a 0.7 GHz bandwidth enhancement at the cost of some isolation. The antenna operates in the range of 22.5– 29.1 GHz, with a peak gain of 6.39 dBi. Each technique is compared based on parameters such as S-parameters (return loss or reflection coefficient), voltage standing wave ratio (VSWR), isolation level, and peak gain. Simulated results are shown for each of the techniques to compare their performance by using Ansys HFSS simulations which confirm that the designed antenna meets the target band requirements and could be used in 5 G communications.

This paper proposes a three-dimensional uniform ultra-high frequency (UHF) near-field radio frequency identification (RFID) reader antenna. The antenna achieves a uniform electric field in the x and y directions by placing a single branch microstrip line along the x-axis and y-axis directions, respectively. It reaches a uniform electric field in the z-direction by a centrosymmetric four-branch microstrip line. The proposed antenna achieves three-dimensional direction uniformity through a reconfigurable method. The impedance matching bandwidth range of <−10 dB for simulation and measurement includes 0.66 to 0.98 GHz, which can meet the near-field RFID operation frequency band demand. The isolation degrees between ports are less than −24.6 dB within the UHF RFID frequency band (0.86 to 0.96 GHz). In addition, the antenna also has the characteristic of low gain in the far field, and the maximum gain in the far field is less than −27 dBi when operating at different ports. The test results show that the proposed antenna three-dimensional uniform volume of dipole tags above the antenna is 99 mm × 99 mm × 20 mm, and the reading volume of the near-field tags is 40 mm × 40 mm × 5 mm. When the tags are placed on a book, there will be a slight variation in the reading range of the tags.

A single-layer differential-fed (DF) wideband metasurface (MTS) antenna is proposed in this paper. As the prototype, a three-by-three MTS formed by identical rectangular patches is investigated at first. We observe that there are many unwanted higher-order modes (HOMs) resonating near the wanted fundamental mode. Two probes with differential signals feed MTS on its centerline to suppress the majority of HOMs. The remaining HOM can be removed from the discussed frequency range by modifying the prototype MTS to a nonuniform structure. Then, the optimal feeding positions (FPs) are determined by a quantitative prediction of the impendence bandwidth (IBW) without any physical feeds involved. The processes of HOMs suppression and FPs determination are based on characteristic mode analysis with the virtual probes. Moreover, two interdigital capacitor plates are loaded on the probes to improve the impedance matching of the antenna. Finally, the proposed DF MTS antenna is fabricated and measured. The measured −10-dB IBW is 18.4% (4.93 to 5.93 GHz) with broadside radiation, stable high gains, and front-to-back ratios better than 21 dB.

In the paper, a wideband miniaturized impedance-transforming quadrature four-feed network with a flat output phase difference is presented and applied to the design of an active integrated GNSS antenna where no extra impedance matching circuit is needed. The features of impedance transformation and flat output phase difference are achieved by the proposed miniaturized rat-race coupler. When combining the proposed rat-race coupler with two trans-directional (TRD) couplers, a four-feed network with stable sequential quadrature phase shifts is obtained in the whole GNSS band. Since the quadrature four-feed network has the feature of impedance transformation, integration with a low-noise amplifier (LNA) can be realized without extra impedance matching circuits, which reduce the overall size and losses. For validation, a simple rectangular patch is applied as the radiator, and the active prototype is fabricated. Measurement results show that over the entire GNSS band from 1.164 GHz to 1.610 GHz, the miniaturized integrated antenna exhibits a return loss of more than 10 dB, an axial ratio of less than 3 dB axial ratio, and a gain of greater than 16 dBic.

Reliable channel estimation is critical for wireless communication performance, especially in vehicle-to-vehicle (V2V) communication scenarios. Aiming at the major challenges of channel tracking and estimating as the highly dynamic nature of vehicle environments, an improved generalized orthogonal matching pursuit (iGOMP) is proposed for V2V channel estimation. The iGOMP algorithm transforms the channel estimation problem into a sparse signal recovery problem and replaces the classical inner product criterion with the Dice atom matching criterion. Additionally, the atomic weak progressive selection method is integrated to avoid the suboptimal selection of atoms from the redundant dictionary using the inner product criterion. The proposed iGOMP method can achieve optimal channel estimation by iterating feedback results. Simulation results demonstrate that the iGOMP method has superior estimation accuracy, mean square error (MSE), and bit error rate (BER) performance compared with traditional channel estimation methods in V2V communications.