International Journal of Antennas and Propagation

In this paper, we propose a miniaturized 2.5-dimensional (2.5D) frequency selective surface (FSS) structure with high angular stability. A novel closed-loop FSS is formed by combining the Jerusalem cross (JC) structure with the conventional rectangular closed loop using vias. This approach further enhances the coupling performance of the FSS and thus achieves miniaturized design. The unit cell size of the proposed FSS is 0.019λ₀ × 0.019λ₀ at the resonant frequency, and the metal is printed on a dielectric substrate with a thickness of 0.003λ₀. The proposed FSS has a resonant frequency of 850 MHz and exhibits band-stop characteristics. It is insensitive to the incident angle with a good operating performance in both the TE and TM wave modes. Therefore, it can be well used as an electromagnetic shield for the GSM 850 band. In order to facilitate the rapid analysis and design of the FSS, the equivalent circuit model is further analyzed and established, and values of the corresponding lumped components are derived. In addition, a prototype FSS is fabricated using printed circuit board technology and is tested in a microwave anechoic chamber. The full-wave analysis simulation, equivalent circuit model simulation, and practical measurement results reflect a high level of consistency.

A miniaturized enhanced isolation 8-unit MIMO antenna for smartphones is proposed in this paper. The units are planar inverted-F antennas with the same structure, and we use the slotting method and shorted probe to miniaturize them. The size of every unit is 14 × 6 mm² (0.149 × 0.064λ²). We insert an L-shaped decoupling element into the middle of adjacent radiating elements and connect the decoupling element to the GND. Note that the decoupling elements are on the outer side of the substrate, and the radiating elements are on the inner side of the substrate. Finally, a prototype is fabricated and measured. The measured results show that the bandwidth of the MIMO antenna is from 3.0 GHz to 5.3 GHz (55.4%), which fully supports the n77, n78, and n79 in the 5G nR frequency band and the 4G LTE 42 frequency band (S₁₁ less than −6 dB). The measured isolation of the MIMO antenna is greater than 25 dB by using the decoupling method in this paper. The envelope correlation coefficient of the proposed MIMO antenna is less than 0.08, its radiation efficiency is greater than 50%, and its gain is between 4.2 and 5.3 dBi in the whole operating frequency band.

This paper presents a triband antenna with a simple design for X-band applications. The proposed antenna is designed based on a patch with a truncated corner slot and complementary split-ring resonators in the ground plane. In this way, the antenna exhibits three operating bands and its resonant frequencies can be controlled independently by changing dimensions of the slot in the patch and the resonator structures in the ground plane. In addition, due to the antiresonant behavior of the complementary split-ring resonator structures, the antenna exhibits a notch-band characteristic at 10.7 GHz. A parametric study is performed to provide a detailed understanding of the independent resonance tuning behavior of the antenna. Both simulated and measured results of the proposed antenna are presented, which are in good agreement. The proposed antenna shows three operating bands in the X-band including (with absolute and relative bandwidths) 9.4–9.7 GHz (300 MHz, 3.14%), 10.3–10.6 GHz (300 MHz, 2.86%), and 11.05–11.32 GHz (297 MHz, 2.66%). In addition to that, a notched band of 10.6–11.05 GHz is introduced to exclude operation in the frequency bands of radiometric observation systems (10.6–10.7 GHz). To the best of our knowledge, this work is unique in its combination of independent tuning of three frequency bands of operation with single-layer implementation in the X-band. Such a structure provides additional degrees of freedom to the antenna design, customizing operation in the required bands while avoiding operation in other bands.

Aiming at the problems of poor data effectiveness, low modeling accuracy, and weak generalization in the tuning process of microwave cavity filters, a parametric model for coaxial cavity filter using kernel canonical correlation analysis (KCCA) and multioutput least squares support vector regression (MLSSVR) is proposed in this study. First, the low-dimensional tuning data is mapped to the high-dimensional feature space by kernel canonical correlation analysis, and the nonlinear feature vectors are fused by the kernel function; second, the multioutput least squares support vector regression algorithm is used for parametric modeling to solve the problems of low accuracy and poor prediction performance; third, the support vector of the parameter model is optimized by the differential evolution whale algorithm (DWA) to improve the convergence and generalization ability of the model in actual tuning. Finally, the tuning experiments of two cavity filters with different topologies are carried out. The experimental results show that the proposed method has an obvious improvement in generalization performance and prediction accuracy compared with the traditional methods.

A low cross-polarization microstrip antenna array for millimeter wave (mmW) applications is proposed in this paper. The antenna element is composed of symmetric T-shaped patches with vias. The adoption of a double-sided symmetric radiation patch structure can suppress the cross-polarized electric field, and the vias reduces energy leakage during the power transmission along the antenna patches. To verify the concept, a 1 × 8 antenna array is fabricated and measured. The measured −10 dB impedance of the antenna array is 28.4% (31 GHz–41.5 GHz) and the peak gain is 15 dBi. The cross polarization ratio is above 35 dB and the 3 dB beamwidths on E-plane and H-plane are 7.5° and 135°, respectively. The proposed compact size and low cross-polarization antenna array might be a good choice for phased array radar and 5th generation (5G) mobile communication applications.

In this paper, a quad-port multiple-input multiple-output (MIMO) semitransparent antenna is designed for automotive applications. The transparent soda lime glass substrate is used in the prototype antenna for windshield applications, and the radiator is nontransparent copper metal. The unit cell radiator of the MIMO antenna is similar to the “NISSAN automobile-like” logo. The proposed MIMO antenna has a −10 dB impedance bandwidth of 3.4 to 11 GHz. The edge-to-edge distance between the elements in the MIMO configuration is 6 mm. The antenna elements are perpendicularly oriented to offer dual (horizontal and vertical) polarization, which aids in providing better isolation and good signal reception in all directions. The isolation between the resonating elements is greater than 15 dB without the use of any decoupling structure. The diversity metrics are examined in order to gain a better understanding of the MIMO antenna performance. The envelope correlation coefficient (ECC) is less than 0.01, diversity gain (DG) is greater than 9.98 dB, and the total active reflection coefficient (TARC) and channel capacity loss (CCL) are less than −10 dB and 0.07 bits/s/Hz, respectively. The quad-port MIMO antenna offers transparency of 52.26% over the entire area. The proposed antenna could be suitable for automotive applications such as intelligent transportation systems (ITS), vehicular communications, and the automatic vehicle identifier (AVI).