An enhanced wideband tracking method for characteristic modes (CMs) is investigated in this paper. The method consists of three stages, and its core tracking stage (CTS) is based on a classical eigenvector correlation-based algorithm. To decrease the tracking time and eliminate the crossing avoidance (CRA), we append a commonly used eigenvalue filter (EF) as the preprocessing stage and a novel postprocessing stage to the CTS. The proposed postprocessing stage can identify all CRA mode pairs by analyzing their trajectory and correlation characteristics. Subsequently, it can predict corresponding CRA frequencies and correct problematic qualities rapidly. Considering potential variations in eigenvector numbers at consecutive frequency samples caused by the EF, a new execution condition for the adaptive frequency adjustment in the CTS is introduced. Finally, CMs of a conductor plate and a fractal structure are investigated to demonstrate the performance of the proposed method, and the obtained results are discussed.

This paper presents a novel dual-band (DB) dual-polarized (DP) shared aperture antenna with high isolation by using a combination of microstrip dipoles and dielectric resonator antennas (DRAs) for S and C bands, respectively. In the S band, two sets of proximity coupled stacked microstrip dipoles which crossed at the center are employed to achieve dual-linear polarization (DLP) and obtain desired bandwidth (BW), isolation, and pure polarization. The rectangle DRA with hybrid feed is selected as the C band element for its advantages of small base area and high isolation, and a 2 × 2 array is presented with the “pair-wise” anti-phase feed technique to achieve a low cross-polarized level. Moreover, benefited from the back feed scheme, the proposed antenna has a symmetrical structure and has the potential of expanding into a larger aperture. The proposed antenna has been manufactured and measured, and the results agree well with simulations, which prove the validity of the proposed design.

This paper proposes a new radar cross section (RCS) reduced microstrip antenna incorporating 475 square slots on the patch. The proposed antenna achieves wideband RCS reduction with radiation performance sustained. The modified and reference antenna are simulated and analyzed in radiating and scattering mode, respectively. Prototypes of two antennas are fabricated and measured. Compared with the reference antenna, the simulated result shows the modified antenna RCS reduced in the frequency range 1.1–2.6 GHz, which contains the in-band and out-of-band frequency band simultaneously. And the maximum RCS reduction is 7.6dB at the frequency of 1.19GHz. Besides, the modified antenna can achieve the antenna RCS reduction in the case of oblique incidence. The prototypes of two antennas are fabricated and measured, and the accuracy of the simulation is proved by the measured result. Due to its advantages of simplicity, wideband RCS reduced, broad-angle RCS reduced, the method in this paper is suitable for wideband antenna RCS reduction in space-limited environment.

A novel online antenna array calibration method is presented in this paper for estimating direction-of-arrival (DOA) in the case of uncorrelated and coherent signals with unknown gain-phase errors. Conventional calibration methods mainly consider incoherent signals for uniform linear arrays with gain-phase errors. The proposed method has better performance not only for uncorrelated signals but also for coherent signals. First, an on-grid sparse technique based on the covariance fitting criteria is reformulated aiming at gain-phase errors to obtain DOA and the corresponding source power, which is robust to coherent sources. Second, the gain-phase errors are estimated in the case of uncorrelated and coherent signals via introducing an exchange matrix as the pre-processing of a covariance matrix and then decomposing the eigenvalues of the covariance matrix. Those parameters estimate values converge to the real values by an alternate iteration process. The proposed method does not require the presence of calibration sources and previous calibration information unlike offline ways. Simulation results verify the effectiveness of the proposed method which outperforms the traditional approaches.

This paper proposes a microstrip antenna with reduced in-band and out-of-band radar cross-section (RCS) by subtracting the area of weak scattered current on the ground plane. Fourteen square slots were subtracted from the ground plane, reducing in-band and out-of-band RCS while maintaining radiation performance. Modified and reference antenna surface current distributions were simulated and analyzed in radiating and scattering modes. Two antenna prototypes were fabricated and measured to verify the simulation. The proposed antenna RCS was reduced compared with the reference antenna in the frequency range 1–4.4 GHz, including in-band and out-of-band frequency bands. Maximum in-band and out-of-band RCS reduction was 16.3 dBsm at the working frequency, and 19.3 dBsm at 3.4 GHz, respectively

In this study, a new microstrip patch antenna with wideband radar cross-section (RCS) reduction is presented. The RCS of the proposed antenna was reduced by subtracting the current-direction slots of the patch, with the radiation performance sustained not only for the current-direction subtraction, but also for the no modification in the ground plane. Modified and reference antenna were fabricated and measured. The simulation and measurement results showed that the modified antenna reduced the in-band and out-band RCS simultaneously with no detriment to the radiation performance. In the frequency band from 3.9 to 8.1 GHz, the RCS of the modified antenna was reduced in the whole band compared with the RCS of the reference antenna. The maximum RCS reduction was 7 dB at a frequency of 6.7 GHz.

In this paper, a metasurface-based aperture-coupled circularly polarized (CP) antenna with wideband and high radiation gain is proposed and analyzed. The proposed antenna is comprised of coplanar waveguide coupling with 4 × 4 corner truncated square patches, which show compact size and low profile. The mechanism of the CP antenna is analyzed theoretically based on the mode analysis and equivalent circuit analysis. The parameters of feeding structure and truncated corner are studied and optimized to achieve wide impedance bandwidth (BW) and axial ratio (AR) BW. Finally, an overall size of 38.8 mm × 38.8 mm × 3.5 mm (0.71λ0 × 0.71λ0 × 0.064λ0 at 5.5 GHz) CP antenna is proposed and fabricated. The simulated results demonstrate that over 41.7% impedance BW (S11 < −10 dB) of 4.55–6.95 GHz and 3 dB AR BW of 5.05–6.15 GHz (fractional BW is about 19.6%) are achieved. In addition, the antenna yielded a broadside CP radiation with a high gain average about 7.5 dBic. Experimental results are in good agreement with the simulated ones.

A wideband and high-efficiency polarization conversion metasurface (PCM) is proposed and applied to reduce radar cross section (RCS). The proposed PCM unit is composed of two oblique asymmetry triangle split rings, which generate multiple plasmon resonances. Simulated and measured results demonstrate that it achieves polarization conversion over 90% from 9.24 to 17.64 GHz. Besides square checkerboard, the proposed PCM units and mirror units are arranged in triangle checkerboard. The mechanisms of both checkerboard PCMs are analyzed based on standard array theory, including the relationship between RCS reduction value and polarization conversion ratio value. The derived formulas provide a guideline to design checkerboard structure based on PCM. Simulated results demonstrate that both checkerboard PCMs achieve over 62% relative bandwidth of 10 dB RCS reduction under normal incidence with respect to the equal-sized metallic plate, which also means that the triangle one could be an alternative solution to reduce RCS. To verify the analyzed and simulated results, the fabricated sample and measured results of both checkerboard PCMs are presented. Good agreements are achieved between measurements, simulations and numerical analysis.

In this paper, a high gain broadband low profile microstrip antenna with the dual-layered substrate and four parasitic metal elements is presented. The proposed microstrip antenna is mainly composed of four parts: four circular parasitic metal patches with dual arced breaches, a rectangular metal patch sandwiched between substrates, a square ground plane, and two-square substrates. The circular parasitic elements are the main radiation structure and determine the characteristics of the proposed antenna are closely related to the parasitic elements. The proposed antenna has been fabricated for experimental measurement. The reflection coefficient, radiation pattern, radiation efficiency, and gain have been studied in detail. The simulated and measured impedance bandwidth is 27.0% (3.30–4.33 GHz), the maximum realized peak gain reaches up to 6.52 dBi at the frequency of 3.65 GHz. The radiation pattern has a single peak which is perpendicular to the surface of the substrate. The proposed antenna is suitable to be applied in the 5G mobile or WiMAX wireless communication. Dual antenna with a pair of parasitic elements has been investigated numerically to explain the principle of the proposed antenna.

In this paper, a coplanar waveguide (CPW)-fed dual-band uniplanar tri-polarization reconfigurable antenna based on the PIN diode switch is proposed. The proposed antenna can be reconfigured between the linear polarization (LP) and the circular polarization (CP) mode, including both the right-handed circular polarization and left-handed circular polarization simultaneously within the dual operating bands. The central frequencies of the bands are 2.63 and 4.42 GHz, respectively, and the overlapped operating bandwidth is 17.8 and 3.40%. The proposed reconfigurable antenna is a closed-slot antenna fed by the CPW transmission line and the reconfigurable mechanism is to regulate the T-shaped driven stub through switching the PIN diodes on and off. The scattering parameters, axial ratio, radiation pattern, gain, and the radiation efficiency of the proposed antenna are all investigated in the following. The optimized antenna has been fabricated to experimental test, the simulated and the measured results agree well with each other. The lower frequency band of the proposed antenna covers the 2.40 GHz WLAN specification and the upper band can be used for the 5 G communication (4.40–4.50 GHz); therefore it is suitable to be applied in the mobile wireless communication.

In this study, a dual-layered polarization and frequency reconfigurable microstrip antenna is proposed based on sequential mechanical axial rotation of the circular metal radiator. The antenna can be reconfigured among three different polarized modes, including the linear polarization (LP), left-handed circular polarization and right-handed circular polarization in the band from 4.68 to 4.80 GHz (2.53%). The resonance frequency of the proposed antenna with the same LP mode could also be tuned in the range from 4.70 to 5.03 GHz by mechanical rotation of the breach-truncated circular metal radiator as well as the circular substrate. Furthermore, the polarization characteristic and frequency can be reconfigured, respectively, as the circular radiator is taken an axial rotation with an angle of 360°. The presented antenna in the four different states has been numerically simulated and fabricated for the experimental measurement, the investigated characteristics includes the port reflection coefficient, axial ratio, radiation pattern, gain, and the radiation efficiency. The simulated and test results agreed well with each other. This antenna enriches the novel mechanical reconfigurable method except for the popular electrical approach.