Search

Abstract This paper proposes an ultrathin K-band Frequency Selective Surface with one narrow passband and wide reflection bands. This 0.254 mm thick and soft FSS has only one passband under 30 GHz. Physical reasonings, simulations and experimental verifications are presented for it. Its measured 1 dB bandwidth is from 23.5 GHz to 24.6 GHz. This FSS structure is very insensitive to different polarizations and a large variation of the RF incident angle. Working as a low-profile radome for its covered antenna, this FSS is electromagnetic transparent within its passband; out of this passband, it helps the antenna achieve Radar Cross Section (RCS) reduction or protects the antenna from interference. It can be a good candidate for the applications such as antenna radomes and spatial filters, in which a wide frequency range of electromagnetic interference needs to be suppressed. [ABSTRACT FROM AUTHOR]

In this paper, a new method for designing stubs loaded SIR filter is presented. We can calculate the reflection coefficient of stubs loaded resonator directly by converting the admittance to input terminal. This method replaces the transmission matrix and even-mode and odd-mode analysis. Then, genetic algorithm (GA) is applied to search the corresponding electrical parameters, which provides a more effective and intuitive way to design filters. Then, an ultra-wideband bandpass filter using short-stub loaded SIR is realized, which exhibits a good frequency selectivity from 3.1 GHz to 10.4 GHz. In addition, by applying this method, a dual-passband filter with short and open stubs is achieved. It contains two wide bands at 2 GHz and 5.8 GHz, which concerns the frequencies of GPS and WLAN. Meanwhile, the sizes of these filters are further minimized by bend structure. Finally, the filters are manufactured. As a result, the measured results are in good agreement with the calculated ones. These filters exhibit great frequency-selection characteristics: flat passbands and extremely sharp rejections around the passband. So, based on the verifications of the manufactured filters, this method can be widely used in microwave filter design field. [ABSTRACT FROM AUTHOR]

In this paper, a new method for designing stubs loaded SIR filter is presented. We can calculate the reflection coefficient of stubs loaded resonator directly by converting the admittance to input terminal. This method replaces the transmission matrix and even-mode and odd-mode analysis. Then, genetic algorithm (GA) is applied to search the corresponding electrical parameters, which provides a more effective and intuitive way to design filters. Then, an ultra-wideband bandpass filter using short-stub loaded SIR is realized, which exhibits a good frequency selectivity from 3.1 GHz to 10.4 GHz. In addition, by applying this method, a dual-passband filter with short and open stubs is achieved. It contains two wide bands at 2 GHz and 5.8 GHz, which concerns the frequencies of GPS and WLAN. Meanwhile, the sizes of these filters are further minimized by bend structure. Finally, the filters are manufactured. As a result, the measured results are in good agreement with the calculated ones. These filters exhibit great frequency-selection characteristics: flat passbands and extremely sharp rejections around the passband. So, based on the verifications of the manufactured filters, this method can be widely used in microwave filter design field. [ABSTRACT FROM AUTHOR]

Based on the substrate integrated waveguide (SIW) and compact microstrip resonant cell (CMRC) technique, a compact and high performance planar bandpass filter (BPF) is proposed in this paper. The SIW cavity, which has the advantages of high quality and low insertion loss, provides a highpass characteristic. The CMRC structure etched on the top metal plane of the SIW cavity behaves as a lowpass filter, and it can also effectively reduce the dimension of the filter. In order to improve the out-of-band rejection and sharpen skirt selectivity, the open circuit lines at the input and output ports of the filter are introduced. Moreover, the bandwidth and center frequency of the proposed filter can be flexibly tuned by adjusting the cutoff frequencies of the SIW and CMRC separately. As a verification, a representative BPF having a center frequency of 4.54 GHz and a 3 dB bandwidth of 1.39 GHz is designed, fabricated, and experimentally evaluated. The simulated and measured results are in good agreement. [ABSTRACT FROM AUTHOR]

In this paper, a low-profile high-selectivity 2.5D FSS based on the dislocation patch structure is proposed and discussed. The dislocation patch structure is used to construct the low-profile transmission line, and a second-order band- pass FSS with a controllable transmission zero is realized by introducing a series LC structure to the dislocation patch structure. The effects of the geometrical parameters on the frequency response of the proposed second-order bandpass FSS are analyzed based on the transmission matrix method and the equivalent circuit simulation. Then, two proposed second-order bandpass FSSs with different transmission zeros are combined and placed crossly to construct two propagation paths, and a high-selectivity third-order FSS is obtained. Finally, the prototype is fabricated and measured to prove the effectiveness of the proposed FSS. The measured results show that the proposed high-selectivity FSS has a wide working bandwidth, proper selective performance, and a thinner profile than other high-selectivity 2D/3D FSSs. [ABSTRACT FROM AUTHOR]

In order to improve the angle measurement precision of LFM signals with a low computational complexity, a direction of arrival (DOA) estimation algorithm STFT-MI-ESPRIT is proposed in this paper. The algorithm is based on short time Fourier transform (STFT) and multiple invariance estimation of signal parameters via rotational invariance techniques (MI-ESPRIT). Firstly, the STFT of the array element’s output is calculated and the signals are transformed to the time-frequency domain. Then the spatial time-frequency distribution matrix can be obtained through selecting multiple single-source time-frequency points in the time-frequency plane and the signal subspace can also be obtained using Eigen decomposition. Finally, the multiple rotational invariant equation of the array based on STFT is obtained and the closed-form solution is obtained using the multi-least-squares (MLS) criterion. The simulation results show that the proposed algorithm can improve the estimation precision greatly compared with the traditional ESPRIT-like algorithms and its computational complexity remains the same in general. This paper also proposes that the STFT-MI-ESPRIT algorithm can use partial rotational invariances of the array instead of all the rotational invariances, which can reduce the computational complexity on the basis of ensuring the estimation precision basically. The simulation results verify the effectiveness of the conclusion. [ABSTRACT FROM AUTHOR]

A miniaturized Vivaldi antenna is presented in the paper. On the basis of original antenna, the miniaturized Vivaldi antenna applies parasitic patch and lumped resistor to improve impedance characteristics. The proposed load can expand the lower operating frequency to 1.96 GHz without changing antenna dimensions. The size of antenna is set as 43 × 40 mm 2 . This size is about 0.28λ L × 0.26λ L , where λ L is the free space wavelength at 1.96 GHz. The loaded Vivaldi antenna is fabricated and measured. The simulated and measured results clarify the viability and effectiveness of the proposed design. The measured impedance bandwidth (VSWR ≤ 2) is from 2 GHz to more than 18 GHz. In addition, the measured radiation patterns and a peak gain between −1 and 9 dB can be obtained in the band of 2–18 GHz. [ABSTRACT FROM AUTHOR]