Search

A broadband biomimetic antenna inspired by avian rib structures is presented in this letter. The antenna is composed of an arched dipole and two pairs of asymmetrical L-shaped stubs, along with dielectric materials conformally embedded to match the contour of avian ribs. Characteristic mode analysis is employed to analyze the operation of the antenna, revealing that the bandwidth expansion is attributed to the excitation of three modes. A prototype of the antenna is then fabricated and measured. The experiments are in good agreement with the simulation, and the results demonstrate that the antenna has a bandwidth of 50.8% with a 10 dB impedance bandwidth, exhibiting omnidirectional radiation and relatively stable gain. This antenna is suitable for use in frequencies used for Global System for Mobile Communication; Industrial, Scientific, and Medical applications; aerospace navigation systems; and the up-link control links of autonomous aerial vehicles.

A deception jamming method for wideband linear frequency modulation radar based on time-modulated array (TMA) is proposed in this letter. Different from other real-time modulation jamming methods using metasurface, the real-time modulated method based on TMA, where the system consists of discreet components of passive antenna, low-noise amplifier (LNA), analogy switches etc., shows merits of wide system bandwidth and extra gain for false targets. Hence, in view of the TMA-based method, this letter establishes the real and false targets’ amplitude model under nonuniform and uniform modulation. The situation of switches’ opening instant linearly varying with antenna order is introduced to manipulate false targets’ energy distribution in both observed angle and range directions. Numerical simulations are conducted to discuss the false-target characteristics under different modulation parameters. In the experiment, a two-element wideband jamming system covering 6 GHz to 18 GHz is constructed to demonstrate the proposed method's feasibility.

In this letter, a novel DNA-like all-metal structure, which can realize quasi-omnidirectional radiation with circular polarization (CP) in even mode and endfire directional radiation with CP in odd mode is proposed. The dispersion characteristics of the spoof surface plasmon polaritons structure in odd mode and even mode are thoroughly investigated. The proposed structure consists of two main components: the double helix arms and strips. The radiation fields of the helix arms and strips under the current distribution of the odd mode and even mode are independently analyzed to understand their contributions to the overall field. To excite the odd mode, a circular monopole is employed, while even mode is excited using a microstrip line. Experimental results demonstrate that the odd mode exhibits an impedance bandwidth of 39.9${\%}$ and an axial ratio (AR) bandwidth of 33.7${\%}$, while the even mode achieves an impedance bandwidth of 22.2${\%}$, along with quasi-omnidirectional CP radiation with an AR bandwidth of 1.03${\%}$.

This letter proposes a low-profile magnetoelectric (ME) dipole antenna based on a comb structure, as well as its application in a frequency-scanning array with the ground. Both the magnetic and electric dipoles of the ME dipole antenna consist of the comb structure. Due to the subwavelength characteristics of the comb structure, the profile of the proposed antenna is reduced by 72% to 0.065λc (λc is the wavelength at the center frequency) compared with the conventional ME dipole antenna. The measured results show that the single antenna has an impedance bandwidth of 14.65% (2.34 GHz to 2.71 GHz), a high gain (∼8 dBi), and high front-to-back ratios (>20 dB). Furthermore, by periodically extending the single antenna on the ground, a series-fed frequency-scanning array is designed to realize 1D scanning from –63° to 63° with gain fluctuation <2.5 dB. The array has the advantages of low cost, wide beam scanning range, low fluctuation of gain, high scanning rate, and small aperture and low profile with ground loaded (< 0.1λc), which owe considerable potential to be installed on the metal surface of the high-speed vehicle replacing the traditional phased array for wireless communication and detection.

A novel parallel calibration method was proposed and verified for phased arrays, by modulating phase shifters of multiple channels with multiple periods. After periodic phase modulation, the amplitude and phase mismatches can be calculated out through analyzing the generated harmonics in the composite signal. Compared with the existing method, two major advantages for the proposed method are as follows. First, the requirement for the dynamic range of the receiver is reduced, improving the calibration accuracy with the same signal-to-noise ratio. Second, the number and position of simultaneously calibrated channels can be flexibly selected. Besides, only one measurement is required to obtain all channel mismatches. Its main computation concentrates on the discrete Fourier transform for several harmonic components. Numeric simulations were provided to verify the effectiveness of the proposed method. An S-band 8-channel phased array was fabricated and tested to examine its performance and accuracy, acquiring root-mean-square-errors of 0.52 dB and 2.41$^\circ$ in amplitude and phase, respectively.

In this letter, a broadband direction-finding method with a three-element time-modulated array (TMA) is proposed. By combining the differences of baselines, a new phase degree of freedom is introduced to solve the problem of ambiguity caused by the large variation of carrier frequency, which enables the correct estimation of direction within broadband. Furthermore, the mathematical relation between the direction-finding bandwidth and baselines is discussed, which provides the guidance for the design of baselines’ distribution to achieve broadband direction finding using TMA within the desired bandwidth. Numerical simulations are provided to demonstrate the validation of the proposed method. A dual-band direction-finding system working at 2.48 and 5 GHz is constructed in the experiment to verify the feasibility of the proposed method.

The design of a high-efficiency single-sideband (SSB) time-modulated (TM) module is introduced, and the factors affecting the efficiency of the TM module, including harmonic efficiency, modulation utilization efficiency of radio frequency (RF) signal, and circuit efficiency, are discussed theoretically. To verify the theoretical analysis, a $C$ -band high-efficiency TM (HETM) module was designed, fabricated, and tested, and the calculated results are in good agreement with the measured results. The experimental results show that the +1st harmonic efficiency, the modulation utilization efficiency, and the circuit efficiency of the proposed HETM module are 81.0%, 98.5%, and 54.8%, respectively. The total efficiency is up to 43.7%, and the designed HETM module has the performance of a 6-bit phase shifter and attenuator, which is very suitable for the application of passive phased array antennas.