Longjian Zhou

Single-Fed Low-Profile High-Gain Circularly Polarized Slotted Cavity Antenna Using a High-Order Mode

In this letter, a single-fed low-profile high-gain circularly polarized slotted cavity antenna using a high-order cavity mode, i.e., TE440 mode, is proposed. The proposed antenna has a simple structure that consists of a radiating linearly polarized slotted cavity antenna and a linear-to-circular polarization converter. An antenna prototype operating at WLAN 5.8-GHz band fabricated with low-cost standard printed circuit board (PCB) process is exemplified to validate the proposed concept. Measured results compared to their simulated counterparts are presented, and a good agreement between simulation and measurement is obtained.

Fast Performance Prediction of Cascaded Bandpass Frequency Selective Surfaces Operating in Circular Polarization Including Oblique Incidence

In this letter, a second order bandpass frequency selective surface (FSS) operating in circular polarization (CP) is analyzed and designed. The transmission line method (TLM) combined with an interpolation scheme is proposed to analyze the FSS. Based on some sampled full wave results of the corresponding single layered FSS, the double layered second order FSS is analyzed efficiently. GFRP with relatively high permittivity and high strength is used as skin to protect the whole FSS. Foam with low permittivity is used as an interlayer to achieve low weight. This kind of dielectric configuration leads to different phase characteristics for TE and TM polarizations at oblique incidence. This difference influences the performance of the FSS operating in circular polarization, such as increasing the axial ratio (AR) of the circularly polarized wave. Optimization for AR in passband is done with the proposed method by varying dielectric thicknesses. Finally, a prototype of the optimized FSS is fabricated and measured. The measured results agree well with the simulated ones.

Calibration method of phased array based on near-field measurement system

A new phased array calibration method based on near-field measurement system such as NSI is proposed in this paper. By measuring a single element antenna near-field and array near-field, calibration parameter is extracted from measured data with twice Fourier Transformation and once Inverse Fourier Transformation. Both amplitude and phase calibration is realized by this method in a very short time. A calibration example of a one-dimensional array is used to validate the proposed method.

Conformal antennas based on holographic artificial impedance surfaces

Advances in artificial impedance surface conformal antennas are presented. A detailed conical impedance modulation is proposed for the first time. By coating an artificial impedance surface on a cone, we can control the conical surface wave radiating at the desired direction. The surface impedance is constructed by printing a dense texture of sub wavelength metal patches on a grounded dielectric slab. The effective surface impedance depends on the size of the patches, and can be varied as a function of position. The final devices are conical conformal antennas with simple layout and feeding. Simulated results are presented, and better aperture efficiency and lower side lobe level are obtained than our predecessors [2].

Design of License Plate RFID Tag Antenna Using Characteristic Mode Pattern Synthesis

A novel design of the passive license plate radio frequency identification tag antenna in UHF band based on the characteristic mode theory (CMT) is proposed in this paper. The license plate is operated as a tag antenna since it is conductor (made of aluminum). A desired up-tilted pattern beam is achieved successfully by using a direct CMT-based radiation pattern synthesis procedure. The pattern can be expanded as a superposition of some specific characteristic modes pattern, which is identified according to characteristic mode analysis of the plate. Four coupling slots are exploited to excite the selected modes current distribution. The mode weighting coefficients can be tuned to form the desired pattern beam by changing the relative phase between the coupling slots. The feed structure is carefully designed without damaging the layout of characters and numbers on the license plate. The synthesized radiation pattern corresponds with the pattern simulated by HFSS. The measured radiation pattern proves that the proposed design is reliable and applicable. The measured read range is about 20 m, which can satisfy the actual requirements.

Fast Amplitude-Only Measurement Method for Phased Array Calibration

A novel amplitude-only measurement method is proposed to measure the signals (complex fields) of individual antenna elements for phased array calibration. The proposed method has minimum measuring time among the known amplitude-only measurement methods. The total number of power measurements with this method is about twice the number of antenna elements of phased array. Phase shifters are required to implement only three phase shifts (0°, 90°, and 180°). Array signal power is measured when the phase setting of an antenna element is one of the three phase shifts. According to the superposition principle of electromagnetic field, array signal is a linear combination of antenna element signals. As signal power is the inner product of a complex signal and itself, a set of linear equations concerning the inner products of the antenna element signals are established and solved with the measured data. The element signals are obtained with the inner products analyzed with a set of nonlinear equations. Numerical simulations and experimental results validated the effectiveness of the proposed method in calibrating phased arrays.

An Efficient Method for Calculation the Physical Optics Integral by Using Complex Source Beam for Electrically Large Reflector Antenna Applications

ABSTRACT The physical optics method is a widely used radiation and scattering estimation for electrically large-scaled objects, and it is finally reduced to the calculation of highly oscillatory integrals. In this article, the physical optics integrals over the reflecting surface for an incident complex source point is evaluated here in closed form. A complex source point can generate a beam field, which is employed to expand an arbitrary source via a complex extension of the surface equivalence principle. Then the complex source beam expansion method is applied to analyze the field of large reflector antennas via physical optics method. Numerical examples are presented to illustrate the accuracy and efficiency of this complex source beam-physical optics hybrid method for analyzing general parabolic reflectors.

Frequency selective surface with wide passband and stopband performance operating in L/S band

Frequency selective surface (FSS) with wide passband and ultra-wide stopband performance is investigated in this paper. The proposed cascaded FSS consists of three metallic layers and multilayer dielectric substrates. A novel inductive layer with the shape of spiral meander line is proposed to synthesize a large inductance to increase the bandwidth of passband. The constituting elements in cascaded structure are non-resonant during the operation band, thus, high order modes are avoided effectively in a wide frequency range. Finally, a flat passband from 1.84 to 2.40 GHz (insertion loss less than 0.86 dB) and an ultra-wide reflection band of 25.1 GHz (transmission coefficients lower than -20 dB) are achieved. This proposed cascaded FSS is a promising candidate for the applications of spatial filter and anti-interference.

ADI Scheme of a Nonstandard FDTD Method and Its Numerical Properties

An alternating direction implicit (ADI) scheme for a nonstandard (NS) finite-difference time-domain (FDTD) method is proposed. The NS FDTD method is derived by analyzing the dispersion relation. Two different groups of update coefficients are used to update the electric field and magnetic field, respectively. The dispersion property of the NS method is similar with that of the standard higher order method, though it is only second order accurate in the space domain. The total number of nonzero update coefficients for this method is fewer than that of the latter. This small stencil property can be used to reduce computational burden in implicit formulation of this method. The one-step leapfrog ADI scheme is adopted to examine this idea. The detailed update equations of this ADI scheme are derived. The dispersion and stability properties are also analyzed and compared with the corresponding standard one. The results show that the computational efficiency of the proposed method is higher than that of the standard one.

Radar cross section reduction of dipole antenna using checkerboard surface

The radar cross section (RCS) reduction technique for dipole antenna using checkerboard surface is investigated. The checkerboard surface is used as ground of dipole antenna instead of a metal ground. In the operating frequency band of the antenna, the checkerboard surface can reflect electromagnetic wave nearly in phase, thus the radiation performance of the antenna is not degraded. However, for the out of band case, the scattered fields by two types of subarrays of the checkerboard surface are out of phase, which lead to reduced RCS of the antenna when compared with that loaded with metal ground. Results show that broadband RCS reduction can be achieved with few influence on the radiation properties in terms of both S-parameter and radiation pattern.