Time-modulated Circular Array Research Articles

Generation and Beam Steering of Arbitrary-Order OAM With Time-Modulated Circular Arrays

In contrast to the popular multimode orbital angular momentum (OAM) generation method that uses uniform circular array combined with phase shifter network, time-modulated circular array (TMCA) does not require multiple radio frequency chains and costly analog devices and it requires only switches. In this article, an arbitrary-order OAM generation and beam steering method for TMCA is proposed, which incorporates the existing integer-order OAM generation and beam steering method as a special case. Furthermore, we analyze the effect of elements <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> – <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> ordering on the generation of OAM beams, and prove that sequential ordering has the lowest power consumption. Finally, the effectiveness of the proposed methods is validated through electromagnetic simulations.

Multiuser Communication by Electromagnetic Vortex Based on Time-Modulated Array

A novel multiuser communication system based on the time-modulated circular array (TMCA) has been proposed in this letter. Different modes of electromagnetic vortex waves are generated through TMCA by the transmitter, and each mode carries a different user's signal. To realize this mode-division multiplexing method, users’ messages are modulated to different intermediate frequencies beforehand. Users’ signals are received also by TMCA. Because of the modulation of the TMCA, different users’ signal are moved to different frequencies so they can be distinguished by bandpass filters. The proposed method implements the mode-division multiplexing with a single RF channel, which has advantages in the hardware complexity and cost. The process of transmitting and receiving is analyzed, and the drawbacks are discussed. Simulations are conducted to verify its effectiveness.

Beam steering for OAM beams using time‐modulated circular arrays

The theory of time-modulated circular arrays in respect of generating orbital angular momentum (OAM) beams at harmonic frequencies is analysed. Without using expensive phase shifters in phased arrays, beam steering for OAM beams is achieved using switches connected to array elements. The model of an eight-element time-controlled circular array is derived with the method of time-modulation beam steering techniques. Simulation results show that beam steering for OAM beams is realised, which indicates the effectiveness of the proposed method.

Pattern synthesis of time-modulated conformal arrays by an improved differential evolution algorithm

In this article, an improved differential evolution algorithm IDE based on two different colonies is proposed and applied to time-modulated conformal arrays syntheses. The whole population of IDE is divided into two parts. The one part searches the solution globally while the other searches the neighborhood of the solution provided by the previous one. Benchmark functions are provided to testify IDE. Furthermore, IDE is applied to synthetize sum-difference patterns with a 1 × 16 elements time-modulated circular array and low sidelobe level SLL patterns with an 8 × 12 elements time-modulated cone array. After optimization, the sideband level SBL of the circular array at the first sideband frequency is -1.00 dB. The SLL and SBL at the first sideband frequency of the cone array are lower than -30.00 and -20.00 dB, respectively. Experiment results verify the superior performance of IDE. Moreover, to accelerate the computation speed, graphics processing unit parallel computing technique is introduced into pattern synthesis and the acceleration ratios of more than 23 times can be achieved. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:697-705, 2014.

Pattern Synthesis with Specified Broad Nulls in Time-Modulated Circular Antenna Arrays

This article presents an approach for the synthesis of time-modulated circular array patterns with specified null width constraints. The time-modulated circular antenna arrays with uniform amplitude excitations are designed through the differential evolution algorithm with their excitation phases, and the switch-on time intervals of each element of the time-modulated circular arrays are the variables to be optimized. Several examples synthesized from the time-modulated circular array with the prescribed null width and depth are compared with some published results of the conventional circular array. Simulation results illustrate the achievable performance of the approach in successfully synthesizing patterns with desirable broad nulls, even if the amplitude excitations are uniform.

Synthesis of Low and Equal-Ripple Sidelobe Patterns in Time-Modulated Circular Antenna Arrays

In this paper, the time modulation technique is applied into circular antenna arrays with uniform amplitude excitations for the synthesis of ultra-low sidelobe and equal-ripple radiation patterns. The differential evolution (DE) algorithm is adopted to optimize the excitation phases and the switch-on time intervals of each element of the time-modulated circular array (TMCA). Several low-sidelobe patterns synthesized from TMCAs were compared to those of the conventional circular arrays. Numerical results show that the TMCA can be successfully used for the synthesis of low SLLs even if the amplitude excitations are uniform.