Ruilin Yao

Directional Modulation Based on 4-D Antenna Arrays

Four-dimensional (4-D) antenna arrays are formed by introducing a fourth dimension, time, into traditional antenna arrays. In this paper, a time-modulated 4-D array with constant instantaneous directivity is proposed for directional modulation. The main idea is that the 4-D array transmits correct signal without time modulation in the desired direction, while transmitting time-modulated signals in other directions. As longs as the time modulation frequency is less than the bandwidth of the transmitted signal, the time-modulated signals cannot be demodulated correctly due to the aliasing effect, implying that time-modulated signals go distorted. Thus, the 4-D array can be used to transmit direction-dependent signals in secure wireless communications. The proposed idea is verified by experiments based on AM signal transmission through the 4-D array. Moreover, BPSK signal transmission through the 4-D array is studied and the bit error rate (BER) performance is investigated. Simulation results show that the BERs of time-modulated BPSK (TM-BPSK) signals transmitted through the sidelobes of the 4-D array are much higher than those of BPSK signals and almost keep unchanged even under higher SNR. Finally, two enhanced methods are presented to improve the feasibility of directional modulation by using random time sequences and random time modulation frequency.

Unified Time- and Frequency-Domain Study on Time-Modulated Arrays

Time-modulated arrays (TMAs) are studied in the time domain and frequency domain in this paper. The studies are based on the “instantaneous” array factor as a function of time and “average” array factor as a function of frequency, respectively. The two analysis approaches are shown to be unified and complementary through the Fourier transform. Antenna parameters including pattern, directivity, and gain are all addressed. Moreover, an experimental setup for the study of signal transmission is built and measured. Experimental results are in good agreement with the theoretical study. Finally, the bandwidth of TMAs is taken into account, and amplitude modulation (AM) signal transmission through the TMA is studied experimentally. The results presented in this paper can be used to explain the fundamental working principle of TMAs in a clear and comprehensive way.

Gain Improvement in Time-Modulated Linear Arrays Using SPDT Switches

Time-modulated linear arrays (TMLAs) based on single-pole-single-throw (SPST) switches usually have higher reduction in gain due to the sideband radiation and power absorption of the off-state absorptive switches. In this letter, a novel approach is proposed to improve the gain of TMLAs using single-pole-double-throw (SPDT) switches. The gain of the proposed TMLA can be improved significantly by controlling two array elements with each SPDT switch. Moreover, the proposed TMLA has a constant instantaneous directivity, which is favorable for some applications. Numerical results are presented to illustrate the proposed approach by considering a 16-element linear array with a -30 dB sidelobe level.

Direction Finding Using Multiple Sum and Difference Patterns in 4D Antenna Arrays

Traditional monopulse systems used for direction finding usually face the contradiction between high angle precision and wide angle-searching field, and a compromise has to be made. In this paper, the time modulation technique in four-dimensional (4D) antenna array is introduced into the conventional phase-comparison monopulse to form a novel direction-finding system, in which both high angle resolution and wide field-of-view are realized. The full 4D array is divided into two subarrays and the differential evolution (DE) algorithm is used to optimize the time sequence of each subarray to generate multibeams at the center frequency and low sidebands. Then the multibeams of the two subarrays are phase-compared with each other and multiple pairs of sum-difference beams are formed at different sidebands and point to different spatial angles. The proposed direction-finding system covers a large field-of-view of up to ±60° and simultaneously maintains the advantages of monopulse systems, such as high angle precision and low computation complexity. Theoretical analysis and experimental results validate the effectiveness of the proposed system.

DESIGN OF A LOW SIDELOBE 4D PLANAR ARRAY INCLUDING MUTUAL COUPLING

An e-cient approach is presented for the design of a low sidelobe four-dimensional (4D) planar antenna array, taking into account mutual coupling and platform efiect. The approach is based on the combination of the active element patterns and the difierential evolution (DE) algorithm. Difierent from linear and circular arrays, the mutual coupling compensation in a planar array is more complicated since it requires numerous data of the active element patterns in difierent azimuth planes. In order to solve this problem, a useful interface program is developed to get these data from commercial software HFSS automatically. Also difierent from conventional low sidelobe arrays with tapered amplitude excitations, the low sidelobe in the 4D array is realized using time-modulation technique under uniform static amplitude and phase conditions. The DE algorithm is used to optimize the time sequences which are equivalent to the complex excitations in conventional arrays. Both computed results and simulated results in HFSS show that a i30dB sidelobe pattern can be synthesized in a 76-element planar array with an octagonal ground plane and a radome, thus verifying the proposed approach.

A dual-polarized circular stacked patch antenna for pico base stations

A compact dual-polarized circular patch antenna with high isolation and low cross-polarization level for pico base station is presented. Stacked structure and dual-feed mechanism are employed in the design. Two slots around each feed point are cut on the lower patch to reduce the antenna size and enhance the bandwidth. The antenna occupies an area of 45mm×45mm and has a thickness of 5.5mm. Simulated results show that the proposed antenna achieves 7.3% bandwidth (VSWR<;1.4), operating between 2.5GHz and 2.69GHz. The isolation between the two polarized ports is more than 40 dB over the entire bandwidth. A stable low cross-polarization level of -40 dB is obtained in both the principle planes.

Analysis and design of Luneberg lens antenna with simultaneous Ku/K/Ka-band feed-system

Multiple frequencies and polarizations Luneberg lens antennas (LLA) suitable for broadband satellite communication terminals have been designed and implemented. An efficient multiobjective evolutionary algorithm based on decomposition (MOEA/D) with differential evolution operator is coupled to the vector spherical wave function expansions (VSWE) to analyze and design a LLA with simultaneous Ku/K/Ka-band feed-system. Numerical performance of a 650mm diameter 7-layer LLA is presented to show the validity of this study.