Jixin Guo

A Study on Linear Frequency Modulation Signal Transmission by 4-D Antenna Arrays

This paper presents a study on linear frequency modulation (LFM) pulsed signal transmission by four-dimensional (4-D) antenna arrays. LFM pulse is used as the input of 4-D antenna arrays and the influence brought by the periodic time modulation is analyzed. The relationship among pulse duration, chirp rate, sample frequency, time-modulation frequency, and propagation direction is analyzed and the restrictions to these parameters are highlighted. The transmitting and receiving structures are introduced and relevant signal processing steps are described. Numerical examples with several different time schemes, including the pulse shifting (PS) scheme and binary phase center motion (BPCM) scheme, are presented to demonstrate the effectiveness of the LFM signal transmission by 4-D arrays. Simulation results validate that original chirp signal can be correctly recovered and low sidelobe power patterns can be simultaneously achieved by 4-D antenna arrays, as long as the proposed limitations are satisfied.

An Improved Phase Modulation Technique Based On Four-Dimensional Arrays

An improved phase modulation technique based on four-dimensional (4-D) antenna arrays is proposed in this letter. The modified control unit consists of two single-pole double-throw switches and four different delay lines (0, 0.5 <italic>π</italic>, <italic>π</italic>, and 1.5<italic>π</italic>). Each control unit connects the feeding network with the array elements. This structure generates nonuniform phase and amplitude excitations at the carrier frequency without using conventional phase shifters and attenuators. It allows the arbitrary angle beam-steering and beamforming by adjusting the time scheme of the switches. It is worth pointing out that all the switches are always in the “<sc>on</sc>” states to improve the radiation efficiency.

4D antenna arrays for LFM signal transmission

The application of four-dimensional (4D) antenna arrays for linear frequency modulation (LFM) signal transmission is investigated in this paper. LFM pulse is used as the input of 4D antenna arrays and the influence brought by the periodic on/off switches are analyzed. The relationship among pulse duration, chirp rate, sample frequency, time-modulation frequency and propagation direction is analyzed, and then two constraints and two conditions are highlighted. Numerical examples with two different time schemes, including the pulse shifting (PS) scheme and binary phase center motion (BPCM) scheme, are presented and compared to demonstrate the effectiveness of the LFM signal transmission by 4D arrays. Simulation results validate that original chirp signal can be correctly recovered with low side lobe power patterns, as long as the proposed limitations are satisfied.

An efficient approach for synthesizing irregularly shaped patterns based on 4D arrays

An efficient approach based on the combination of Woodward-Lawson method and differential evolution algorithm is proposed for synthesizing the irregularly shaped radiation patterns based on 4D planar arrays. Owing to the time-modulation of 4D arrays, the ripples in the coverage area and the side lobe levels are suppressed effectively. By combining the analytical method and optimization algorithm, the optimized time sequences and element excitations can be obtained. Radiation efficiency of time-modulated planar arrays also has been optimized and a significant improvement is achieved. Results of numerical examples demonstrate the effectiveness of the proposed method.

4D-arrays for MIMO radar applications

A novel approach for multiple-input multiple-output (MIMO) radar applications is proposed, namely four-dimensional orthogonal frequency (4D-OF), which applies the technique of four-dimensional arrays (4D-arrays) and frequency stepping. The sidebands of the 4D array are utilized to generate multiple orthogonal carrier frequencies and transmit signals. The time sequences are optimized by the differential evolution (DE) algorism to synthesize a desired radiation pattern with a better directivity compared to frequency division MIMO. A linear FM (LFM) pulse signal is input to the 4D array and is spread at the center frequency and a few sidebands in the same direction. An analytic expression for the cross correlation function of these sideband signals is presented to study the relationship between pulse duration and time-modulated frequency. Without the use of numerical mixers, the 4D-OF is a good candidate for the MIMO radar. Some simulation results are presented to demonstrate the effectiveness of this method.

Realization of multiple orbital angular momentum modes simultaneously through four-dimensional antenna arrays

Electromagnetic waves carrying orbital angular momentum (OAM) in radio frequency range have drawn great attention owing to its potential applications in increasing communication capacity. In this paper, both single-pole single-throw (SPST) switches and single-pole double-throw (SPDT) switches are designed and implemented. Optimal time sequence allows four-dimensional (4-D) circular antenna array to generate multiple OAM-carrying waves as well as enhance the field intensity of each OAM-carrying wave. A novel experimental platform is developed to measure the phase distribution when the transmitting antenna and the receiving antenna operate at different frequencies. The good agreement between the measurement and simulation results demonstrate that 4-D circular antenna array is able to generate multiple OAM modes simultaneously. Furthermore, the superiority of the 4-D circular antenna array in receiving and demodulating multiple OAM-carrying signals is validated through the filter and bit error rate (BER) simulations.

Efficient Sideband Suppression in 4-D Antenna Arrays Through Multiple Time Modulation Frequencies

A novel approach, named multiple time modulation frequency, is proposed for the effective suppression of the sideband radiations in 4-D antenna arrays. The time modulation frequency, different for each array element, is exploited as additional design parameter to avoid the superposition of the sideband frequencies generated by the array elements. A customized optimization strategy including the analysis of the mutual coupling effects among the array elements is proposed for the 4-D array synthesis. Selected numerical and experimental results are provided to show that the sideband level of a 4-D antenna array can be significantly reduced by properly designing the switch-on time intervals of each element, even with uniform amplitude excitations.

A Study on the Application of Subarrayed Time-Modulated Arrays to MIMO Radar

A novel application of time-modulated arrays to multiple-input–multiple-output (MIMO) radar is presented and studied. The proposed scheme is to partition the transmit antenna of MIMO radar to a number of time-modulated subarrays that are overlapped. A series of orthogonal waveforms are emitted by these time-modulated subarrays with the unidirectional phase center motion time scheme. The resulting system can be referred to as subarrayed time-modulated MIMO (STM-MIMO) radar. As the tradeoff of conventional phased-array and MIMO radars, the STM-MIMO radar can obtain the coherent processing gain and waveform diversity gain simultaneously. The performance in terms of output signal-to-interference-plus-noise ratio and transmit/receive beampattern for the STM-MIMO radar is highlighted and compared to that of phased-array and MIMO radars. Simulation results validate the effectiveness of the proposed STM-MIMO radar technique.

An effective hybrid optimization algorithm for the synthesis of 4-D linear antenna arrays

Some major global optimization algorithms, which involves all the optimized variables in one problem, were used to synthesize time-modulated linear antenna arrays (TMLAs) in the existing literature. In this work, a hybrid approach, combining differential evolution (DE) algorithm and convex optimization, is proposed. This hybrid method is performed to optimize the static excitations amplitude and the switch-on duration time of TMLAs in order to achieve ultralow sidelobe and low sideband radiation at the same time effectively. In one iteration, as long as a set of switch-on duration time is fixed by the DE algorithm, Then the problem with respect to the static excitation is convex. So a convex optimization programming can solve the static excitation which is best for the corresponding set of switch-on time. The approach makes full use of the convexity of the problem with respect to the static excitation variables. Consequently, DE algorithm is used to optimize the switch-on time variables only. Which means fewer optimized variables are needed and it is more likely to find the global optimal solution in a less iterations. So that faster convergence can be obtained compared to DE algorithm which includes all optimized variables, especially for larger arrays. Furthermore, some examples are presented to demonstrate the effectiveness of this hybrid approach. First is a 32-element broadside TMLAs, with half wavelength uniform spacing, which is concerned for synthesizing a ultralow sideband at the same time suppress the sideband radiation pattern. Second is to sparse a uniform spaced 30-element TMLAs with fewer element satisfies the requirement of pattern. The last is to synthesis shaped beams. For the first example, numerical results show that a -61.4 dB sidelobe pattern with a static excitation amplitude ratio 4 can be synthesized, while the sideband level (SBL) is suppressed to -32.1 dB. For the second example, we can only use 18-element to achieve a -23.8 dB sidelobe and -31.3 dB SBL pattern with a static excitation amplitude ratio 2.77.

Efficient sideband suppression in 4D antenna arrays with multiple time modulation frequencies

A novel approach named multiple time modulation frequency (MTMF) is proposed for the effective suppression of sideband radiations in four-dimension (4D) antenna arrays. Each array element is operating at different frequencies and the sidebands of different units are avoided to be superimposed at the same frequencies. It results in the effective reduction of the maximum sideband levels. With the combination of MTMF and optimization strategy, a hybrid pattern synthesis approach is then proposed. This method is expected to pave the way of novel wireless systems with the lowest possible sideband radiations.