The direction finding method by the time modulated linear array (TMLA) is analyzed and verified. The direction of arrival (DOA) can be calculated out by analyzing the spectrum characteristic of the received signal after the time modulation. Its principle is as follows. Because of the periodic modulation, the fundamental and harmonic components are generated in each element simultaneously. After the combiner, the harmonic components’ characteristic of the combined signal is influenced by the DOA. Through analyzing their mathematical relationship, the DOA can be calculated out directly. Compared to existing direction finding methods, the proposed method has two main advantages. One is that only a single RF channel is used, the other is that its precision can be improved by the time accumulation. The main calculation amount of the proposed method locates in the spectrum estimation for the received signal and the matrix inversion for the harmonic characteristic matrix (HCM). Numeric simulations are provided to verify the proposed method, and related factors influencing on the direction finding precision is analyzed. A simple S band 8-element TMLA is constructed and tested to verify its effectiveness. Finally, some conclusions are drawn and the further research is sketched out.

A general high-efficiency time-modulated module and harmonic beam scanning time-modulated array (TMA) are proposed and investigated in this paper. By introducing the periodically controlled phased-shifters, a significant improvement on theoretical overall efficiency and transmitted bandwidth can be realized in harmonic beam scanning. Then equivalent cascade structure of the general modulation module is proposed for RF circuit simplification and practicability in actual applications. Theoretical derivation and simulation results show that increased efficiency, 100% feeding network efficiency and theoretical overall efficiency tending to 100% without consideration of insertion loss, can be achieved with the increase the phase-shifter states when only a single sideband is utilized. Compared to the existing state-of-the-art harmonic beam scanning TMAs, the proposed TMA exhibits a much higher overall efficiency while keeps a similar hardware complexity. Additionally, with acceptable increase of circuit complexity less than existing works, similar level of the wide transmission bandwidth can also be achieved. To experimentally verify the feasibility of the proposed general design, a 4-bit time-modulated module with reconfigurable states and the corresponding 8-element harmonic beam scanning TMA are fabricated and tested. The experiments on signal transmission and harmonic beam scanning demonstrate the effectiveness of power loss reduction and improvement in transmitted bandwidth with the increase of modulation phase states.

A novel beam scanning method utilizing the carrier frequency component for time modulated array (TMA) is proposed and a significant algorithm based on the non-uniform period modulation is implemented to suppress the maximum sideband radiation (SR) level. The signal in each channel is modulated by a pair of high-speed radio- frequency (RF) switches and totally three or four delay lines with different phases. In each modulation period, three selected delay lines are connected successively with proper pulse durations to keep the switches in ”ON” states constantly and ensure the maximum efficiency in the feeding network. Additionally, in order to suppress the relatively higher SR generated by both switches and delay lines, each channel of the TMA system has a different modulation period, which will separate the harmonic components of different elements on the frequency axis. A desired relatively low maximum SR level without complicated optimization is obtained compared to uniform period modulation and optimization algorithms. Several numeric simulations are brought out to examine the performance of the proposed methods, and the results for comparison to existing methods are also provided. A group of experiments have been done to verify its effectiveness.

Through modulating the echo linear frequency modulation (LFM) signal and analyzing its harmonic characteristic, a novel direction-finding method with time modulated array (TMA) is proposed. Unlike conventional analysis method where each coefficient of harmonic component is analyzed by discrete Fourier transform, in the proposed method, the harmonic coefficients of modulated signals are calculated by using the pulse compression technology. After the modulated LFM signal is compressed by matched filter, the close form expression of the corresponding output signal is derived and the harmonic coefficients of input modulated signals can also be obtained. Meanwhile, in order to avoid being affected by other harmonic components in the process of analyzing each harmonic coefficient, the constraints to acquire independent harmonic coefficients are highlighted. Numerical simulations are provided to verify the performance of the proposed method, and a simple S-band 8-element TMA is constructed to experimentally verify its feasibility.

A 2-D scanning phased array with large element spacing using pattern reconfigurable stacked patch antenna at Ka-band is presented. The pattern reconfigurable stacked patch antenna is composed of four patches on the top integrated with four p-i-n diodes and a driven patch on the lower layer, where the top patches are located along the diagonals of the proposed antenna. By switching the reverse/forward bias states of p-i-n diodes, the phase gradients in different directions are generated and beam steering on the E-, D-(diagonal), and H-planes can be delivered. Subsequently, a 2-D scanning $4\times 4$ phased array with large element spacing is proposed by applying the pattern reconfigurable stacked patch antenna. The 2-D space is divided into nine subsets and covered by nine states of the proposed antenna. The measured results show that a scanning range of ±55° on the E-, D-, and H-planes can be provided. The maximum realized gain is 20.9 dBi at 26.5 GHz with an aperture efficiency of 62.0%. Compared with conventional half-wavelength phased array, the complexity and cost can be reduced for 2-D scanning phased array by introducing the proposed pattern reconfigurable stacked patch antenna.

Time modulated array (TMA) suffers from relatively low efficiencies due to the power absorption in switches during off state. In this paper, we present the design of a novel TMA by using a reconfigurable power divider/combiner (RPDC) for improving the array's efficiency, where the power absorbed during off state can evenly be transferred to other array elements during on state. An improved pulse sequence strategy is developed to control the radiation pattern of the TMA with RPDC. The impact of the RPDC on radiation features of the TMA is further discussed. To experimentally verify the feasibility of the proposed design, a six-element TMA with RPDC is constructed and characterized. Compared with a six-element conventional TMA with single-pole single-throw switches, the TMA with RPDC shows a significant enhancement of gain by 0.98, 1.27, and 1.65 dB when the sidelobe levels are -20, -25, and -30 dB, respectively.