Beamforming of active antenna array with self-oscillating harmonic mixers

研究了采用自振谐混频器的有源天线阵的波束控制问题。该有源天线由一个接收射频信号的贴片天线和一个并行反馈振荡器组成，该振荡器作为自激振荡器工作，并将接收到的射频信号下变频为中频信号。混频器有两个用于本地振荡(LO)信号的端口。一个是提取LO信号的输出端口。另一个是注入信号的输入端口，用于同步本地振荡。通过将输出端口连接到下一个混音器中的输入端口，可以在没有其他非互易元件的情况下单向耦合混音器。在单向耦合阵列中，通过改变自激振荡器的局部自激频率，在注入锁定状态下，可以在没有移相器的情况下改变相邻混频器之间的LO信号的相差。可以通过组合来自各个有源天线的中频信号来控制接收模式，其中各个有源天线具有与LO信号相关的相位。RF和LO频率的两倍之间的IF是不同的，因此可以向输出IF信号提供0到2π弧度的任意相位差。使用二元阵和三元阵的实验证明了波束控制能力。此外，通过优化自振荡混频器反馈环上定向耦合器的耦合强度，提高了从射频到中频的转换效率。

Beam control using active antenna arrays with self-oscillating harmonic mixers has been investigated. The active antenna is composed of a patch antenna receiving RF signal and a parallel feedback type oscillator which operates as the self-oscillating harmonic mixer, and down-converts the received RF into IF signal. The mixer has two ports for local oscillating (LO) signal. One is an output port extracting the LO signal. The other is an input port for an injection signal to synchronize the local oscillation. The mixers can be coupled unilatarally without other nonreciprocal components by connecting the output port to the input port in the next mixer. In the unilaterally coupled array, the phase differents of the LO signals between the adjacent mixers can be varied without phase shifters in injection locking state by changing the local free-running frequencies of the self-oscillating mixers. The receiving pattern can be controlled by combining the IF signals from the individual active antennas, which have phases associated with the LO signals. The IF is different between the RF and double of the LO frequency so that arbitrary phase differences from 0 to 2π radian can be providedto the output IF signals. The experiments using the two- and three-element arrays demonstrated beam control capability. In addition, conversion efficiency from RF to IF was increased by optimizing coupling strength of a directional coupler on a feedback loop in the self-oscillating mixer.