Adaptive Closed-loop Phase Source

Nowadays, more and more researchers pay attention to phased array antennas, which play an important role in the fields of radio frequency identification (RFID), radar, and wireless communications because of their wonderful characteristics of beam forming. In order to maintain good performance in phase shift and feasibility, many techniques have been applied. Such as an electronic phase control circuit for microwave system, which changes the phase velocity along a section of diode-loaded transmission line, was proposed in 1999 [1]. This technique was further developed with a microelectromechanical system (MEMS) variable capacitor diode, which takes place of transmission lines, can be processed to be a commercial integrated circuit (IC) to give us a very good performance [2]. However, this kind of phase shifter suffers from insertion loss and noise as the signal needs to pass through the phase shifter. What’s more, as lossy power dividers used to provide signals to each element, signal power at each antenna element would be decreased with the increase of the number of antenna elements in array. In order to eliminate the problem of power dividing, some ideas of active phase shifters or phase control circuits are implemented in the phased source techniques, such as active phased array antenna based on DDS [3], where phased signals were provided by a direct digital signal synthesizer at low frequency and up-converted to desire high frequency; phase control was implemented at high frequency with the help of phase lock loop (PLL) [4] [5]. However, this kind of technique applies phase control through high frequency component, which is expensive and complicated. To improve the performance of both microwave phase shifter and active phase control circuit, an Indirect Controlled Phased Source (ICPS) was implemented in 2006, where phase control was realized by changing the phase of the reference signal of PLL at low frequency to give a corresponding phase shift at desire high frequency [6]. By this approach, not only the problem of lossy power dividing system can be solved, but also the complexity of phase control at high frequency can be reduced a lot. However, as ICPS technique has an open-loop construct, it may suffer from the change of environment or acuminate noise of components as it cannot monitor the instant phase information of the output signal. In this paper, we propose an adaptive closed-loop phase source (ACPS), which is developed from the original ICPS. With the help of a novel phase detector array, the whole construct works like a PLL, i.e. it can monitor the instant phase information and lock the output signal to a certain phase. In ACPS, a varactor type low frequency phase shifter (LFPS) takes place of the 2 n type one in [6] to provide a continuous phase shift. In this paper, a two-path prototype is fabricated to implement phase locking.