STUDY ON ACTIVE PHASED ARRAY ANTENNAS RADIATING HIGHER HARMONIC OUTPUT WAVE .

微波场效应管的输出功率随工作频率的增加而减小，目前很难在60 GHz以上获得基波振荡的输出功率。在X波段的实验中已经证实，在基波振荡不能产生输出功率的频率处，在相对高的输出功率水平下，可以有效地获得二次谐波输出功率。为此，负载阻抗被采取，以便基波振荡输出功率被很好地抑制，并且二次谐波输出功率可以被最大化。其次，在二次谐波有源天线阵列中，相邻有源天线的微带线之间的适当互耦已被证明是在基频中，其相位为2π的倍数。这种耦合不仅可以给出较宽的锁定范围，从而容易实现同步，而且还可以给出相邻有源天线之间的最大相位间隔。在二维、三阶和四阶二次谐波有源天线阵列的实验中，分别得到了63、73和81度的输出波束转向角，这些波束转向角对应于相邻有源天线间二次谐波的最大相差近350度。由于相邻有源天线之间的基波振荡的最大相位差为180度，所以二次谐波的最大相位差几乎可以是具有基波振荡输出波的有源天线阵列中的两倍大。

Output powers of microwave FETs decrease with increasing working frequency, and it is difficult at present to obtain output powers of fundamental oscillation using microwave FETs at more than 60 GHz. It has been confirmed in experiments at X band that at second harmonic output powers can be efficiently obtained in conparatively high output power level at frequencies where no output power can be yielded by fundamental oscillation. For this purpose, the load impedance is taken so that the fundamental oscillation output power is well suppressed and the second harmonic output power can be maximized. Next, in second harmonic active antenna arrays, appropriate mutual coupling between microstrip lines of adjacent antive antennas has been shown to be in the fundamental frequency with its phase of a multiple of 2π. This coupling can give not only relatively wide locking range which results in easy synchronization but also the maximum phase spacing between adacent active antennas. In the experiment of one dimensional array of 2, 3 and 4 second harmonic active antennas, we could attain the output beam sreering angle of 63, 73 and 81 degrees, respectively ; these beam steering angles correspond to the maximum phase differences of second harmonics of almost 350 degrees between adjacent active antennas. Since the maximum phase differences of fundamental oscillation between adjacent active antennas are 180 degrees, the maximum phase differences of second harmonics can be almost twice as large as in active antenna arrays with output waves of fundamental oscillation.