Figure 5 Scatterplot constellation of the waveform shown in Figure 4 Ž . the same nonideal signal standards as in Table 3 on SPW is made, and the results of the SPR output data are shown in Figures 4 and5. It is clear that the distortion of the SPR output data is unimportant and quite acceptable in this case of reception.
7. PRACTICAL REALIZATION OF THE PROPOSED CALIBRATION METHOD
The proposed calibration method may be realized using QPSK incoming signals for calibration. When the incoming signal and the local oscillator are ideally synchronized and their frequencies are exactly the same, then the outputs of the power detectors of the six-port are changing dc voltages. In this case, we may simply take these output voltages to calculate the calibration parameters of the six-port. With poor synchronization between the incoming signal and local oscillator signal, the outputs of the power detectors of the six-port will rotate with jumps which correspond to the changes of the phases of the incoming signal. In this case, sampling should be done at a fixed time interval after the jumps. Such output data of the power detectors of the six-ports are then used for the calculation of six-port calibration parameters. It is important to note that the calibration rate can be significantly lower than the data rate.
8. CONCLUSION
From the above analysis, we conclude the following.
- A simple and effective real-time calibration method of SPR is proposed using four known sets of I, Q values. 2. This calibration method is especially suitable for QPSK reception, but good results are also obtained for 64 QAM. Modulation errors can be cancelled by the SPR if the received signal is selected for calibration purposes. 3. Simplified calculation equations of the receiver output w Ž . Ž .x data Eqs. 4 , 5 are introduced. 4. The possibility to use only three known sets of I, Q values in the calibration procedure is discussed. 5. SPW simulation results for a 64 QAM signal validate the proposed calibration method. On six-port junction bases K-band direct receiver, 2nd Ka Band