Solution for Challenging 4G Radio Measurement for Precise Phase Center Tilting
Measurement for special types of radios in tele-communications can be tricky. For example, we encounter a testing requirement for solving OTA problems for multiple precise tilting angular positions. This is important for those radios with specific designed tilt angles, and the phase centers of the antennas can vary from product number to product numbers. As shown in the left hand photo, one wants to measure precise ERIP for LOS without any tilt angle first, after phase center gets allocated, exact testing shall be repeated with tilt angle of 3 deg along elevation rotation about the phase center. Note the phase center may not be prior info for the test, which requires a flexible testing system that support on-sight programmable adjustment. F&MM's FM57 product serials support such possibility.
A typical testing radio involves multiple design freedoms, hence many configurations have to be incorporated during testing. For example, a radio can have 4-8 ports, and each of them may require assessment under same testing environment. Besides, the phase centers will change once the model is changed, one has to take into account the thickness of different radomes, displacement from antenna aperture in order to find correct phase center. The tilt angle is also variable for different models. F&MM testing system provides software GUI that help testing engineer to pin down the right configurations in most efficient and accurate manner.
Depending the DUT specification, various data has to be extracted from either RF instrument or radio itself. Typical RF instrument includes signal generator, spectrum analyzer, oscilloscopes and vector network analyzers. Under any testing scenario, a typical system calibration has to be carried out in order to minimize the system errors. This is especially true for testing case with extremely small transmitting power or in noisy environment, and one has to assure the dynamic range or sensitivity of testing system is sufficient enough. Given testing instrument has valid calibration date, one would find testing procedure and testing technology play more vital role to achieve the utmost accuracy and efficiency.