Measurements of the Cross-Loop Antenna Patterns in High-Frequency Surface Wave Radars

In this letter, measurements of the cross-loop antenna patterns in the Ocean State Measuring and Analyzing Radar type S (OSMAR-S) for monitoring ocean environments are discussed. First, the patterns of the cross-loop antenna are measured by using a moving transponder. The results are not so good, as expected, due to the unstable transmitting signals and impacts of the environments. Then, an improved measurement method of the cross-loop antenna patterns is presented. The transmitting antenna is fixed, and the cross-loop antenna is fixed on a turntable and rotated with it to receive signals coming from different directions. In addition, the cross-loop antenna is connected to capacitors to resonate at the operating frequency. Then, the receiving signals of the operating frequency are strengthened, and the effects of environment are reduced. The near-field and far-field experiments are performed, and the measured patterns are of “8” shapes. Impacts of metal obstacles are also discussed, which provide a basis for evaluating antenna erection of the OSMAR-S. The ocean currents calculated from the patterns measured by the method in this letter are compared with that measured by an acoustic Doppler current profiler. They are in a good agreement, which proves the validation of the measurement method.