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SWEEPING ANTENNAS

Antenna system testing is one of the more common and useful applications for using the swept-frequency technique. The main parameters that an antenna system is tested for are vswr, Frequency response, and impedance. Figure 5-31 shows a typical test setup for testing a transmitting antenna for vswr. Remember that any transmitting antenna can also act as a receiving antenna and send induced power from adjacent antennas back to the test equipment. You should make an initial power check on the antenna to prevent damage to your test equipment. Figure 5-32 shows a typical hf transmitting antenna vswr display as measured using the swept-frequency technique. The setup for testing a receiving antenna vswr, shown in figure 5-33, is similar, with the exception of the attenuators. The measured vswr (within the operating frequency range) of any broadband antenna should not exceed a vswr of 2.5 to 1. The vswr for any single-tuned antenna should not exceed 1.5 to 1 at the tuned frequency.

Figure 5-31. - Vswr test for transmitting antennas.

Figure 5-32. - Typical spectrum analyzer vswr display.

Figure 5-33. - Vswr test for receiving antennas.

Q.12 What precautions must be taken when sweeping a transmitting antenna?