Intuitive Broadband Matching Technique for Top-Loaded Monopole Antennas

Wheeler/Chu's theoretical limit serves as a guideline when designing for the optimum performance of small antennas. It relates the electrical size of the antenna to its quality factor, which can be further related to the bandwidth × efficiency product. Friedman designed a top-loaded monopole that is particularly broadband given its size, but it is not intuitively obvious how to design the matching structure in terms of effective circuit parameters. In this article, we follow Friedman's approach in that we start with designing a matching circuit for a simple top-loaded monopole and obtain performance similar to Friedman's. However, our design is advantageous in two important ways: 1) the circuit is easily understandable and 2) the correspondence between circuit elements and geometrical features on the antenna is clear and straightforward. These advantages may potentially allow this method to be applied to other types of antennas or scaled to different performance parameters.