Compact Broadband Antennas with Series and Parallel Resonances

Multi-mode excitation with complementary resonance for radiation resonance is useful for broadbanding of electrically small antennas. Bandwidth of a small antenna with series resonance such as short dipole, small helical and meander line antennas can be expanded by using no-radiation parallel resonance. Another antenna type with parallel resonance like a microstrip antenna (MSA) is also able to get wideband characteristics using series resonance. We have studied compact broadband small antennas with multi-mode excitation and evaluated them in the view point of practical use. In the paper, we will show evaluation results of a miniaturizing factor, product of bandwidth and radiation efficiency ( Bη product), for practical inverted-L antenna (ILA) and MSA.