Miniaturisation of λ/4 microstrip antenna using perturbation effect and plate loading for low-VHF-band applications

An electrically small microstrip antenna is proposed for low-VHF-band applications. The design is based on a λ/4 microstrip antenna in which the size of the ground plane is equal to that of the radiating patch. Miniaturisation is achieved by a combination of cavity perturbation and plate loading. The radiating edge of the microstrip antenna is modified to achieve the desired perturbation effect, and zigzag plates are loaded in the aperture to reduce the size further. The dimensions of the perturbed and plate-loaded microstrip antenna operating at 40 MHz are 55.5 × 30 × 30 cm, which correspond to an electrical size (kr) of 0.30. An omnidirectional radiation pattern is obtained for E_θ in the yz-plane, while a nearly omnidirectional pattern is obtained for E_φ in the xz-plane. The measured radiation efficiency of the antenna is 77.7%.