Compact helical antenna with small ground fed by spiral-shaped microstrip line

A compact helical antenna with a small ground is proposed for 5.2/5.8 GHz WLAN applications. The proposed antenna can be easily mounted in the space-limited systems. Good impedance matching is achieved by a spiral-shaped microstrip line feed structure. Relatively uniform current along the helix is observed owing to the travelling-wave current on the feed structure, which contributes to high-gain performance even with a small ground. The measured 3 dB axial ratio bandwidth and impedance bandwidth for S₁₁ ≤ -10 dB overlap over 5-6 GHz, whereas the realised gain of about 13-14 dBic is achieved over the 5.2/5.8 GHz WLAN band.