A frequency-tunable dual-band multi-ring microstrip antenna fed by an L-probe with varactor diodes

This paper presents a frequency-tunable multi-ring microstrip antenna (MR-MSA) fed by an L-probe with varactor diodes. In order to realize a frequency-tunable multiband microstrip antenna, multiple ring patches are arranged concentrically and two varactor diodes are mounted on each ring patch. An L-shaped feeding probe is used to excite the ring patches. Resonant frequencies of the proposed antenna can be controlled by the DC bias voltage applied to the varactor diodes. In order to demonstrate the basic operation of the proposed frequency-tunable multiband microstrip antenna, a dual-band MR-MSA composed of two ring patches are designed and tested. The fractional bandwidth of the frequency-tunable range of the test MR-MSA is measured to be around 10% under the condition of 1 dB gain reduction from the maximum and of the reflection less than -10 dB. The antenna configuration can be easily extended to multiband operation more than dual-band by arranging more ring patches.