CPW-fed frequency-reconfigurable slot-loop antenna with a tunable matching network based on ferroelectric varactors

A frequency-reconfigurable slot-loop antenna with a tunable matching network (TMN) is designed, fabricated, and measured. The frequency-reconfigurable antenna is designed by loading ferroelectric (FE) varactors along a slot loop. The varactor-loaded slot-loop antenna is fed using a coplanar waveguide (CPW) line rather than a microstrip line to preserve the advantage of being uniplanar. However, because it is more difficult to achieve a good matching over wide bandwidth with a direct CPW feed, we propose to add a TMN. It is found that the TMN can be realized using a series varactor, which does not increase the size of the antenna. Measurement results show that by adjusting the bias of the FE varactors from 0 to 15 V, the operating frequency of the antenna can be tuned from 6.71 to 9.14 GHz, translating into a 30.6% frequency tuning range (FTR). At 6.71 GHz, the size of the slot loop is 0.056λ₀ × 0.056λ₀. When biased at 15 V, the antenna gain is -3.1 dBi. Over the entire FTR, the return loss is greater than 20 dB, demonstrating the effectiveness of the tunable matching technique.