Using the method of moments, a dual-wire antenna with a single balanced feed is proposed. To enlarge a 3 dB axial ratio bandwidth, non-resonant radiation elements and a coplanar feedline for sequential rotation (SR) are used. It is revealed that the bandwidth reaches 49%, which is 1.7 times as wide as that without SR. Subsequently, the balanced feed is transformed into a quasi-balanced one to consider voltage standing wave ratio (VSWR). It is found that the VSWR remains less than two in the axial ratio bandwidth. Simulated results are verified with experimental ones.

Curl and truncated spiral antennas are studied for input impedance matching a coaxial line. Each antenna is located at quarter wavelengths above the ground plane and analyzed using the moment method. It is found that the curl antenna shows a voltage standing wave ratio (VSWR) of less than two in a 3-dB axial ratio bandwidth of 30% using a crank feedline with an unbalanced feed. It is also found that the spiral antenna has an axial ratio bandwidth of 24%, where the VSWR remains less than two using parallel feedlines with a quasi-balanced feed.