Investigations on a Novel without Balun Modified Archimedean Spiral Antenna with Circularly Polarized Radiation Patterns

The proposed novel modified twolayered Archimedean spiral (Mod Arspl) antenna achieves a simple feed without balun and maintains the antenna input impedance close to 50 ? over extremely wide (10:1) frequency band for antenna design. It shows excellent impedance matching, higher peak gain and acceptable axial ratio over the operating frequencies compared to the conventional Archimedean spiral geometry on two-layers with the same aperture area. The working of this antenna and important design parameters to achieve frequency independent response with respect to matching and CP radiation patterns are discussed. The best case with free-space Mod Arspl has impedance BW (S11 < - 10 dB) of 3.2-19.2 GHz (6:1 band), AR BW (AR < 3dB) of 3-20 GHz (6.6:1 band), stable broadside gain of 4-5.5 dBic and quasi-axial patterns in the usable 6:1 band. Radiation patterns show some beam squint towards higher frequency end attributed to spacing between the two layers of the spiral arms. The fabricated prototype antenna using microwave substrate shows CP operating BW over 5.21:1 frequency band (2.8 - 14.6 GHz) and peak gain varying between 4 - 8 dBic in this frequency band. Measured results show reasonable agreement with the simulated ones.