This paper presents low-profile broadband antennas, which are composed of four parasitic patches placed between planar\nradiators and a perfect electric conductor ground plane. Two types of planar radiators, a conventional dipole and a crossed\ndipole, are employed to produce linearly polarized (LP) and circularly polarized (CP) radiations, respectively. The radiator\nand parasitic patches are realized on thin substrates to lower the cost. Owing to the presence of parasitic patches, the antenna\nperformance improves in terms of profile reduction, resonant frequency decrease, and bandwidth enhancement. These\nimprovements are discussed and confirmed computationally and experimentally. The LP design with the overall dimensions of\n120mmÃ?â?? 120mmÃ?â?? 16.3mm (0.64Ã?»0 Ã?â?? 0.64Ã?»0 Ã?â?? 0.087Ã?»0 at 1.6 GHz) has a |S11| < âË?â??10 dB bandwidth of 1.465ââ?¬â??1.740 GHz (17.2%),\na broadside gain of 8.5ââ?¬â??8.8 dBi, and a radiation efficiency > 96%. The CP design, which has the same physical size as the LP case,\nhas a |S11| < âË?â??10 dB bandwidth of 1.388ââ?¬â??1.754 GHz (23.3%), a 3 dB AR (axial ratio) bandwidth of 1.450ââ?¬â??1.685 GHz (15.0%), a\nright-hand CP broadside gain of 7.8ââ?¬â??8.7 dBic, and a radiation efficiency > 90%.
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