A bandwidth-improved slotted circular microstrip antenna (CMSA) for High Altitude Platform Stations (HAPS)

An investigative design of a circular microstrip antenna (CMSA) and its related geometry intended for 5850–7075 MHz Malaysia HAPS operating band is presented. The structure consists of three layers, with the radiator at the top (layer three), a feed on the middle layer (layer two) and finally a grounding copper plate at the bottom (layer one). A commercial microwave laminate with permittivity ∊r = 2.2 was used to fabricate layer one, and this was fed via a smaller circular copper sheet, via capacitive coupling. The layer 1 and layer 2 height variation was investigated, as well as its x-y feeding location. Apart from normal circular form, slots resembling complementary circular split ring resonators (CCSRR) were placed in each circular structure for bandwidth and gain improvement. The dimension suitability was also investigated. From this work, it was found that the application of a lower dielectric permittivity value for the microwave laminate and a larger thickness was proven to be favourable. A HAPS antenna with bandwidth of more than 2.0 GHz (VSWR < 2), centred at 5850 MHz was successfully designed, when implementing CCSRR slots. In addition, backlobes were also significantly suppressed.