Combined spiral-discone broadband antenna for indoor applications

A novel design of a broadband omnidirectional antenna is presented. It combines advantages of both the spiral and discone designs. An antenna of this type can find application in indoor radio communication systems. The designed antenna frequency band is suitable for the radio communication services in the indoor environment (GSM 900, GSM 1800, DECT, WLAN). The other advantage of this design is its good impedance match to 50 ohm coaxial transmission lines and undirectional radiation pattern. Two prototypes were made which cover the frequency bands of 650-3000 MHz and 1270-3000 MHz with VSWR<2. The method of moments was applied to calculate radiation characteristics of the antennas. The results of impedance matching and radiation pattern measurements are presented.