Design Note DN038 SWRA416 Pag e 1 o f 24 Miniature Helical PCB Antenna for 868 MHz or 915/920 MHz By Richard Wallace Keywords Miniature Helical PCB Antenna Optimized for compact designs 868 or 915/920 MHz ISM Bands CC11xx CC12xx 1 Introduction This do cument describes a co mpact PCB helical antenna that has been specifically desig ned fo r 868 MHz o r 915/920 MHz ISM bands. The PCB helical antenna requires two matching co mpo nents fo r matching to a 50-o hm lo ad. When a larg e PCB area (38 mm x 24 mm) is available fo r the antenna then the reco mmended antenna is DN024 [1] since the impedance is clo ser to 50 o hm witho ut any external matching co mpo nents (868 MHz: 30+j11; VSWR 1.8) and the bandwidth is aro und 90 MHz. The miniature PCB helical antenna is mo re co mpact (19 mm x 11 mm) with appro ximately quarter o f the size o f the DN024 [1] but requires matching co mpo nents since the impedance is far fro m 50 o hms (868 MHz: 10-j88; VSWR 22). When the miniature helical antenna is matched then the bandwidth is aro und 40 MHz and has similar efficiency as DN024 [1] antenna when measured o n the TRXEB platfo rm. All measurement results presented in this do cument are based o n measurements perfo rmed o n the CC110L EM Rev 1.0 Reference Desig n [3], sho wn in Fig ure 1. Figure 1. CC110L EM 868 / 915 MHz Design Note DN038 SWRA416 Pag e 2 o f 24 Table of Contents KEYWORDS .............................................................................................................................. 1 1 INTRODUCTION ............................................................................................................. 1 2 ABBREVIATIONS ..........................
