Design Note DN038 - TI.com
Design Note DN038 SWRA416 Page 1 of 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 document describes a compact PCB helical antenna that has been specifically designed for 868 MHz or 915/920 MHz ISM bands. The PCB helical antenna requires two matching components for matching to a 50-ohm load. When a large PCB area (38 mm x 24 mm) is available for the antenna then the recommended antenna is DN024 [1] since the impedance is closer to 50 ohm without any external matching components (868 MHz: 30+j11; VSWR ) and the bandwidth is around 90 MHz. The miniature PCB helical antenna is more compact (19 mm x 11 mm) with approximately quarter of the size of the DN024 [1] but requires matching components since the impedance is far from 50 ohms (868 MHz: 10-j88; VSWR 22).
Design Note DN038 SWRA416 Page 3 of 24 3 Antenna Design 3.1 Physical Dimensions Figure 2. Top Layer Layout Figure 3. Zoom of Top and Bottom Layer Layout with Via Markings
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