## 2 Embedded Antenna Boosters vs Off-PCB FPC Antennas  
The two antenna technologies for IoT devices are compared: antenna booster technology and FPC technology (Figure 1). The comparison is made at the frequency range of 698-960 MHz and 1710-2690 MHz, where most cellular IoT protocols are allocated. The embedded antenna comprises a 12 mm \(\times\) 3 mm \(\times\) 2.4 mm (height) antenna booster mounted on a 131 mm \(\times\) 60 mm PCB, including a 120 mm \(\times\) 60 mm ground plane. An antenna booster is an electrically small (\(\lambda/30\)) non-resonant chip antenna like component  
Figure 1: (**a**): a 12 mm \(\times\) 3 mm \(\times\) 2.4 mm antenna booster on a 131 mm \(\times\) 60 mm PCB comprising a 120 mm \(\times\) 60 mm ground plane and a matching network with lumped SMD components for multiband performance at 698–960 MHz and 1710–2690 MHz. (**b**): a 96 mm \(\times\) 21 mm \(\times\) 0.2 mm FPC antenna connected to the 131 mm \(\times\) 60 mm PCB through a 50 \(\Omega\) micro-coaxial transmission line. that is easily embedded on a PCB of an IoT device thanks to its SMD nature and small size (Figure 1a). Being so small, an antenna booster is off-resonance, needing a matching network to provide a good impedance match to the RF front-end [20]. By designing the proper matching network following network synthesis microwave tools [14], a multiband performance is obtained from the booster-ground plane set. For the present case, the antenna booster is 12 mm \(\times\) 3 mm \(\times\) 2.4 mm (height, representing about \(\lambda/35\) at 698 MHz). The antenna booster is available through CST Microwave Studio [21] for simulation purposes or can be modelled as a 3D conductive parallelepiped with a conductivity \(\sigma=5.9\times 10^{7}\) S/m. Once the input impedance is measured, the multiband matching network for the antenna booster is easily designed using a network synthesis tool. The network synthesis tool optimises total efficiency (\(\eta_{\text{t}}\)), which is the ratio between the power delivered to the antenna booster and the available power from the generator. Optimising total efficiency and not return loss ensures that the selected lumped components of the matching network introduce low losses. The optimisation process considers available commercial SMD components. Murata SMD 0402 and SMD 0603 high-quality factor components have been used (Figure 2). The set-up for the FPC antenna is simple: the FPC antenna is directly connected to the PCB through a 50\(\Omega\) micro-coaxial which is included with the FPC antenna (Figure 1b). The feeding location on the PCB is maintained in the same position as the antenna booster. The FPC antenna has a rectangular size of 96 mm \(\times\) 21 mm, representing \(\lambda/5\) at the lowest frequency region (698 MHz). This maximum electrical size is eight times more than the size of the antenna booster. In terms of area, the antenna booster (12 mm \(\times\) 3 mm) is 56 smaller than the FPC antenna (96 mm \(\times\) 21 mm). Most FPC antennas rely on self-resonant structures, and therefore, there is no need to use a matching network [22]. After averaging seven multiband FPC antennas operating from 698-960 MHz and 1710-2690 MHz [23], the average length and width are 89.6 mm and 25.3 mm, respectively. Therefore, the FPC antenna analysed here is representative of an average FPC antenna. To compare the performance of both antenna technologies, total efficiency is measured in an anechoic chamber (Satimo Stargate-32) using 3D pattern integration (Figure 3). Since total efficiency \(\eta_{\text{t}}\) (Equation (1)) considers radiation efficiency and impedance match, \(\eta_{\text{t}}\) is used as a figure of merit for comparison purposes. Figure 2: Multiband matching network using SMD inductor and capacitors. The part numbers are: 4.0 nH LQW15 AN4N0G80; 19 nH LQW18 AN19 NG80; 0.7 pF GJM1555C1 HR70 WB01; 0.6 pF GJM1555C1 HR70 WB01; 12 nH LQW18 AN12 NG10; 1.5 pF GJM1555C1H1R5 WB01; 4.5 nH LQW15 AN4N5G80. Total efficiency shows similar average values (Table 1).