## 1 Introduction
### Literature Review  
Antennas are key parts in connected devices as they ensure connectivity attention, given to them from design to integration. Some IoT applications impose the use of miniaturized devices; this makes antenna design a challenging task, especially in sub-GHz bands. In fact, antenna miniaturization results in low radiation efficiency. This in turn results in low gain and a short communication range. For the present application, the antenna should work at the three frequency bands: 401 MHz (uplink) and 466 MHz (downlink) for satellite communication, and 868 MHz for terrestrial LoRaWAN communication (Europe). Besides acceptable gain, bandwidth, low cost, being easy to integrate the internal antenna should be a triband, have good mechanical robustness, and be waterproof. To fulfil the two last criteria, the antenna should be internal. To obtain a natural mechanical robustness, printed antennas on Printed Circuit Boards (PCBs) are more adequate than some commercial ceramic [22] or PIFA [23] antennas. Regarding the dimension of the device, designing a PCB triband antenna covering the 401/466/868 MHz bands at the same time is a hard task. One simple solution is to use a reconfigurable antenna; this allows exploiting all available surfaces on the PCB to obtain the best radiation efficiencies at 401/466 MHz bands. For the frequency reconfigurability function, PIN diodes are a low-cost solution and are widely used for this purpose [24; 25]. In the literature, there is no specific method that the designer is limited to. The continuous development of 3D EM solvers and simulators make them powerful tools. The method is quite simple and consists on modeling the antenna with all parts of the device in a 3D EM simulator [26; 27; 28], setting up the simulation correctly, and allowing the simulator to do the rest. The designer only has to understand the relation between the antenna response and the parameters of the global model, which are geometric parameters and material properties. Meandered radiating structures and folded inverted F antennas are widely used to achieve compact-sized antennas with dual-band operation in the UHF band. One technique used to achieve a low profile is loading the radiating structure with a floating ground plane. In [29], a set of compact antennas based on meandered line structure are presented. The antenna structures are scaled for operation at 433, 868, 1600, and 2450 MHz. A compact size active antenna for UHF satellite communication is proposed in [28]. The antenna radiating part is a Folded Inverted F Antenna (FIFA) loaded with a Split Ring Resonator (SRR) and the antenna's total size is 32 mm \(\times\) 32 mm \(\times\) 1.5 mm. The results of the simulation show that the antenna gain is much better with loading the FIFA, with an SRR cell than with a floating ground plane. Loading a radiating structure with a floating structure can reduce the overall size of the antenna at 401/466 MHz. However, this results in a poor gain. In [30], a compact meandered type monopole antenna with total dimensions of 87 mm \(\times\) 32.5 mm \(\times\) 1.6 mm is presented. The proposed design covers several wireless applications, such as M-bus, M2M, IoT, LoRaWAN, RFID, Wi-Fi, and Bluetooth. The main meandered structure is designed to achieve a lower UHF frequency band (433 MHz). To achieve the upper bands (868/915 MHz), two straight conductors are placed at the end of the main structure. In [31], the authors propose a dual band compact size meandered (folded) Inverted F Antenna (IFA), working at 433 and 868 MHz for WSN Tyna-dall multi-radio application. The antenna has a total size of 27 mm \(\times\) 77 mm \(\times\) 1.124 mm. In the same way, a Folded Inverted F antenna, with a total size of 70 mm \(\times\) 70 mm \(\times\) 1.6 mm, is proposed for a TPMS receiver, working at 433 MHz [23]. Another antenna design based on a meandered radiating structure proposed for the TPMS application is presented in [32]. The antenna has a total size of 165 mm \(\times\) 17 mm \(\times\) 2 mm.