This paper describes the design of a miniaturized multiband Inverted-F Antenna (IFA) suitable for integration in compact Internet-of-things (IoT) terminals. The antenna efficiently operates over the LoRa (915 MHz) and GPS L1 (1.57 GHz) and L2 (1.23 GHz) bands. Its dimensions are m ( compared to the lower operating frequency) for a total device size of m. Measurements of the antenna when integrated into an IoT position tracking device as well as of the whole terminal in a real application scenario are reported.

This paper revisit and extend the interesting case of bounds on the Q-factor for a given directivity for a small antenna of arbitrary shape. A higher directivity in a small antenna is closely connected with a narrow impedance bandwidth. The relation between bandwidth and a desired directivity is still not fully understood, not even for small antennas. Initial investigations in this direction have related the radius of a circumscribing sphere to the directivity, and bounds on the Q-factor have also been derived for a partial directivity in a given direction. In this paper, we derive lower bounds on the Q-factor for a total desired directivity for an arbitrarily shaped antenna in a given direction as a convex problem using semidefinite relaxation (SDR) techniques. We also show that the relaxed solution is also a solution of the original problem of determining the lower Q-factor bound for a total desired directivity. SDR can also be used to relax a class of other interesting nonconvex constraints in antenna optimization, such as tuning, losses, and front-to-back ratio. We compare two different new methods to determine the lowest Q-factor for arbitrary-shaped antennas for a given total directivity. We also compare our results with full electromagnetic simulations of a parasitic element antenna with high directivity.