The physical-layer wireless security has long been regarded as a promising complementary or alternative to conventional mathematic-based cryptographic solutions as it requires little computation capability while endowing systems quantum-immune security.
New communication systems require high-speed data transfer and need high frequency, wideband, and directive antennas. Leaky-wave antennas are a desirable type of antennas for millimetre and sub-millimetre waves since they can produce a high directive radiation with a single feeding. The latter is an enormous advantage to reducing the cost and losses at high frequency. Despite these advantages, their dispersive nature inherently produces a beam squint effect in their radiation patterns.
Wireless communication based on the electromagnetic field properties of orbital angular momentum (OAM) has gained a lot of interest for multi-input-multi-output (MIMO) communication schemes. From a field theoretical perspective, OAM is well understood and can be easily quantified in electromagnetic radiation. However, when it comes to the optimization of OAM-based communication, there are still many unknowns, e.g., relative position, orientation, size, and termination of transmitting and receiving arrays.
Electromagnetic (EM) emission from substrate edges is increasing significantly when the communication systems move from the first generation to the fifth generation using millimeter waves. It is reasonable and very interesting to utilize the substrate edge to design antennas. Substrate edge antennas (SEAs) are easy to form arrays with multiple beams or steering beams, and also very suitable to be employed together with packaging technologies. SEAs and the arrays are very promising in the next generation communication systems, like in handset terminals, indoor mmWave stations and unmanned aerial vehicles (UAVs).