Pattern reconfigurable antennas (beam steerable antennas) are essential for various applications in electronic engineering such as telecommunication and radar. They mitigate interference by channelling the antenna’s radiation to the direction of interest. This ability is vital for millimetre wave frequency applications such as small cell backhaul links where high path loss, attenuation from obstacles, and misalignment due to wind sway and accidents are prevalent. Several techniques have been used to implement beam steering over the years, most of which achieves steering at the expense of antenna performance. In this article, we surveyed the various techniques used in achieving beam steering and analyse each based on some figures of merit with the aim of identifying areas of improvements for each beam steering technique.

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Survey of Beam Steering Techniques Available for Millimeter Wave Applications

By modification of the classical retrodirective array architecture, a directional modulation (DM) transmitter can be realized without the need for synthesis. Importantly, through analytical analysis and exemplar simulations, it is proved that, besides the conventional DM application scenario, i.e., secure transmission to one legitimate receiver located along one spatial direction in free space, the proposed synthesis-free DM transmitter should also perform well for systems where there are more than one legitimate receiver positioned along different directions in free space, and where one or more legitimate receivers exist in a multipath environment. None of these have ever been achieved before using synthesis-free DM arrangements.

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A Synthesis-Free Directional Modulation Transmitter Using Retrodirective Array

This paper proposes a novel antenna for dental implants. The proposed antenna can be attached to minimally invasive biomedical devices to monitor health conditions. Based on a combination of Archimedean spirals and a Hilbert-based curve, this 3D folded antenna was embedded on a ceramic denture $({\rm ZrO}_{2})$ , and operates within the medical radio (MedRadio) band. An omnidirectional radiation pattern was obtained from simulations of human models to eliminate specific orientation dependence. A realistic measurement of an oral cavity was also performed under the Institutional Review Board (IRB) protocol to evaluate its practical biomedical effects. A miniature antenna with a total area of less than 245 ${\rm mm}^{2}$ was designed and implemented. The measured performance achieved an antenna gain of $-$ 6.78 dBi, and had an impedance bandwidth of approximately 60 MHz. Therefore, a compact high-gain antenna with a large bandwidth was achieved.

Implantable High-Gain Dental Antennas for Minimally Invasive Biomedical Devices

In this paper, a new type of architecture for secure wireless key establishment is proposed. A retrodirective array (RDA) that is configured to receive and re-transmit at different frequencies is utilized as a relay node. The RDA is able to respond in “real time,” reducing the required number of time slots to two. More importantly, in this architecture, equivalent reciprocal wireless channels between legitimate keying nodes can be randomly updated within one channel coherence time period, leading to greatly increased key generation rates in slow fading environment. The secrecy performance of this RDA-assisted key generation system is evaluated under several eavesdropping strategies and it is shown that it outperforms previous relay key generation systems.

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Retrodirective-Assisted Secure Wireless Key Establishment

Near-field radio frequency identification (RFID) technology at ultra high frequency (UHF) bands is of increasingly interest because of its promising opportunities in item-level RFID applications. The conventional single solid-line loop antenna is unable to generate strong and uniform magnetic field within an electrically large interrogation zone at the UHF bands. Segmented loop antennas are promising for UHF near-field RFID applications since they are able to generate uniform and strong magnetic field in an electrically larger interrogation zone. The reported segmented loop antennas have been able to offer an interrogation zone with a perimeter of around two operating wavelengths. In this paper, the segmented loop antennas with enlarged interrogation zone are presented. Using dual or multiple segmented loop configurations, the perimeters of the interrogation zone of the antennas can be larger than three operating wavelengths at the UHF bands.

UHF near-field segmented loop antennas with enlarged interrogation zone

This paper presents an overview on the phase conjugation techniques of the retrodirective antenna array. The concepts, advantages, and disadvantages of phase conjugation techniques are introduced. The self-phasing characteristic and technical difficulties of the array are presented as well as their structures and applications. Further researches in this area are presented finally.

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Tian Ling Zhang

Papers

Overview on the Phase Conjugation Techniques of the Retrodirective Array