Dielectric resonator antennas (DRAs) are developed antennas that are lightweight, wideband, small-sized and have high radiation efficiency. A DRA is an appropriate candidate for any radio communication including radar applications mainly because of its high efficiency and wideband performance. As the development of DRAs has been a continuous process for more than five decades the plethora of the same has become magnificent in all possible ways. Scientists have walked the technical path for more than centuries and tried to meet the various challenges in the most graceful ways. Reduction of loss, lightweight, and desired radiation patterns are some of the issues which are effectively met by DRAs. This paper presents a brief comprehensive review of the state of art techniques, giving an exhaustive idea of achieving broadband and multi-frequency operations in the areas of DRAs. The paper associates the references of the past and correlates with the current and future trends of research in DRAs that could be of immense help to the young upcoming researchers interested in this field.

Global Navigation Satellite System (GNSS) observations contain various errors, the separation and measurement of which is a popular research topic. Multipath effect on code measurements is investigated through the multipath combination, but carrier multipath error is small, and it is difficult to distinguish from other errors, such as hardware delay, carrier noise and satellite inherent biases. However, as the number of frequency points increases during the rapid development of GNSSs, it is possible to analyse the abovementioned errors in detail. Triple-frequency combination can be used to eliminate the first order ionospheric error, and a quad-frequency combination has one degree of freedom, which may be used to minimise carrier error effects. For this reason, an optimum method has been developed for multi-frequency GNSS code-multipath combination measurements, which has been verified by exploiting BeiDou System (BDS), three frequency data from an International GNSS Service (IGS) station and a city canyon as well as actual sampled quad-frequency data. By comparative analysis, we found that the fluctuations of an optimum triple-frequency combination are smaller than that of the non-optimum combination, which decreases the influence of inherent errors and biases on carrier phase. At the same time, second-order ionospheric error can be effectively eliminated as well. This provides a new code-multipath combination measurement optimisation methodology for future multi-frequency BDS and other GNSSs.

In this paper, we present a near-field microwave microscopy method for the characterization of dielectric materials samples in the Industrial, Scientific and Medical (ISM) band. The system proposed is composed of a probe coupled to a dielectric resonator (DR) operating in the TE011 mode. Latter this is used to fix the resonance frequency of the resonator at 2.45 GHz. This system is used for the characterization of dielectric samples with accuracy and high spatial resolution, knowing that they do not have predetermined forms, but a small plane surface.The same device is used for a multi-frequency characterization (4–20 GHz) using resonance frequencies of the cavity instead of one resonance frequency of the DR.

This work presents a method to observe pelagic fish around drifting fish aggregating devices (DFADs). A triple-frequency vertical echosounder was employed to observe fish distributions in the vicinity of DFADs. Surveys were conducted in a star pattern that was centred at the DFADs. The objective of the study was to define a methodology for future acoustic studies. This goal was pursued by (i) studying the spatial distribution of fish aggregations, (ii) developing concepts for the grouping of observed aggregations and (iii) developing specifications for future autonomous acoustic tools. For this purpose 5 cruises were carried out in the western Indian Ocean. The multi-frequency approach proved useful as a means of separating acoustic detections into sound-scattering layers (e.g. plankton and micronekton), fish aggregations and individual fish. Fish target strength (TS) was measured. Four types of aggregations were found near DFADs: (i) dense structure (ii) medium structure (iii) loose structure and (iv) structure consisting of separated targets. More than 90% of these structures were found within a radius of 400 m and about 75% within 200 m of the DFADs. The spatial configuration of DFAD fish aggregations appeared to be more dynamic compared to aggregations near moored FADs. The spatial distribution and structure of DFAD aggregations have direct implications for their catchability by tuna purse-seiner. We have carried out the first quantitative acoustic recordings around DFADs, and obtained a better understanding of the spatiotemporal dynamics of fish aggregations around DFADs in the Indian Ocean. Based on this knowledge we are now working on specifications for instrumented buoys that are intended as autonomous data recording observatories for such pelagic environments.