Due to exponential growth in wireless communication in the last decade, which continues towards future applications, mm-wave has shown tremendous potential and has been established as the backbone of most modern-day high data rate communication systems. Despite many challenges associated with this technology, several inherent advantages have established it as an attractive and essential choice for high data rate communication systems. It is well known that antennas are crucial integral components of any communication system. Most modern-day mm-wave communication devices require a low profile, wideband, and highly efficient antenna system. Recent advancements in research and development in this field have been reported through many publications. This article reviews the mm-wave antennas with briefs about their characterization setup, fabrication technologies and some of the associated challenges.

In this paper, a novel approach to achieve multiband antenna operation using metamaterial based resonant structures is presented. Multiband antenna operation is achieved by employment of complementary split ring resonators (CSRR) printed in the ground plane. The CSRRs resonate at different frequencies according to their optimized dimensions. Proposed approach features simple design and fabrication possibility compared to other methods of achieving multiband antenna operation such as usage of composite right/left-handed (CRLH) transmission line or split ring resonators (SRR) or CSRR around the patch surface. The proposed method is demonstrated through simulation and experimental measurements using three CSRRs with different resonant frequencies together with a tuning CSRR and a radiating patch. Contribution of different CSRRs to obtain multiple resonances have been shown by surface current plots. Measured antenna gain of 2.78, 1.27 and 3.45 dB has been obtained at frequencies of 5.25, 6.28 and 7.29 GHz respectively. The measurements done on developed antenna exhibits close agreement with the simulation results. In context with the current communication application trends involving multiple operating bands like 5G, this approach may have immense application potential since the same can be adopted to achieve compact multiband antennae operation in other frequency bands of interest.

This article describes the computer-aided design of the RF-cavity for a S-band klystron operating at 2856 MHz. State-of-the-art electromagnetic simulation tools SUPERFISH, CST Microwave studio, HFSS and MAGIC have been used for cavity design. After finalising the geometrical details of the cavity through simulation, it has been fabricated and characterised through cold testing. Detailed results of the computer-aided simulation and cold measurements are presented in this article.

The multiple-beam klystrons (MBKs) are well known for some distinct performance advantages over their single-beam versions. The advantages of the MBKs include higher average power, relatively lower operating voltages, higher bandwidth, and low individual beam current. However, the design of the MBKs is more extensive and requires thorough and careful three-dimensional electromagnetic simulations and analysis. In this article, design of a four-beam klystron compatible with a predesigned electron gun is reported. Starting with simple analytical approach, detailed design and electromagnetic simulation results of the radiofrequency (RF) cavities are presented. Uniformity of the RF coupling between the external circuitry and the cavity RF field has been investigated in detail with the help of commercially available three-dimensional electromagnetic design code. A cold-test model of the RF cavity has been fabricated and its resonant frequency has been characterized experimentally. Design of the individual cavities, electromagnetic analysis of the same, simulation results of the beam-wave interaction, as well as the experimental frequency characterization of a fabricated cavity is presented in this paper.

V-band Klystrons find applications in satellite communications and 5G technology. Here, we present a V-band Klystron using radial re-entrant square cavities (RRSCs). The RRSCs are easy to fabricate, assemble, align, and tune to the operating frequency, which are significant concerns in V-band. We have optimized the number of cavities and the gap for best possible gain and bandwidth. The eigenmode and particle-in-cell (PIC) simulation results of the CST microwave studio are presented. The optimum design uses eleven equidistantly placed RRSCs, producing the maximum gain of 27.17 dB at 60.1 GHz with a bandwidth of ∼150 MHz.