An approach is proposed to reduce mutual coupling between two closely spaced radiating elements. This is achieved by inserting a fractal isolator between the radiating elements. The fractal isolator is an electromagnetic bandgap structure based on metamaterial. With this technique, the gap between radiators is reduced to $\sim 0.65\lambda $ for the reduction in the mutual coupling of up to 37, 21, 20, and 31 dB in the ${X}$ -, Ku -, ${K}$ -, and Ka -bands, respectively. With the proposed technique, the two-element antenna is shown to operate over a wide frequency range, i.e., 8.7–11.7, 11.9–14.6, 15.6–17.1, 22–26, and 29–34.2 GHz. Maximum gain improvement is 71% with no deterioration in the radiation patterns. The antenna’s characteristics were validated through measurement. The proposed technique can be applied retrospectively and is applicable in closely placed patch antennas in arrays found in multiple-input multiple-output and radar systems.

/pdf/mutual-coupling-suppression-between-two-closely-placed-25phqnquax.pdf

Mutual Coupling Suppression Between Two Closely Placed Microstrip Patches Using EM-Bandgap Metamaterial Fractal Loading

An approach of reducing Mutual Coupling between two patch antennas is proposed in this paper. Here, a meander line resonator is placed in between the radiating elements. By inserting the meander line resonator between the patch antennas with the edge-to-edge distance less than λ/18, about 8 dB reduction of Mutual Coupling throughout the 10-dB bandwidth has been achieved without degrading the radiation pattern. The circuit model of the proposed configuration is carried out in this paper. The envelope correlation coefficient investigation has been done and the results are presented. The proposed structure has been fabricated and measured.

/pdf/mutual-coupling-reduction-between-closely-placed-microstrip-3e8n2xzgmi.pdf

Mutual coupling reduction between closely placed microstrip patch antenna using meander line resonator

Traveling wave tubes are rapidly evolving to provide unprecedented power level in comparison to solid state devices in the millimeter waves region of the spectrum (80–300 GHz) thus enabling a wide ...

https://www.tandfonline.com/doi/pdf/10.1080/09205071.2020.1848643

Millimeter wave traveling wave tubes for the 21st Century

This paper presents a novel 2D meta-surface wall to increase the isolation between microstrip patch radiators in an antenna array that is operating in the teraherz (THz) band of 139-141 GHz for applications including communications, medical and security screening systems. The meta-surface unit-cell comprises conjoined twin ‘Y-shaped’ microstrip structure which are inter-digitally interleaved together to create the meta-surface wall. The proposed meta-surface wall is free of via holes and defected ground-plane hence easing its fabrication. The meta-surface wall is inserted tightly between the radiating elements to reduce surface wave mutual coupling. For best isolation performance the wall is oriented orthogonal to the patch antennas. The antenna array exhibits a gain of 9.0 dBi with high isolation level of less than -63 dB between transmit and receive antennas in the specified THz-band. The proposed technique achieves mutual coupling suppression of more than 10 dB over a much wider frequency bandwidth (2 GHz) than achieved to date. With the proposed technique the edge-to-edge gap between the transmit and receive patch antennas can be reduced to 2.5 mm. Dimensions of the transmit and receive patch antennas are 5×5 mm2 with ground-plane size of 9×4.25 mm2 when constructed on a conventional lossy substrate with thickness of 1.6 mm.

/pdf/meta-surface-wall-suppression-of-mutual-coupling-between-4tjob4ekiu.pdf

Meta-Surface Wall Suppression of Mutual Coupling between Microstrip Patch Antenna Arrays for THz-Band Applications

A novel planar slow wave structure (SWS) for traveling wave tube (TWT) is proposed. The major advantage of the planar architecture is its easy realization with respect to the typical 3-D SWSs. The particle in cell simulations of the TWT show an achievable gain up to 36.4 dB and a maximum output power of 17.4 W for an operating frequency of 92 GHz. The planar structure can be realized using the standard photolithographic techniques, which improve the reproducibility and performance.

$W$ -Band Traveling Wave Tube Amplifier Based on Planar Slow Wave Structure

A novel slow-wave structure (SWS), named ridge-loaded sine waveguide (RLSWG), has been proposed to develop the wideband high-power terahertz traveling-wave tube (TWT). The slow-wave characteristics of the RLSWG SWS, including dispersion properties and interaction impedance, are analyzed by using the 3-D electromagnetic simulation software Ansoft high frequency structure simulator (HFSS). From our calculation, the average interaction impedance of the RLSWG SWS at 0.22 THz is 42.2% higher than the conventional SWG SWS. Meanwhile, the simulation results demonstrate that the RLSWG SWS possesses low ohmic losses and reflection. Moreover, the particle-in-cell (PIC) simulation results reveal that, with the cylindrical electron beam of 20.9 kV and 45 mA, the output power and electron efficiency of the RLSWG TWT at the typical frequency of 0.22 THz can reach 52.1 W and 5.54%, respectively. In addition, the 3-dB bandwidth of the RLSWG TWT exceeds 25 GHz. Compared with the SWG TWT, the RLSWG TWT has the shorter tube length and can generate the larger output power.

A Ridge-Loaded Sine Waveguide for $G$ -Band Traveling-Wave Tube

Meander lines (MLs) in two configurations are presented to reduce the mutual coupling (MC) between two microstrip patch antenna elements. Inserting a slot in the ground plane between the antenna elements is a simple method to reduce the MC, while adding the MLs in the slot of the ground can further reduce the MC. In the first configuration, one ML is inserted in the slot of the ground and a maximum MC reduction of 39 dB throughout the −10 dB bandwidth is achieved. What’s more, the radiation patterns are not changed compared with the dual-element microstrip antenna array with a slotted ground. For the second configuration, two MLs are added in the slot of the ground. It is found that a maximum isolation of 53 dB can be obtained. However, the radiation patterns are slightly changed compared with the dual-element microstrip antenna array with a slot in the ground. Meanwhile, the measured peak gain and efficiency of the dual-element microstrip antenna array in the two configurations are given. Along with this paper, several prototypes have been fabricated and measured. The simulated results are in good accordance with the measurements, which are presented to verify that MC reduction can be achieved between microstrip antenna elements by adding the MLs in the slotted ground.

/pdf/mutual-coupling-reduction-between-patch-antennas-using-22vx8an8wy.pdf

Mutual Coupling Reduction between Patch Antennas Using Meander Line

A novel ridge-loaded folded waveguide slow-wave structure has been firstly employed to manufacture a W-band continuous wave traveling wave tube (TWT). This letter reports the processes of the design and experimental test for this TWT. From the experimental results, over 25-W output power are produced within the operation bandwidth from 93.1 to 94.8 GHz, which is in accordance with the simulation results.

Novel W -Band Ridge-Loaded Folded Waveguide Traveling Wave Tube

A novel planar monopole antenna with dual-band circularly polarisation (CP) is presented here. The antenna consists of a modified L-shaped monopole, an inverted-L strip, and a modified ground. The utilisation of the modified L-shaped monopole not only generates dual-band operation, but also excites CP radiation in the lower band. In order to achieve CP in the upper band, a parasitic inverted-L strip is added on the top plane of the substrate and a modified ground is designed. The proposed antenna has been fabricated and tested, the measured -10 dB reflection coefficient bandwidths are 370 MHz (2.38-2.85 GHz) in the lower band and 2330 MHz (4.05-6.38 GHz) in the upper band. The measured corresponding 3 dB axial ratio (AR) bandwidths are 610 MHz (2.39-3 GHz) and 850 MHz (5.15-6 GHz), respectively. The overlapped -10 dB reflection coefficient and AR bandwidths can totally cover the WLAN bands, Wi-Fi bands, Bluetooth band, and partly cover the WiMAX bands. The proposed antenna owns bidirectional radiation characteristic and reasonable gain at both the lower band and the upper band.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-map.2017.0523

Dual-band circularly polarised planar monopole antenna for WLAN/Wi-Fi/Bluetooth/WiMAX applications

A W-band sheet electron beam (SEB) traveling-wave tube (TWT) based on flat-roofed sine waveguide slow-wave structure (FRSWG-SWS) is proposed. The sine wave of the metal grating is replaced by a flat-roofed sine wave around the electron beam tunnel. The slow-wave characteristics including the dispersion properties and interaction impedance have been investigated by using the eigenmode solver in the 3-D electromagnetic simulation software Ansoft HFSS. Through calculations, the FRSWG SWS possesses the larger average interaction impedance than the conventional sine waveguide (SWG) SWS in the frequency range of 86-110 GHz. The beam-wave interaction was studied and particle-in-cell simulation results show that the SEB TWT can produce output power over 120 W within the bandwidth ranging from 90 to 100 GHz, and the maximum output power is 226 W at typical frequency 94 GHz, corresponding electron efficiency of 5.89%.

Chong Ding

Papers

A Ridge-Loaded Sine Waveguide for $G$ -Band Traveling-Wave Tube

Mutual Coupling Reduction between Patch Antennas Using Meander Line

Novel W -Band Ridge-Loaded Folded Waveguide Traveling Wave Tube

Dual-band circularly polarised planar monopole antenna for WLAN/Wi-Fi/Bluetooth/WiMAX applications

Study on W-band sheet-beam traveling-wave tube based on flat-roofed sine waveguide