Design and Measurement of a Broadband Compact TE₁₁ Mode Input Coupler for an X-Band Gyrotron Traveling Wave Tube

A Compact Circular Waveguide Directional Coupler for High-Order Mode Vacuum Electronic Devices

“…The traditional solution is to increase the number of coupling holes, which is suitable for conventional couplers with a parallel connection of the main and secondary waveguide due to the sufficient space; however, it is not suitable for the orthogonal one due to its limited space. In order to satisfy the design requirements of high-order mode VEDs for broad bandwidth, high transmission efficiency and high directivity, the length of the entire device increases with the increasing number of coupling holes, usually reaching more than ten wavelengths [12,18], which is very unfavorable to the pursuit of device miniaturization and system compactness. To solve this problem, we propose a method of loading an adjustable load at the isolating port, and adjustable metal stubs that adjust the isolation of directional couplers are introduced in this investigation.…”

“…As the operating frequency extends to millimeter-wave and terahertz bands, the power capability reduces as the size of the interaction circuits shrinks [4]. Therefore, in order to obtain sufficient power capability and high output power, operating in high-order mode is proposed and attempted in a large number of research works [5][6][7][8][9][10][11][12]. For example, the TM 01 mode is commonly employed for BWOs [7], the TE 0n mode or higher-order TE mn mode is adopted for gyrotrons [8], and the TE n1 mode is usually utilized for the relativistic magnetrons [9].…”

“…Until recently, the mainstream research into directional couplers applied for the power monitoring of VEDs has mainly been focused on traditional aperture-type directional couplers [12][13][14][15][16][17][18][19][20][21][22], which are conventionally composed of a high-order mode circular waveguide (main waveguide) and a standard or non-standard rectangular waveguide (secondary waveguide), connected in a parallel or orthogonal way through two or more coupling apertures with various shapes. For structures where the primary and secondary waveguides are connected in a parallel arrangement, it is necessary to adjust the size, spacing, and number of the coupling holes to obtain excellent performance.…”

“…For structures where the primary and secondary waveguides are connected in a parallel arrangement, it is necessary to adjust the size, spacing, and number of the coupling holes to obtain excellent performance. However, since these variables are designed in the axial direction (the direction in which the electromagnetic wave propagates) of the coupler, it inevitably leads to a doubling of the axial length, which is usually more than ten times the wavelength [12][13][14][15][16][17][18], which makes the experimental operation inconvenient and reduces the compactness of the overall system. Another traditional structure is to connect the main and secondary waveguides of the coupler in an orthogonal way, which has the advantage of greatly reducing the axial length of the device.…”