Development of V-band Doppler reflectometer based on frequency steering phased array antenna

Abstract KSTAR Doppler reflectometer (DR) is designed based on frequency steering phased array antenna (FSPAA) operating in X-mode over the full V-band (50–75 GHz). In the FSPAA system, the microwave radiation angle varies as a function of frequency, allowing rapid changes in the radiation angle without mechanical movement. This is a very attractive advantage in fusion reactor environments where the concept of maintenance-free is important. However, FSPAA has limitations in microwave radiation in the broadside direction due to the open-stopband problem. In this paper, various types of series feeds are developed to suppress open-stopband and their performance is tested based on computer simulations. Directional coupling feed shows the best performance. Two prototype FSPAAs consisting of 8 antenna elements with directional coupling feed networks have been manufactured using electroforming technology. The performance of the manufactured FSPAAs are experimentally measured. Since microwaves are radiated with uniform power over an angular range of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>±</mml:mo> <mml:msup> <mml:mn>40</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> for a frequency sweep of 3 GHz, the angular scan is repeated 9 times over the entire V-band. A prototype KSTAR DR based on a bistatic antenna configuration is assembled using the two FSPAAs. The performance of the prototype DR is tested using a rotating corrugated aluminum wheel in the laboratory.