International Symposium on Antennas and Propagation
Bandwidth of Multi-Port Microstrip-to-Waveguide Transitions in Millimeter-Wave Band
K. Sakakibara, D. Takagi, K. Seo, N. Kikuma, H. Hirayama,
PDF download (280.8KB)
Various types of microstrip-to-waveguide transitions are developed for feeding microstrip antennas and for connection of RF circuits in the millimeter-wave band. Ordinary transitions are composed of a microstrip line on the substrate inserted into the back-shorted waveguide with spacing of a quarter wavelengths from the microstrip line to the short circuit. Broad frequency bandwidth is achieved by using a back-shorted waveguide with the novel metal pattern on the substrate . However, the metal block for the back-shorted waveguide causes performance degradation due to shift of the metal block from the waveguide center. Requirement of the additional part of the metal block causes further disadvantage for cost reduction. Two types of transitions are developed to prevent using the metal block. One is a transition with the back-shorted waveguide in a multi-layer substrate . A microstrip line is located on the lower substrate attached over the open-ended waveguide. The back-shorted waveguide is formed in the upper layer of the additional substrate. Consequently, the transition is composed in the double layer substrate. In this case, bandwidth is narrower than the previous transition with a metal block but is still broader than the next transition of the single layer substrate. Another solution is a transition with a single layer substrate . The waveguide is shorted by the upper metal ground plane on the substrate. A microstrip line is inserted into the ground plane, which results in the coplanar line. The electromagnetic wave from the waveguide excites the microstrip patch at the center of the waveguide aperture on the lower plane of the substrate. The electric current on the patch couples to the coplanar line and transmits to the microstrip line port. Mode transformation is achieved from the waveguide to the microstrip line. Transitions with multi microstrip-line ports are useful for feeding array antennas. Therefore, the transition with a single-layer substrate is applied to the multi-port transitions with one, two and four microstrip lines in this study. Multi microstrip-lines are inserted into the upper ground plane on the substrate. Electric current on the patch couples to the multi coplanar lines and equal power transmits to all microstrip-line ports simultaneously. Three types of transitions are introduced as transitions with a metal block for the backshorted waveguide, single and double layer substrates. Bandwidths of these transitions are compared in Sec. 2. Transitions with multi microstrip-line ports are designed and bandwidths are compared in Sec. 3.