Slot—coupled directional couplers on a both—sided substrate MIC and their applications

A slot‐coupled directional coupler is proposed and analyzed. In the slot‐coupled directional coupler, microstrip lines set on both sides of a common ground plane are coupled through a slot in the common ground plane. This coupler can easily realize a tight coupling such as 3 dB with a small physical size. This paper shows that it is possible to form a planar multiport directional coupler with 2 n ( n : integer) input or output ports without line crossings by combining slot‐coupled directional couplers. Using such a planar multiport slot‐coupled directional coupler, a multiport power amplifier and a BMN (Butler matrix network) can easily be formed in a small physical size. The 3‐dB slot‐coupled directional coupler fabricated for trial has a coupling of 3.2 ± 0.2 dB, a return loss of more than 25 dB, and an isolation of more than 28 dB in the frequency range of f O ±20 percent ( f O = 1.5 GHz). These measured values agreed well with computed data.