A circuit comprising: a first input and output unit configured such that a current, a voltage, or an electromagnetic wave can be applied to said first input and output unit; a second input and output unit configured such that a current, a voltage, or an electromagnetic wave can be applied to said second input and output unit; a first board including a matrix circuit which is formed by a first microstrip line and includes a 90-degree hybrid circuit and a delay line, the first microstrip line in which one end is connected to the first input and output unit and a tip of the other end is opened; a second board including a second microstrip line in which one end is connected to the second input and output unit, and a tip of the other end is opened; a shielding plate including an opening portion; a phase shifter configured to adjust a phase of a current, a voltage, or an electromagnetic wave excited in the second microstrip line; and a first amplifier configured to increase an amplitude of the current, the voltage, or the electromagnetic wave excited in the second microstrip line, wherein the shielding plate is configured to cause a current, a voltage, or an electromagnetic wave directed from the other end of the first microstrip line, which has the opened tip, toward the shielding plate to propagate to the other end of the second microstrip line, which has the opened tip, through the opening portion and configured to cause a current, a voltage, or an electromagnetic wave directed from the other end of the second microstrip line, which has the opened tip, toward the shielding plate to propagate to the other end of the first microstrip line, which has the opened tip, through the opening portion; the phase shifter is connected to the second microstrip line; and the first amplifier is connected to the second microstrip line. a first input and output unit configured such that a current, a voltage, or an electromagnetic wave can be applied to said first input and output unit; a second input and output unit configured such that a current, a voltage, or an electromagnetic wave can be applied to said second input and output unit; a first board including a matrix circuit which is formed by a first microstrip line and includes a 90-degree hybrid circuit and a delay line, the first microstrip line in which one end is connected to the first input and output unit and a tip of the other end is opened; a second board including a second microstrip line in which one end is connected to the second input and output unit, and a tip of the other end is opened; a shielding plate including an opening portion; a phase shifter configured to adjust a phase of a current, a voltage, or an electromagnetic wave excited in the second microstrip line; and a first amplifier configured to increase an amplitude of the current, the voltage, or the electromagnetic wave excited in the second microstrip line, wherein the shielding plate is configured to cause a current, a voltage, or an electromagnetic wave directed from the other end of the first microstrip line, which has the opened tip, toward the shielding plate to propagate to the other end of the second microstrip line, which has the opened tip, through the opening portion and configured to cause a current, a voltage, or an electromagnetic wave directed from the other end of the second microstrip line, which has the opened tip, toward the shielding plate to propagate to the other end of the first microstrip line, which has the opened tip, through the opening portion; the phase shifter is connected to the second microstrip line; and the first amplifier is connected to the second microstrip line.