A Novel Waveguide-Microstrip Sealed Transition Structure

1 Introduction

The conversion of electromagnetic signals between different transmission media has always been an important part of microwave and millimeter wave technology research. In the millimeter wave band, in order to facilitate the connection between the test, the antenna and the independent microstrip circuit, it is often necessary to transition the microstrip circuit input and output ports through the conversion structure to the rectangular waveguide. When it is necessary to transmit a signal over a distance, the circuit is often converted from a microstrip to a waveguide to reduce transmission loss. Therefore, millimeter wave integrated circuits using microstrips often must include a waveguide-microstrip transition interface.

In practical applications, an additional factor that cannot be ignored in the transition is the airtight requirement. Many microstrip circuits, especially military microstrip circuits, have higher requirements for the airtightness of the system in order to ensure the stability of performance under various harsh environmental conditions. In addition, the current microwave and millimeter wave circuits are developing toward miniaturization. In order to facilitate the miniaturization of the overall circuit, the volume and interface direction of the transition device have also become an important consideration. At present, the conventional rectangular waveguide-ridge waveguide-microstrip transition, waveguide-microstrip probe transition and waveguide-to-polar fin line-microstrip transition structure can not solve the problem of airtightness well, and the opening on the waveguide is large. Larger perturbations will also occur for the field distribution within the rectangular waveguide. Waveguide-coaxial probe-microstrip transition is often used to solve the problem of airtightness. The general form is familiar to everyone. It is different from the traditional waveguide-coaxial probe-microstrip transition. On the basis of airtightness, the microstrip line is taken out from the through direction.

2 Basic principles

We can think of the probe deep into the waveguide as an antenna. If the coaxial line is connected to the wave source, it radiates electromagnetic waves in the direction defined by the waveguide. Generally speaking, as long as the electric or magnetic field component of the electromagnetic wave is consistent with the electric field or magnetic field component of a certain mode of the waveguide. The model will be motivated. According to the reciprocity theorem, if the waveguide port is connected to the wave source, then the energy can also be coupled out from the waveguide. The probe is inserted from the short-circuit surface of the waveguide, perpendicular to the direction of the electric field in the waveguide, and the probe will affect the field structure in the waveguide (see Figure 1). Therefore, the energy cannot be coupled out, so it is necessary to Insert an adjustment screw directly above it to disturb the field structure in the waveguide (Figure 2). A capacitor is formed between the probe and the top surface of the screw, from which energy can be coupled out.