There are more and more applications of millimeter wave. We also have some knowledge about millimeter wave. 5g millimeter wave and millimeter wave radar are technologies we are familiar with, but in addition, do you know more about millimeter wave? In this paper, we will explain the four channel millimeter wave spatial power synthesis technology to enhance our understanding of millimeter wave. If you are interested in this article, you may as well read on.

1、 Introduction

High power millimeter wave source is the core component of the front-end of millimeter wave radar, communication, jammer and precision weapon guidance system. Solid state devices have attracted much attention due to their low DC voltage, high reliability, strong shock resistance, compact circuit structure, small size and light weight. However, with the increase of frequency, the power output of a single solid-state device will decrease rapidly, which is difficult to meet the requirements of practical application. The power synthesis method by combining multiple coherent solid-state devices or superimposing multiple separated devices is an effective method to improve the output power of millimeter wave system, which has been widely used.

In this paper, a four channel spatial power synthesis network based on waveguide is proposed. This structure can ensure equal amplitude and phase power. At the same time, using waveguide as input and output can reduce the loss of high power output. The simulation results show that in the range of 31ghz-38ghz, the amplitude imbalance of the four channels is less than 0.05db, the phase consistency is good, and the return loss of the input is less than – 20dB. The return loss of input and output of the whole synthetic network is less than – 12dB, and the insertion loss is less than 0.6dB.

2、 Design of power divider

The basic structure of the waveguide based four channel power divider is shown in Fig. 1. Because the T-junction power distribution network itself is not matched, it is necessary to put appropriate matching elements in the branch joint to adjust the matching of each port. In this paper, a matching discontinuity structure is added at the branch joint, which can adjust the center frequency and bandwidth of the power distribution network. Because the power divider is symmetrical, the amplitude and phase of the four output ports are consistent.


Figure 1 four channel power distribution structure

The results of HFSS simulation of power divider are shown in Figure 2


Figure 2 simulation results of power divider

It can be seen from Figure 2 that the four-way power divider can realize power distribution in a wide band, and the return loss of the input port is less than – 15dB. At the same time, due to the symmetry of the power division network, its phase consistency is very good.

3、 Design of power synthesis network

Probe waveguide microstrip transition is the most widely used transition structure in millimeter wave planar integrated circuits. According to the different relationship between the microstrip circuit plane and the wave propagation direction in the waveguide, it can be divided into two structural forms. One is that the microstrip circuit plane is perpendicular to the wave propagation direction in the waveguide, as shown in Figure 3; The other is that the plane of the microstrip circuit is parallel to the propagation direction of the wave in the waveguide, as shown in Fig. 4.

In this paper, the structure of the microstrip plane parallel to the wave propagation direction shown in Fig. 4 is used to realize the Ka band waveguide microstrip transition. In this structure, a microstrip probe is used to couple the electromagnetic field in the waveguide to the microstrip, and a high impedance line is used to transition to a 50 Ω microstrip line. Appropriate coupling size is adopted to reduce the influence of microstrip circuit on the electric field in the waveguide.


The model of four-way power synthesis network is shown in Figure 5


Figure 5 model of four way power synthesis network

Firstly, four equal power distribution networks divide the waveguide energy equally into four reduced height waveguides, and then realize power synthesis through four power synthesis networks through waveguide microstrip probe transition. The simulation results are shown in Figure 6

As can be seen in Figure 6, in the frequency range of 31ghz-38ghz, the return loss of the input and output ports of the synthetic network back-to-back simulation is less than – 12dB, and the insertion loss is less than 0.6dB.


Figure 6 simulation results of power combiner

4、 Conclusion

This paper presents a waveguide based four channel spatial power distribution / synthesis network for millimeter wave band. The network uses rectangular waveguide as input and output ports, and uses a quarter power distribution structure for power distribution / synthesis. The simulation and optimization of HFSS software show that the structure has very low insertion loss and return loss, which is a practical power synthesis structure.

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