A Design Of A Ku-band Pulse Solid-state Power Combined Amplifier

As the most important part of the microwave and millimeter wave radar system, the radar transmitter has always been taken seriously. With the growing demands, the radar transmitter is developing to work at higher frequency, to output more power, to be smaller and lighter. Along with the development of the semiconductor process technology, the vacuum devices are replaced the solid-state power devices in more occasions. But the power level of the single solid-state device’s output is not enough to satisfy the radar transmitters’requirements,mainly in the peak and average output. It is necessary to use the power-combined technology for higher power output. For the project’s demand, we analyzed the situation of the Ku-band solid-state power amplifier and various of power combiner technology. Depending on the analysis, we selected the waveguide-based multi-leveled binary circuit power-combining techniques, so as to achieve the amplifier which can output more than80W pulsed peak power.In the article, the pulsed solid-state power amplifier (SSPA) is divided into two parts to analyze and design. Part one is the pulse modulation’design of power supply, it used the switch of MOSFET as the drain’s modulator of the amplifier, in order to support more current, we made two MOSFET in parallel. And then we achieved fast rising edge and falling edge, and low pulse waveform drop,etc; Another part is the power combining networks. On the basis of analyzed the3dB branch-waveguide coupler, T-junction, the magic T, we chose the magic T as the basic combiner. Using the binary form of power combining network, we designed a four-way power divider/combiner network and then processed it. The structure is a ingenious design, can save more space,be easy to process and get less insertion loss; In order to solve the matching problem of the magic T’s isolation port, we designed a waveguide load on the basis of the microstrip probe coupling principle,then made the divider/combiner network be stable. We produced the20W power module which integrated the MMIC power amplifier and2-way0°power divider chip. By means of the structure’s design, we skillfully put two module of20W into one cavity, sharing one modulation circuit board. This structure greatly reduced the difficulty of assembly, and saved the space; The power amplifier’s stability were improved by some assembling and cooling method.Finally using the pulse modulator and power distribution/synthesis network, we completed the Ku-band pulsed solid-state power amplifier’s assembly and test. Within1GHz frequency bandwidth, working with8KHz pulsed repetition frequency and3.2%duty cycle, the output peak power is greater than80W, the highest output peak power is91.2W. The rising edge and falling edge of output pulse power waveform are all less than30ns,, and pulse waveform drop was less than0.7dB. Eventually the whole size of the80W amplifier is70×54×80mm3.