Unmanned aircraft jamming and counterattack equipment power regulation
▪Background
UAV interference impact counterattack equipment is usually composed of impact transmitter module, transmit antenna, corresponding battery management and control circuit, among which the impact transmitter module and transmit antenna are directly related to the counterattack effect, especially the counterattack distance. If the antenna has been determined, the distance to affect the counterattack basically depends on the impact of the launch module (neglecting environmental and engineering factors). Specifically, the output power of the impact transmitter module determines the impact counterattack distance of the entire system.
▪Requirements
In some UAV jammer counterattack systems, users require that the influence power can be adjusted and controlled for the following reasons:
①Customers have protection level requirements: In special periods, the system is required to have the longest impact counterattack distance; but usually the system is required to have a moderate impact counterattack distance.
② To comply with the standards: Under certain standards, there is a certain limit on the equivalent isotropic radiated power (E.R.I.P) of the transmitting equipment, which generally can only meet the most basic requirements of the impact distance. In order to achieve the effect of customer satisfaction, the equipment will try to reach the limit as much as possible, or even exceed the limit. If the equipment wants to meet the limit requirements during the acceptance or testing process, the equipment needs to have the ability to adjust the power.
③In order to prolong the service life of the equipment: In high-power equipment, the transmission module will be in a high temperature state when it exports high power, and long-term work will have a great impact on the service life of the transmission module and even the whole machine. In order to prolong the service life of the equipment, when the target UAV is approaching, it can achieve effective counterattack through the impact launch of small and medium power without causing frequent high temperature of the equipment.
The relationship between the life of the transmitter module power amplifier tube and the junction temperature
The picture shows "Transmission" magazine. Liao Yuanyuan studied "The Relationship between Transmitter Power Amplifier Lifetime and Temperature". MTF is MTBF the average working time without failure. The conclusion is that when the power amplifier tube junction temperature of the power amplifier (which can be understood as the chip temperature, not the module shell temperature) increases by 10°C, its service life will decrease by a factor of 2.5. In other words, if the junction temperature of the launch tube can be reduced by 40°C every time it works, the working life of the launch module can be delayed by 10 times. Although we don't have much requirement on the service life of the launch module, its service life can be converted into working reliability. (The MTF in the figure is MTF)
④ In order to save power: This is especially reflected in portable devices. Due to the size and weight limitations of portable UAV jamming and counterattack equipment, the battery power is usually very small. In addition, in recent years, the requirements for portable UAV jamming and counterattack equipment have become higher and higher, and there are more and more transmitting frequency bands. The interior usually needs to integrate navigation deception, detection and early warning, and even target measurement modules, which increases the demand for battery energy. The large power consumption in portable equipment is mainly the transmitting module. Therefore, power can be saved by reducing the transmit power when the target is very close.
⑤In order to improve the effect of equipment: in portable equipment, the selection of the output power index of the module should not be too large, because there are problems of heat dissipation and power consumption. But sometimes it is necessary to provide high power export for a short time. For example, when the target UAV is too close to the controller (controller) or when demonstrating the effect of affecting the counterattack, we all hope that the device can provide the "afterburning" function similar to the engine of a sports car or a fighter jet, that is, to provide output power beyond the usual in a short period of time, so as to temporarily improve performance when needed. This should also equip the device with a high power module, usually running normally at medium power and then "shut down" when needed.
To sum up, we need to provide a simple and efficient solution for adjusting the output power of the transmitter module. The adjustment range is generally between 25% and 100% of the nominal output power of the module, and can be adjusted in several levels or non-level continuous (or similar). Considering customer experience, fixed equipment is the best choice for stepless continuous (or similar) adjustment, and portable equipment is divided into 2~3 levels.
▪Principle
This paper introduces the principle of power regulation affecting the transmitting module.
The general composition of the impact launch module is shown in the figure below:
The composition of the launch module
The signal source of the transmitting module usually works in the way of scanning frequency, that is, the output frequency cycles back and forth between f1 and f2, and f1 and f2 are usually between tens to hundreds of MHz. What we hope is that the output power is smooth and stable throughout the scanning frequency range, and so is the actual transmitting module. The actual 50W impact transmitter module (2.4~2.5GHz) power-frequency characteristics are as follows:
The power-frequency characteristics of the actual transmitting module
It can be seen that the output power of this module is relatively flat while meeting its basic power supply requirements, which can meet our demand for flatness. However, what we need now is to adjust its power. Generally speaking, we think that reducing the output power of its internal signal source can reduce the output power of its driver level, thereby reducing the output power of the export level. In fact, by reducing the output power of the signal source, the output power-frequency characteristics of the transmitting module are as follows:
The power-frequency characteristics of the transmitting module after reducing the power of the signal source
It can be seen that although the overall power drops as we wish, the specific situation is not ideal. The output power of different frequencies fluctuates greatly, and the power value at the highest point is about 50% higher than the power at the lowest point. This is what we don't want to see. The reason for this is that, in fact, the working states of the promotion stage and the output stage of different frequencies are different, and the signal amplification factor (power gain) of the signal source also changes with the frequency, which causes the output power of the transmitting module to change within the frequency sweep range. Why is the output power of the transmitting module relatively flat when the output power of the signal source is sufficient? (As shown in Figure 3) This is because the output power of the driving stage and the output stage of the transmitting module has a limit, that is, the saturation power. When the output power is close to this limit, even if the input power increases, the increase in output power is small. However, the power is still increasing until the frequency at which the output power limit is reached. Finally, when the input signal is sufficient, the output power at all frequencies is close to this limit, that is, all frequencies are derived around the saturation power.
Power-frequency characteristics of different signal source power transmitter modules
Therefore, it is not feasible to adjust the output power of the entire module, at least it is not ideal. It is necessary to adjust the output power of the signal source or the power of the booster stage inside the module. If you want to adjust the output power in this way, it is estimated that you need to change the output stage scheme, increase the cost, and use a high-power device with better linearity, but this will lead to a significant drop in module efficiency, and an increase in cost and power consumption.
At present, the only thing that is easy to do is to adjust the output power of the transmitter module by adjusting the working voltage of the export stage. The working voltage of the deriving stage directly determines the saturation power of the transmitting module, that is to say, under the premise of constant signal source power, the smaller the working voltage of the deriving stage is, the more serious the saturation is, but the saturation power value decreases as the working voltage decreases. The same goes for the driver stage. Since the signal source power supply of the transmitting module is provided by the voltage stabilizing circuit inside the transmitting module, it can be kept stable within a certain supply voltage range, so that the output of the transmitting module can be stably adjusted by controlling the working voltage of the entire transmitting module.
The above test is also a 2.4GHz/50W transmitter module, testing its power-frequency characteristics under different power supply voltages. It can be seen that the power regulation effect is very ideal.
photo
Figure 6 Power-frequency characteristics of different signal source power transmitting modules
It can be seen from the above figure that although the output power of the transmitting module still fluctuates to a certain extent under low voltage, the fluctuation range is limited. Through the actual test of multiple transmitting modules, it is found that adjusting the output power by reducing the power supply voltage of the transmitting module has good consistency and stable performance. The most important thing is that the efficiency of the whole module is improved to a certain extent, which is conducive to saving and discharging the battery capacity of portable devices. To sum up, choosing power supply voltage regulation is an ideal power regulation solution.
▪Program
For practical applications, different types of equipment require different specific implementations to adjust the impact on the module power supply voltage.
Generally speaking, battery-powered portable devices are more suitable for 2-3 gear output power regulation. This is because portable devices are simple to operate and require quick and easy operation, often requiring only a few mechanical buttons for quick operation. At this time, the output power of the equipment can be quickly adjusted according to the needs, through one or more gear switches, which is an ideal operation scheme.
