Advertising machine Doppler radar module induction antenna knowledge revealed, with the radar sensor more infiltrated into people's life, as the industry shipment front of the enterprise, we will popularize some correct radar knowledge, in order to better use the radar module.
Antennas should be impedance matched, no so-called low impedance antenna is better, or 0 ohm impedance antenna is better! Let's first look at the role of the antenna, the advertising machine Doppler radar module induction antenna reception is to collect electromagnetic wave energy in space, and then efficiently transmitted to the receiver. Since antennas are easy to each other, they have the same receiving and transmitting performance, so only one of them needs to be discussed. Therefore, the suitability of antenna impedance depends on whether the space electromagnetic wave energy collected by it can be efficiently transmitted to the receiver.
1, antenna impedance and impedance matching
Let's look at the difference between load impedance and source resistance. Advertising machine Doppler radar module induction antenna responsible for collecting electromagnetic waves, equivalent to signal source, load, naturally is the receiver. Assume that the potential of the voltage source is E, the internal resistance is R0, and the load impedance is RL. High school students know this problem only when the load can get large power P=E*E/4RL. For example, if the internal resistance is 50Ω, the potential is 1V, the load is also 50Ω, and then the power obtained by the load is 5mW. But if the load impedance is different from the internal resistance of the source, such as low impedance 10Ω, it can be calculated from the circuit that the actual load voltage after voltage division is 1/6V, so the actual load power is only 2.78mW, almost half the impedance matching result.
From the above point of view, the optimal value of antenna impedance is entirely determined by the receiver. Furthermore, the optimal input impedance of the antenna is only 50Ω, including all test instruments unless all systems are independently designed.
2. Analyze the low impedance antenna
From the above analysis, microwave mobile sensor as the application of microwave industry, advertising machine Doppler radar module induction antenna is almost impossible to avoid complying with industry rules, antenna input impedance of 50Ω, there is a saying in China too much, high impedance is not good, low impedance is not good. Recently, I heard about an antenna innovation, the so-called low-impedance antenna. Let's analyze whether it's a so-called low-impedance antenna or a true innovation.
The general operation mode of patch microstrip antenna is called TM10 mode, which has a field distribution structure. As a popular science, we will not discuss site distribution characteristics in detail. We only draw its equivalent circuit, which can be equivalent to LCR parallel resonant circuit. When resonant, the susceptance of LC is cancelled out, or when we often say parallel resonance, equivalent to open circuit, leaving only R, the radiation resistance. We've already analyzed it, and the appropriate value is 50Ω.
If the advertiser Doppler radar module induction equivalent circuit is redrawn as shown in the diagram, the inductor and capacitor are divided into two series, further connecting the two midpoints, or not connected, has no effect on the resonant circuit, the radiation resistance R part is completely unaffected, or the original impedance. This midpoint is actually the midpoint of the microstrip patch antenna, which is grounded with a ground through hole and has no effect on the characteristics of its working frequency! So, has this characteristic of the electromagnetic field only been discovered in recent years? Decades ago, theoretical analyses of microstrip patch antennas resolved the field map, which points of the antenna are the zeros of the electric field. As for electromagnetic field theory, adding pieces of metal to a surface or path where the electric field is tangential to zero and the line does not change the electromagnetic field has been around for at least a few hundred years.
Therefore, it is pseudoscientific to add a ground through hole in the midpoint of the microstrip patch antenna to create a so-called low-impedance antenna. The real situation is that adding a ground hole at this particular location does not change the characteristics of the antenna operating frequency, and some changes may occur to the characteristics outside the operating frequency, such as DC from suspension to ground state.
3. Antenna gain
Advertiser Doppler radar module antenna gain is the second important index that we often mention antenna. Unlike amplifier gain, antennas are passive networks and cannot amplify signals! The amplifier has a gain and really amplifies the signal. The antenna is not, so the antenna gain can be understood as the antenna radiation is not uniform, radiation energy concentrated in a particular direction. Due to conservation of capacity, the radiated energy in other directions must be reduced. Consider that the efficiency is 100%, such as an antenna with no direction. If the antenna radiates uniformly only up half space and not down half space, then we say that the gain of the antenna is 2. If the antenna radiates uniformly only to the x, y, and z positive axes including the corner cone, then we say that the antenna gain is 8, or 9dB.
So is high antenna gain bad or bad? Antenna gain is actually efficiency times the directional factor. The efficiency part is naturally high, good is 100%. The directional coefficient is what we talked about above. Not high is bad, only suitable for not suitable. For example, military long-range radar aims at a direction, hoping that the working distance is far, the interference is small, and the direction coefficient is large. For example, GPS receiving antenna, high directional coefficient has problems, can only receive a few satellite signals, is not conducive to positioning settlement. Specifically for our mobile microwave sensor, the direction coefficient should not be too high in the general hanging high scene, because to perceive the direction that 360° omnidirectional antenna is more suitable for human movement, for example, in specific applications, such as toilets and mirrors, rather than the Doppler radar module of advertising machine sensing and sensing the surrounding objects, a higher direction coefficient is required.
As you can see, different application scenarios need to match different advertiser Doppler radar module induction antennas. In lighting industry applications where it is not easy to make the radiation field uniform, radar can detect human movement or presence from different directions, which is a very important aspect of the user experience. As an industry brand, the stability and consistency of our products are well received by many well-known brand customers. Advertising machine Doppler radar module induction always adhere to the product stability and reliability as an element, easy to use as the second element, solid production of products, but not misleading consumers some pseudo-concepts.
