What are microwave antennas used for?

The main parameters of the microwave antenna

1. Antenna gain

Gain is an important parameter of the microstrip microwave antennas. In the case of a certain antenna size, the antenna gain directly reflects the efficiency of the antenna.

2. Half power angle

Deviating from the direction of the main lobe to both sides, when the deviation reaches the point where the power drops by half, this point is called the half-power point. The angle between two half-power points is the half-power angle. When the antenna aperture is fixed, the higher the operating frequency, the smaller the half-power angle, and the higher the degree of energy concentration; When the operating frequency is constant, the larger the antenna aperture, the smaller the half-power angle.

3. Cross-polarization identification rate

Cross-polarization discrimination (XPD) is defined as the ratio of the level of the copolarized signal received by the receiving antenna to the level of the quadrature polarized signal when the transmitting antenna transmits only one polarized signal. The high requirement for XPD is to suppress interference from orthogonal polarization signals, especially because large-capacity microwave relay systems (such as SDH microwave systems) widely use co-channel orthogonal polarization frequency multiplexing technology to improve communication capacity and save valuable spectrum resources, and the requirements for XPD are very strict.

4. Antenna defense

Antenna defense refers to the degree of attenuation of the antenna's receiving capacity in a certain direction relative to the receiving capacity in the direction of the main lobe. The degree of defense in the 180° direction is also called the front/back ratio, which is a very important indicator in microwave communication.

5. Voltage standing wave ratio

The impedance of the antenna and the feeder connection should match, and the standing wave ratio at the input must be small. Generally, the VSWR of the antenna is between 1.05~1.2.

Applications of microwave antennas

Microwave is an electromagnetic wave with a wavelength of 1m~1mm, which not only has the nature of electromagnetic waves, but also is different from ordinary radio waves and light waves. Microwaves have the following characteristics relative to electromagnetic waves with relatively wavelengths: (1) devices for space radiation are easy to manufacture; (2) It is easy to reflect when encountering various obstacles; (3) poor diffraction ability; (4) The transmission characteristics are good, and the influence of smoke, dust, strong light, etc. is very small during the transmission process; (5) The absorption of microwaves by the medium is proportional to the dielectric constant of the medium, and the absorption effect of water on microwaves is the strongest.

Microwave oscillators and microwave antennas are important components of microwave sensors. A microwave oscillator is a device that generates microwaves. Because microwaves are short and the frequency is very high (300MHz~300GHz), the oscillation loop is required to have very small inductance and capacitance, so ordinary transistors cannot be used to form microwave oscillators. Devices that make up a microwave oscillator are klystron tubes, magnetrons or certain solid elements. Small microwave oscillators can also use bulk transistors.

The oscillation signal generated by the microwave oscillator needs to be transmitted with a waveguide (coaxial line with a wavelength above 10 cm) and transmitted through the antenna. In order for the transmitted microwaves to have consistent directivity, the antenna should have a special structure and shape. Commonly used antennas include horn-shaped antennas and parabolic antennas.

The microwaves emitted by the transmitting antenna are absorbed or reflected when they encounter the measured object, causing a change in power. If the receiving antenna is used to receive microwaves reflected by or reflected by the measured object, and convert it into an electrical signal, which is then processed by the measurement circuit, microwave detection is realized. According to this principle, microwave sensors can be divided into two types: reflective and blocking.

1. Reflective sensor

This sensor expresses parameters such as the position and thickness of the measured object by detecting the microwave power reflected back by the measured object or elapsing time intervals.

2. Blocking sensor

This sensor detects the amount of microwave power received by the receiving antenna to determine whether there are parameters such as whether there is a measured object or the location of the measured object between the transmitting antenna and the receiving antenna.

Microwave antenna technology is the bottleneck restricting the development of radar and measurement control technology. Different from other electronic products, the electrical performance and function of microwave antennas are mainly guaranteed by the structure of the feed network, so the design and process manufacturing of the feed network is the key technology of antenna product manufacturing.

Microwaves mainly rely on space wave propagation, and antennas are erected higher to increase the communication distance. In microwave antennas, the widely used parabolic antennas, horn parabolic antennas, horn antennas, lens antennas, slotted antennas, dielectric antennas, periscope antennas, etc. are widely used.

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