High gain antenna
Antenna Popular Science - Operating Bandwidth
Estimated 15minutes to finish reading
I. Definition and Classification
1. Definition: Antenna bandwidth generally refers to the frequency range corresponding to when a certain parameter of the antenna (such as gain, voltage standing wave ratio, etc.) meets specific requirements.
2. Classification
Absolute Bandwidth: It is the actual frequency range within which the antenna can operate. The calculation formula is Δf = fmax - fmin, where fmax is the highest frequency at which the antenna can operate, and fmin is the lowest frequency at which the antennacan operate.
Relative Bandwidth**: It is expressed as the ratio of the difference between the upper and lower limit frequencies to the center frequency. The calculation formula is Relative Bandwidth = (f_high - f_low) / f_center.
II. Influencing Factors and Representation Methods
1. Influencing Factors: The bandwidth of an antenna is affected by various factors, including the physical size, shape, material of the antenna, and design objectives. For example, techniques such as using thicker metal wires, metal “wire cages” to approximate even thicker metal wires, and integrating multiple antennas into a single component can all increase the antenna's bandwidth.
2. Representation Methods:
Voltage Standing Wave Ratio (VSWR) Condition: Under the condition that the voltage standing wave ratio VSWR ≤ 1.5, the operating frequency band width of the antenna is called the antenna's bandwidth. This is a commonly used definition in mobile communication systems.
Gain Drop Condition: The frequency band width within which the antenna gain drops by 3 decibels is also called the antenna's bandwidth. This representation method focuses on the characteristic of the antenna gain changing with frequency.
III. Practical Applications and Significance
1. Practical Applications: In communication systems, the selection of antenna bandwidth is crucial for the system's performance. If the antenna bandwidth is too narrow, it may not be able to cover the required communication frequency range, resulting in a decline in communication quality or failure to establish a communication connection. Therefore, when choosing an antenna, comprehensive consideration should be given to factors such as the communication frequency range, bandwidth requirements, and antennaperformance of the system.
2. Significance: Antenna bandwidth is one of the important indicators for measuring the performance of an antenna. It determines the radiation and reception capabilities of the antenna at different frequencies and is of great significance for ensuring the stability and reliability of the communication system.
Types of Antenna Bandwidth
I. Absolute Bandwidth
1. Definition: Absolute bandwidth refers to the actual frequency range within which the antenna can operate, that is, the difference between the highest frequency and the lowest frequency when the antenna's performance indicators (such as voltage standing wave ratio, gain, etc.) meet specific requirements. The calculation formula is: B = fh - fl, where fh is the highest frequency within the bandwidth, and fl is the lowest frequency within the bandwidth.
2. Characteristics: Absolute bandwidth directly reflects the size of the frequency range that the antenna can cover and is an intuitive way to represent antenna bandwidth.
II. Relative Bandwidth
1. Definition: Relative bandwidth is expressed as the ratio of the difference between the highest and lowest frequencies at which the antenna can operate to the center frequency. The calculation formula is: Br = (fh - fl) / f0 × 100%, where fh is the highest frequency within the bandwidth, fl is the lowest frequency within the bandwidth, and f0 is the center frequency.
2. Characteristics:
- Since relative bandwidth takes into account the center frequency of the antenna's operation, it can more accurately reflect the performance changes of the antenna at different frequencies.
- According to the size of the relative bandwidth, antennas can be classified into narrow - band antennas, broadband antennas, and ultra - wideband antennas. Generally, antennas with a relative bandwidth of less than 10% are called narrow - band antennas, and those with a relative bandwidth of more than 20% are called broadband antennas. Broadband antennas can also be directly represented by the ratio of fh to fl. Antennas with fh/fl greater than 2:1 are called broadband antennas. If fh/fl is greater than 3:1, they can be called very - wideband antennas. For fh/fl greater than 10:1, they are usually called ultra - wideband antennas. There is also a saying that the relative bandwidth of narrow - band antennas is less than 1%, that of broadband antennas is between 1% and 25%, and that of ultra - wideband antennas is greater than 25%.
III. Other Representation Methods
In addition to absolute bandwidth and relative bandwidth, antenna bandwidth can also be represented by ratio bandwidth, that is, the ratio of the upper and lower limit frequencies (fh:fl). However, this representation method is less commonly used than absolute bandwidth and relative bandwidth.
