MIMO Antenna
Regarding dB, dBm, and dBi
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DB (decibels)
DB is a relative unit used to represent the ratio between two quantities. It is usually used to describe the ratio of power or voltage (or current).
Definition: (dB=10 \ log_ {10} \ left (\ frac {P_2} {P_1} \ right)) or (dB=20 \ log_ {10} \ left (\ frac {V_2} {V_1} \ right))
Among them, (P_1) and (P_2) are two power values, and (V_1) and (V_2) are two voltage or current values.
Note: dB is a relative unit that represents the ratio between two quantities, not an absolute value.
1. The decibel calculation formula for power ratio:
When comparing two power values, the decibel calculation formula is:
DB=10log10 (P1P2), where (P_1) is the reference power (usually a fixed value), and (P_2) is the power to be measured. If (P_1) is 1 watt, the above formula can be simplified as: dB=10log10 (P2), where (P_2) is the power value in watts.
2. The decibel calculation formula for voltage (or current) ratio:
When comparing two voltage (or current) values, the decibel calculation formula is:
dB=20log10(V1V2)
perhaps
dB=20log10(I1I2)
Among them, (V_1) and (I_1) are reference voltages and currents (usually fixed values), while (V_2) and (I_2) are the voltages and currents to be measured. If (V_1) or (I_1) is 1 volt or 1 ampere, the above formula can be simplified as:
dB=20log10(V2)
perhaps
dB=20log10(I2)
Here (V_2) and (I_2) are voltage and current values in volts or amperes.
Note: In these formulas, (\ log_ {10}) represents the logarithm based on 10. If (P_2/P_1) or (V_2/V_1) (or (I_2/I_1)) is greater than 1, then the decibel value is positive; If it is less than 1, the decibel value is negative. The larger the decibel value, the greater the multiple of (P_2) relative to (P_1) (or (V_2) relative to (V_1), or (I_2) relative to (I_1)).
DBm (decibels milliwatts)
DBm is an absolute unit used to represent power values, with a reference point of 1 milliwatt (0.001 watt).
Definition: (dBm=10 \ log_ {10} \ left (\ frac {P} {1mW} \ right))
Where (P) is the power value to be measured.
For example, if the power of a signal is 1 watt, then its power is (10 \ log_ {10} (1000)=30 dBm).
DBm is commonly used to describe the power of wireless signals or the sensitivity of receivers.
DBm calculation formula
dBm=10log10(1mWP)
Among them,
(P) is the power value to be measured, in milliwatts (mW).
(1mW) is the reference power value, which corresponds to the power of 0dBm.
Related information
1. Unit conversion:
0dBm corresponds to 1 milliwatt (1mW).
For every 3dBm increase, the power doubles; For every reduction of 3dBm, the power is halved.
For example, 30dBm corresponds to 1 watt (1W), because (10 \ log_ {10} (1000)=30) (because 1W=1000mW).
2. Common conversion values:
o 30dBm = 1W
o 40dBm = 10W
o 50dBm = 100W
3. Precautions:
DBm represents the absolute value of power, not the power ratio.
In the calculation, pay attention to the unit of power and ensure that it is consistent with the unit of reference power (1mW).
Example
If the power of a signal is 4 watts (4W), then its power (in dBm) can be calculated as follows:
dBm=10log10(1mW4000mW)=10log10(4000)=10*(3+log10(4))≈36.02dBm
(Here (\ log_ {10} (4) \ approx 0.602) is the base 10 logarithm of 4)
DBi (decibels relative to isotropy)
DBi is a unit used to describe antenna gain, with its reference point being an idealized isotropic antenna (i.e. an antenna that uniformly radiates or receives in all directions).
Definition: (dBi=10 \ log_ {10} \ left (\ frac {G} {G_ {iso}} \ right))
Among them, (G) is the gain of the antenna to be measured, and (G_ {iso}) is the gain of an isotropic antenna (theoretically 1).
Note that since isotropic antennas do not exist in reality, dBi is a relative unit, but it provides a convenient reference point to compare the gains of different antennas.
DBi is commonly used to describe the gain of antennas used in wireless communication.
DBi calculation formula
dBi=10log10(E0E)
Among them:
(E) is the effective radiation power or gain of the actual antenna.
(E0) is the effective radiation power or gain of an ideal isotropic antenna. An ideal omnidirectional antenna has uniform radiation in all directions, and there is no such antenna in practice, so it serves as a reference benchmark.
Related information
1. Reference benchmark: The reference benchmark for dBi is an omnidirectional antenna, which is a theoretically ideal model used to compare the gain of other antennas.
2. Relationship with dBd: dBi and dBd are both units that describe antenna gain, but their reference standards are different. The reference benchmark for dBi is omnidirectional antenna, while the reference benchmark for dBd is dipole antenna
(Dipole antenna). It is generally believed that when representing the same gain, the value represented by dBi is 2.15 larger than the value represented by dBd (i.e., dBi=dBd+2.15).
3. Example: If the gain of an antenna is represented as 16dBd in dBd, then its gain is represented as 18.15dBi in dBi (usually ignoring decimal places, it is 18dBi).
In summary, dBi is a unit used to describe antenna gain, and its calculation formula is based on the ratio of the effective radiation power of the actual antenna to the effective radiation power of the ideal omnidirectional antenna. Compared to dBd, dBi's reference is omnidirectional antenna, so when representing the same gain, the value of dBi will be 2.15 larger than the value of dBd.
