Electromagnetic Wave Parameters 
Electromagnetic Wave Parameters
Parameters that describe electromagnetic waves include frequency, wavelength and period. Frequency is cycles per second (Hertz), wavelength is distance traveled to complete 1 cycle and period is time to complete 1 cycle. The higher the frequency, the shorter the wavelength.
f = c / L T = 1 / f L = c / f = c T 
f = frequency L = Wavelength T = period (time to complete 1 cycle) c = speed of light 
Calculate Wavelength and Period
Frequency 
Band  Frequency  Period  Wavelength  

S  2.455 GHz  0.409 ns  4.83 inch  12.261 cm 
X  10.525 GHz  0.095 ns  1.12 inch  2.848 cm 
K  24.15 GHz  0.041 ns  0.49 inch  12.41 cm 
Ka  33.4  36.0 GHz 
0.030  0.028 ns 
0.35  0.33 inch 
8.976  8.328 cm 
IR  333,600 THz  0.000 003 ns  0.000 035 inch  904 nm 
Source  Frequency  Period  Wavelength  

House Current (U.S.)  60 Hz  0.0167 sec  3,105 mi  
AM Radio  530  1,700 kHz  1.89  0.589 µs  1,856  579 ft  
Citizens Band (CBs)  26.96  27.41 MHz  37.09  36.48 ns  36.48  35.88 ft  
FM Radio  88  108 MHz  11.36  9.26 ns  11.18  9.11 ft  
DTV  470  806 MHz  2.13  1.24 ns  25.11  14.64 in 
Electromagnetic Wave Propagation 
PROPAGATION
Electromagnetic waves consist of an electric field and a magnetic field at right angles to each other. The electric field, Efield, is measured in volts/meter. The magnetic field , H field, is measured in amperes/meter. The electric and magnetic fields are analogous to voltage and current in circuits. The ratio of electric field to magnetic field in free space is 377 ohms. Power is the vector cross product of the electric and the magnetic fields.
POLARIZATION
Polarization is the plane of the electric field. In the USA overtheair digital television signals are horizontally polarized while commercial AM and FM broadcast are vertically polarized. Radar waves may be polarized horizontally, vertically, angled, or circular.
Circular polarization is a technique where the electric and magnetic fields rotate at a rate proportional to frequency. Right hand polarization has the fields rotating in a clockwise direction looking from the antenna to the direction of travel, counter clockwise to a target. Left hand circular polarization is just the opposite.
Circular polarization tends to propagate better in rain, but has some signal loss in the polarization process. Circular polarized signals tends to be more reflective for some targets.
Power Density, ERP, Electric and Magnetic Fields 
Effective Radiated Power, ERP, is the most common unit for measuring signal propagation power. ERP is a function of transmitter power, signal loss to antenna, and antenna gain. ERP equals the product of antenna gain (G) and power delivered to the antenna (P_{t}/L).
P_{ERP}  =  Effective Radiated Power (watts) 
P_{t}  =  transmitter power (watts) 
G  =  antenna gain (ratio) 
L  =  transmitter to antenna loss (ratio) 
Power Density:  P_{d} = P_{ERP} / (4 pi R^{2} )  W/m^{2} 
Electric Field:  E = (P_{d} Z)^{0.5}  V/m 
Magnetic Field:  H = E / Z  A/m 
Free Space Impedance:  Z = E / H  ohms 
R  =  Range (meters) 
pi  =  3.1415926... 
Z  =  376.73 ohms (Free Space) 
The electromagnetic field is a function of the inverse square (1/R^{2}) of range. Radar signals take a 2way path, the loss is much greater and a function of the inverse to the fourth power (1/R^{4}) of range.
MEASUREMENTS
Power density and electric and magnetic field strengths measurements must be measured in the antenna FarField. The farfield is the range greater than twice the maximum antenna diameter squared divided by wavelength.
R_{min} = 2 D^{2} / L
R_{min} = Approximate start of FarField D = Maximum Antenna Diameter L = Wavelength 
R_{min} = 0.17 D^{2} f_{o}
R_{min} = FarField Range in inches D = Antenna Diameter in inches f_{o} = Frequency in GHz 

Measurements taken in the nearfield have absolutely no relation and do not apply to the farfield. Radar manufacturers have a bad habit of listing power densities measured in the nearfield, a meaningless number. Just as bad power density measurements are sometimes listed without stating the range of the measurement, another meaningless number.
Password Section:
 Frequency, Wavelength, Period Calculator
 Convert Power Densities Calculator
 Power Density, E/H Fields Calculator
 Convert Power Calculator