Agilent Technologies 8753ET User Manual page 440

Operating Concepts
TRL*/LRM* Calibration (ES Models Only)
increase significantly when the insertion phase nears zero or is an integer multiple of 180 degrees, and this
condition is not recommended.
For a transmission media that exhibits linear phase over the frequency range of interest, the following
expression can be used to determine a suitable line length of one-quarter wavelength at the center
frequency (which equals the sum of the start frequency and stop frequency divided by 2):

Electrical length cm



Electrical length cm
let:
f1 = 1000 MHz
f2 = 2000 MHz
VF = Velocity Factor = 1 (for this example)
Thus, the length to initially check is 5 cm.
Next, use the following to verify the insertion phase at f1 and f2:

 
Phase degrees
where:
f = frequency
l = length of line
v = velocity = speed of light  velocity factor
which can be reduced to the following using frequencies in MHz and length in centimeters:
  approx
Phase degrees



So for an air line (velocity factor approximately 1) at 1000 MHz, the insertion phase is 60 degrees for a 5 cm
line; it is 120 degrees at 2000 MHz. This line would be a suitable line standard.
For microstrip and other fabricated standards, the velocity factor is significant. In those cases, the phase
calculation must be divided by that factor. For example, if the dielectric constant for a substrate is 10, and
the corresponding "effective" dielectric constant for microstrip is 6.5, then the "effective" velocity factor
equals 0.39 (1  square root of 6.5).
7- 72

LINE
  = –
0 length THRU
 
15000
  = ------------------------------------------------ -
 
f1 MHz f2 MHz
+
  l  
360 f
= ----------------------------
v
 
0.012 f MHz
= -------------------------------------------------------- -



V F

 
   
l cm

VF