I notice that TRL calibration in David M. Pozar's book Microwave Engineering page 193 (3rd edition) has a different description. It says "It is not necessary to know the length of the line and it is not required that the line be lossless...". However, in Agilent TRL appnotes have already stated that we must know the characteristics of the standards Thru, Reflect and Line.

Can someone explain on this issue?

Thanks a lot.

Can someone explain on this issue?

Thanks a lot.

You must know the impedance of the Thru. It is often presumed to be Z0

You must know the impedance of the Line. It is also often presumed to be Z0, and must be the same as the Thru

You must know that difference in length between the Thru and the Line is between 20 and 160 degrees, when expressed as phase shift. This is a "rule of thumb" and not so hard and fast.

You must know that the reflect on port 1 equals the reflect on port 2, and the phase with in 1/4 wavelength.

From the PNA help Page:

Cal Standards Used in TRL

These standards must be defined in your TRL cal kit:

THRU

Note: All THRU calibration methods are supported in a TRL Cal EXCEPT Unknown Thru.

The THRU standard can be either a zero-length or non-zero length. However, a zero-length THRU is more accurate because it has zero loss and no reflections, by definition.

The THRU standard cannot be the same electrical length as the LINE standard.

If the insertion phase and electrical length are well-defined, the THRU standard may be used to set the reference plane.

Characteristic impedance of the THRU and LINE standards defines the reference impedance of the calibration.

If a THRU standard with the correct connectors is NOT available, an adapter removal cal can be performed.

REFLECT

The REFLECT standard can be anything with a high reflection, as long as it is the same when connected to both PNA ports.

The actual magnitude of the reflection need not be known.

The phase of the reflection standard must be known within 1/4 wavelength.

If the magnitude and phase of the reflection standard are well-defined, the standard may be used to set the reference plane.

LINE

The LINE and THRU standards establish the reference impedance for the measurement after the calibration is completed. Learn more. TRL calibration is limited by the following restrictions of the LINE standard:

Must be of the same impedance and propagation constant as the THRU standard.

The electrical length need only be specified within 1/4 wavelength.

Cannot be the same length as the THRU standard.

A TRL cal with broad frequency coverage requires multiple LINE standards. For example, a span from 2 GHz to 26 GHz requires two line standards.

Must be an appropriate electrical length for the frequency range: at each frequency, the phase difference between the THRU and the LINE should be greater than 20 degrees and less than 160 degrees. This means in practice that a single LINE standard is only usable over an 8:1 frequency range (Frequency Span / Start Frequency). Therefore, for broad frequency coverage, multiple lines are required.

At low frequencies, the LINE standard can become too long for practical use. The optimal length of the LINE standard is 1/4 wavelength at the geometric mean of the frequency span (square root of f1 x f2).

MATCH

If the LINE standard of appropriate length or loss cannot be fabricated, a MATCH standard may be used instead of the LINE.

The MATCH standard is a low-reflection termination connected to both Port 1 and Port 2.

The MATCH standard may be defined as an infinite length transmission line OR as a 1-port low reflect termination, such as a load.

When defined as an infinite length transmission line, both test ports must be terminated by a MATCH standard at the same time. When defined as a 1-port load standard, the loads are measured separately. The loads are assumed to have the same characteristics.

The impedance of the MATCH standard becomes the reference impedance for the measurement. For best results, use the same load on both ports. The load may be defined using the data-based definition, the arbitrary impedance definition, or the fixed load definition.