Q: This seems straightforward one you but the VNA, but what are the realities?Ī: First, any measurement of amplitude and phase at higher frequencies is challenging and gets more so as the frequency increases. (Note that the term “network analyzer” is rarely abbreviated as “NA” since that could also refer to communication networks or even optical parameters such as numerical aperture, while the vector network analyzer is often called the VNA – it’s just one of those things.) These are used by RF/microwave technicians for setup, adjustment, and troubleshooting, but are usually not adequate for initial design efforts. But there are lower-cost, ruggedized vector network analyzers that can perform the measurements in the field. The reason is that the term “network analyzer” also refers to an unrelated instrument that checks the performance of a data link or data network and provides data such as bit error rate (BER) versus SNR. Q: I see test instruments called portable network analyzers offered for a few thousand dollars – can I use those here?Ī: It depends. Some VNAs also can perform a time domain reflectometry (TDR) measurement, which allows for comparison and correlation with the VNA measurements. In general, high-performance VNAs (as determined by frequency range, dynamic range, noise floor, and other specifications) are among the more expensive class of RF test equipment. As shown in (Figure 2), s-parameters S11 = A/R1 and S21=B/R1, and are determined by measuring the magnitude and phase of the incident (R1), reflected (A) and transmitted (B) voltage signals when the output is terminated in a perfect Zo, the characteristic impedance of the test system.įig 5: Some VNAs such as the Tektronix TTR500 use a separate front-end RF interface and support circuitry, then link to a PC via a USB cable. It looks simple enough, but there are many subtleties and complexities in the internal architecture, components, and actually making of the measurements. This narrow-band receiver achieves low noise and high dynamic range of the VNA. Q: What is the physical set-up using a VNA?Ī: The VNA uses a precise sine wave and sweeps the frequency as a narrow-band receiver tracks the swept input response. There are also 4-port analyzers for differential circuits. Of course, the cost goes up with each increase in range. (Image: Tektronix, Inc.)ĭifferent instruments are available for a variety of maximum frequency ranges, such as up to 1 GHz, 10 GHz, and even into the tens of GHz. Fig 1: The s-parameter test-configuration concept requires injecting a known signal at the input and then measuring it at both the output port and the signal reflected back to the input port.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |