Articles
Straight Talk About Directivity
May 14, 2004
Directivity plays a critical role in determining the accuracy of your RF power, VSWR and return loss measurements. Errors due to directivity can be significant and may influence the decisions you make based upon your test results. The purpose of this article is to explore the subject of directivity and to set appropriate expectations.
Figure 1 and Examples 1 & 2 illustrate the effects of directivity. As you can see, an in-line power meter or antenna monitor with 25 dB of directivity will produce measurements with a wide margin of error when compared with those of a 40 dB device. This could make the difference between judging your antenna as in or out of specification. This may also cause false alarm conditions when monitoring your antenna (i.e. alarm when all is well or, worse yet, no alarm when there actually is a problem!)
A step-by-step procedure to arrive at these figures in a straightforward manner is discussed later in this paper. For your convenience, the "Directivity Chart" which lists error ranges for given VSWR and return loss levels may be found in the appendix of this application note.
Click here to download this complete application note in PDF format.
To help streamline our process and get you the most appropriate information, please indicate in your comments which market is most applicable to you: Cellular, LMR, Broadcast, Semiconductor, Medical, Government, or Military. Thanks.
