- Buyers Guide
Military Microwaves Supplement
Published October 25, 2006
From: Shi Bo, IZR Science Park
There are a number of commercially available probes and noise figure test sets that can be used to make measurements. However, the absolute noise figure may be degraded when the chip is actually mounted in a circuit. On-wafer measurements are usually regarded as go/no-go tests for chip evaluation prior to dicing.
From: Ima Essiet, Beyond Third
All electromagnetic propagation is affected by transmission through any medium other than free space. Microwaves are absorbed by water vapor and by rain, thus attenuating them. There are frequencies that are less susceptable than others. There is a good discussion of this along with propogation loss charts in Introduction to RF Propagation, Seybold, Wiley, 2005, ISBN#0-471-65596-1.
From: Amipara M D, Twin Engineers
The transmission coefficient is not 1+p. It is 1-p^2. Thus, if p = 1 (100% reflection) the transmission is 0.
From: Arun Kumar, Broadwave Technologies
The bandwidth calculation is the same as for multiple quarter-wave transformers. The original paper on this type of divider is "A Class of Broadband, Three-port TEM Mode Hybrids," S. Cohn, MTT-Transactions 16, No. 2, February 1968, pp. 110-118. Consolidated design equations and curves are included in Chapter 3 of my book Stripline Circuit Design, H. Howe, Artech House Inc., 1974, ISBN#0-89006-020-7.
From: Hossein Hadidian, IUST
You cannot measure noise figure with a spectrum analyzer with no additional equipment. In order to measure noise figure you must have a calibrated noise source.
The usual approach is to use a basic antenna structure that will support multiple polarizations such as a dish or patch antenna elements and then switch the feed network to create alternate polarizations. This will not work with elements such as slots, which will only support one polarization.
From: Bal Virdee, London Metropolitan University
Yes. Dielectric resonators are very effective in reducing noise due to their generally high unloaded Q.
From: Jawad Hussain, Student
I am not familiar with the vagaries of the plotting functions of the ADS program. You will need to contact the software supplier. If you are trying to learn filter design, I suggest that you not rely on commercial software programs but rather go back to theory and manual design procedures. A good basic text is Microwave Filters, Impedance-matching Networks and Coupling Structures, Matthaei, Young & Jones, Artech House Inc., 1980, ISBN#0-89006-099-1.
From: Filiks O, Justifel Computer International Ltd.
Your question is outside our technical area, so I am afraid I cannot answer it. You may be able to get some help from someone in the IEEE Power Society. You can visit their web site at www.ieee.org.
From: Leia Zhou, SDSU
S-parameters can and do apply to antenna measurements. S11 is easy since it is still in a closed system. S21 is more difficult to measure since it now includes antenna gain. However, both are in common usage.
Harlan Howe, Jr. received his BS degree in optics from the University of Rochester in 1957. He has been actively engaged in the microwave industry for 48 years, first as a design engineer and then as an engineering manager. In 1990 he became the publisher/editor of Microwave Journal. He retired as publisher in 2001, but remains the editor. He is a Life Fellow of IEEE, past president of MTT-S and the recipient of an IEEE Third Millennium Medal in 2000 and the MTT-S Distinguished Service Award in 2005.
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