Ask Harlan, August 14, 2006

From: Ky-Hien Do

Dear Harlan,
How do you build a coaxial balun?

Dear Ky-Hien,
In its simplest form a coaxial balun can be made from two quarter-wave sections of coaxial line. The unbalanced input is to one line. The outer conductors at this end are connected together. At the other end, the two center conductors are connected together and the two outer conductors are the balanced output. There is an excellent description of many types of baluns in Chapter three of Classic Works in RF Engineering, Walker, et al., Artech House, 2006, ISBN#1-58053-056-7.

From: Jose Rayas-Sanchez

Dear Harlan,
What are the most promising structures for low cost ultra high speed PCB interconnects?

Dear Jose,
Most standard low frequency PCB connectors are not appropriate for ultra high speed boards due to inadequate ground continuity and shielding. At high speeds even simple plated vias need ground continuity, and edge pins and tabs need to be impedance matched. There is a good discussion of high speed boards in High-Speed Circuit Board Signal Integrity, Thierauf, Artech House, 2004, ISBN#1-58053-131-8.

From: Alan Leaman

Dear Harlan,
Is there a computer design program that can synthesize the Bob Wenzel "Digital Elliptic Diplexer" (originally published about 25 years ago)?

Dear Alan,
If you can model it, I am sure there are synthesis and simulation programs that can be applied. While I do not know of a specific program, there is a great deal on information on modeling techniques in Microwave Circuit Modeling Using Electromagnetic Field Simulation, Swanson & Hoefer, Artech House Inc., 2003, ISBN#1-580053-308-6.

From: Nor Azzahra Ibrahim, Student

Dear Harlan,
I am doing research about planar analysis on a radial stub. I'm really having difficulty trying to understand the planar circuit analysis. Could you explain it?

Dear Nor Azzahra,
I am afraid that I cannot help you since you do not define the planar circuit analysis that you are using. Most circuit analysis is based on specific models of the circuits. A book that may be of some help is Microwave Circuit Modelling Using Electromagnetic Field Simulation, Swanson & Hoefer, Artech House Inc., 2003, ISBN#1-58953-308-6.

From: Morgan Chen

Dear Harlan,
Is it possible to make a waveguide in standard printed circuit processes with vias for side walls?

Dear Morgan,
Yes, people have done this. The vias need to be slots rather than holes since the spaces in between the holes will radiate like the holes in a waveguide directional coupler. It is not a very practical technique, since the a/b ratio will be very small unless the board is quite thick or the frequency is very high, in which case the losses will be high due to the dielectric losses.

From: Noaa Spiekermann

Dear Harlan,
If you had a sensitive enough receiver, would it be possible to listen to radio waves sent 10 years ago?

Dear Noaa,
Yes, if they were sent from a source 10 lightyears away. This is the basis of the radio astronomy search for extraterrestrial intelligence. It would not be possible for signals generated here on Earth.

From: Michael Hoft

Dear Harlan,
Once I tried to get a .pdf file of your publication's articles, but it was too expensive. Why don't you lower the price?

Dear Michael,
You can download a printed copy of an article from our web site at no charge. If you want a .pdf file for personal or educational purposes there is a nominal charge of $35.00, which we frequently waive for advertisers or accredited educational institutions. If you want the file for commercial purposes, such as inclusion in a catalog, the fee is significantly higher and you should contact us to discuss its usage.

From: Roldan Perez Morales

Dear Harlan,
What is the impact of using a ceramic capacitor in the loop filter in PLL oscillators?

Dear Roldan,
There are many types of ceramic capacitors. The effect will be a function of the Q of the specific capacitor at your frequency and bandwidth of operation. I suggest that you have a look at Lumped Elements for RF and Microwave Circuits, I. Bahl, Artech House Inc., 2003, ISBN#1-58053-309-4.