Ask Harlan, November 27, 2006
Harlan Howe has 34 years experience as a microwave design engineer and fifteen as publisher and editor of Microwave Journal ® , and is an IEEE Fellow and past president of MTT-S. He's here to answer your questions on RF and Microwave engineering.
Published November 27, 2006
From: Mike O’Driscoll, student
I have always regarded sensitivity as the signal level needed for a minimum detectable signal above the noise level. It is a function of noise temperature of the nonlinear element, conversion loss and bandwidth. The method of measurement is to increase the input signal level until an output signal appears above noise. There is an excellent discussion of all the sensitivity factors in Microwave Mixers, S. Maas, Artech House Inc., 1993, ISBN#0-89006-605-1.
From: Kamal Jeet, ISRO
Yes, the resistivity will affect the dielectric loss. The higher the resistivity the lower the loss.
From: Rahul Lal, engineering student
I cannot put block diagrams in this column and there is no universal simplified answer; however, there are a number of block diagrams for different types of systems in Advanced Techniques for Digital Receivers, P. Page, Artech House Inc., 2000, ISBN#1-58053-053-2.
From: Eduard Pfaeffli, Ruag Electronics
I am not familiar with project H.A.A.R.P.; however, power levels in the many Megawatt range have been available for years and Terawatt levels have been demonstrated for short pulses.
From: Peter Thigpen, University of Connecticut
EHF frequencies (30 to 300 GHz) are being used for high resolution mapping, remote sensing, satellite-to-satellite communications, covert battlefield radios, police speed radars, radio astronomy, wireless LANs and a number of other applications. The August 2005 and July 2006 issues of Microwave Journal have papers on some of these applications. You can access them on our web site at www.mwjournal.com Click on archives.
From: Gholamhossein Heidari Roodaki, Tehran University
I do not have access to old IEEE papers. You will have to contact the IEEE directly. However, the Marchand paper has been reprinted in Classic Works in RF Engineering, Walker, et al., Artech House, 2006, ISBN#1-58053-056-7.
From: Kamal Singh, Semiconductor Laboratory
Leakage current will affect both circuit losses and circuit isolation and cross talk. I am not a semiconductor chemist, but I believe that resistivity can be altered by appropriate doping; however, it will certainly affect the RF performance.
From: Suram Verma, SLIET
It is possible to transfer power using microwaves now. There have been a number of examples of power transfer such as power transfer in space to rectennas and even some experimental transfer to helicopters. The pioneer in this work was the late Bill Brown at Raytheon Co. There are many of his papers included in the literature.
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.