|
VK5KK's 24 GHz PROJECT PAGE
|
On this Page we will
discuss the frequency standards and various equipment options for
Narrowband and Wideband systems. Input is welcome from all
interested operators. As I get time it will be updated, the
latest update was on 16/5/98. Take a Look at Russell VK3ZQB's
excellent 24 Ghz Project page .... leaves this one for dead!
Some sites to
look at ...
VK3ZQB 24 GHz PROJECT PAGE 
To register your
interest or submit information please Email me.
INTRODUCTION
24 GHz presents a new
set of challenges over and above those faced on the lower
microwave bands. While the actual circuitry is not all that
different to what would be used on say 10 GHz the following
factors are a play requiring some changes to design approaches.
In free space a quarter
wavelength is only 3mm at 24 GHz. Suddenly the physical size of a
whole series of components we would use at 10 GHz is now a
problem at 24 GHz. For example the following problems are
highlighted with a suggested solution.
A standard SMA
flange mount socket with a 4.1mm dia Teflon extension is
over a 1/4 wave in diameter, infact the average SMA
socket will resonate at around 22- 24 GHz.
Various
manufacturers have available SMA sockets with a
2.17mm-dia extension (and an extension pin width suitable
for 0.7mm wide stripline). SMA connectors that do not use
"epoxy holes" to secure the insulator exhibit a
better return loss at 24 GHz, usually rated to 26.5 GHz.
K type connectors (mateable to SMA) can also be used,
however are easily damaged by misalignment.
A standard ATC
chip cap (1.2mm sq.), used to DC decouple stages at 10
GHz, becomes too lossey to use at 24 GHz.
Smaller
capacitors are available, however difficult to obtain.
Small capacitors can be fabricated from 0.7 x 1.5mm
pieces of 0.125mm Teflon PCB. A preferred solution is to
use 1/4 wave lambda split coupling, 0.1mm separation
however requires good etching accuracy.
Teflon PCB of
0.79mm thickness is not usable due to excessive stripline
radiation (only passable at 10 GHz)
Teflon PCB of
0.25mm thickness is commonly available from several
manufacturers. We have standardized on Rogers 5880
0.25mm, 1/2 ounce copper.
None of the 10
GHz power devices are usable at 24 GHz. Commercially,
very few power devices exist over 50 - 100-mW level.
Some power
devices rated at 18 GHz have been found to be useful at
24 GHz, however they are not cheap. At this point we will
be happy to get -30 - 40mW from a single device. The
MGF1303 is capable of this as well as FHX35LG's, etc.
Power measuring
equipment and attenuators used at 10 GHz are of limited
use at 24 GHz.
The odd 26 GHz
power head has been found in commercial use so atleast we
have a standard to compare too. Several overseas
constructors have reported being able to use suitably
calibrated 18 GHz HP heads at 24 GHz. Ultimate
calibration is the only concern, several Spectrum
Analyzers are amongst the group usable to 40 GHz that can
then give relative readings.
The design adopted for
the project draws heavily from several sources. Designs are
largely by DB6NT, JE1AAH and HB9MIN, published in the various
publications listed at the end of this page. These original
designs have been used as the basis for this project, unifying
the packaging size of each module and standardizing on the one
type of PCB material. Functionality and interchangeability of
modules has been preserved so as to allow the qualifying of
various types modules.
OVERVIEW
OF THE PROJECT 24 GHz TRANSVERTER
LOCAL
OSCILLATOR GENERATION
To be
continued……..
RETURN TO VK5KK's HOMEPAGE