The following article entitled "Top 5 Clever Solutions to Common Problems of
RF and Microwave PCB Designs" was prepared for and submitted to RF Cafe by its author, Ken
Ghadia, of TechnoTronix Electronics Manufacturing
Services. He wrote asking whether he could provide an article on an aspect
of PCB design relevant to RF Cafe visitors, so I suggested addressing the issue
of placing digital and analog / RF signals on a common substrate. TechnoTronix has a state of the art facility here in the United States
that enables clients to successfully overcome production and PCB fab challenges
to produce the innovative, cutting-edge electronics products and providing PCB prototype
services, PCB, PCB assembly service,
PCB manufacturing service, PCB fabrication
service & more in U.S. and around the world.
Top 5 Clever Solutions to Common Problems of RF and Microwave PCB Designs
With the ability of RF and Microwave PCB designs to capture higher frequencies,
there importance cannot be overstated. RF & Microwave circuits are today a part
of a wide variety of products, with communication devices being the most notable
among them. PCB Manufacturing for RF And Microwave PCB is done in huge numbers to
utilize in different devices. However, higher frequencies also come with a host
of design challenges. Here are some handy solutions to mitigate some of these issues:
#1 Effective Design Hacks
Be mindful of using these design hacks to ensure that the potential for any errors
can be minimized during the assembly process:
- Isolation- If you are dealing with PCBs that have analog, digital as well as
RF components, the one thing that you need to keep an eye on at the design stage
is to keep such parts separate.
- Ground layer- In case of multilayer PCBs, the
one thumb rule to go by is to have a ground layer below any layer that has RF or
microwave signal lines.
- Tackling Noise- With high frequency signals being extremely sensitive to noise,
here are the many ways to tackle it:
- Thermal Noise- This kind of noise is the result of thermal agitation. It is
imperative, therefore, to minimize the effects of the temperature on the circuit
by regulating the temperature through cooling systems as well as heat-dissipation
- Shot Noise- Caused on account of the fluctuations in electrical current, this
kind of noise can be minimized through the use of metallic resistors.
- Phase Noise- Affecting radio frequency signals, this appears as fluctuations
or phase jitters. Clean signals are the best way to reduce this noise.
- Flicker Noise- Caused by direct current flow, this kind of noise manifests itself
like phase noise. The solution to this lies in processing the signal through a specialized
- Avalanche Noise- This noise results on account of the fact that a junction diode
operates close to the point of avalanche breakdown. The best solution for this is
to use a capacitor based filter.
#2 Impedance Matching
With high frequency signals having low tolerance for impedance matching, here
are some aspects to watch out for:
- Skin effect loss- Skin effect refers to the flow of electrons along the outer
surface of the conductor, at higher frequencies. At the trace, there is a small
area that is used to funnel electrons. However some electrons are also trapped here.
The signal energy is converted to heat. To minimize this loss, proper impedance
matching is crucial. Also plating the PCB with gold works as an antidote.
- Line Lengths- Signal loss is impacted by the line lengths. The longer the lines,
the more the signal loss. It is ideal to ensure that the line is 1/20 of the wavelength.
Either way it should be longer than 1/16 of the wave length, which is the critical
#3 Return Loss
Caused by signal reflection, the way to minimize the return loss is to ensure
that the ground planes should be continuous from the driver to the receiver. In
the absence of this, the return signal will pass through other power planes and
cause signal noise.
#4 Cross Talk
Simply put, cross talk is the transfer of energy between conductors that causes
a coupled signal. Typically, the incidence of crosstalk increases as the density
as well as the performance of PCB increases. The other aspects that play a role
- Proximity of conductors
- Distance over which they run parallelly
- Edge rate of the active line
Some of the ways to reduce cross talk include:
- Ensuring the distance from center to center is kept at four times the trace
- Minimizing parallel lines
- Minimizing the dielectric spacing
- Inserting a ground plane between the traces
- Ending the line on its characteristic impedance
#5 Laminate Properties
The properties of the laminate impact the functionality of the RF or microwave
PCB. For example, FR4 has a high dissipation factor resulting in higher insertion
losses as signal frequencies increase. Also the dielectric constant of FR4 is higher
than that of high frequency laminates, which has an impact on impedance. The property
of the laminate impacts dielectric loss. The use of substrates with low dissipation
factors is recommended to be able to avoid this loss.
Here's to solving common problems of RF & Microwave PCB designs and to improving
Goodluck on your RF/Microwave PCB Designing!
One of the PCB assembly magnate, TechnoTronix adopts advanced production techniques
and manufacturing practices with specialization in a varied range of PCB fabrication
process, producing high quality multi-layered PCBs from tailor-made layouts.
With over 40 years of combined experience in rendering high tech PCB assembly
and manufacturing services, we are not just an assembler, we can completely test
at board level to box build level to provide the benefit of unparalleled technical
expertise and the most progressive solutions at competitive prices.
TechnoTronix Electronics Manufacturing Services
1381 N. Hundley St.
CA 92806, U.S.
Posted August 20, 2021