Double stub impedance matching for RF and Microwave design

 

Its interesting how many techniques exist today for impedance matching of complex loads to transmission lines. A really interesting one is the technique of double stub matching which is a popular one. Its simpler cousin is single stub matching which can be used but runs out of steam under some circumstances

Double stub impedance matching is more involved than single stub matching. First of all we need to discuss the rationale for using double stub matching. In order to understand all this, consider the points below:

1.0 A single stub match involves the use of a stub of fixed length placed at a fixed position on the transmission line from the load for a specific load.

2.0 If the value of the load changes then the length of the stub and the position at which it is placed must also change.

3.0 A better technique would be where we could fix the positions of the stubs in relation to each other and only change the lengths of the stubs to match varying loads. This is done using the techniques of double and triple stub matching.

4.0 Both analytic and graphical techniques are available to do double stub matching. The graphical method is usually the Smith Chart method and that is what we have focused on. However analytical techniques can be enlightening as well, and are recommended if you are mathematically minded.

5.0 In order to further understand the technique of double stub matching you need a reasonable amount of the understanding of how the Smith Chart works.

6.0 There are some loads that cannot be matched using double stub matching by simply altering the length of the stubs. However if we are willing and able, to move the stubs together a distance away (or towards the load) from the load then we can accommodate the load. This can be discussed and illustrated using the Smith Chart method. These loads form an area of the Smith Chart collectively known as the forbidden zone for double stub matching.

7.0 Additional techniques can be used to overcome the limitations of double stub matching if needed. Similar techniques to that of double stub matching are used for triple stub matching.

The interesting situation as far as learning about double stub matching is that there are very few articles available that really discuss the technique for the newbie. We know as we did a web search and came up with very few articles that deal with this.

A forthcoming book from Ain Rehman of Signal Processing Group Inc, addresses these techniques in some detail with a minimum of math. The title is VSWR and Impedance matching techniques. This book will be available on Amazon both as a paperback and as a Kindle book shortly for interested readers.

Please visit our website www.signalpro.biz for more information and other articles of interest.

Signal Processing Group Inc., delivers RF Design, RF IC design, rf circuit design, ic design, analog design, rf technology, analog circuit design, asic chip, integrated circuit design and various rf devices

This is low noise RF Amplifier by Signal Processing Group Inc., available from Amazon

A low noise RF amplifier by Signal Processing Group Inc.

SPG designs, develops and delivers custom analog and RF/wireless asics and modules.

LNA

SPG designs, develops and delivers custom analog and RF/wireless asics and modules.

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A wideand RF detector ( 40 Mhz to 3 Ghz) -75 dBm to 5 dBm input

A wideband RF detector

A wideband RF detector

Linear detector performance

Linear detector performance curves

A wideband linear RF detector

Price for one unit: $25.00. Lead time for delivery 3 days. 30 Day return policy. Pricing for 100 units or more: $20.00 per unit.  Please contact Signal Processing Group Inc. for details for purchase from Signal Processing Group Inc. Email: spg@signalpro.biz 24/7

Wideband RF detector perforamce , more details

Contact Signal Processing Group Inc.

Please contact Signal Processing Group Inc. on email: spg@signalpro.biz . We will answer within 24 hours.

2 stage 35 dB gain RF amplifier. Front of the module

Full range frequency response

2 stage amplifier deta

Please see details at http://www.signalpro.biz/2rf_amplifier_details.htm    Delivery lead time is 3 days. Return within 30 days for a full refund. Price is $15.00 for one unit and $10.00 per unit in volumes of 100. For higher volumes than 100 please contact Signal Processing group Inc.

miniature LNA module

Mni LNA performance

Delivery lead time is 3 days. Return within 30 days for a full refund. Price is $15.00 for one unit and $12.00 per unit in volumes of 100. For higher volumes than 100 please contact Signal Processing Group Inc. at email: spg@signalpro.biz or call 602-626-0272 for fastest service.

A high frequency divider from 500 Mhz to % Ghz+

The input interface.
The frequency divider has a differential analog interface. The following parameters apply:
The minimum frequency that can be input is 500 Mhz and the maximum frequency is 6.0 Ghz.
The RF input level is 5 dBm to – 5 dBm. For lower frequencies make sure that the slew rate is
greater than 560 V/us. The input is biased by two 500 Ohm resistors connected to a 1.6V DC bias.
Therefore AC coupling is used at the input. These are two 100pF capacitors.
The output interface.
The output is single ended. The output driver is capable of sourcing and sinking 24 mA. The
equivalent output impedance is 50 Ohm. To avoid reflections it is recommended that the divider
work into a 50 Ohm load.
General operation.
The inputs are applied to the input SMA I/O. The product will work with both a differential input as
well as a single ended input. However, a differential input works best. The division ratio is applied
to the N1 and N2 control inputs as follows:
N2 N1 Division ratio
0 0 8
0 1 16
1 0 32
1 1 64
The logic levels are:
Logic level Voltage
1 1.4V minimum
0 0.6V maximum
The supply voltage interface.
The operating supply voltage is 3.3V typical. The quiescent (DC) operating supply current is 2 mA.

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SPDT DC to 3 Ghz RF switch

DC to 3 Ghz RF SPDT switch

RF Switch typical features

Supply voltage = Vcc = 0/+5 Vdc
Operatng temperature = TA = -50° C to 125 Deg C
Operating impedance = 50 Ohm
Input power for 1 dB
compression ( 5.0V system) = 37 dBm ( f = 0.5 to 3 Ghz)
Input third order Intercept = 64 dBm ( 0 to 5.0V system, f = 0.5 to 3 Ghz)
Operating frequency range = DC to 3 Ghz.
Insertion loss DC to 3 Ghz = 0.8 dB
Isolation DC to 3 Ghz = 14 dB minimum
Return loss DC to 3 Ghz = 20 dB
50% contl to 10/90 %
( ON/OFF) = 120 ns

A single stage RF amplifier as a gain block

A single stage RF amplifier summary specifications

Summary Specifications

Gain,  Operating: 19.5 dB
Operating frequency range: 1.0 – 2700 Mhz
OIP3: (Pout = 19.0 dBm),  -8.5 dBm
P1dB: 4.6 dBm
N.F: 4.2 dB
Supply voltage Operating: 3.3  – 5.5 Volts

Price: single unit $7.50, 100 units : $5:50.

Free delivery, shipping lead time 2 days.

30 day return policy, buyer ships.
Supply current Supply = 5.0V,  23.0 mA

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