## Messing with Substrates (10 GHz bandpass filter) [silly]

In this post we will take a reasonable 10 GHz bandpass filter (at least for a new grad student) and see how a new substrate will change how this filter works.

This is the original bandpass filter with the standard substrate:

If you can read the numbers on the above pic, you could also build this filter. Let’s get a better picture of what the substrate is for the original circuit:

Let’s try a silicon dielectric, shall we?

One thing is for sure – it’s not a bandpass filter anymore.

Let’s add a 20 mil Indium conductive layer below the dielectric:

Voilà! It’s centered at 8 GHz! Brilliant!

Here’s a thought – how well does your bandpass filter work underwater?

It looks like your bandpass filter might give you a little gain there at some frequencies in water!

## Microstrip Lange Coupler (5 GHz)

The Lange Microstrip (quadrature) coupler is known for it’s low loss, wide bandwidth and compact layout. Similar to other couplers, it consists of an isolated port, through port and coupled port.

You can build a microstrip Lange coupler using the DesignGuide tool in ADS:

These are the results for the equation-based simulation. These results admittedly look considerably better.

This is the substrate used:

These are the results for the momentum simulation. Admittedly, some tuning would improve this considerable.

And here is the layout component:

## 027/100 Shunt Reactance on Smith Chart

Example 3.5-2A: Measure the effect of susceptance on Smith Chart impedance matching.

First, build the circuit and run the Smith Chart Matching tool.

A shunt capacitor moves in a clockwise direction across the smith chart tool:

Also note that a shunt inductor moves counter-clockwise across the smith chart tool:

The following matches a 50 Ohm line to a 100 Ohm load at 10 GHz using a double-stub component. This was designed using the ADS passive circuit DesignGuide tool. This method is a great alternative to using the Smith Chart matching tool for lumped elements if you need a microstrip line for matching.

Circuit:

Substrate:

Momentum simulation result (can be tuned to center better at 10 GHz):

Layout component:

## 026/100 Lumped Element Smith Chart Movements: Series Inductor

Example 3.5-1: Measure the amount of movement caused by the reactance added to the circuit below. Measure the change from the starting point to the end point on the Smith Chart.

The circuit simulated gives the following result:

Recall that the circuit without a series inductor had the following result:

Through this simulation, it is shown that adding a series inductor causes the smith chart diagram plot to move in a clockwise direction.

Note the change using the Smith Chart matching tool:

## Microstrip Stepped Impedance Low-Pass Filter

Passes Freqeuncies below 10 GHz:

## 025/100 Smith Chart Impedance Plotting

Example 3.4-1: Plot the impedance Z = 25 + j25 Ohm on the standard Smith Chart.

In order to plot a schematic simulation on a smith chart diagram, run a simulation.

## Half-Wave Dipole Antenna Transmitter

Full PDF of project:

ece435final_michaelbenker

## 034/100 Loaded Q and External Q

100 ADS Design Examples Based on the Textbook: RF and Microwave Circuit Design
November 2019
Michael Benker

Example 4.2-3: Analyze the parallel resonator that is attached to a 50 Ohm source and load as shown.

This problem is specifically asking to define the Q factor related to this circuit. The Q factor is a ratio of energy stored (by an inductor or capacitor) to the power dissipated in a resistor. The Q factor varies with frequency since the effect of a capacitor or inductor also vary with frequency. For a series resonant circuit, the “unloaded” Q factor is defined by the following function: Qu = X / R = 1/(wRC) = wL/R

The unloaded Q factor of a parallel resonant circuit: Qu = R / X = R/(wL) = wRC

Overall, the Q factor is a measure of loss in the resonant circuit. A higher Q corresponds to lower loss, while a lower Q indicated higher loss. An “unloaded” Q factor means that the resonator is not connected to a source or load. The above circuit can no longer apply the “unloaded” Q factor formulas due to the presence of a source and a load. There are two further Q factor formulas that need to be considered: loaded Q factor and external Q factor. The loaded Q factor includes the source resistance and load resistance with the resistance of the circuit. The external Q factor refers to only the source resistance and load resistance together.

For the above circuit, the loaded Q factor for the parallel resonator is defined as:

Loaded Q = (Rs + R + Rl)/(wL) = (Source resistance + R + load resistance) / (wL)

The external Q factor for the source resistance and load resistance is:

External Q = (Rs + Rl)/(wL) = (Source resistance + load resistance)/(wL)

The relationship between the different types of Q factors are:

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