How do you design RF microstrip circuits to minimize loss and dispersion?

Pay attention to loss tangent info over frequency. Many material datasheet specify losses at 10GHz at maximum, leaving out important information about material behaviour on higher frequencies.

Make traces between component as short as possible. Loss increases with length. Also short paths reduce the amplitude and group delay ripple by making the ripple spread over wider bandwidths. Choose pwb materials carefully for low loss tangent. Also at higher frequencies pay attention to surface roughness. Choose dielectric thickness to give a trace width close to the pin size of components.

Substrate selection is a very key decision for RF designing. The key considerations for the selections are as below: 1. Dielectric Constants 2. Loss tangent 3. Frequency of operation 4. Substrate Thickness 5.Thermal Stability 6. Manufacturability 7.Cost 8. Availability

Dispersion will primarily depend on the variation of dielectric constant with frequency. As dielectric constant varies with frequency, the velocity will vary with frequency as velocity is inversely proportional to the square root of dielectric constant. This will cause dispersion.

1. Select a substrate material with low dielectric loss and appropriate electrical properties. 2. Consider factors like substrate thickness, dielectric constant, and material type to minimize signal loss.

1. Adjust the width and length of microstrip lines to achieve the desired impedance and minimize signal loss. 2. Ensure that the dimensions are optimized for the specific frequency range of operation.

Note for active RF circuits it often makes more sense to choose a track width that matches the components on the board. For example let say your circuit contains 2 DC blocking 0402 caps (0.5mm pad width) and a LNA (0.25mm pad width), it makes little to no sense to use a track width of 3mm. The optimal choice would probably be to go with something between 0.25 and 0.5mm to minimise the amount of discontinueties on the RF chain.

1. Implement impedance matching techniques to ensure smooth transitions between components and minimize reflection losses. 2. Utilize matching networks like transformers, stubs, and matching networks at critical points.

Ensure the type of interference happening whether it is a co channel or adjacent channel interference. Once the above effect gets determined, compute the distance between sender and receiver and desired signal to noise ratio. As per the type of interference, derive the values, hence this a way to compensate the loss.

1. Implement compensation techniques to counteract the effects of dispersion and loss. 2. Techniques may include adding equalization circuits or using materials with controlled dispersion characteristics.

Isolation techniques need to be identified carefully considering the presence of the component's, transmitting and receiving stations, etc.. One technique is to ensure proper application of filter design such that only desired signals are able to pass through it. There are many other techniques which needs to identified based on the application and constraints.

1. Incorporate isolation structures to minimize crosstalk and interference between adjacent components. 2. Techniques may include adding ground planes, shielding, or using appropriate layout techniques.

1. Employ simulation tools (e.g., electromagnetic simulators) to model and optimize circuit performance. 2. Use measurement tools, such as vector network analyzers, to validate and fine-tune the designed circuit.

Simulation and measurement tools are two powerful ways to ensure validation. Few tools: 1) MATLAB - Simulink: Design the model with all the components and by adding all the accurate parameters (may bw upto 3 decimal places) like capacitance, inductance, etc. Ensure to choose the type of filter and its parameters and accordingly put the scope. Manage the time intervals to visualize signal characteristics. 2) Proteus, LTSpice: Another tool to perform simulation.

It’s good to always do EM simulation after designing the basic circuit where microstrip elements were used to build the circuit. EM simulation is an added layer of accuracy in the circuit design - making it easier to test and tune the circuit on the bench. It is also important to know the optimum ways to perform and set up the EM simulation, to get good results.

Simulation and measurement tools are two powerful ways to ensure validation. Few tools: 1) MATLAB - Simulink: Design the model with all the components and by adding all the accurate parameters (may bw upto 3 decimal places) like capacitance, inductance, etc. Ensure to choose the type of filter and its parameters and accordingly put the scope. Manage the time intervals to visualize signal characteristics. 2) Proteus, LTSpice: Another tool to perform simulation.

From my point of view, it is important to validate the simulations carried out in ADS or CST, for example, with measurements and to rethink the models and check where the deviations in the results come from. This improves the simulation models and saves resources the next time. In most cases, simulations and measurements go hand in hand.

Tuning the circuit on the test bench for optimising the performance is an indispensable step towards improving the performance of the circuit, no matter how accurately it was designed using the EDA tools.