How many ports (min and max) ports a SIW antenna can have ? and why?

[B4M]

Hello!
* I would like to know why the SIW structures are simulated using two ports or more?

* and for the in the case of SIW antennas why there is also two ports ? how can we explain the difference if there is one between the use of one port or two ports or more?


thank you!

 

[AndreyG]

Two ports can be there for number of different reasons. Send the image of the design it will be easier to figure it out.

 

[B4M]

Please find the design in here!
thank you in advance!

 

[AndreyG]

I see only one port in the picture - the feedline. Am i missing something?

 

[B4M]

yes there is only one port they use such schemes to illustrate the parameters of the geometry, but in doing simulation and measurements they use the following scheme shown in the picture below, actually this is what is confusing me ? why two ports to simulate such structures?

 

[Terminator3]

yes there is only one port they use such schemes to illustrate the parameters of the geometry, but in doing simulation and measurements they use the following scheme shown in the picture below, actually this is what is confusing me ? why two ports to simulate such structures?View attachment 131496

SIW (Substrate Integrated Waveguides). I understand your confusion.

About 1-port simulations of SIW.
Usually can be used for resonant slot array SIW antannas. Resonant siw antenna is terminated with short. The same as waveguide slotted arrays.
Also for SIW-cavity resonators. Only one port is needed. You obtain S11 and can use SIW in further design (oscillator, etc.)

About 2-port simulations of SIW.
Mainly used for simulations where you must know S21 scattering parameter. As you know, in 2-port network we have S11, S21, S12, S22 parameters. in 1-port network we only one scattering parameter S11. Main idea of 2-port simulation for SIW is to know cut-off frequency of SIW, and characteristics of microstrip-to-SIW transition. So SIW can be used as high-pass filter. But mainly here idea is to measure S21 from simulation and see if transition is made good.

Also there can be SIW bandpass filters, which again require 2-ports.

Another purpose of 2-port SIW simulation.
Another place where two-port SIW simulation can be used is for non-resonant slot arrays. SIW slot array antennas with non-resonant slots may use 50-ohm termination on the end of SIW. Non-resonant slots can be used for beam-scanning SIW antenna, and reflection from the second port may be unwanted, so they terminated with 50-ohm.

Purpose of 3-port SIW and N-port SIW simulations (many ports).
Used in
- siw coupler simulations (hybrid coupler, 3dB coupler, directional coupler, etc.)
- siw diode mixer simulations, may include couplers
- siw Rotman lens
- siw inter-pcb transitions, SIW power dividers, etc.

So as you can see mainly design steps are:
1. Use 2-port simulation to estimate if microstrip-to-SIW transition is good enough
2. Use required number of ports to continue your design. It can be 1,2,3,4,5 for different purposes and much more ports in case of rotman lens simulation.

Hope it helps.

 

[Terminator3]

Although I already know pretty much on SIWs, i have question too.
When using high dielectric constant substrate (Er>4) it seems that it is difficult to excite slot of a SIW slot antenna. Ideal results can be obtained with air-filled waveguide. I suspect that if wavelength in air and dielectric differs too much, the problem shows up. Also i recall some paper saying that high dielectric constant makes wideband approach more difficult for waveguides. So why dielectric constant makes so much problem for SIW antenna design? Maybe adding layer of dielectric above the slots will somehow eliminate this problem?