Hi Srinivas

In CST 2016 you got the CMA analysis, different modes are separated, you can check spatially the geometric dependence on each mode, fields etc. If your antenna is only metal you use the I-solver; if not use the M-solver (multilayer). It works pretty nice.

good luck,

I don't have the latest version of either CST or HFSS. In CST 2013, you can choose the number of modes when defining an excitation. When defining a new waveguide port, you can choose the number of modes in the mode settings. Once you'll have simulated with correct port definitions, you'll then use field monitors to visualise the field distributions to identify modes. In HFSS 2013, you can define the number of modes when defining a new port. You'll have to define the integration lines corresponding to each port.

I hope this helps. 

Hi Srinivas

In CST 2016 you got the CMA analysis, different modes are separated, you can check spatially the geometric dependence on each mode, fields etc. If your antenna is only metal you use the I-solver; if not use the M-solver (multilayer). It works pretty nice.

good luck,

To identify different modes, plz follow the link (my answer) as given below:

https://www.researchgate.net/post/Why_dielectric_resonator_antenna_have_dual_resonance_Electric_and_magnetic_Resonance

From your antenna structure, it is found that it is simply a 'Microstrip Antenna' with some slots. As the size of the slots are small compared to the patch antenna, the resonant frequency will be controlled by patch geometry only. Due to perturbation (slots), there is a possibility to have some shift in resonant frequency. no of half cycle will define modal index. Those half cycles may not be have same size due to slots. I can see that left fig. contain 1 half cycle along height (slight disturbance due to middle slot) and three half cycles along height. hence, first and second  modes are TMz_100 and TMz_300. In summary:

1. plot Zin (not S11)

2. Identify different resonant frequency from the plot of Zin

3. If the height of the patch is along x, y or z-direction, it will support TMx, TMy or TMz  modes respectively. Practical excitation of TE mode is not possible for thin substrate

4. Plot surface currents (or magnitude of E-field on patch surface).

5. just count the no of half cycle to find the modal index

Plot Real(Zin) and Imag(Zin) with respect to frequency. You will find several peak point on real part of Zin (or +ve to -ve crossing of imaginary part of Zin). These are the resonant frequency. S11 shows dip where the real part of Zin is nearly equal to 50ohm. You may get different resonant frequency than actual one if you use S11. But if you optimize your antenna, normally it is found that the dip occurs at resonant frequency..

Thanking you all for helping me to understand the modes concept. It will help me so much.

Simply you can plot the reflection coefficient S11 versus frequency, and observe where the coeffiecient has peaks, at these frequencies (resonance frequencies) you can plot the surface currents to observe the corresponding mode

From the plot of S11, we can get those modes which has real part of Zin close to 50. If a mode has 1000 ohm Zin, it will not be found from the plot of S11. For example, probe fed 30-60-90 Deg Triangular Microstrip antenna (with base length 100mm) shows 5-6 modes from 0.5GHz - 3.5GHz irrespective of probe position (provided, modes must have some zin. Modes with 0 ohm zin will not be shown for some value of probe position.) If the probe is placed (10mm,0mm) point, all modes can be found from Zin whereas there will be no dip in the plot of S11. S11 shows only radiating modes (Zin close to 50 produce a dip) whereas Zin shows all modes including radiating modes. It should be pointed here that due to excitation, some modes of an antenna may be suppressed. For example, TM mode is suppressed due to excitation for rectangular DRA

Mr Marcelo i also used the same method as you said but my problem is i need to do the modal analysis for three different frequencie the first one is ok but the second frequency is taking much time stopping at 82% instead of 100% i dont know why please what do you think i can do? Or should i continue to wait may be it will finish?