question answers on microstrip patch antenna
Are there any ways to reduce the surface wave in the patch antenna? The radiation efficiency of my microstrip patch antenna is too low. By the way, I can't change the depth of the substrate.
Thanks,
it is strange. I input "patch antenna" in my title, but it showed as "fix antenna". How weird! Anyway, are there any great ideas to reduce the surface wave?
Thanks
Yes, this forum eliminates those phrases that could mean something different which lead to complaints by corporate firms.
About your query, how do you know that the poor efficiency is caused by the surface waves? Isn't it more likely that the antenna is mismatched or the printed element/geometry is not optimised/desirable.
If you are quite sure that the surface waves are the cause of the problem, then the most recent well-known technology called the Electromagnetic Bandgap Structure (EBG) would be most appropriate. A brief discription of EBG for you - they are most common configured by periodically arranged metallised square patch elements. The lattice constant, the patch size and the substrate properties set the range of operation of the so-called electromagnetic band gap. By operating in the frequency band gap, no modes can exist inside the periodic structure.
Therefore, by putting printing these EBG elements around the radiating object of about 2 periods away can effectively eliminate most substrate modes.
I hope this is a good start in answering your question.
Hello Sassyboy,
Thank you very much for your answer. I am pretty sure it is caused by the surface wave. I have no mis-matching problem.
I know few about the EBG structure concept. However, I have a question about it. Do I need to make the substrate to be periodically arranged as the metal patches? Or nothing is changed to the substrate?
Thanks,
Good question. EBG structures can be seen as two types. The first structure is known as a periodic dielectric structure. This structure was the earliest to be introduced to have an forbidden frequency bandgap i.e. EBG. Researchers can either place dielectric rods periodically, or have a piece of dielectric and have holes periodically drilled through it (to form the so-called perforated substrate). Therefore if the periodic dielectric EBG structure is chosen for antenna application such as the printed antenna, then the perforated EBG substrate is used due as it is easier to fabricate. Depending on what sort of surface wave modes, i.e., TE or TM types, one needs to consider the lattice structure of the periodic structure. It is well-known that if the periodic structure of holes are arranged in a square lattice, then only the TE or TM type bandgap exists. Whereas, it the holes were arranged in a triangular lattice, both the TE and TM type bandgap exists, hence result in a Complete Electromagnetic Band Gap. So, in future if you come across some publications or magazines articles and you saw lattice arrangement usually of triangular/hexagonal lattice, this is why!
Unfortunately, substrate comes with metallisation on both sides. Hence if we were to form holes only in the dielectric, this would mean we would have drilled a hole in the metallisation. But we want to keep a uniform ground plane for the patch antenna with no holes in it. At this point, it is clear to us that the perforated dielectric structure has its weakness.
A group in the UCLA proposed a new type of structure. This structure has periodic metallisation on the substrate known as the metallodielectric EBG (MEBG) structure. If you are familiar with frequency selective surfaces (FSS), one can convert FSS to MEBG by adding a metal layer for the ground plane and perhaps make the substrate thicker. So, if you have a piece of FR4 material of thickness about 2 mm and pattern some periodic square patches of size 7.7 mm and lattice constant of 8.2 mm on one side of the metal layer, you should obtain a bandgap center around 3.5 GHz. This is an extremely popular configuration due to its simplest form of fabrication. In addition, it has a bonus feature of a in-phase reflection which act like a perfect magnetic conductor and hence the name Artificial Magnetic Conductor (AMC) or High-Impedance Surface. This is again discovered and patented by the ULCA. The key people behind this work were Yablonovitch et. al. and Sievenpiper et. al.
I hope this give you a better idea of this potential technology. This is a hot topic in this forum and in many EBG conferences are available to attend. Periodic structures for microwave and antenna applications are now referred as a family of Metamaterials.
That is an awesome answer. It did answered all my questions. Thank you very much for it.
Maybe you can use DGS technique. It's a simple EBG design.
Use slots in the ground plane...that wil reduce the
surface wave
I'm still confused about the EBG concept,who can give some concrete material to explain this concept.
thanks in advance...
I can't use the slots on the ground plane. I want only one-side radiation.