[SOLVED] LPDA design parameters for receiver and transmitter

[Martin52]

Hi. I want start to design this broadband antenna. What parameters must to realization of LPDA like transmitter and receiver?

Thanks

 

[rizoeda]

Hi
Your question isn't clear but you should decide on bandwidth (highest and lowest frequency), directivity and gain, feeding approach, construction materials (dipoles and spacers), and son on, then you can start to design and construct your antenna. Generally speaking there is no difference between transmitter and receiver antenna.

 

[Martin52]

My question is. Which construct conditions must LPDA keep to use like transmit or receive antenna? How many elements this antenna should have etc.

 

[Azulykit]

Log Periodic Antenna Design Handbook, Carl Smith is a pretty good reference to get you started. Design of log-periodic dipole antennas, C. Peixeiro makes some useful corrections and you might look at the procedure discussed by Carrel (his thesis on the subject is also useful in spite of some errors, University of Illinois 1961)

LPD's can be quite useful. The longest elements determine the low frequency end of the operating band while the shorter elements design the high frequency end. The more pointy the antenna, the higher the gain will be. they can easily range from a few dBi to on the order of 15 dBi and cover many octaves.

MI technologies makes a range of them. There are other sources as well.

The above references will do a good job of describing the interaction between the various parameters. When you have a preliminary design I would suggest modeling it with HFSS for additional fine tuning and it is very good at exposing any design blunders.

I would put the practical limit on the upper end of one of these at around K band. The feed gets difficult at higher frequencies.

 

[Martin52]

I know this things. But i dont know which construct parameters have to be satisfy to LPDA work like transmitting and receiving antenna. Or is this necessary? I i have LPDA designed to frequency range 700 MHz - 1500 MHz so this antenna will work like transmitting and receiving antenna because frequency range 700 - 1500 MHz includes GSM range (UP, Down link)?

 

[rizoeda]

Hi, as you may know, there are only three independent variables for the log periodic antenna design, which can be chosen from the directivity, length of the antenna, apex angle, the upper frequency and the lower frequency. [Huang, Yi and Boyle, Kevin, Antennas: From Theory to practice, Wiley, 2008 ]
Once you've choosed these three parameters (lower frequency, upper frequency and one another ) two other parameters and also construction specifications such as the number of elements, spacing between them, etc. can be obtained through the designing procedure.
Your antenna's frequncy band includes some GSM types band: GSM-750, GSM-810, GSM-850, P-GSM-900, E-GSM-900, R-GSM-900, T-GSM-900, T-GSM-900.
You should also choose proper diameter for dipoles and gap between the poles to achieve good impedance matching and VSWR < 2 for GSM. The formula is g=d*cosh(Z0/120) where g is gap and d is diameter of a dipole.

 

[Martin52]

Yes. I know this things but my question is different. How design LPDA to work like transmitting and receiving antenna? First condition is VSWR<1.5 and other conditions?

 

[Azulykit]

As long as you are not applying enough power to burn up an antenna there is no difference between a transmitting and a receiving antenna. They are interchangeable and identical. Look up the subject of reciprocity.

 

[Martin52]

Yes. But have to by some construct conditions to work like transmitting or receiving antenna no?

 

[rizoeda]

Yes. I know this things but my question is different. How design LPDA to work like transmitting and receiving antenna? First condition is VSWR<1.5 and other conditions?

Hi Martin You mean one antenna to work as transmitting and receiving antenna simultaneously? In applications like radar, that sending and receiving occurs at same frequency, transmitting and receiving with a shared antenna is possible with a duplexer. But if you want to use for GSM, Uplink and Downlink frequency bands are separated and you don't need the duplexer.
VSWR<1.5 is very good! You should also consider max. power and intermodulation (IM3).

 

[Martin52]

I mean one antenna to work as transmitting and receiving antenna. No simultaneously. For simultaneous work exist some kit MIMO. My teacher ask me which construct parameters LPDA must to have to work like transmitting and also receiving antenna and i dont know what he means.

 

[rizoeda]

I mean one antenna to work as transmitting and receiving antenna. No simultaneously. For simultaneous work exist some kit MIMO. My teacher ask me which construct parameters LPDA must to have to work like transmitting and also receiving antenna and i dont know what he means.

In transmitting radiation efficiency and gain are important, in receiving radiation efficiency and gain are important, also because of importance of signal to noise ratio (S/N) , you should have better performance, I mean side lobe level and back lobe. So you can consider use of ground plane in your antenna structure. Good Luck! Hope you high antenna score!

 

[Martin52]

Thanks for your answer! So if i connect ground plane to LPDA i can improve my transmitting and receiving characteristics?