Hello Kanchan, It depends what application your phased antenna is designed for. If you designing it for the wideband communication system it could be beneficial to improve the bandwidth of the antenna or make it multi-band. However, you should be aware that for the optimal performance of the phased array, the radiation patterns along the bandwidth of antenna should have a similar shape. Maximum gain and maximum scan angles along the frequency range would be an important metric to consider.

For many applications the side lobe level and gain of array is also important. However,it is also very important to design an array with a high scan angle. Higher scan angles can be achieved by increasing number of array elements and elements with omnidirectional radiation patterns. Finally, it is very important have a low grating lobe when scanning to high angles. Grating lobes and sidelobes of the phased arrays can be reduced by choosing specific complex weights at the antenna element inputs. However, this usually comes at price of lower maximum gain.

Thank you Igor Sir. My application is radar system. So is bandwidth need to be higher for this application ? I have read various papers but they not focused on bandwidth. They talked about the improvement of gain , SLL, scan angle, directivity would you please suggest me.

Hello Kanchan,

For radar similar holds. However, it depends whether you are talking about an antenna for the transmitter or the receiver.

Transmitter: A narrow main beam usually brings a higher antenna gain in the look direction. This is often wanted if no direction of arrival (DOA) estimation exists at the receiver, or only a small part of the scene is examined.

Receiver without (e.g. digital) DOA estimation: A narrow main beam means that you are able determine the direction of the target well (through scanning). High sidelobes mean that targets which are actually located at a sidelobe might be mistaken for a target at the main beam.

Transmitter & Receiver: If a larger part of the scene has to be monitored simultaneously (DOA estimation at the receiver), a narrow beam is not beneficial.

Bandwidth: If a high bandwidth is fully exploited by the radar system, your range (radial distance) measurement improves.

As Igor pointed out, for a separable range and DOA estimation, the beampattern should be constant over frequency. However, some special approaches particularly exploit a frequency-varying beampattern (e.g. frequency divers arrays, FDA) for better localization.

To summarize:

- define your gain (main beam) according to your minimum specification (target RCS at a certain range)

- define your bandwidth according to your desired range resolution

- define your peak sidelobe level according to the ratio of the highest expected interference (target RCS at range) and the minimum detectable target (first bullet)

- no additional DOA estimation: according to the previous specification, design the main beam as narrow as possible; additional DOA estimation desired: talk to the DOA estimation people which observation angle they want (dont forget that a narrower observation interval means a higher antenna gain) and design the main beam accordingly.

I hope this helps,

Michael

Thank you very much Michael for the brief description. Here I would like to design an array for X band. Is 10 element linear array is the good choice for it or I ca go for planar array .For the SL:L minimization I must go for weights ( Taylor series / GA) etc na. Or is there any technique for reducing the SLL. Can you suggest me any book on this.

Dear Kanchan,

Please provide more details:

- Is your array meant for transmit or receive or both?

- Is the phased array steering done electrically (phase shifters with certain shifts and weights for each element) or digitally after sampling the signals of all elements?

Your answers:

- Whether you use a linear or planar array depends on whether you want to focus the beam only in azimuth (linear array) or also in elevation (planar array). In case of electrical/digital beamforming in one direction (e.g. azimuth) only, the beam should be focused in the other direction (elevation) by other means, e.g. using a fixed electrical steering or dielectric lens. Otherwise the antenna gain will be very low.

- The number of elements depends on how much money you can spend ;-) and on the performance you want to achieve. More antennas generally improve the array performance.

- For the weighting design , you can take a look at "Optimum Array Processing" by Harry van Trees, in particular the 3rd chapter. Alternatively, you can also vary the antenna positions to obtain a certain optimization goal (e.g. low SLL and/or narrow main beam). Furthermore, antenna tapering is a technique for SLL reduction.

Regards,

Michael

Thanks Michael. My array antenna is meant for transmit. Planar array is more complicated than linear array na. I have not yet decided about the linear or planar array. Can you suggest for which design I have to go further. If antenna main beam decrease ( half power beamwidth ) then it will also affect gain. So while talking in terms of antenna performance on which parameters we have to concentrate. Gain, directivity , HPBW , BW ? I have to choose two parameters on which I am going to work. But there is a trade off between gain and SLL. So I am getting confused in terms of selection of parameters. Please suggest me two parameters. For SLL I have to work on power divider network also. I read in a book that BW improvement is a big issue in radar antennas. But if I used Microstrip patch antenna then MPA itself have less BW. So again is the question of BW improvement.

Dear Kanchan,

Gain, HPBW, SLL and BW are all important. In my opinion it does not make sense to concentrate on two of them while the other parameters grow to values which make the array unusable in practice.

For a classical radar system, the BW depends mainly on the desired range resolution, as mentioned earlier. Of course, there are always some special concepts (such as FDA, Multicarrier-MIMO and so forth) which require more bandwidth.

However, most wideband antennas I know (this is not my main research area) are quite large in dimension. To build a phased array, antenna elements are usually placed relatively close to each other (e.g. half wavelength), which may be possible only with path antennas. Focusing is then done by dielectric lenses rather than phased arrays.

You seem to have no particular application in mind for your research; I recommend you to decide about the application first and care about the array design later. There is no one-fits-all solution (I guess this why array design is still an active research area). Furthermore, many application have additional constraints, such as cost, weight or array aperture limitations.

Regards,

Michael