Hi..

Bandwidth BW=f0/Q, where f0 is the freq of resonance and Q is the Quality factor..

Q=2*pi*Energy stored/Energy dissipated per cycle..

Therefore one way to increase BW is to decrease Q, i.e.  either by decreasing stored energy, or by increasing losses.

a) Decreasing stored energy: i) By increasing substrate height and ii) by reducing dielectric constant (which you told you can't change). Both these methods increase the fringing and hence reduce the energy stored in microstrip resonator.. However careful!! Increasing substrate height can excite unwanted surface waves.

b)Increasing Losses: i) By introducing losses in dielectrics (Which you told you won't alter) ii) By introducing Chip resistor.. However, introducing chip resistor and thus introducing losses reduces the gain, which can be elevated using superstrates.

c) Using multi-mode techniques: Many resonant modes can be stagger-tuned together to have large BW..by i) having stacked elements ii) having coupled parasitic elements iii) or by introducing slots which individually introduces resonances which can be near enough together to form a wider band.

You can refer:

a) Microstrip antennas (Garg et al.)  b) Compact and broadband microstrip antennas (Wong) c) Microstrip patch antennas (Lee, Luk)

Thanks

Strongly depends on the geometry of the antenna. By increasing substrate's thickness maybe you can increase impedance bandwidth. Maybe by using another feeding technique or the use of a broadband balun for your dipole antenna.

Hi..

Bandwidth BW=f0/Q, where f0 is the freq of resonance and Q is the Quality factor..

Q=2*pi*Energy stored/Energy dissipated per cycle..

Therefore one way to increase BW is to decrease Q, i.e.  either by decreasing stored energy, or by increasing losses.

a) Decreasing stored energy: i) By increasing substrate height and ii) by reducing dielectric constant (which you told you can't change). Both these methods increase the fringing and hence reduce the energy stored in microstrip resonator.. However careful!! Increasing substrate height can excite unwanted surface waves.

b)Increasing Losses: i) By introducing losses in dielectrics (Which you told you won't alter) ii) By introducing Chip resistor.. However, introducing chip resistor and thus introducing losses reduces the gain, which can be elevated using superstrates.

c) Using multi-mode techniques: Many resonant modes can be stagger-tuned together to have large BW..by i) having stacked elements ii) having coupled parasitic elements iii) or by introducing slots which individually introduces resonances which can be near enough together to form a wider band.

You can refer:

a) Microstrip antennas (Garg et al.)  b) Compact and broadband microstrip antennas (Wong) c) Microstrip patch antennas (Lee, Luk)

Thanks

If you want to maintain the same substrate material with the same dielectric constant and height as well as maintaining the same design/technique (dual band dipole), then you only have the type of feeding and feeding point to play around with. Otherwise, using multi-mode arrays would provide better antenna characteristics.

Reduction of ground plane area will improve the bandwidth.

use aperture coupuling to improve bandwidth.(or) take semi ground plane  it is used in UWB antennas. 

Create perturbation in the copper area i. e. narrow slots/slits or  using narrow slits, create some shape preferably balanced way with reference to patch centre. 

It depends on what kind of antenna you design. For a lot of antennas, You can try to add the parasitic element, of cut a slit on the ground to increase the bandwidth