Tuesday, October 14, 2008

BW Enhancement Using air substrates

One way of improving the bandwidth to 10-20% is to use parasitic patches, either in another layer (stacked geometry) or in the same layer (coplanar geometry). However, the stacked geometry has the disadvantage of increasing the thickness of the antenna while the coplanar geometry has the disadvantage of increasing the lateral size of the antenna. It would therefore be of considerable interest if a single-layer single-patch wideband microstrip antenna could be developed. Such an antenna would better preserve the thin profile characteristics and would not introduce grating lobe problems when used in an array environment.

Fig: Using air or foam substrates


BW Enhancement Using Chip resistor loading

This method increases the bandwidth of the antenna by decreasing the quality factor. This method is used by itself or in conjunction with other methods in order to miniaturize the antenna also. Thus this method strives to achieve the two main goals for microstrip elements – bandwidth enhancement and miniaturization. Chip Resistor is basically a kind of low resistance short.




Fig: Using Chip Resistor Loading

Three dimensional patches like V-shaped patch or wedge -shaped patch

project report

Decreasing the quality factor of the microstrip antenna is also an effective way of increasing the antenna’s impedance bandwidth. In the former case, for feeding using a probe feed, a large reactance owing to the long probe pin in the thick substrate layer is usually a problem in achieving good impedance matching over a wide frequency range. To overcome this problem associated with probe-fed microstrip antennas, designs have been reported that bend the patch into a 3D V-shaped patch or the ground plane into an inverted V-shaped ground


project report

Fig: Stacked Configuration


BW enhancement Using Stacked Configuration or Parasitic Coupling

Stacked configurations are possible with aperture coupled feeding, proximity feeding and co-axial feeding. Probe feeding technique is re-emerging in variety of antenna system due to its robust nature. It provides good isolation between feed network and radiating elements and due to direct contact with the radiator reduces dielectric layer misalignment difficulties. It also yields good front to back ratio which is very important where multiple arrays are located back-to-back in closed proximity. Therefore stacked configurations with probe –fed have been considered. The combination of low dielectric constant and high dielectric constant can yield good impedance behavior. The broadest bandwidth can be achieved when the first-order mode on the lower patch is considerably greater in magnitude than corresponding mode on the top patch or in other words the top patch is loosely coupled. For this the substrate of lower patch should have higher dielectric constant than the upper substrate.


fig: Parasitically Coupled Coaxial fed Microstrip Antenna



project report

project report

Fig: Multilayer Stacked Configuration