Abstract:
Ultrawide band (UWB) communication as evident from the name is a communication
method which utilizes wide range of the frequency spectrum. The excessive bandwidth
gives UWB communication decisive edge over the existing narrowband communication
systems. Real break through came in 2002 when FCC authorized the unlicensed use of
3.1GHz-10.6GHz frequency band for UWB communication. However UWB emission
pose significant interference risk to existing services like GPS, Earth Resource Satellite
and Radio Astronomy. Therefore FCC has defined a emission mask for UWB systems
for the safe operation of existing services. UWB bandpass filter with pass band 3.1GHz- 10.6GHz and high rejection in stop bands are crucial to ensure that FCC regulations
regarding UWB emission are fulfilled. Thesis work is based on the development of compact UWB bandpass filter for UWB
communication in band 3.1GHz-10.6 GHz. Main challenge in UWB filter design is to
achieve such high coupling required for UWB. One such structure is a compact planar E- shape microstrip structure which is composed of coupled resonators and has second order
bandpass response. Two fourth order UWB filters are designed(using ADS software), one by direct coupling of three E-structures and other by capacitive coupling of two E- structures. Coupling gap in case of capacitive coupling is modeled as a chip capacitance
to relax fabrication difficulties.
Filter based on directly coupled E-shape structures is fabricated on TMM10i substrate
using milling technique. Size of the fabricated filter is 7.62x4.34x0.635mm. Measured
filter has fractional bandwidth of 97%, maximum flat band insertion loss of 1.3dB, maximum returnloss of 9dB and rejection better than 20dB in GPS band. Chip loaded
filter is fabricated on Rogers 4003 substrate using milling technique. Size of the
fabricated filter is 4.3x5.2x0.508 mm. Filter has fractional bandwidth of 115%, maximum flat band insertion loss of 0.25dB, maximum return loss of 11 dB and rejection
better than 25dB in GPS band.
