Compact Narrow-Band Sharp Rejection Bandstop Filter Using U-Shaped Resonator for GNSS Receiver

An U-shaped resonator based bandstop filter (BSF) has been reported in this paper to reject the high power unwanted signal or interfere near to the desired signal. The BSF uses mixed coupling technique - electrical and magnetic - to realize its performance. The U-shaped resonators which are open on both sides are coupled to the feed-line or main line using a coupling gap. The resonators are approximately half-wavelength at the desired frequency of the BSF. As the RF signal passes through the filter the U -shaped resonator selectively captures the particular frequency and allows other frequencies to appear at the output. The mode analysis has been performed to understand the behavior of the circuit. To demonstrate the concept, a bandstop filter rejecting two undesired signals at 1.30 GHz and 1.35 GHz has been designed and fabricated. The filter allows to pass L1 and L5 frequencies with lower insertion loss.

I. Introduction

In satellite communication, to track the launch vehicles and low earth orbit (LEO) satellites, ground stations or launch- pads are equipped with tracking radar. Generally the tracking radars operate in skin mode for tracking the objects. In skin mode operation these radar systems transmit the radar signal in L-band at the center frequencies of 1300 MHz and 1350 MHz typically. These two operating frequency bands are closer to the global navigation satellite system (GNSS) receiver operating in Ll (1575.42 MHz) & L5 (1176.45 MHz) Bands. Due to high level of power at radar frequencies there is a chance of LNA saturation. Furthermore, the gain may also reduce at the desired Ll and L5 frequencies. The inclusion of notch filter can overcome these issues. The notch filter will suppress the signals at 1.30 GHz and 1.35 GHz while allows the signals at Ll and L5. To avoid the bulky waveguide based bandstop filters, microstrip bandstop filters are the best candidate for this kind of application.