Continuously Tunable 0.55-1.9-GHz Bandpass Filter With a Constant Bandwidth Using Switchable Varactor-Tuned Resonators

This paper reports on tunable 2- and 3-pole bandpass filters with a wide frequency tuning range (tuning ratio >3) and a constant bandwidth using switchable varactor-tuned resonators. The wide center frequency tuning range is obtained using p-i-n diodes to switch in and out quarter-wavelength (λ/4...

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Vydáno v:IEEE transactions on microwave theory and techniques Ročník 65; číslo 3; s. 792 - 803
Hlavní autoři: Feng Lin, Rais-Zadeh, Mina
Médium: Journal Article
Jazyk:angličtina
Vydáno: New York IEEE 01.03.2017
The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Témata:
Bandpass filters
Bandwidth
Bandwidths
Capacitance
Coupling
Couplings
Electric filters
Insertion loss
Microstrip filters
PIN diodes
Resonant frequency
Resonators
Substrates
Switches
Third order intercept point
tunable filters
Tuning
ultrahigh frequency (UHF) band
varactor diode
Varactor diodes
Varactors
wide tuning range
ISSN:0018-9480, 1557-9670
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Shrnutí:This paper reports on tunable 2- and 3-pole bandpass filters with a wide frequency tuning range (tuning ratio >3) and a constant bandwidth using switchable varactor-tuned resonators. The wide center frequency tuning range is obtained using p-i-n diodes to switch in and out quarter-wavelength (λ/4) or half-wavelength (λ/2) resonators for low-band or high-band modes, without increasing the tuning capacitance range of the varactors. A combination of electric and magnetic coupling is utilized to realize a near constant absolute bandwidth across the tuning range. A switchable feed line with a fixed matching capacitance is used to realize the external coupling. Two filters are designed and fabricated on a Duroid substrate with ε r = 2.2 and h = 0.787 mm. For the 2-pole filter, the center frequency is tuned from 550 to 1900 MHz while maintaining a 3-dB bandwidth of 92 ± 6 MHz, insertion loss of 3.2~4.4 dB, and return loss of better than 15 dB. For the 3-pole filter, the center frequency is tuned from 540 to 1800 MHz while maintaining a 3-dB bandwidth of 89 ± 4 MHz, insertion loss of 4~5.4 dB, and return loss of better than 12 dB. For both filter types, the third-order intercept point and 1-dB compression point (P 1 dB) are 11 and 7 dBm, respectively. The rejection level at 200-MHz offset frequency from the passband center frequency is better than 25 and 41 dB for 2- and 3-pole filters, respectively, across the entire tuning range. To the best of our knowledge, this planar bandpass filter exhibits the widest tuning range with a near-constant bandwidth.
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ISSN:0018-9480
1557-9670
DOI:10.1109/TMTT.2016.2633270