Tunable microwave filters offer a great deal of versatility. And when they are based on monolithicmicrowave- integratedcircuit (MMIC) technology and housed within a 5 x 5 mm surface-mount package, they can fit almost any application. New families of varactor-tuned MMIC lowpass and bandpass filters from Hittite Microwave Corp. provide this flexibility with high stability and fast tuning speeds over a tuning range of 1.0 to 7.6 GHz.
Models HMC881LP5E and HMC882LP5E are lowpass filters that provide stopband rejection of at least 30 dB through 30 GHz. The HMC881LP5E filters have adjustable cutoff frequencies from 2.2 to 4.0 GHz while the HMC882LP5E filters provide adjustable cutoff frequencies from 4.5 to 7.6 GHz. In both, a tuning voltage of 0 to 14 determines the tuned cutoff frequency. The stopband frequencies (rejection greater than 20 dB) for the model HMC881LP5E are typically 1.25 times the cutoff frequency, or 5 GHz for a 4-GHz cutoff frequency. The passband insertion loss is typically 3.8 dB while the return loss is typically 10 dB. For the model HMC882LP5E, the stopband frequencies are typically 1.23 times the cutoff frequency, with passband insertion loss of typically 2.9 dB and return loss of typically 10 dB.
For both lowpass models, the tuning speed is typically 150 ns for a transition from a 0-percent voltage control signal to 90 percent of the tuned frequency. Both lowpass filters are rated for maximum input power of +10 dBm for linear operation.
Models HMC890LP5E and HMC891LP5E are bandpass filters that use two independent voltage controls to adjust passband frequency and bandwidth. Model HMC890LP5E has a tunable center frequency from 1 to 2 GHz while HMC891LP5E offers a tunable center frequency from 2.0 to 3.9 GHz. As with the lowpass filters, a control voltage of 0 to 14 V adjusts the center frequency. An additional 0 to 14 V control voltage tunes the bandwidth within 3 percent of the center frequency. For the model HMC890LP5E bandpass filter, the 3-dB bandwidth is typically 11 percent of the center frequency, with low-side rejection (greater than 20 dB) at 0.86 times the center frequency and below and high-side rejection (greater than 20 dB) at 1.19 times the center frequency and beyond. Out-of-band rejection drops below 30 dB at 9 GHz. For model HMC890LP5E, passband insertion loss is typically 9 dB with return loss of typically 10 dB.
For the model HMC891LP5E bandpass filter, the 3-dB bandwidth is typically 9 percent of the center frequency, with low-side rejection (greater than 20 dB) at 0.88 times the center frequency and below and high-side rejection at 1.15 times the center frequency and beyond. Out-of-band rejection drops below 30 dB at 22 GHz. For model HMC890LP5E, passband insertion loss is typically 7 dB with return loss of 10 dB. For both models, the maximum input power is +10 dBm. For both, the tuning speed is typically 200 ns.
These tiny MMIC filters (see figure) are housed in RoHS-compliant, 32-lead plastic QFN surface-mount packages that represent considerably smaller alternatives to mechanically tuned filters. Hittite Microwave Corp., 20 Alpha Rd., Chelmsford, MA 01824; (978) 250-3343, FAX: (978) 250-3373, Internet: www.hittite.com.