Microelectromechanical system (MEMS) bridge capacitors have been used to design miniature and tunable bandpass filters at 18-22 GHz. Using coplanar waveguide transmission lines on a quartz substrate (/spl epsiv//sub r/ = 3.8, tan/spl delta/ = 0.0002), a miniature three-pole filter was developed with 8.6% bandwidth based on high-Q MEMS bridge capacitors. The miniature filter is approximately 3.5 times smaller than the standard filter with a midband insertion loss of 2.9 dB at 21.1 GHz. The MEMS bridges in this design can also be used as varactors to tune the passband. Such a tunable filter was made on a glass substrate (/spl epsiv//sub r/ = 4.6, tan/spl delta/ = 0.006). Over a tuning range of 14% from 18.6 to 21.4 GHz, the miniature tunable filter has a fractional bandwidth of 7.5 /spl plusmn/ 0.2% and a midband insertion loss of 3.85-4.15 dB. The IIP/sub 3/ of the miniature-tunable filter is measured at 32 dBm for the difference frequency of 50 kHz. The IIP/sub 3/ increases to >50 dBm for difference frequencies greater than 150 kHz. Simple mechanical simulation with a maximum dc and ac (ramp) tuning voltages of 50 V indicates that the filter can tune at a conservative rate of 150-300 MHz//spl mu/s.

Miniature and tunable filters using MEMS capacitors

A dual-band antenna matching system and a method for dual-band impedance matching are provided. The method comprises: accepting a frequency-dependent impedance from an antenna; and, selectively supplying a conjugate impedance match for the antenna at either a first and a second communication band, or a third and a fourth communication band. More specifically, the method comprises: tuning a first tuning circuit to a first frequency; and, simultaneously tuning a second tuning circuit to a second frequency. In response, a conjugate match is supplied to the antenna in the first communication band in response to the first frequency. Simultaneously, the antenna is matched in the second communication band in response to the second frequency. When the first tuning circuit is tuned to a third frequency, and the second tuning circuit is tuned to a fourth frequency, then conjugate matches are supplied for the third and fourth communication bands, responsive to the third and fourth frequencies, respectively.

System and method for dual-band antenna matching

This paper presents a state-of-the-art RF microelectromechanical systems wide-band miniature tunable filter designed for 6.5-10-GHz frequency range. The differential filter, fabricated on a glass substrate using digital capacitor banks and microstrip lines, results in a tuning range of 44% with very fine resolution, and return loss better than 16 dB for the whole tuning range. The relative bandwidth of the filter is 5.1 /spl plusmn/ 0.4% over the tuning range and the size of the filter is 5 mm /spl times/ 4 mm. The insertion loss is 4.1 and 5.6 dB at 9.8 and 6.5 GHz, respectively, for a 1-k/spl Omega//sq fabricated bias line. The simulations show that, for a bias line with 10-k/spl Omega//sq resistance or more, the insertion loss improves to 3 dB at 9.8 GHz and 4 dB at 6.5 GHz. The measured IIP/sub 3/ level is > 45 dBm for /spl Delta/f > 500 kHz, and the filter can handle 250 mW of RF power for hot and cold switching.

A differential 4-bit 6.5-10-GHz RF MEMS tunable filter

A new combline filter structure with a continuous tunability for both the center frequency and bandwidth is presented in this paper. The passband-width tunability is achieved by placing variable coupling reducers between the filter resonators. The coupling reducers, operating as bandwidth control subnetworks, are designed as detuned resonators made up of a line segment ending in a variable capacitor. The proposed filter structure is experimentally validated with the design, construction in suspended stripline technology, and characterization of a low-cost filter prototype for terrestrial digital video broadcasting receivers operating in the UHF band (470-862 MHz). Other relevant factors, such as the intermodulation distortion produced by the varactors used to control the bandwidth electronically or the power-handling performance of the constructed filter, are also discussed. The reconfigurable filter module described in this paper is very suitable for the design of flexible multifunction receiver subsystems simultaneously supporting signals with a different bandwidth.

Tunable combline filter with continuous control of center frequency and bandwidth

This paper presents a state-of-the-art RF microelectromechanical systems (MEMS) wide-band tunable filter designed for the 12-18-GHz frequency range The coplanar-waveguide filter, fabricated on a glass substrate using loaded resonators with RF MEMS capacitive switches, results in a tuning range of 40% with very fine resolution, and return loss better than 10 dB for the whole tuning range The relative bandwidth of the filter is 57/spl plusmn/04% over the tuning range and the size of the filter is 8 mm/spl times/4 mm The insertion loss is 55 and 82 dB at 178 and 122 GHz, respectively, for a 2-k/spl Omega//sq bias line The loss improves to 45 and 68 dB at 178 and 122 GHz, respectively, if the bias line resistance is increased to 20 k/spl Omega//sq The measured IIP/sub 3/ level is >37 dBm for /spl Delta/f>200 kHz To our knowledge, this is the widest band planar tunable filter to date

A 12-18-GHz three-pole RF MEMS tunable filter

A microstrip active varactor tunable bandpass filter is presented. The filter is based upon the negative resistance method using a microstrip combline network. A 1.8-GHz, two-pole device with a bandwidth of 2% was constructed. 0.6 octave tuning with significant improvement in passband performance was achieved compared with its passive counterpart. >

Active varactor tunable bandpass filter

A method for increasing the skirt selectivity on one side of a bandpass filter is presented. One such application is the receive filter of a personal communication network (PCN) mobile terminal. An asymmetric synthesis method has been used, realizing finite transmission zeros as cross couplings. A novel microstrip structure has been devised to demonstrate the electrical design. Although the insertion loss measured was greater than that required for a practical system, the procedure is applicable to compact dielectric resonator structures with potentially lower loss capability. >

Asymmetric bandpass filter using a novel microstrip circuit

This paper presents measured results for active microwave bandstop and bandpass varactor tuned filters. These filter designs were based on the negative resistance method and were realised using microstrip with future MMIC implementation in mind. Tuning ranges of 0.3 and 0.6 octaves around a centre frequency of 1.8GHz were achieved. A significant improvement in filter performance was observed with results approaching those for lossless filters.

Active varactor tunable microwave filters

A ceramic bandpass filter with increased selectivity on the lower side of the passband is presented. One application is the receive filter of a mobile radio transceiver operating in the 1.8-GHz bands. Finite transmission zeros have been introduced by using a network with additional cross couplings. The circuit was constructed with four coaxial ceramic resonators capacitively coupled using a microstrip PCB. For a 75-MHz passband filter, a stopband attenuation of 37 dB was attained at 20-MHz offset from the passband. A midband insertion loss of 1.2 dB and bandedge loss of 3 dB were achieved. >

J.G. Gardiner

Papers

Active varactor tunable bandpass filter

Asymmetric bandpass filter using a novel microstrip circuit

Active varactor tunable microwave filters

Asymmetric bandpass filter using a ceramic structure