Broadband Reconfigurable Matching Network of Reduced Dimensions for the UHF Military Satellite Communication Band Marc J. Franco, David Dening Outline • Motivation • Network topology • Implementation • Experimental results • Conclusion Motivation • Good impedance match between transmitter and antenna is needed to maximize radiated power • Antenna impedance varies significantly in portable equipment • A reconfigurable matching network between the transmitter and the antenna can overcome this problem Design goals • Convert 10:1 VSWR into 2:1 or better • 220 to 450 MHz operating frequency range (~ 1 octave) • Input power up to 35 dBm • Harmonics below -60 dBm • Very low insertion loss • Small size and low power consumption Network topology TX LINE TX LINE INPUT OUTPUT TX LINE TX LINE • Network can be configured as PI, T or L, offering great flexibility and bandwidth • Transmission lines are paralleled to decrease their characteristic impedance • Insertion loss is minimized by avoiding series switches at low impedance points Alternative network INPUT OUTPUT • For low frequency applications and size reduction, the transmission lines can be replaced by inductors • This is the approach followed in this design Switching element • 6 x 4 mm depletion mode RFMD GaAs pHEMTs stacked up to withstand the off-state voltage swing • Each branch was laid out as two triple gate transistors in series to reduce size • On-state resistance 0.8 ohms • Off-state capacitance 0.3 pF • GaAs switch can be replaced by SOI or RF MEMS Implementation • Size 1” x 1”, but easily reduced • Passive elements: size 0603 capacitors (6 and 12 pF on each branch) and 22 nH size 0908 inductors Measurement setup HARMONICS IMPEDANCE MATCHING MATLAB (PC) MATCHING NETWORK NETWORK ANALYZER SIGNAL GENERATOR POWER AMP. LOW PASS FILTER MATCHING NETWORK SPECTRUM ANALYZER NOTCH FILTER TUNER/LOAD HIGH DIRECTIVITY DIR. COUPLER COUPLED • S- parameters measured with a 2-port vector network analyzer for each one of the 512 possible tuning patterns at different frequencies • Matlab code used to control tuning and to record the data • Harmonics measured by attenuating the fundamental frequency with a notch filter Evaluation setup VSWR < 2:1 Insertion loss < 3 dB Tuner S-parameters Term Term1 Num=1 Z=50 Ohm Variable load impedance (optimized value) S2P_Eqn S2P1 Term Term2 Num=2 Z=R+j*X • The measured S-parameters were included in an Agilent ADS simulation • The load impedance was optimized for each tuning pattern to obtain a VSWR of 2:1 or better at various frequencies • All tuning patterns that did not provide an input VSWR better than 2:1 or an insertion loss of less than 3 dB were discarded • A few tuning patterns were verified experimentally to confirm the accuracy of the simulation Impedance match capability 220 MHz 335 MHz 450 MHz • Insertion loss • Green: < 0.5 dB Blue: 0.5 dB to 2 dB Red: 2 dB to 3 dB • Plots show single points that map into a 2:1 VSWR region surrounding the 50 ohm system impedance • There is an area around each point which also maps into the desired 2:1 VSWR region, expanding the coverage of the matching network • In regions where the density of tuning states is high the lowest loss state should be chosen System gain 220 MHz 335 MHz 450 MHz • System gain is calculated by comparing the powered delivered to the load before and after the insertion of the matching network • Green: 1 dB to 2 dB Blue: 0 dB to 1 dB Red: loss up to 0.5 dB • Small loss is expected when the load is perfectly matched • Gain is obtained for mismatched loads • The antenna impedance in portable equipment is usually mismatched Tuning methods POWER AMP. RECONFIG. MATCHING NETWORK 3D LOOK UP TABLE (Z mag & phase, freq) IMPEDANCE DETECTOR IMPEDANCE & FREQUENCY DATA • The tuning algorithm for this reconfigurable matching network depends on the particular requirements of the system where it will be installed • Several known methods could be employed, including look-uptable based solutions with appropriate search algorithms or load impedance measurements Summary • Reconfigurable matching network can match up to 10:1 VSWR to 2:1 from 220 to 450 MHz • Easily scalable to other frequencies using inductors or transmission lines • Maximum input power of 35 dBm • Can be increased by stacking up more transistors or using a different type of RF switch • Low insertion loss • Typical 0.25 dB into a 50 ohm load • Harmonics below -66 dBm • Size 1” x 1”, easily reduced • Based on GaAs FET switch technology • Can be redesigned for SOI or MEMS

- Similar pages