RF MEMS on RADAR

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RF MEMS ON THE RADAR:

Presented by: Neelesh N H Under the guidance of: Mrs. H Sudha (Asst. Prof) Venue: Bangalore Institute of Technology, Bangalore RF MEMS ON THE RADAR

RADAR:

RADAR Radar senses angle, range, and velocity of moving scatterers in the environment. The angle of a target is detected by scanning the field of view with a directive beam. Scanning is done electronically, by steering the beam of an array, or mechanically, by rotating an antenna. The range, R , and radial velocity, v , of a target are detected through frequency modulation (FM) ranging and range differentiation [frequency modulated continuous wave (FMCW) radar], or through pulse delay ranging and the Doppler effect (pulse-Doppler radar).

Electronically Scanned Arrays :

Electronically Scanned Arrays Electronically scanned arrays, or phased arrays offer several advantages over mechanically revolving antennas, such as multiple agile beams and concurrent radar modes.

Active versus passive :

Active versus passive An active electronically scanned array has distributed solid-state power amplification and exceeds the search and track capabilities of a passive electronically scanned array. A passive electronically scanned array has centralized power amplification based on vacuum electronics devices but offers cost, power consumption, size, and weight savings . A passive electronically scanned array can be air-cooled, whereas an active electronically scanned array generally requires liquid cooling.

RF MEMS Technology:

RF MEMS Technology RF MEMS refers to components for which moving submillimeter -sized parts provide RF functionality. There are various types of quintessential RF MEMS components, such as RF MEMS resonators and oscillators; RF MEMS tunable inductors; and RF MEMS switches, switched capacitors, and varactors . The components and subsystems used in radar and discussed here are based on RF MEMS switches, switched capacitors, and varactors . These can be used instead of field effect transistor (FET) and high electron mobility transistor (HEMT) switches (FET and HEMT transistors in common gate configuration), and p- i -n diodes.

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RF MEMS switches, switched capacitors, and varactors are classified by actuation method (electrostatic, electrothermal , magnetic, piezoelectric), axis of deflection (lateral, vertical), circuit configuration (series, shunt), clamp configuration (cantilever, fixed-fixed beam), or contact interface (capacitive, ohmic ).

RF MEMS Switches:

RF MEMS Switches

RF MEMS Components:

RF MEMS Components RF MEMS components for radar systems include attenuators, limiters, oscillators, phase shifters, T/R switches and tunable matching networks. RF MEMS oscillators can be used within an RF frontend for an FMCW radar. RF MEMS attenuators, limiters, phase shifters, T/R switches and tunable matching networks can be used within an active electronically scanned arrays. Whereas duplexers and phase shifters can be used within a passive electronically scanned array.

Attenuators:

Attenuators Attenuators provide (non)uniform symmetric amplitude weighing to control the side lobe level of the RF beamforming electronically scanned array. The attenuation/noise figure is inversely related to the Q factor of the RF MEMS switches, switched capacitors or varactors . To date, no RF MEMS attenuators have been demonstrated, although the design of a digital RF MEMS attenuator would be similar to the design of the switched LC network phase shifter.

Limiters:

Limiters Limiters protect active microwave circuitry from damaging power levels. The breakdown power handling of a limiter is a function of the exposure time and the damaging power level. The response time of a limiter is the time necessary to switch from the transmission to the limiting state. The recovery time is the time necessary to switch from the limiting state to the transmission state.

Local Oscillators:

Local Oscillators The transmit power of an FMCW radar is limited by the isolation between the transmitter and the receiver, as well as by the phase noise of the local oscillator. RF MEMS oscillators with low phase noise, based on fixed-fixed beam or disc RF MEMS resonators with high Q factor, can be used in local oscillators.

(True-Time-Delay) Phase Shifters:

(True-Time-Delay) Phase Shifters A (true-time-delay) phase shifter provides (group delay) phase shift control to steer the beam of an RF beamforming electronically scanned array. Advantages of RF MEMS phase shifters are lower insertion loss, higher linearity, lower noise figure, and no power consumption. Disadvantages of RF MEMS phase shifters are higher RMS amplitude and phase errors due to process variations on the RF MEMS switches, larger size and slower switching.

Classification of Phase Shifters:

Classification of Phase Shifters Distributed loaded-line PS. Reflection PS. Switched LC network PS. Switched line PS.

Phase Shifters:

Phase Shifters

T/R Switches (Duplexers):

T/R Switches (Duplexers) T/R switches are single pole double throw (SPDT) switches, which can be used instead of large ferrite circulators to time-share the antenna between the transmitter and receiver of a T/R module. RF MEMS T/R switches can only be used in combination with low and medium pulse repetition frequency pulse-compressed radar waveforms for long-range detection, where the radiated pulses have a duty cycle on the order of microseconds.

Tunable Matching Networks:

Tunable Matching Networks RF MEMS tunable matching networks can be used to maintain maximum transmit power while changing carrier frequency or while scanning. Maximum transmit power can be maintained by transforming the optimal load impedance to the changing active antenna element impedance.

Radar Subsystems: Active Electronically Scanned Arrays:

Radar Subsystems: Active Electronically Scanned Arrays RF MEMS components are passive and reciprocal, and offer lower insertion loss, higher linearity and power handling, obviating distributed amplification within the T/R module. T/R modules also allow for amplitude and (group delay) phase shift control. Therefore a single duplexer can route the RF signal through a reciprocal common T/R path, solving the on-chip feedback problem.

T/R Module:

T/R Module

Passive Electronically Scanned Arrays:

Passive Electronically Scanned Arrays The p- i -n diodes can be replaced with RF MEMS switches, switched capacitors and varactors , to yield light-weight passive electronically scanned Arrays with low power consumption for airborne and spaceborne platforms. Lenses : The unit cell of a lens is a cascade of an antenna, a (true-time-delay) phase shifter, and an antenna. A lens captures an unbounded wave, phase shifts and reradiates the guided wave.

Lens:

Lens

Reflect Arrays:

Reflect Arrays Reflect arrays are resonant tile assemblies based on tunable impedance surfaces or wideband brick assemblies based on end-fire radiating antennas and (true-time-delay) phase shifters. An unbounded wave is reflected by a tunable surface in a desired direction by tuning the surface impedance of unit cells to obtain a linear reflection phase shift progression over the surface. A unit cell of a tunable impedance surface consists of electrically small reflecting strips that are connected by RF MEMS switches, switched capacitors, or varactors .

Brick-assembled reflect arrays:

Brick-assembled reflect arrays Brick-assembled reflect arrays based on antennas and (true-time-delay) phase shifters capture the unbounded wave, and (group delay) phase shift, reflect and reradiate the guided wave.

Switched Beamforming Networks:

Switched Beamforming Networks A switched beamforming network based on a combination of a focal plane scanner and an RF MEMS single pole N throw switch provides true-time-delay beam steering by commutating between the N beam ports on the focal arc. But lacks the long-range search and track capability of (true-time-delay) phase shifter based lenses, reflect arrays and subarrays .

Radomes:

Radomes A radome protects the radar antenna against adverse environmental conditions. It may be a frequency selective surface, a limiter, a polarization transformer, or a shutter. RF MEMS technology can be used to tune a frequency selective surface, to limit the input power using self-actuation, to reconfigure the polarization of a polarizer, or to shut the radome .

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