Search

In this work, the design, fabrication, and testing of low sidelobe level (SLL) Butler matrix-based beamformers is presented. The paper is divided in two parts. The first part deals with the conventional technique of simultaneous excitation of input ports. The second part introduces some novel modified low SLL Butler matrices, as an alternative advantageous design choice. Circuit architecture makes use of asymmetric branch line couplers able to provide high values of output power division ratios. Radiation patterns with SLLs far lower than −23 dB are achieved, without the use of any additional circuitry, in opposition to the case of simultaneous port excitation. Apart from SLL reduction, the switched line-phase shifter technique is applied in order to increase the number of radiated beams and improve scanning coverage. The beamformers are suitable for interference suppressing point-to-multipoint ground communications, satellite and radar/EW/SIGINT systems. Several microstrip circuit prototypes are designed, fabricated, and tested, whereas extended simulation and measurements results are adduced.

A new type of cascaded series feed beamforming networks (BFNs) is introduced. The network architecture is based on a dual- series Nolen matrix topology. It is able to produce tapered output amplitude distributions from N £ N conflgurations. The general concept, analysis and systematic design of the BFNs are given. The networks are designed and intended to be used mainly for low Sidelobe Level (SLL) linear Multibeam Antennas (MBAs). Several design examples are presented, along with fabrication and measurements of an S-band prototype.

This work addresses a beam steering scheme for RFID readers. The proposed architecture uses a double Butler matrix network configuration in order to provide polarization diversity to the antenna array. The array is placed on a faceted surface, aiming at a coverage sector increase. Circuit architecture and simulation results are presented.

The design of passive circulators/duplexers for RFID applications in the UHF band is presented. The design idea is based on the use of simple passive directional couplers, offering simplicity and low cost compared to ferrite devices or active architectures. The Tx/Rx isolation problem is solved exploiting a mismatched load, which creates a cancelling signal on the Rx port. Additional impedance matching is applied at the Tx port, in order to balance the effects of the mismatch load at the input (Tx). Both branch-line and ring couplers are alternatively used, designed mainly for unequal power division between output ports. A variety of design examples is presented, including miniaturized topologies, aiming at the reduction of size and cost. Design frequency is chosen at 900MHz, trying to cover both 860MHz and 910MHz bands.

A new type of beamformers, based on the widely known Butler Matrix, is presented. The new type retains the basic topology which is being modified to produce a tapered output amplitude distribution. The resulting pattern has a Side Lobe Level, (SLL), less than −20dB. The new design makes use of unequal Wilkinson power dividers. Further improvement can be achieved by appropriately shaping the antenna excitation amplitude distribution. This asks for increased power split ratios in the Wilkinson dividers, which causes higher power losses.