Surface acoustic wave (SAW) radio-frequency identification (RFID) tags are soon expected to be produced in very high volumes. The size and cost of a SAW RFID tag will be key parameters for many applications. Therefore, it is of primary importance to reduce the chip size. In this work, we describe the design principles of a 2.4-GHz SAW RFID tag that is significantly smaller than earlier reported tags. We also present simulated and exper-

Surface acoustic wave (SAW) -based radio-frequency identification (RFID) tags are soon expected to be produced in very high volumes. The size and cost of a SAW RFID tag will be key parameters for many applications. Therefore, it is of primary importance to reduce the chip size. However, the number of distinct codes to be realized and the used frequency band impose limitations on the delays of coded responses and, consequently, on the tag size. The coded signal should arrive at the reader with a certain delay, that is, after the reception of the environmental echoes. An adequate initial delay is typically about 1 mus. If the tag uses a bidirectional interdigital transducer (IDT), the initial delay is needed on both sides of the IDT. In this work, we have replaced the bidirectional IDT by a unidirectional IDT. This allows to halve the space required by the initial delay, since all the reflectors must now be placed on the same side of the IDT. We have reduced the tag size even further by using a Z-path geometry with two strong inclined reflectors. In this configuration, the same space in the x-direction (the initial propagation direction) is used for both the initial delay and the code reflectors, which means that the chip length is finally determined only by the space required by the code reflectors. In this way, the tag length is reduced by about 2 mm compared to an equivalent single-track configuration using a unidirectional IDT with the code reflectors placed in line. The proposed configuration is especially advantageous for tags having a relatively long initial delay compared to the space required by the code reflectors. For such devices, a chip size of less than 2 mm by 1 mm (at 2.45 GHz) is realizable

Longitudinally coupled resonator filters provide unbalanced-balanced operation with wide bandwidth, low loss, and high suppression levels. However, reducing the insertion loss in the 1.8-2.2 GHz range remains a challenging problem because at high frequencies the resistive losses arising from the relatively wide aperture of the filter may degrade the performance. A 5-interdigital transducer (IDT) filter has six gaps at which the periodicity of the grating is broken, resulting in additional loss due to scattering into the bulk. In this paper, we show that replacing the gaps between the transducers with short transducer sections having their pitch different from that of the main transducers reduces the insertion loss of the device. We present devices with balun operation at 1842 MHz with wide bandwidth of 4.5% and -40 dB suppression, with a minimum insertion loss less than 1 dB in the best devices, and a maximum insertion loss of -1.2 dB in the passband. The passband is quite flat, with <1 dB ripple. We also discuss the layout of the contact pads and the connections, and its effect on the device performance and balance characteristics.

Longitudinally coupled resonator filters (CRFs) provide unbalanced-balanced operation with wide bandwidth, low loss and high suppression levels. One-track filters with five transducers show good performance at 2-GHz frequencies. At high frequencies, however, the resistive losses arising from the relatively wide aperture of the CRFs can degrade the performance. Reducing the insertion loss in the 1.8-2.2 GHz frequency range remains a challenge. A 5-IDT filter has 4 gaps between IDTs where the periodicity of the grating is broken, resulting in additional loss. We show that replacing these gaps with short transducer sections reduces the insertion loss of the device. We present devices on 42/spl deg/-LiTaO/sub 3/ at 1842 MHz with wide bandwidth of 4.5% and 40 dB of suppression, with a minimum insertion loss less than 1 dB in the best devices, and a maximum insertion loss of 1.2 dB in the passband. We also discuss the layout of the contact pads and the connections and its effect on the device performance and balance characteristics.