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The devices were research demonstration vehicles tested using wafer probing techniques and were not packaged. Given the presence of MEM varactors, however, it is clear that packaging techniques and considerations similar to those employed in the case of phase shifters would be applicable. Figure 5.16 shows the measured performance [34]. The lumped-element filter exhibited a [...]

The filters were implemented in grounded coplanar waveguide (GCPW) media , and their design was carried out via a full-wave electromagnetic simulator [34]. For the lumped-element realization, the simulation entailed varying the inductive (magnetic) coupling between the spiral inductors of the LC resonators, which was achieved by optimizing the filter response as a function of [...]

Two filters intended for application in highly integrated transmitters and receivers utilized in millimeter-wave multiband communication systems were implemented: a lumped-element version with a 4.7% bandwidth, centered at 26.8 GHz, and a coupled-resonator version with a 8.5% bandwidth, centered at 30.6 GHz. The filter topologies are shown. In the lumped-element version , the LC resonators [...]

The motivations for developing tunable filters might be traced to three factors: cost, weight, and power dissipation. In modern satellite communications, for instance, where an enormous number of filters are employed, there is extreme interest in minimizing both manufacturing cost, weight, and power consumption. The potential of MEMS technology to permit the batch fabrication of [...]

When it comes to filtering, MEMS fabrication technology has been exploited for two main purposes [32]: (1) the micromaching of structures (e.g., cavities) so small that their fabrication utilizing conventional machining techniques would be prohibitively expensive or virtually impossible due to tolerance limitations, and (2) the creation of micromechanical resonatorbased filters, typically utilizing polysilicon beam [...]

In this section we study the design of an FBAR filter developed for application in integrated single-chip radios [29]. Specifications and Topology: The filter was intended for applications in the 1.9-GHz PCS band and employed FBAR resonators in the ladder topology . In this T-cell, the filtering characteristics were realized by combining the impedance properties [...]

The devices were prototype vehicles tested using wafer probing techniques and were not packaged. It is clear, however, that packaging techniques and considerations similar to those employed in the phase shifter case studies previously discussed would be applicable. A photograph of the 4-bit RF MEMS TTD phase shifter is shown. The total area of the [...]

The circuit design of the switched-line TTD phase shifter consists of choosing the line lengths, tailoring their bends to minimize reflections, and properly locating and impedance-matching the switches in the proximity of the T-junctions so as to maintain optimum return loss [24] across frequency even when one of the switches is in the open state [...]

The phase shifter was to be of 4 bits with particularly wide bandwidth, as required by radar systems tasked with acquiring frequency-dependent target response and multipath signals [23]. At first sight, these specifications would suggest that an analog phase shifter of the distributed periodic capacitor load type (discussed in Section 5.2.1) might be called for. [...]

While traditional microwave packages place MMICs in a box that is hermetically sealed (to keep moisture out), these schemes require connectors and DC feed-throughs exhibiting losses at high frequencies (e.g., Ka-band), which defeats the purpose of the low-loss device inside. Therefore, the approach followed in [18] involved etching an approximately 0.007-in cavity in a lid [...]

While traditional microwave packages place MMICs in a box that is hermetically sealed (to keep moisture out), these schemes require connectors and DC feed-throughs exhibiting losses at high frequencies (e.g., Ka-band), which defeats the purpose of the low-loss device inside. Therefore, the approach followed in [18] involved etching an approximately 0.007-in cavity in a lid [...]

The phase shifter was to be of the digital type with 4 bits of commandable phase shifts; this means, 24 = 16 phase-shift states. The insertion loss was to be smaller than what is achievable with conventional technology (e.g., smaller than 6.5 dB), which is approximately what is exhibited by a 4-bit Ka-band pseudomorphic high [...]

The assembled 4-bit MEM phase shifter circuit is shown. As observed in the circuit schematic of Figure 5.3, connections to ground play a prominent role in this design. However, the fabrication technology employed lacked vias to ground. As a result, the circuit was laid out so that the connections to ground could be implemented with [...]

The fundamental function of a phase shifter circuit is to produce a replica of the signal applied at its input, but with a modified phase. Its performance is characterized by its insertion loss, bandwidth, power dissipation, power handling capability, and insertion phase [12]. Depending on the nature of the insertion phase (i.e., whether switchable continuously [...]

The design of RF MEMS?based circuits for wireless applications is predicated upon the well-established principles of RF and microwave electronics and on the novelty of RF MEMS devices. The well-established principles of RF and microwave electronics may be readily found in a variety of books [1?11], which are, no doubt, familiar to both the RF/microwave [...]

So far in this chapter we have addressed techniques for the reconfigurability of more or less discrete circuit elements. Another vein in the area of reconfigurability?namely, the MEMS microswitch array [14]?addresses the reconfigurability of distributed microwave components (i.e., of the very metal traces, or patterns, that would otherwise define the interconnection transmission lines and tuning [...]

The tunable dipole antenna and the aperture-coupled microstrip line resonator antenna are made reconfigurable by changing the length of the radiating elements, which is directly related to the wavelength at which they resonate. Another popular radiating element, the microstrip patch, is two-dimensional in nature and finds extensive application in antenna arrays. Interest in multifrequency patch [...]

As is well known, the radiation properties of antennas depend on the relationship between some characteristic length in their structure and the frequency being radiated. For example, dipole antennas are nearly resonant at a length close to one-half the wavelength of the excitation signal [18]. It is logical, then, that in order to increase the [...]

Phase shifters are at the heart of phased array antennas [23]. In simple terms, a phased array antenna consists of a set of phase shifters that control the amplitude and phase of the excitation to an array of antenna elements in order to set the beam phase front in a desired direction. While phase shifters [...]

Many communications systems demand the ability to receive narrowband signals that can occur anywhere, in any one of a number of channels, within a wide frequency band. Since the equipment receiving these signals must operate in coexistence with high-power transmitters [22] and because it is imperative to avoid interference, it is required that excellent filters [...]

Many modern wireless systems use resonator tuning schemes for changing communication frequencies. Most methods for changing communication frequencies are predicated upon coupling a voltage-controlled capacitor (varactor) to a resonator in order to change its resonance frequency. The tunable CPW resonator [13] discussed in Section 4.2.4 is an example of such a scheme, although in that [...]

It is well known that one of the factors limiting the self-resonance frequency of spiral inductors is the inevitable need to use an air-bridge for connecting the inner terminal of the spiral to the output terminal, and the concomitant parasitic capacitance between the air-bridge and the underlying spiral traces. The tunable CPW resonator, demonstrated by [...]

The Binary-Weighted Inductor Array: It is well known that inductors and capacitors for operation at microwave frequencies may be realized from short sections of transmission lines (e.g., of length less than one-quarter the operating wavelength) [11]. Thus, a tunable inductor may be obtained by interconnecting, preferably via MEMS switches, network unit inductor cells so that [...]

In addition to the systematic (binary-weighted) inductor array considered above, other arrangements for tuning series and shunt inductors, in the context of MEMS switch switching, have been advanced, as shown in Figures 4.5 to 4.7 [12]. In Figure 4.5, MEMS switches S1, S2, ?, Sx are connected in parallel with inductors L1, L2, ?, Lx, [...]

In the most general case, there are at least two types of tuning needs to be considered in RF/microwave circuits and systems. First, one might be interested in changing the frequency-determining parameters of a circuit/system, designed originally to operate in a given frequency band, so that it can operate at a different frequency band. An [...]

Variable capacitors, or varactors, were discussed at length in Chapter 3. In this chapter, we revisit the subject of varactors, but in the context of implementations that emphasize their application in circuits other than voltagecontrolled oscillators (e.g., filters). The Binary Capacitor: The binary capacitor function, a capacitance that is made to change between two values, [...]

At the fundamental level, passive RF/microwave circuits and systems consist of switches, capacitors, inductors, transmission lines, and resonators. These devices/circuit elements were the first on which the impact and implications of RF MEMS were studied. The MEM switch, in particular, due to its noninvasive properties (i.e., virtually ideal insertion loss and isolation [1]), may be [...]

Introduction: For the first time in recent history, a technology is emerging that promises to enable both new paradigms in RF circuits and systems topologies and architectures as well as unprecedented levels of performance and economy. RF MEMS is widely believed to be such a technology [1?3]. There are at least two fundamental approaches for [...]

The electromagnetic modeling step, familiar to most RF/microwave engineers, involves the electromagnetic analysis of the structure using a 3-D fullwave solver tool. It begins by transferring the solid model developed in the mechanical simulation tool into the EM tool and proceeds with the definition of its constituent materials and boundary conditions. The analysis yields the [...]

The mechanical modeling process begins with a statement of the desired mechanical and electrical/microwave specifications of the device. Typical mechanical specifications include actuation voltage, mechanical resonance frequency, and contact forces; while typical electrical specifications include scattering parameters (insertion loss, return loss, and isolation), switching time, and power dissipation?induced temperature rise. Before detailed numerical simulation begins, [...]