2. MHMIC fabrication process

to higher loss in common building materials, which make 60 GHz communication most suitable for short-range wireless applications, several meters for low power to max 1 km for backhaul solutions. However, to operate reliably at even short ranges, 60 GHz communication systems must also employ a highly focused, narrow-beam antenna to increase the level of

86 Advanced Electronic Circuits - Principles, Architectures and Applications on Emerging Technologies

Today, the demand for high-data-rate wireless communications and broadband transceiver/ receiver systems with reduced hardware requirements and high flexibility is highly increased. However, the existing hardware architectures for radio communication systems suffer from a number of limitations including high cost, design complexity, as well as high power consumption. For instance, for most mixers in conventional receivers, to obtain a good conversion gain, the power of the local oscillator must be more than 10 dBm, which is a relatively high power level compared to other alternatives reported in literature [3]. Moreover, in conventional receiver systems, the phase noise of the local oscillator (LO) is transformed directly into the phase noise in the baseband. This results in neighbor channel interference, usually caused by

Radio architectures having a potential to get beyond the previously mentioned limitations include radio communication systems based on multi-port architectures. The design simplicity combined with the wideband characteristics of multi-port receiver structures may provide RF receiver architectures, which can solve many of the current challenges of receiver systems. It provides a straightforward approach for broadband operations, low power consumption, and low manufacturing costs, making it a serious candidate for various indoor millimeter-wave

In the recent years, several designs of multi-port (six-port) circuits have been investigated and presented in literature. They range from microstrips to LC lumped element designs, for different microwave and millimeter-wave frequency bands [6]. The first reported multi-port circuit was employed in the 1970s by Glenn F. Engen and Cletus A. Hoer as an alternative solution to network analyzers for the measurement of complex scattering parameters [7, 8]. A couple of years later, it was used in radar applications and has recently been proposed as an alternative to the conventional receiver architectures such as the homodyne and heterodyne receivers.

In this chapter, a fully integrated 60 GHz front-end receiver based on the multi-port (six-port) technique is presented and analyzed. All parts composing the proposed front-end receiver such as an 8 2 antenna array, a low-noise amplifier (LNA), a six-port circuit, and the power detectors are presented and characterized separately. This chapter is therefore organized as follows. First, Section 2 gives a comprehensive overview on the MHMIC fabrication process used to manufacture the proposed 60 GHz front-end receiver prototype. Next, Section 3 shows the theoretical concept of the six-port circuit and how it operates as an amplitude/phase discriminator; moreover, it describes in detail the basic building blocks of the designed 60 GHz front-end receiver. The experimental characterization procedure and the obtained measurement results, as well as the final fabricated front-end receiver prototype with the experimental M-PSK/M-QAM demodulation results are also discussed in the same section.

reciprocal mixing, consequently decreasing the selectivity of the receiver [1].

signal available to the target receiver.

wireless applications [4, 5].

Finally, a conclusion is drawn.

Today, there are few promising high-quality fabrication processes, offering potentially low-cost and highly integrated millimeter-wave components, such as the monolithic microwave integrated circuit (MMIC) based on GaAs, silicon, or SiGe technology for large-scale production and the miniature hybrid microwave integrated circuit (MHMIC) for prototyping or smallscale production [9]. The latter adopts a thin-film process in which a wide range of passive components are fabricated on an alumina substrate having typically a high dielectric constant. These components are not limited only to the basic lumped passive components such as thinfilm resistors, spiral inductors, and overlay capacitors, but they also include a large number of RF passive circuits including power dividers, directional couplers, printed antennas, and filters. The active devices such as diodes, power amplifiers (PAs), and low-noise amplifiers (LNAs) are implemented at the end of the process, using gold wire bonding technology.

The most frequently used materials for the substrate metallization are gold, copper, or coppergold. High-precision thin-film resistors are typically implemented using nichrome or tantalum nitride films on a thin-film ceramic substrate. However, various processing techniques are usually used, such as photolithography techniques, e-beam, and, more recently, the excimer laser micromachining [10].

It is to be noted that the choice of a thin substrate is due to the reduced guided wavelength in high-permittivity ceramic substrates. In order to keep the required circuit aspect ratio (the guided wavelength versus the line width), the substrate thickness has to be as thin as possible. The optimal choice for frequencies higher than 60 GHz is the 127-μm-thick alumina substrate that is commercially available. This substrate is also easily compatible with the regular 100-μmthick MMIC active components, to be integrated with planar passive MHMICs. MMIC chips are implemented in rectangular cuts on ceramics, on the top of the same metallic fixture, allowing thermal dissipation and easy wire bonding with MHMIC components, which are typically at the same height.

The MHMIC technology represents today an excellent alternative for low-cost and rapid prototyping of highly miniaturized circuits with improved performances at millimeter-wave frequencies up to 86 GHz [6].
