Millimeter Wave Integrated Circuits For Communications And Radar Applications

Abstract This paper discusses the develppment of millimeter wave dielectric image guide inte­ grated circuit components and their application in communications and radar systems. Itdescribes specific systems such as a 60/70 GHz communication set, a 70 GHz binocular radio, a pulsed radar, a FM-CW radar using a self-oscillating mixer and a FSK radar transceiver, all at 94 GHz, to demonstrate the feasibility of dielectric waveguide type components in practical systems applications.IntroductionMilitary systems requirements in communications, radar, guided weapons and electronic warfare provide a strong impetus in the millimeter wave field. The frequencies of interest range from 35 GHz to 220 GHz. Advantages to be gained range from high resolution all- weather capability to anti-jam, low probability of intercept potential with the added benefits of small size and weight for portable operation. For nearly a decade, the Army has spearheaded the development of millimeter wave components and integrated circuits. A principal thrust is to combine low cost designs with advanced millimeter wave technology for practical hardware and systems I/2. In the device area, the Gunn device is emerging as a key component, and in the circuit technology area, the dielectric image guide integrated circuit is gaining stature for these applications. Its principal advantages are low loss, single mode operation with practical tolerance requirements, good heat sinking capability, and simple and rugged construction. These features will be highlighted in the following discussions.Dielectric Image Guide Integrated Circuit ComponentsHot pressed boron nitride, BN, has attractive properties as a dielectric transmission line material. It has a dielectric constant of 4, a loss tangent of less than 0.001 and is easily machinable. It was exclusively used here for the development of integrated circuit components.For moderate power levels, as required for the 60/70 GHz communications set, the IMPATT diode transmitter design as shown in Figure 1 was used. A packaged IMPATT diode positioned in a metallized ceramic or boron nitride cavity is soldered to a gold-plated aluminum ground plane. A gold ribbon provides impedance transformation to the tapered end of the BN guide. A metallized cover for frequency and power adjustment completes the cavity. Bias and effective RF choke are provided through a silver epoxied slot in the sidewall of the cavity. The output end of the BN guide is again tapered for proper matching into a regular metal waveguide. Figure 2 shows a photograph of the simple and rugged dielectric image guide transmitter. A fairly consistent power output of about 100 mW was common, however, power outputs greater than 300 mW have also been measured. An improved bias network and suitable impedance tuning remain as two important problems.With minor modifications, the same circuit can be used for Gunn oscillators. However, more recently a radial line structure was developed whose principal construction is shown schematically in Figure 3. It consists of a Gunn oscillator mounted in a metal plane serving as heat sink and support. Boron nitride is again the dielectric image guide. The diameter of the hole which houses the packaged Gunn device determines the operating fre­ quency. The top metallization provides the ground path, DC bias is applied through the bottom with an anodized aluminum insert separating device from metal support. A finished dielectric image guide Gunn oscillator is shown in Figure 4.Next, the basic design of the dielectric image guide balanced mixer is shown in Figure 5. Signal and. local oscillator input are coupled into the GaAs Schottky beam-lead diodes through a BN image guide 3-dB coupler. Tv;c image guides separated by a small gap along a specific length form the coupler. The mixer diodes are mounted at the end of the image guide. Each mixer diode is located in an air-filled cavity to provide ^-wavelength termina­ tion. The mixer cavities are metallized and covered with a metal cap to prevent radiation leakage. The IF output of the mixers is fed directly to an IF amplifier beneath the metal substrate. The boron nitride is metallized by sputtering Cr-Au and soldered to the metal substrate. Factors affecting the balanced mixer performance are the physical dimensions of