Beam Diffraction by a Planar Grid Structure at 93 GHz

The idea of using diode grids for electronic beam steering was introduced by Lam et al [l]. As shown in Figure 1, when an incident beam reflects off the diode grid, the direction of the reflected wave can be controlled by progressively varying the ref1ection phase across the grid. The reflection phase of the diode grid can be controlled by varying the DC bias on the diodes. Later, a monolithic diode grid was fabricated with l600 varactor diodes, and a relative phase shift of 70° at 93 GHz was measured [2]. This work verified the transmission-line theory used to design the grid, but the phase shift was not sufficient to steer the beam, recently, Johansson [3] designed and built a passive planar grating reflector antenna that focused a beam. A rigorous moment-method solution was applied to choose a grating geometry to select the first-order diffracted wave. In this work, using the transmission-line model approach, the goal was to demonstrate that the beam can be steered by building a grid structure without diodes to give a fixed beam shift. In these grids, diodes were replaced by gaps with different sizes to obtain different capacitances needed to steer a beam at 93 GHz. The result show a successful beam shift of 30° with a loss of 2.5 dB

A 100-element planar Schottky diode grid mixer

The authors present a Schottky diode grid mixer suitable for mixing or detecting quasi-optical signals. The mixer is a planar bow-tie grid structure periodically loaded with diodes. A simple transmission line model is used to predict the reflection coefficient of the grid to a normally incident plane wave. The grid mixer power handling and dynamic range scales as the number of devices in the grid. A 10-GHz 100-element grid mixer has shown an improvement in dynamic range of 16.3 to 19.8 dB over an equivalent single-diode mixer. The conversion loss and noise figure of the grid are equal to those of a conventional mixer. The quasi-optical coupling of the input signals makes the grid mixer suitable for millimeter-wave and submillimeter-wave applications by eliminating waveguide sidewall losses and machining difficulties. The planar property of the grid potentially allows thousands of devices to be integrated monolithically

A 6.5 GHz-11.5 GHz source using a grid amplifier with a twist reflector

The authors have constructed and tested an oscillator using a grid amplifier with external feedback from a twist reflector. The twist reflector serves two functions; it changes the output polarization to match the input, and its position sets the feedback phase. This permits a wider tuning range than has been possible with previous grid oscillators. The source could be continuously tuned from 8.2 GHz to 11.0 GHz by moving the twist reflector. By moving the polarizer and mirror in the twist reflector independently, a 1.8-to-1 frequency range from 6.5 GHz to 11.5 GHz was achieved. The peak effective radiated power was 6.3 W at 9.9 GHz

A 10-Watt X-Band Grid Oscillator

A 100-transistor MESFET grid oscillator has been fabricated that generates an effective radiated power of 660 W at 9.8 GHz and has a directivity of 18.0 dB. This corresponds to a total radiated power of 10.3 W, or 103 mW per device. This is the largest recorded output power for a grid oscillator. The grid drain-source bias voltage is 7.4 V and the total drain current for the grid is 6.0 A, resulting in an overall dc-to-rf efficiency of 23%. The pattern of the SSB noise-to-carrier ratio was measured and found to be essentially independent of the radiation angle. The average SSB noise level was -87 dBc/Hz at an offset of 150 kHz from the carrier. An average improvement in the SSB noise-to-carrier ratio of 5 dB was measured for a 100-transistor grid compared to a 16-transistor gri

A 100-element HBT grid amplifier

A 100-element 10-GHz grid amplifier has been developed. The active devices in the grid are chips with heterojunction-bipolar-transistor (HBT) differential pairs. The metal grid pattern was empirically designed to provide effective coupling between the HBTs and free space. Two independent measurements, one with focusing lenses and the other without, were used to characterize the grid. In each case, the peak gain was 10 dB at 10 GHz with a 3-dB bandwidth of 1 GHz. The input and output return losses were better than 15 dB at 10 GHz. The maximum output power was 450 mW, and the minimum noise figure was 7 dB. By varying the bias, a signal could be amplitude modulated with a modulation index as large as 0.65. Tests show that the grid was quite tolerant of failures-the output power dropped by only 1 dB when 10% of the inputs were detuned. The grid amplifier is a multimode device that amplifies beams of different shapes and angles. Beams with incidence angles up to 30° were amplified with less than a 3-dB drop in gain

Quasi-optical solid-state microwave sources

Quasi-optical power-combining offers the most promising method for extracting large amounts of power from solid-state devices in the microwave and millimeter-wave range. This technique can be applied to a variety of devices. The difficulties associated with traditional waveguides power-combiners such as skin-effect losses are eliminated because the signals are combined in free-space. The solid-state devices are embedded in a two-dimensional grid configuration and placed in a Fabry-Perot cavity. In this respect, the quasi-optical power-combiner is analogous to a laser oscillator in which the active medium of the laser is replaced with an array of active devices. The grid presents a reflection coefficient to an incident plane wave which is larger than unity and the resonator provides feedback to couple the devices together. The two-dimensional structure of the grid is amenable to modern photolithographic processing and potentially allows thousands of devices to be integrated monolithically

An X-Band MESFET Grid Oscillator with Gate Feedback

In this work we present a design for a quasi-optical MESFET power-combining array that utilizes gate feedback. This circuit is different from previous MESFET grids that utilized packaged devices and source feedback to produce an oscillator at 5 GHz. The present configuration allows the drain and source leads to couple directly to the radiated field. Simulations indicate that this configuration can be used to build a high-frequency oscillator, A transmission-line model for the grid is presented and used to design a 25-element grid for operation at 10 GHz. Measurements show that the grid delivers an effective radiated power (ERP) of 2.4 W at 10.9 GHz

A 100-element Schottky diode grid mixer

The authors present a 100-element planar grid mixer consisting of Schottky beam-lead diodes placed in bow-tie shaped unit cells. Preliminary results show that the reflection coefficient of this grid agrees well with theory. A grid conversion loss of 9.3 dB at 10 GHz has been measured. This grid of Schottky diodes is suitable for use as a quasi-optically coupled mixer. The mixer grid is attractive for millimeter-wave applications because of its low-loss quasi-optical coupling, and because its dynamic range can be increased by a factor of the number of devices in the grid. This is important for SIS (superconductor-insulator-superconductor) receivers where dynamic range is fundamentally limited

Quasi-optical solid-state microwave sources

Quasi-optical power-combining offers the most promising method for extracting large amounts of power from solid-state devices in the microwave and millimeter-wave range. This technique can be applied to a variety of devices. The difficulties associated with traditional waveguides power-combiners such as skin-effect losses are eliminated because the signals are combined in free-space. The solid-state devices are embedded in a two-dimensional grid configuration and placed in a Fabry-Perot cavity. In this respect, the quasi-optical power-combiner is analogous to a laser oscillator in which the active medium of the laser is replaced with an array of active devices. The grid presents a reflection coefficient to an incident plane wave which is larger than unity and the resonator provides feedback to couple the devices together. The two-dimensional structure of the grid is amenable to modern photolithographic processing and potentially allows thousands of devices to be integrated monolithically