No abstract

Phased array radar systems are used for a wide variety of applications including the precise tracking of airborne craft for air traffic control and providing accurate atmospheric condition information important in weather forecasting. Reducing the cost and size of these radar systems will open new fields to the use of this technology. Using phase control implemented through liquid crystal materials we have created a compact, phased array radar system operating in the microwave range. We report on the construction and testing of a linear, eight element phased array antenna system operating at 32 GHz with element phase controlled by a dual frequency nematic liquid crystal media used as a tunable dielectric. The system was designed using CST Design Studios and Ansys HFSS software. Dual frequency liquid crystals are used to improve beam steering response times. We demonstrate 42 millisecond beam switching times, defined as the time to change the beam focus from one point to another point, controllable beam formation, and beam steering profiles consistent with analytical results and simulation models. The device footprint is a square with sides 9.5 cm long and a thickness less than 2.5 mm. Such a module is easily stackable to create an 8 × 8 phased array system. Our design incorporates a modular construction using PCB for the antennas and input circuitry and a liquid crystal phase control cell with microwave glass substrates. This design simplifies design, construction, and testing as compared to on-glass designs. The device shows an improvement in point-to-point scanning speeds by a factor of 3 as compared to similar liquid crystal based devices and provides continuously variable tuning. Such a device can be used in a system for reduced visibility, directional range finding suitable for automobile collision avoidance systems and rotary wing aircraft landing aids.

Electrically tunable double‐spurline notch filters with a nematic liquid crystal (LC) material as a dielectric medium were modeled, manufactured, and characterized. The spurlines, which were embedded into an inverted microstrip, consisted of quarter‐wavelength resonant elements. A Finite Difference Time Domain solver was used to model the filters. Photolithography and thin film deposition were employed to create the filters, followed by standard LC cell assembly. The filters, with central notch frequencies at 50 and 85 GHz, were characterized on‐wafer with a vector network analyzer. The stopband frequencies were tunable by 3% when a 14 volt peak‐to‐peak AC bias was applied across the 38 μm thick LC layer (electric field of 0.19 V/μm). The minimum stopband insertion loss of both filters achieved lower than −50 dB, while the stopband return loss varied from −4 to −12 dB. The −3 dB passband widths of the stopband filters were 12.2 and 28.3 GHz for the 50 and 85 GHz filters, respectively, giving a Q‐factor of 3–4.

We investigate the effect of different alignment methods on the performance of dual frequency liquid crystal-based phase shifters operating at 30 GHz to determine the optimal alignment method for such devices. We measure the response time, total phase shift and repeatability of devices with the liquid crystal alignment created by a rubbed polyimide alignment layer deposited on the metallization elements, devices with the alignment created by direct rubbing of the metallization elements, and devices with no initial treatment for alignment. For these tests, we used a commercial, dual frequency liquid crystal. We find that the devices with a polyimide alignment layer in an anti-parallel rubbing orientation produce the best results; however, the other devices produce acceptable results due to the nature of the dual frequency liquid crystal and they may be alternatives to polyimide in certain applications.

We report the development of a microwave interferometer using a quadrature intermediate frequency (IQ) mixer designed to measure the relative phase change and response time of microwave devices tested in the Ka and upper K bands (22–40 GHz). The interferometer is currently used to test liquid crystal based devices. The system allows for the application of an AC bias beyond the amplitude/frequency limitations imposed on vector network analyzer bias ports. Our IQ mixer based design uses bias signals ranging from 0 to 100 V peak-to-peak in a frequency range from DC to 100 kHz. This range of bias signals is necessary to properly test the response of microwave devices designed with liquid crystal materials. The setup enables us to measure changes in the output phase of the device as a function of both the voltage and frequency of the applied bias signal. The setup also measures the phase difference as a function of microwave frequency and response times for the device under test. Our system can be integrated into a stand-alone test setup without the need for a vector network analyzer.