A novel photonic approach for simultaneously measuring both the Doppler frequency shift (DFS) and the angle of arrival (AOA) of a microwave signal in a radar system is presented. It has the same structure as a fiber optic link consisting of a laser, an optical modulator and a photodetector. The incoming microwave signal and a reference signal are applied to the optical modulator. Beating of the echo and reference signal sidebands at the photodetector generates a low-frequency electrical signal. The DFS and the AOA can be determined from the frequency and the power of the low-frequency electrical signal measured on an electrical spectrum analyzer. The system has a very simple structure and is low-cost. It has a wide operating frequency range and a robust performance. Experimental results demonstrate a DFS measurement at around 15 GHz with errors of less than ±0.2 Hz, and a 0° to 90° AOA measurement with less than ±1° errors.

A new microwave photonic system for determining the angle of arrival (AOA) of a continuous wave (CW) or pulsed microwave signal is presented. It is based on a dual-polarisation dual-drive Mach Zehnder modulator followed by an optical notch filter for carrier suppression. Two orthogonal-polarised carrier- suppressed optical signals are detected by low-frequency photodetectors that generate two DC voltages. An incoming microwave signal AOA can be obtained from the ratio of the two DC voltages, without the need of a calibration procedure or measuring the incoming microwave signal power level, which are required in previously reported structures. The proposal system can be incorporated with a conventional radar receiver front end consists of mixers and filters, for measuring the AOA of a pulsed microwave signal. Experimental results demonstrate 0° to 63° AOA measurement with less than 2° errors for an input microwave signal having different frequencies and different power levels.

A new technique for determining the angle of arrival (AoA) of an RF signal is presented. It is based on a cascaded modulator structure, where continuous wave light from an optical source is modulated by an incoming RF signal twice. The AoA of an RF signal can be determined by the system output RF signal power. The proposed structure is capable for measuring the AoA of both narrow and broadband RF signals. This overcomes the limitation in all previously reported photonics-based AoA measurement systems, which are applicable to either a single-frequency RF signal or a broadband RF signal. It also does not involve electrical components and high extinction ratio modulators, which are required in reported structures. Experimental results are presented that show an AoA measurement range of 0° to over 65° with errors of less than 1.9° for a microwave signal at 2.65 and 12.62 GHz. Results also show that the system is capable to measure the AoA of a pseudorandom binary sequence signal at a microwave frequency.

A technique to provide independent control on the amplitude and phase of two orthogonal linearly polarised light is presented. It is based on operating a commercial dual-polarisation dual-drive Mach Zehnder modulator (DPol-DDMZM) in reverse direction that routes the input light in slow and fast axis into two different DDMZMs. The technique has the advantage of controlling the phase of the slow-axis light and the amplitude of the fast-axis light has no effect on the light travelling in the orthogonal polarisation state. It has applications in linearised microwave photonic links, frequency multipliers and microwave phase shifters. A new microwave photonic Hilbert transformer based on using the reverse operating DPol-DDMZM to alter the phase of an RF modulation sideband without affecting the orthogonally polarised optical carrier is developed. Experimental results demonstrate 24.3 dB attenuation in the fast-axis light with no change in the slow-axis light, and 0°–360° RF phase shift for only 3.3 V change in DC voltage. The new Hilbert transformer with less than 2.5° phase imbalance and 0.4 dB amplitude ripples over 4–18 GHz frequency range is also demonstrated.

The objective of this paper is to present a microwave photonic system that can measure the angle of arrival (AOA) of multiple microwave signals with improved measurement accuracy. It is based on a photonic mixer approach to down convert the incoming microwave signals into IF signals, which enables a low-frequency electrical spectrum analyser to be used for measuring the power of the IF signals to determine the incoming microwave signal AOAs. AOA measurement errors can be reduced by operating the optical modulator at a different transmission point for a different range of microwave signal AOA. The system also has the ability to remove the incoming microwave signal amplitude dependence in the AOA measurement. Measured results demonstrate 0°-81.5° AOA measurement with less than ±2° errors over the 0°-30° and 30°-81.5° AOA measurement range when the optical modulator is biased at the minimum and maximum transmission point respectively. The errors remain below ±2° even when there is a ±0.1 dB change in the output IF signal power. AOA measurement of two microwave signals is also demonstrated.

A new dual-function photonic microwave signal processing structure that has the ability to realize both frequency up/down conversion and RF/IF phase shifting, is presented. In the proposed signal processor, a dual-polarization dual-parallel Mach Zehnder modulator (DP-DPMZM) is used to generate an orthogonally polarized single RF/IF signal and local oscillator (LO) modulation sideband without an optical carrier. The optical phase difference between the two sidebands can be controlled by controlling a DC voltage applied to a LiNbO3 electro-optic phase modulator that is connected after the DP-DPMZM. Beating between the two sidebands at a photodetector generates an RF/IF signal with a phase equal to the optical phase difference between the IF/RF signal and LO sidebands. The dual-function photonic microwave signal processor has a wide bandwidth and does not require a precise control of the laser wavelength. Experimental results demonstrate that a flat >-3 dB down/up conversion efficiency is achieved for an RF signal from 3.5 to 26.5 GHz and for an IF signal from 0.5 to 3 GHz, and a full 360° continuous phase shift of the output IF/RF signal.