Design and simulation the impact of microwave circuit imbalances on digital instantaneous frequency measurement receiver

Frequency is one of the more important microwave signal parameters. Various systems and processing methods are used for frequency measurement. The instantaneous measurement of RF and microwave frequencies is widely used in Electronic Warfare (EW) for the determination of unknown signals over a broad frequency band by perform fast measurements of very short microwave signals. Instantaneous Frequency Measurement (IFM) receivers have been used for wideband monitoring of radar environments in naval, airborne and ground-based Electronic Support Measures (ESM) systems worldwide in the last 50 years. The discriminators are generally interferometers composed of delay lines and power dividers, where delayed signals are compared with the original signal to identify the instantaneous frequency of an input RF/Microwave signal. The important components of an IFM device include a microwave frequency discriminator and a microwave Phase Discriminator (PD). The PD principle of operation is based on vector summing of microwave signals. The coupled line or branch line directional couplers are often used to quickly handle these operations. Its most important feature is the ability to perform accurate phase measurements, even in the millimeter range. Phase difference between two RF signals is determined from four power measurements. The circuit often has no active device also it is suitable for low-cost and compact-size applications in the EW receivers. The first step in the design of such receivers is to study and analyze the IFM receivers and finding out the structure of the phase discriminator which has the advantages of simple fabrication, compact realization and could be designed over broad bandwidth. Then, the RF front-end for IFM receiver aim to use microstrip technology, which is particularly important due to its lower cost and easy integration using conventional PCB technology. In this thesis, a phase discriminator has been analyzed and designed to cover the whole S Band. A structure consisting of three quadrature hybrid couplers and a power divider has been selected. The DIFM receiver has been analyzed in Visual System Simulator (VSS) environment from NI AWR®, and the receiver's specifications has been computed. Then, some design requirements have been found out to helping the design of discriminator's components. over the whole S band, and finally we have been studied effects of many important and essential paramters of receiver components, which affect the resolution of the measurements such as losses in delay line, power dividers and directional couplers, in addition to amplitude and phase imbalance in both power dividers and hybrid couplers. We designed these components, the quadrature hybrid coupler and the power divider, by performing an electromagnetic simulation using High Frequency Structure Simulator (HFSS) software; we also took into account many technological constraints on the fabrication. As a result, a quadrature hybrid coupler operating on a bandwidth larger than one octave has been implemented, with excellent phase imbalance (90°±0.5°) and amplitude imbalance (-3±1 dB) over the whole S band. Also, a power divider has been implemented having amplitude imbalance better than 0.2 dB and phase imbalance better than 0.4° over the whole S band.